Note: Descriptions are shown in the official language in which they were submitted.
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Field Device Electronics Fed by an External Electrical Energy Supply
The invention relates to a field-device electronics for a field device. The
field-device electronics is fed by an external electrical energy, or power,
supply. The invention relates, as well, to a field device having such a field-
device electronics.
In the technology of industrial process measurements and automation,
especially also in connection with the automation of chemical or technical-
method processes and/or the control of industrial plants, measuring
devices installed near to the process, so-called field devices, are used for
locally producing measured-value signals as analog or digital
representations of process variables. Likewise, field devices can be
embodied as adjusting devices for varying one or more of such process
variables and, in such respect, actively guiding the flow of the process.
Such process variables to be registered, or adjusted, as the case may be,
include, for example, and as can also be perceived from the cited state of
the art, mass flow rate, density, viscosity, fill level, limit level,
pressure,
temperature, or the like, of a liquid, powdered, vaporous or gaseous
medium, conveyed, or stored, as the case may be, in a corresponding
containment, such as e.g. a pipeline or a tank. Additional examples for
such field devices, which are known, per se, to those skilled in the art, are
described extensively and in detail in WO-A 05/040735, WO-A 04/048905,
WO-A 03/048874, WO-A 02/45045, WO-A 02/103327, WO-A 02/086426,
WO-A 01/02816, WO-A 00/48157, WO-A 00/36379, WO-A 00/14485, WO-
A 95/16897, WO-A 88/02853, WO-A 88/02476, US-B 7,200,503, US-B
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7,004,191, US-B 6,932,098, US-B 6,799,476, US-B 6,776,053, US-B
6,769,301, US-B 6,577,989, US-B 6,662,120, US-B 6,574,515, US-B
6,535,161, US-B 6,512,358, US-B 6,487,507, US-B 6,480,131, US-B
6,476,522, US-B 6,397,683, US-B 6,352,000, US-B 6,311,136, US-B
6,285,094, US-B 6,269,701, US-B 6,236,322, US-A 6,140,940, US-A
6,014,100, US-A 6,006,609, US-A 5,959,372, US-A 5,796,011, US-A
5,742,225, US-A 5,687,100, US-A 5,672,975, US-A 5,604,685, US-A
5,535,243, US-A 5,469,748, US-A 5,416,723, US-A 5,363,341, US-A
5,359,881, US-A 5,231,884, US-A 5,207,101, US-A 5,131,279, US-A
5,068,592, US-A 5,065,152, US-A 5,052,230, US-A 4,926,340, US-A
4,850,213, US-A 4,768,384, US-A 4,716,770, US-A 4,656,353, US-A
4,617,607, US-A 4,594,584, US-A 4,574,328, US-A 4,524,610, US-A
4,468,971, US-A 4,317,116, US-A 4,308,754, US-A 3,878,725, US-A
3,764,880, EP-A 1 158 289, EP-A 1 147 463, EP-A 1 058 093, EP-A 984
248, EP-A 591 926, EP-A 525 920, or EP-A 415 655, DE-A 44 12 388 or
DE-A 39 34 007. The field devices disclosed therein are, in each case, fed
by an external, electrical energy supply, which provides a supply voltage
and a supply current driven thereby, flowing through the electronics of the
field devices.
For the case in which the field device serves as a measuring device, it
additionally contains an appropriate physical-to-electrical, or chemical-to-
electrical, measurement pickup, or transducer, for electrically registering
the relevant process variables. Such pickup is, most often, inserted in the
wall of the containment carrying the medium or into the course of a line, for
instance a pipeline, conveying the medium, and serves to produce a
measurement signal, especially an electrical measurement signal,
representing the primarily registered process variable as accurately as
possible. For processing the measurement signal, the measurement
pickup is, in turn, connected with the operating and evaluating circuit
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provided in the field-device electronics and serving especially for a further
processing or evaluation of the at least one measurement signal. In a
large number of such field devices, the measurement pickup is additionally
so actuated by a driving signal generated, at least at times, by the
operating and evaluating circuit, that the pickup interacts at least directly
with the medium in a manner suitable for the measurement or,
alternatively, essentially directly with the medium via an appropriate probe,
in order to provoke reactions reflecting the parameter to be registered.
The driving signal can, in such case, be controlled, for example with
respect to an electrical current level, a voltage level and/or a frequency.
Examples of such active measurement pickups, thus measurement
pickups appropriately converting an electric driving signal in the medium,
are, especially, flow measurement pickups serving for the measurement of
media flowing at least at times. The pickups utilize at least one coil
actuated by the driving signal to produce a magnetic field, or at least one
ultrasound emitter actuated by the driving signal, or a fill level, and/or
limit
level, pickup serving for measuring and/or monitoring fill levels in a
container, such as e.g. microwave antennas, Goubau lines, thus a
waveguide for acoustic or electromagnetic surface waves, vibrating
immersion elements, or the like.
For accommodating the field-device electronics, field devices of the
described kind further include an electronics housing, which, as e.g.
disclosed in US-A 6,397,683 or WO-A 00/36379, can be situated remotely
from the field device and connected therewith only via a flexible cable, or
which, as shown e.g. also in EP-A 903 651 or EP-A 1 008 836, is arranged
directly on the measurement pickup or in, or on, a measurement pickup
housing separately housing the measurement pickup. Often, the
electronics housing then serves, as shown, for example, in EP-A 984 248,
US-A 4,594,584, US-A 4,716,770, or US-A 6,352,000, also to
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accommodate some mechanical components of the measurement pickup,
such as e.g. membrane, rod, shell or tubular, deforming or vibrating
members deforming during operation, under the influence of mechanical
forces; compare, in this connection, also the above-mentioned US-B
6,352,000. Field devices of the described kind are, furthermore, usually
connected together and/or with appropriate process control computers via
a data transmission system connected to the field-device electronics. The
field devices transmit their measured value signals to such locations e.g.
via (4 mA to 20 mA)-current loops and/or via digital data bus and/or
receive operating data and/or control commands in corresponding manner.
Serving as data transmission systems here are especially fieldbus
systems, such as e.g. PROFIBUS-PA, FOUNDATION fieldbus, as well as
the corresponding transmission protocols. By means of the process
control computers, the transmitted measured value signals can be
processed further and visualized as corresponding measurement results
e.g. on monitors and/or converted into control signals for other field
devices embodied as actuators, e.g. in the form of solenoid-controlled
valves, electric motors, etc..
Furthermore, a large number of field devices of the described kind,
especially also measuring field-devices, are electrically so designed that
they satisfy the requirements for intrinsic explosion-safety. Accordingly,
the field devices are operated with such a low electrical power that, for
lack of reaching ignition conditions, sparks or arcs can electrically not be
released. Intrinsically safe explosion protection is, for example, given
according to the European Standards EN 50 014 and EN 50 020, when
electronic apparatuses are so constructed that they satisfy the ignition
protection classification "Intrinsic Safety (Ex-i)" defined therein. According
to this ignition protection classification, thus electrical currents, voltages
and powers occurring in the field device are, at all times, not permitted to
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exceed specified current, voltage and power, limit values. These three
limit values are so selected that, in the case of malfunction, or in the case
of a short circuit, the maximally released amount of energy is not sufficient
to produce an ignition-capable spark. Usually, in the case of intrinsically
5 safe, field devices, the electrical power is not permitted to exceed 1 W (=
watt). The voltage can be kept below the specified limit values e.g. by Z-
diodes, the current e.g. by resistors, and the power by appropriate
combinations of voltage- and current-limiting components.
In the case of modern field devices, these are often so-called two-wire field
devices, thus field devices in the case of which the field-device electronics
is electrically connected with the external, electrical energy supply solely
via a single pair of electrical lines and in the case of which the field-
device
electronics also transmits the instantaneous measured value via the single
pair of electrical lines to an evaluation unit provided in the external,
electrical energy supply and/or electrically coupled therewith. The field-
device electronics includes, in such case, always an electrical current
controller for setting and/or modulating, especially clocking, such as
strobing, triggering or firing, the supply current, an internal operating and
evaluating circuit for controlling the field device, as well as an internal
supply circuit lying at an internal input voltage of the field-device
electronics derived from the supply voltage, feeding the internal operating
and evaluating circuit and having at least one useful-voltage controller,
e.g. regulator, flowed through by a variable electrical current component of
the supply current and providing an internal useful voltage in the field-
device electronics which is regulated, or controlled, to be essentially
constant at a predeterminable voltage level. Examples of such two-wire
field devices, especially two-wire measuring devices or two-wire actuators
can be found in, among others, WO-A 05/040735, WO-A 04/048905, WO-
A 03/048874, WO-A 02/45045, WO-A 02/103327, WO-A 00/48157, WO-A
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00/26739, US-B 7,200,503, US-B 6,799,476, US-B 6,577,989, US-B
6,662,120, US-B 6,574,515, US-B 6,535,161, US-B 6,512,358, US-B
6,480,131, US-B 6,311,136, US-B 6,285,094, US-B 6,269,701, US-A
6,140,940, US-A 6,014,100, US-A 5,959,372, US-A 5,742,225, US-A
5,672,975, US-A 5,535,243, US-A 5,416,723, US-A 5,207,101, US-A
5,068,592, US-A 5,065,152, US-A 4,926,340, US-A 4,656,353, US-A
4,317,116, US-A 3,764,880, EP-A 1 147 463, EP-A 1 058 093, EP-A 591
926, EP-A 525 920, EP-A 415,655, DE-A 44 12 388, or DE-A 39 34 007.
In certain cases, there is provided within the field device electronics, as
described, for example, in US-A 3,764,880 or WO-A 04/048905, also a
galvanic separation, for example between the internal operating and
evaluating circuit, on the one hand, and the current controller, on the other
hand, in order to prevent that possible potential differences, which are not
always avoidable with certainty, between the plant, into which the field
device is installed, and the external, electrical energy supply, are dropped
uncontrolled.
For historical reasons, such two-wire field devices are, for the most part,
so designed that a supply current instantaneously flowing in the single-pair
line in the form of a current loop at an instantaneous electrical current
level
set at a value lying between 4 mA and 20 mA (= milliamperes), at the
same time, also represents the measured value produced by the field
device at that instant, or the actuating value instantaneously being sent to
the field device, as the case may be. As a result of this, a special problem
of such two-wire field devices is that the electric power at least nominally
dissipatable or to be dissipated by the field-device electronics - in the
following referenced in short as "available power" - can fluctuate during
operation in practically unpredictable manner over a wide range. To
accommodate this, modern two-wire field devices (2L, or two line, field
devices), especially modern two-wire measuring devices (2L measuring
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devices) with (4 mA to 20 mA)-current loops, are, therefore, usually so
designed that their device functionality implemented by means of a
microcomputer provided in the evaluating and operating circuit is variable,
and, to this extent, the operating and evaluating circuit, which, for the most
part, does not dissipate much power anyway, can be adapted to the
instantaneously available power.
A suitable adapting of the field-device electronics to the available power
can e.g., as also proposed in US-B 6,799,476, US-B 6,512,358, or US-A
5,416,723, be achieved by matching the power instantaneously dissipated
in the field device to the instantaneously available power, and, indeed, in a
manner such that individual functional units of the operating and
evaluating circuit are operated with appropriately variable clock speeds, or,
depending on the level of the instantaneously available power, even
turned off for a period of time (ready, or sleep, mode). In the case of field
devices embodied as two-wire measuring devices with active
measurement pickup, the electric power instantaneously dissipated in the
field device can, as disclosed in, among others, US-B 6,799,476, US-A
6,014,100, or WO-A 02/103327, additionally be matched to the
instantaneously available power by adapting also the electric power
instantaneously dissipated in the measurement pickup, for example by
clocking of the, as required, buffered driving signal, along with a
corresponding matchable strobe rate, with which the driving signal is
clocked, and/or by reducing a maximum electrical current level and/or a
maximum voltage level of the driving signal.
However, in the case of field devices embodied as two-wire measuring
devices, a varying of the device functionality has, for the most part, the
result that, during operation, an accuracy, with which the operating and
evaluating circuit determines the measured value, and/or a frequency, with
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which the operating and evaluating circuit, for example, updates the
measured value, are/is subject to changes in the instantaneously available
power. Also the buffering of excess power present at times can only
conditionally remedy this disadvantage of two-wire measuring devices with
(4 mA to 20 mA)-current loops. On the one hand, due to the intrinsic
explosion safety often required for such two-wire measuring devices, at
best, existing excess electrical energy can be stored in only very limited
amounts internally in the field-device electronics. On the other hand,
however, the instantaneous supply current, and, to such extent, also the,
at best, available excess energy, depends only on the instantaneous
measured value, so that, in the case of a lastingly very low, but, timewise,
strongly varying, measured value, a correspondingly provided energy
buffer can, over a longer period of time, become completely discharged.
Moreover, for establishing such a complex power management in the field
device, a very comprehensive and, thus, also very demanding power
measurement is required, both with respect to circuitry and with respect to
energy; compare, in this connection, also WO-A 00/26739, US-B
6,799,476, US-B 6,512,358, or EP-A 1 174 841
Apart from this, it has been found, in the case of field devices of the
described kind having a measurement pickup for the conveying and
measuring of media flowing at least at times, that the adaptive clocking of
driving signals and/or of individual components of the operating and
evaluating circuit is only conditionally suitable. This is true, especially in
the application of a vibration-type measurement pickup, such as
described, for example, in the above-mentioned US-B 6,799,476, US-B
6,691,583, US-A 6,006,609, US-A 5,796,011, US-A 5,687,100, US-A
5,359,881, US-A 4,768,384, US-A 4,524,610, or WO-A 02/103327. The
field devices disclosed there serve to measure parameters of media
flowing in pipelines, mainly mass flow rate, density or viscosity. To this
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end, the corresponding measurement pickup will include at least one
measuring tube vibrating during operation and serving for the conveying of
the medium, an exciter mechanism electrically connected with the field-
device electronics and having an oscillation exciter mechanically
interacting with the measuring tube for driving the measuring tube, as well
as a sensor arrangement, which generates measurement signals by
means of at least one oscillation sensor arranged on the measuring tube,
for locally representing the measuring tube oscillations. Both the
oscillation exciter and the oscillation sensor are, in such case, preferably
of the electrodynamic type, thus constructed of a magnet coil and a
plunging armature interacting therewith via a magnetic field.
Due to the highly accurate amplitude and frequency control of the exciter
mechanism driving signal required for the operation of such a
measurement pickup, unavoidable, for one thing, is a timewise high-
resolution sampling of the measuring tube oscillations. Equally, in the
case of measurements made on flowing media, the issued measured
value must also itself be updated often. On the other hand, a, most often,
very high mechanical time constant of the oscillation system formed by the
measurement pickup leads to the fact that, in the case of possible
accelerations of the same, especially during non-stationary, transient
happenings, a high driving power must be used and/or relatively long
settling times assessed. Further studies in this connection have, however,
additionally shown that, because of the usually limited storage capacity for
electric power, even a buffering of excess energy in the field device
scarcely leads to any significant improvement of the signal-to-noise ratio
dependent on the amplitude of the measuring tube oscillations. In this
respect, even a temporary and partial switching-off of the operating and
evaluating circuit is little suited for two-wire measuring devices with active
measurement pickup of the described kind, especially for two-wire
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measuring devices having a vibration-type measurement pickup involving
the conveyance of flowing media.
A further possibility for improving the power capability of field devices of
5 the described kind, especially two-wire measuring devices, is, at least in
the case of minimal available power, to use as much thereof as possible
actually for the implementing of the device functionality, thus to optimize a
corresponding efficiency of the field device, at least in the region of small
available power. Supply circuits for the internal supply of the field
10 electronics built on this principle are discussed in detail, for example,
in
US-B 6,577,989, or US-A 6,140,940. Especially, the solutions proposed
therein aim to optimize the internally actually dissipatable, electrical
power.
For this purpose, provided at the input of the field-device electronics, for
adjusting and maintaining the above-mentioned, internal input voltage of
the field-device electronics at a predeterminable, as required also
adjustable, voltage level, is an input voltage controller with a voltage
adjuster, which acts at the input of the field device electronics and which,
as a function of the instantaneously available power and an
instantaneously actually needed power, has flowing through it, at least at
times, a variable electrical current component branched from the supply
current. However, a disadvantage of this field-device electronics is that all
internal consumers are supplied practically from one and the same internal
useful voltage and a possible collapse of this single useful voltage, for
instance because of too little supply current, can lead to a state in which
normal operation of the field device is no longer possible, or even to an
abrupt, temporary, total stoppage of the field-device electronics.
Starting from the above-discussed disadvantages of the state of the art, as
viewed on the basis of the given examples of conventional 2L-measuring
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devices, an object of some embodiments of the invention is to provide, for a
field
device of the described kind, a suitable field-device electronics, which makes
it possible,
at least in normal operation of the field device, to keep the evaluating and
operating circuit, especially a microprocessor provided therein,
continuously in operation and, in such case, to supply at least individual,
selected, function units, especially the provided microprocessor, always
with electric energy in sufficient measure. Additionally, the field device
electronics should be so designed that individual assemblies or
components can, with least possible technical complexity and in as loss-
free and energy-saving manner as possible, be kept . effectively
galvanically separated from one another. Furthermore, the field device
electronics should be so designed that individual assemblies or
components can, with comparatively little complexity, be modularly
brought together in such a manner that at least the assemblies or
components provided on the input side of the field device electronics can
be used for a large number of types of field devices, especially also field
devices designed according to principles of diversity. Such an input
module formed by means of the assemblies or components provided on
the input side should, in such case, be able to be maintained, in an as low
loss and energy saving manner as possible, galvanically separated from a
circuit module that includes at least parts of the evaluating and operating
circuit, in any case, however, the driver circuit provided therein.
Additionally, the field device electronics should be so designed, that
individual assemblies or components can be effectively maintained
galvanically separated from one another, in an as low loss and energy
saving manner as possible, and with as little technical complexity as
possible. Furthermore, the field device electronics should be so designed
that individual assemblies or components can be brought together
modularly with relatively little effort in such a manner that at least the
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assemblies or components provided on the input side of the field device
electronics can, on the one hand, be used for a large number of types of
field devices, especially also field devices designed according to principles
of diversity, and, on the other hand, an effective galvanic separation of
such assemblies from other, especially sensor-near, assemblies of the
field device electronics can be effected in a manner as simple as possible.
For achieving such object, some embodiments of the invention provide, for a
field
device, a field-device electronics fed from an external electrical energy
supply providing
an, especially unipolar, supply voltage and delivering, driven by such
voltage, an, especially unipolar and/or binary, variable supply current. The
field-device electronics of some embodiments of the invention includes: a
current
controller, flowed-through by the supply current, for adjusting and/or
modulating,
especially clocking, the supply current; an internal operating and
evaluating circuit for controlling the field device; as well as an internal
supply circuit lying at an internal input voltage of the field-device
electronics derived from the supply voltage, and feeding the internal
operating and evaluating circuit, the internal supply circuit including
-a first useful-voltage controller flowed-through, at least at times, by an,
especially variable, first electrical current component of the supply
current and providing in the field-device electronics an internal, first
useful voltage essentially constantly controlled at a first,
predeterminable, voltage level,
--a second useful-voltage controller flowed-through, at least at times, by
.25 an, especially variable, second electrical current component of the
supply current and providing in the field-device electronics an
internal, second useful voltage variable over a predeterminable
voltage range, as well as
--a voltage adjuster flowed-through, at least at times, by an, especially
variable, third electrical current component of the supply current
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and providing for the setting and maintaining of the internal input
voltage of the field-device electronics at a predeterminable voltage
level, especially a voltage level which can vary during operation.
Moreover, in the case of the field device electronics of some embodiments of
the
invention, both of the useful-voltage controllers are galvanically separated
from one
another. Both useful-voltage controllers can, in such case, be coupled
together, for example, by means of at least one transformer.
Additionally, some embodiments of the invention provide a field device
including
the aforementioned field-device electronics. In a first variant of the field
device
of the invention, such serves for measuring and/or monitoring at least one,
predetermined, physical and/or chemical parameter, especially a flow rate,
density, viscosity, fill level, pressure, temperature, pH-value or the like,
of
a medium, especially a medium conveyed in a pipeline and/or a container,
and the field device includes therefor, additionally, a physical-electrical
measurement pickup electrically coupled with the field-device electronics,
for reacting to changes of the at least one parameter and for issuing, at
least at times, at least one measurement signal corresponding with the
parameter, especially a variable signal voltage and/or a variable signal
current. In a second variant of the field device of the invention, such
serves for the adjusting of at least one predetermined physical and/or
chemical parameter, especially a flow rate, a density, a viscosity, fill
level,
pressure, temperature, pH-value or the like, of a medium, especially a
medium conveyed in a pipeline and/or container, and the field device
includes therefor, additionally, an electrical-to-physical actuator
electrically
coupled with the field-device electronics and reacting to changes of at
least one applied control signal, especially a variable signal voltage and/or
a variable signal current, with an adjusting movement of the actuator for
influencing the parameter to be adjusted.
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In a first embodiment of the invention, it is provided that the first useful-
voltage controller and the internal operating and evaluating circuit are
galvanically separated from one another. The first useful-voltage
controller and the internal operating and evaluating circuit can, in such
case, be coupled together, for example, by means of at least one
transformer.
In a second embodiment of the invention, it is provided that the second
useful-voltage controller is fed by a useful voltage delivered by the first
useful-voltage controller or by a secondary voltage derived therefrom.
In a third embodiment of the invention, it is provided that the current
adjuster and the second useful-voltage controller are galvanically
separated from one another.
In a fourth embodiment of the invention, it is provided that the current
adjuster and the internal operating and evaluating circuit are galvanically
separated from one another.
In a fifth embodiment of the invention, it is provided that the voltage
adjuster and the second useful-voltage controller are galvanically
separated from one another.
In a sixth embodiment of the invention, it is provided that the voltage
adjuster and the internal operating and evaluating circuit are galvanically
separated from one another.
In a seventh embodiment of the invention, it is provided that the operating
and evaluating circuit is flowed through, at least at times, both by a first
useful current, especially a variable, first useful current, driven by the
first
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useful voltage and also by a second useful current, especially a variable
useful current, driven by the second useful voltage.
In an eighth embodiment of the invention, the internal input voltage of the
field device electronics and/or the second useful voltage of the field device
electronics are/is controlled as a function of an instantaneous voltage level
of a terminal voltage divided from the supply voltage and dropping from
the input across the field device electronics. In a further development of
this embodiment of the invention, the internal input voltage of the field-
device electronics is held by means of the voltage adjuster at a
predeterminable voltage level, especially an operationally variable voltage
level, which is lower than the terminal voltage. The voltage level, at which
the internal input voltage is held by means of the voltage adjuster, can be
variable, especially step-wise or essentially continuously, during operation.
In a ninth embodiment of the invention, the second useful voltage is
controlled as a function of an instantaneous voltage level of the internal
input voltage of the field-device electronics and/or as a function of an
instantaneous voltage level of a terminal voltage divided from the supply
voltage and dropping from the input across the field-device electronics.
In a tenth embodiment of the invention, the second, the second useful
voltage is controlled as a function of an instantaneous electrical-current
level of at least one of the three electrical-current components. In a further
development of this embodiment of the invention, it is provided that the
second useful voltage is controlled as a function of the instantaneous
electrical-current strength of the third electrical-current component. In
another further development of this embodiment of the invention, it is
further provided that the second useful voltage is controlled as a function
of the instantaneous strength of the second electrical-current component
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and an instantaneous voltage level of the internal input voltage of the field-
device electronics.
In an eleventh embodiment of the invention, the feeding, external energy
supply provides a supply voltage showing a variable, especially fluctuating,
voltage level.
In a twelfth embodiment of the invention, the supply voltage delivered by
the external energy supply drives a supply current showing a variable
electrical-current level, especially an electrical current level fluctuating
essentially in a manner not determinable in advance.
In a thirteenth embodiment of the invention, a storage circuit serving for
the temporary storage of electrical energy is provided in the operating and
evaluating circuit.
In a fourteenth embodiment of the invention, the voltage adjuster contains
a component, especially a semiconductor element or the like, serving
principally for the dissipation of electrical energy and for getting rid of
the
heat energy arising in this way.
In a fifteenth embodiment of the invention, at least one microprocessor is
provided in the operating and evaluating circuit, with the first useful
voltage, or a secondary voltage derived therefrom, serving, at least in part,
as an operating voltage of the microprocessor. In a further development of
this embodiment of the invention, the first useful-voltage controller and the
microprocessor are galvanically separated from one another. In another
further development of this embodiment of the invention, the
microprocessor is kept galvanically separated from the current adjuster
and/or from the voltage adjuster.
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In a sixteenth embodiment of the invention, at least one digital signal
processor is provided in the operating and evaluating circuit, with the first
useful-voltage, or a secondary voltage derived therefrom, serving, as least
in part, as an operating voltage of the digital signal processor. In a further
development of this embodiment of the invention, the first useful-voltage
controller and the digital signal processor are galvanically separated from
one another. In another further development of this embodiment of the
invention, the digital signal processor is kept galvanically separated from
the current adjuster and/or from the voltage adjuster.
In a seventeenth embodiment of the invention, there is provided in the
operating and evaluating circuit at least one amplifier, in which at least one
of the two useful voltages, or a secondary voltage derived therefrom,
serves, at least partially, as operating voltage. In a further development of
this embodiment of the invention, it is additionally provided that the first
useful-voltage controller and the at least one amplifier are galvanically
separated from one another.
In an eighteenth embodiment of the invention, there is provided in the
operating and evaluating circuit at least one A/D converter, in which the
first useful voltage, or a secondary voltage derived therefrom, serves, at
least partially, as operating voltage. In a further development of this
embodiment of the invention, it is additionally provided that the first useful
voltage controller and the at least one A/D converter are galvanically
separated from one another.
In a nineteenth embodiment of the invention, there is provided in the
operating and evaluating circuit at least one D/A converter, in which at
least one of the two useful voltages, or a secondary voltage derived
CA 02656329 2008-12-29
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December 15, 2008
therefrom, serves, at least partially, as operating voltage. In a further
development of this embodiment of the invention, it is further provided that
the first useful voltage controller and the at least one D/A converter are
galvanically separated from one another.
In a twentieth embodiment of the invention, means are provided in the
operating and evaluating circuit for comparing electric voltages dropping in
the field-device electronics and/or electric currents flowing in the field-
device electronics, with reference values. In a further development of this
embodiment of the invention, the operating and evaluating circuit produces
an alarm signal signalling an under-supplying of the field-device
electronics, at least when the operating and evaluating circuit detects a
subceeding, or falling beneath, by the second useful voltage, of a
minimum useful voltage limit value predetermined for the second useful
voltage and a subceeding, or falling beneath, by the third electrical current
component, of a minimum electrical current component limit value
predetermined for the third component. In another further development of
this embodiment of the invention, the field-device electronics further
includes at least one comparator, which compares a sense voltage derived
from the third electrical current component of the supply current with an
associated reference voltage, and/or a comparator, which compares the
second useful voltage with at least one associated reference voltage.
In a twenty-first embodiment of the invention, such further includes sense
resistors serving for producing sense voltages essentially proportional to
current.
In a twenty-second embodiment of the field-device electronics of the
invention, such further includes a measuring and control unit for registering
and adjusting voltages dropping in the field-device electronics, especially
CA 02656329 2008-12-29
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December 15, 2008
the second useful voltage, and/or currents flowing in the field-device
electronics, especially the second and/or third electrical current
components. In a further development of this embodiment of the
invention, the measuring and control unit controls the voltage adjuster
such that the third electrical current component flows, when the
comparator comparing the second useful voltage with at least one
associated reference voltage signals an exceeding by the second useful
voltage of a maximum useful voltage limit value predetermined for the
second useful voltage. In another further development of this embodiment
of the invention, the measuring and control unit maintains a voltage
difference between the input voltage and the terminal voltage at a
predetermined voltage level on the basis of the input voltage and/or the
terminal voltage.
In a twenty-third embodiment of the invention, the field device electronics
further includes at least one comparator, which compares a sense voltage
derived from the third electrical current component of the supply current
with an associated reference voltage, with the at least one comparator for
the third electrical current component being kept galvanically separated
from the second useful-voltage controller and/or from the internal
operating and evaluating circuit.
In a twenty-fourth embodiment of the invention, the field device electronics
further includes at least one comparator, which compares the second
useful voltage with at least one associated reference voltage, with the at
least one comparator for the second useful voltage being kept galvanically
separated from the second useful-voltage controller and/or from the
internal operating and evaluating circuit.
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In a twenty-fifth embodiment of the invention, further included is a
measuring and control unit for registering and adjusting voltages dropping
in the field device electronics, especially the second useful voltage, and/or
currents flowing in the field device electronics, especially the second
and/or third electrical current component, and the second useful-voltage
controller is controlled by the measuring and control unit. To this end, the
measuring and control unit delivers, in a further development of the
invention, at least at times, for controlling the second useful-voltage
controller, a voltage control signal, which represents a voltage level to be
set instantaneously for the second useful voltage. In another further
development of this embodiment of the invention, it is provided that the
measuring and control unit and the second useful-voltage controller are
galvanically separated from one another. In such case, the measuring and
control unit and the second useful-voltage controller can be coupled to one
another for example by means of at least one transformer and/or by
means of at least one optocoupler. In another further development of this
embodiment of the invention, it is provided that the measuring and control
unit and the internal operating and evaluating circuit are galvanically
separated from one another. In such case, the measuring and control unit
and the internal operating and evaluating circuit can be coupled together
for example by means of at least one transformer and/or by means of at
least one optocoupler.
In a twenty-sixth embodiment of the invention, the field-device electronics
is electrically connected with the external electrical energy supply solely
via a single pair of electric lines.
In a first embodiment of the field device of the invention, such
communicates via a data transmission system, at least at times, with a
control and review unit, with there being provided in the field-device
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electronics for such purpose additionally a communication circuit
controlling the communication via the data transmission system. In a
further development of this embodiment of the invention, the first useful
voltage, or a secondary voltage derived therefrom, serves, at least
partially, as operating voltage for the communication circuit. In another
further development of this embodiment of the invention, the current
regulator and the communication circuit are galvanically separated from
one another.
In a second embodiment of the field device according to the first variant,
the operating and evaluating circuit of the field-device electronics
produces, at least at times, by means of the at least one measurement
signal, a measured value representing instantaneously, especially digitally,
the at least one parameter to be measured and/or to be monitored. In a
further development of this embodiment of the invention, the current
controller adjusts the supply current on the basis of the measured value
instantaneously representing the at least one parameter to be measured
and/or monitored. In another further development of this embodiment of
the invention, the supply current is a changeable direct-current, and the
current controller is adapted to modulate the measured value, at least at
times, onto an amplitude of the supply current.
In a third embodiment of the field device according to the first variant, the
supply current is, at least at times, a clocked current, with the current
controller being correspondingly adapted for clocking the supply current.
In a fourth embodiment of the field device according to the first variant, the
operating and evaluating circuit includes at least one driver circuit for the
measurement pickup, with the second useful voltage, or a secondary
voltage derived therefrom, serving, at least partially, as operating voltage
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December 15, 2008
in the driver circuit. In a further development of this embodiment of the
invention, the driver circuit contains at least one operational amplifier. In
another further development of this embodiment of the invention, the driver
circuit has at least one D/A converter and/or at least one signal generator
for producing the driver signal. According to a next further development of
this embodiment of the invention, the measurement pickup has a variable,
electrical impedance fed by the driver circuit, especially a magnet coil of
variable inductance and/or a measuring capacitor of variable capacitance.
Furthermore, it is provided that the electrical impedance of the
measurement pickup changes as a function of at least one parameter to
be measured and/or to be monitored. Additionally, it is provided that a
signal voltage falling across the changing electrical impedance and/or a
signal current flowing through the changing electrical impedance serves as
measurement signal.
In a fifth embodiment of the field device according to the first variant, the
operating and evaluating circuit has at least one A/D converter for the at
least one pickup signal, in which the first useful voltage, or a secondary
voltage derived therefrom, serves, at least partially, as operating voltage.
In a further development of this embodiment of the invention, the operating
and evaluating circuit has at least one microcomputer connected with the
A/D converter, especially a microcomputer formed by means of a
microprocessor and/or a signal processor, for generating the measured
value, with the first useful voltage serving, at least partially, as an
operating voltage of the microcomputer.
In a sixth embodiment of the field device according to the first variant, the
measurement pickup includes at least one measuring tube inserted into
the course of a pipeline for conveying the medium, especially a measuring
tube vibrating, at least at times, during operation. In a further development
CA 02656329 2008-12-29
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December 15, 2008
of this embodiment of the invention, at least one magnet coil is arranged
on the measurement pickup for producing a magnetic field, especially a
variable magnetic field. In an embodiment of this further development of
the invention, the magnet coil has, during operation of the measurement
pickup, at least at times, an exciter current flowing through it, especially
an
exciter current which is bipolar and/or variable in an electrical current
level,
for generating the magnetic field. Such exciter current is driven by the
second useful voltage, or a secondary voltage derived therefrom. In
another embodiment of this further development of the invention, the
magnet coil interacts via a magnetic field with a plunging armature, with
magnetic field coil and armature being movable relative to one another. In
another embodiment of this further development of the invention, the at
least one measuring tube of the measurement pickup vibrates, at least at
times, during operation, driven by an electromechanical, especially
electrodynamic, exciter mechanism formed by means of the magnetic field
coil and the plunging armature.
In a further development of the field device according to the first variant,
the measurement pickup includes two measuring tubes inserted into the
course of the pipeline for conveying the medium and vibrating, at least at
times, during operation.
In a seventh embodiment of the field device according to the first variant,
the measurement pickup serves for registering at least one parameter,
especially a fill level, of a container containing the medium, and includes
therefor at least one measuring probe, especially a microwave antenna, a
Goubau line, a vibrating immersion element, or the like, protruding into a
lumen of the container or at least communicating with the lumen.
CA 02656329 2012-08-10
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24
In an eighth embodiment of the field device according to the first variant,
the field-device electronics is electrically connected with the external
electrical energy supply solely via a single pair of electric lines and
transmits the measured value, produced, at least at times, for representing
instantaneously, especially digitally, the at least one parameter to be
measured and/or monitored, via the single pair of electric lines to an
evaluating circuit provided in the external electrical energy supply and/or
electrically coupled therewith. In a further development of this
embodiment of the invention, an instantaneous electrical current level of
the supply current, especially an instantaneous electrical current level
adjusted to a value lying between 4 mA and 20 mA, represents the
instantaneously produced, measured value.
A basic idea of some embodiments of the invention is to divide consumers
provided
in the field-device electronics - not counting the supply circuit itself - on
the one hand,
at least into a first group of electric circuits, or consumers, of higher
priority
and into a second group of electric circuits, or consumers, of lower priority,
and, on the other hand, to design the supply circuit so that, in normal
operation of the field device, at least the power, or energy, requirements of
the first group of electric circuits is always covered. Moreover, those
circuits or components, which mainly serve for storing energy internally in
the field device and/or cause electric energy to dissipate out of the field
device, can be assigned to a third group of electric consumers, which has
current flow through it and thus is supplied with electric energy solely in
the case of a sufficient supply of the first and second groups.
To the first group of electric circuits of higher priority there may be
assigned, among others, the at least one microprocessor provided in the
field-device electronics, along with the communication circuits serving for
communication with possible, superordinated, control and review units.
CA 02656329 2009-02-25
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The field device can, on the one hand, be kept permanently
functioning and, on the other hand, can also at least be kept
permanently on-line. Furthermore, for the case in which the field device is
a measuring device, also the measuring channel serving for the registering
5 and conditioning of the at least one measurement signal can primarily be
assigned to the first group of electric circuits, while possibly present,
exciter channels serving mainly for the operation of the electrical-to-
physical measurement pickup can be implemented as electric circuits of
lower priority. In the case of use of the field-device electronics of
10 some embodiments of the invention in a measuring device having a
vibration-type measurement pickup, practically the entire measuring
channel extending from the oscillation sensors through to the
microprocessor can be operated with the essentially constantly controlled,
first useful voltage and, therefore, can be supplied permanently in normal
15 operation with the required electric power. To such extent,
the measuring tube oscillations produced during operation
can always be sampled at equally high frequency and can also be
processed with high resolution. Additionally, even though the exciter
channel is operated partly or exclusively with the variable, second useful
20 voltage, the measuring tube can, in normal operation, be excited
essentially without any gaps, thus permanently, although, -'perhaps, with
fluctuating oscillation amplitude. Some embodiments of the invention are based
on, among other things, the discovery that neither temporary shut-down of the
microprocessor, nor intermittent operation of, for example, the exciter
25 channel can bring-about significant improvements in the energy balance.
Rather, it is a matter of, on the one hand, supplying the components vital
for the operation of the field device, and, as required, the communications
with energy as permanently and sufficiently as possible, and, on the other
hand, in case required, undersupplying or shutting off components which
are less essential. Further, it has been found that, especially also in the
CA 02656329 2009-02-25
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26
case of continuously, or at least quasi continuously, measuring field
devices, for example Coriolis mass flow measuring devices, it can be far
more beneficial to invest the available electrical energy preferentially into
the at least one microprocessor, especially the measured value processing
and evaluation, as compared, for example, with the exciter mechanism of
the sensor system, which is operated, then, only with the remaining,
available energy. In this way, it is, it is true, not always possible to
achieve
an optimal signal-to-noise ratio for the measurement signal, however, the
possibly present deficit in the quality of the measurement signal can be
removed by the measured value processing and evaluation, as
implemented by the still efficiently operating microprocessor.
As a result of the fact that the second useful-voltage controller is fed by
the
useful voltage delivered by the first useful-voltage controller and/or by a
secondary voltage derived therefrom, it is additionally possible, by just a
few transformers and, as required, just a few optocouplers, to provide, in
very simple and cost-favorable manner, a very effective galvanic
separation between individual components or assemblies of the field
device electronics. This is especially true, when a galvanic separation is
to be created between the aforementioned groups of electrical circuits of
different priority and/or the field device electronics is to be modularly
constructed.
In such a cascaded interconnecting of
the two useful-voltage controllers at
least the assemblies or components initially provided for the field device
electronics can nevertheless be used also for a large number of types of
field devices, especially also field devices designed according to principles
of diversity. Especially is this use also possible when individual
assemblies or components are modularly combined and/or embodied
CA 02656329 2009-02-25
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27
galvanically separated from one another. For example, in this way, an
input module formed by means of the initially provided assemblies or
components can be kept galvanically separated from a circuit module
including at least parts of the evaluating and operating circuit, especially
the driver circuit provided therein.
A further advantage of some embodiments of the invention is that the field
device, because of the
small power required for its operation, can, without more, meet the
specifications of the various explosion-protection classes. This makes the
field device specially suited also for application in those explosion-
endangered areas, wherein only devices of intrinsic safety are allowed.
Furthermore, the field device can, in such case, be so embodied, that it
can work together with the usual field busses. This can, on the one hand,
occur by direct connection to the field bus, e.g. corresponding to the
FIELDBUS-protocol (FIELDBUS is a registered mark of the FIELDBUS-
FOUNDATION). On the other hand, the working together can occur
indirectly by means of a bus-coupler, e.g. corresponding to the so-called
HART-protocol (HART is a registered mark of the HART User Group).
CA 02656329 2012-08-10
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27a
In accordance with a broad aspect of the invention, there is provided for
a field device, a field-device electronics fed by an external, electric energy
supply,
said external electric energy supply providing a supply voltage and delivering
a
variable supply current driven thereby, and said field-device electronics
comprising:
an electric current adjuster flowed-through by the supply current, said
electric current
adjuster being adapted for at least one of: adjusting and modulating the
supply
current; an internal operating and evaluating circuit for controlling the
field device;
and an internal supply circuit feeding the internal operating and evaluating
circuit and
lying at an internal input voltage of the field-device electronics derived
from the
supply voltage, said internal supply circuit including a first useful-voltage
controller
flowed-through, at least at times, by an first current component of the supply
current
for providing in the field-device electronics a first internal, useful voltage
essentially
controlled to be constant at a predeterminable, first voltage level, a second
useful-
voltage controller flowed-through, at least at times, by a second current
component of
the supply current for providing in the field-device electronics a second
internal,
useful voltage variable over a predeterminable voltage range, and a voltage
adjuster,
flowed-through, at least at times third current component of the supply
current, for
adjusting and maintaining the internal input voltage of the field-device
electronics at a
predeterminable voltage level; wherein the two useful-voltage controllers are
galvanically separated from one another.
There is also provided a field-device for at least one of: measuring and
monitoring at least one of a specified physical parameter and chemical
parameter of
a medium, said field device comprising: a field-device electronics, fed by an
external,
electric energy supply, said external electric energy supply providing a
supply voltage
and delivering a variable supply current driven thereby, and said field-device
electronics including: an electric current adjuster flowed-through by the
supply current
for at least one of adjusting and modulating the supply current; an internal
operating
and evaluating circuit for controlling the field device; and an internal
supply circuit
feeding the internal operating and evaluating circuit and lying at an internal
input
CA 02656329 2012-08-10
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27b
voltage of the field-device electronics derived from the supply voltage, said
internal
supply circuit including a first useful-voltage controller flowed-through, at
least at
times, by a first current component of the supply current for providing in the
field-
device electronics a first internal, useful voltage essentially controlled to
be constant
at a predeterminable, first voltage level, a second useful-voltage controller
flowed-
through, at least at times, by a second current component of the supply
current for
providing in the field-device electronics a second internal, useful voltage
variable over
a predeterminable voltage range, and a voltage adjuster, flowed-through, at
least at
times, by a third current component of the supply current, for adjusting and
maintaining the internal input voltage of the field-device electronics at a
predeterminable voltage level, wherein the two useful-voltage controllers are
galvanically separated from one another; and said field device further
comprising a
physical-to-electrical, measurement pickup, which reacts to changes of the at
least
one parameter and issues, at least at times, at least one measurement signal
corresponding with the parameter, said physical-to-electrical, measurement
pickup
being electrically coupled with the field-device electronics.
Another aspect of the invention provides a field device for adjusting at
least one predetermined physical and/or chemical parameter of a medium, said
field
device comprising: a field-device electronics, fed by an external, electric
energy
supply, said external electric energy supply providing a supply voltage and
delivering
a variable supply current driven thereby, and said field-device electronics
including:
an electric current adjuster flowed-through by the supply current for at least
one of
adjusting and modulating the supply current; an internal operating and
evaluating
circuit for controlling the field device; and an internal supply circuit
feeding the internal
operating and evaluating circuit and lying at an internal input voltage of the
field-
device electronics derived from the supply voltage, said internal supply
circuit
including a first useful-voltage controller flowed-through, at least at times,
by a first
current component of the supply current for providing in the field-device
electronics a
first internal, useful voltage essentially controlled to be constant at a
predeterminable,
CA 02656329 2012-08-10
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27c
first voltage level, a second useful-voltage controller flowed-through, at
least at times,
by a second current component of the supply current for providing in the field-
device
electronics a second internal, useful voltage variable over a predeterminable
voltage
range, and a voltage adjuster, flowed-through, at least at times, by a third
current
component of the supply current, for adjusting and maintaining the internal
input
voltage of the field-device electronics at a predeterminable voltage level,
wherein the
two useful-voltage controllers are galvanically separated from one another;
and said
field device further comprising an electrical-to-physical actuator
electrically coupled
with the field-device electronics, said actuator reacting to changes of at
least one
applied control signal with an adjusting motion of the actuator for
influencing the
parameter to be adjusted.
Example embodiments of the invention will now be explained in greater
detail on the basis of the drawing.
Functionally equal parts are provided in the separate figures with the
same reference characters, which, however, are repeated in subsequent figures
only
when such appears helpful. The figures of the drawing show as follows:
CA 02656329 2009-02-25
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27b
Functionally equal parts are provided in the separate figures
with the same reference characters, which, however, are
repeated in subsequent figures only when such appears
helpful. The figures of the drawing show as follows:
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December 15, 2008
Fig. 1 perspectively in side view, a field device, as well as an
external energy supply electrically connected therewith via a
pair of electric lines;
Fig. 2 perspectively in a first side view, partially in section, an
example of an embodiment of a vibration-type measurement
pickup suitable for the field device of Fig. 1;
Fig. 3 perspectively in a second side view, the measurement pickup
of Fig. 2;
Fig. 4 an example of an embodiment of an electromechanical
exciter mechanism for the measurement pickup of Fig. 2;
Fig. 5 in the form of a block diagram, a field-device electronics
suitable for application in a field device, especially a two-wire
field device;
Figs. 6 to 8 partly in the form of block diagrams, circuits of examples of
embodiments of an exciter circuit suited for application in a
field device of Fig. 1 having a vibration-type measurement
pickup of Figs. 2 to 4;
Figs. 9 to 12 circuit diagrams of examples of embodiments of end stages
suitable for the exciter circuits of Figs. 6 to 8; and
Fig. 13 schematically, dependencies of voltage components in the
field device electronics of Fig. 5.
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Fig. 1 shows an example of a field device suited for application in industrial
measuring and automation technology, along with a field-device
electronics 20 fed from an external, electrical energy supply 70. In
operation, the external, electrical energy supply 70 provides an, especially
unipolar, supply voltage Uv and delivers in accompaniment therewith a
variable, especially binary, supply current I correspondingly driven by the
supply voltage Uv. For this purpose, the field-device electronics is
electrically connected, during operation, with at least a pair of electric
lines
2L. As a result of the voltage drop naturally occurring between external
energy supply 70 and the input of the field-device electronics 20, the
supply voltage Uv is, however, reduced over this distance to the terminal
voltage UK actually present at the input to the field-device electronics.
The field device serves, in an embodiment of the invention, for measuring
and/or monitoring, as well as for repeatedly delivering, measured values
appropriately representing at least one, earlier designated, physical and/or
chemical parameter, such as e.g. a flow rate, density, viscosity, fill level,
pressure, temperature, pH-value, or the like, of a medium, especially a gas
and/or a liquid, conveyed in a pipeline and/or a container. To this end, the
field device includes, additionally, a physical-to-electrical measurement
pickup electrically coupled with the field-device electronics for reacting to
changes of the at least one parameter and for issuing, at least at times, a
measurement signal corresponding to the parameter, especially in the
form of a variable signal voltage and/or a variable signal current.
Alternatively or supplementally, there can be provided in the field device
an electrical-to-physical actuator electrically coupled with the field-device
electronics for reacting to changes of at least one applied control signal,
especially in the form of a variable signal voltage and/or a variable signal
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December 15, 2008
current, with the actuator providing an adjusting movement for influencing
the parameter to be adjusted, or, stated differently, the field device can
also, for example, be so designed that it serves for adjusting at least one
of such physical and/or chemical parameters of the medium. For
controlling the field device, especially also for activating the mentioned
measurement pickup or for activating the mentioned actuator, there is
further provided in the field-device electronics an internal operating and
evaluating circuit 50. For the case in which the field device is a measuring
device serving for the measuring of the at least one, earlier designated,
physical and/or chemical parameter, it is further provided that the
operating and evaluating circuit 50 determines the at least one measured
value, or a plurality of corresponding measured values, for the parameter.
In the case of the field device illustrated in Fig. 1, such is an in-line
measuring device serving especially for registering parameters, e.g. a
mass flow rate, density and/or viscosity, of a medium, especially a gas
and/or a liquid, flowing in a pipeline (not shown), and for reflecting such in
a measured value XM instantaneously representing this parameter.
Accordingly, the field device can be, for example, a Coriolis mass flow
measuring device, a density measuring device, or also a viscosity
measuring device. For producing the at least one measurement signal,
the field device shown here includes a vibration-type measurement pickup
10 accommodated within a corresponding measurement pickup housing
100, as well as field-device electronics 20 accommodated in the illustrated
electronics housing 200 and electrically connected in suitable manner with
the measurement pickup 10.
Figs. 2 to 4 show an example of an embodiment for such a measurement
pickup, whose construction and manner of operation is comprehensively
described e.g. also in US-A 6,006,609. It is noted, however, already here,
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that, although the example of an embodiment of a field device in this
instance concerns an in-line measuring device with a vibration-type
measurement pickup, the invention, of course, can be put into practice
also in other field devices, for example an in-line measuring devices using
magneto-inductive measurement pickups or acoustic measurement
pickups. Equally as well, the present invention can also be used in field
devices which serve for measuring parameters, for example fill level
and/or limit level, such as are determined in connection with containers
containing media. Such field devices are usually implemented by means
of measurement pickups having at least one measurement probe
protruding into a lumen of the container or at least communicating with the
lumen, for example a microwave antenna, a Goubau-line, a vibrating,
immersion element, or the like.
For conveying the medium to be measured, the measurement pickup 10 of
the example of an embodiment as shown in Figs. 2 to 4 includes at least
one measuring tube 13, having an inlet end 11 and an outlet end 12, a
predeterminable measuring tube lumen 13A elastically deformable during
operation, and a predeterminable nominal diameter. Elastic deformation
of the measuring tube lumen 13A means, here, that, for producing the
above-mentioned, medium-internal, and, consequently medium-
characterizing, reaction forces, a spatial shape and/or a spatial position of
the measuring tube lumen 13A is cyclically, especially periodically,
changed in predetermined manner within an elastic range of the
measuring tube 13; compare e.g. US-A 4,801,897, US-A 5,648,616, US-A
5,796,011 or US-A 6,006,609. In case required, the measuring tube can,
as shown e.g. in EP-A 1 260 798, also be bent, for example. Moreover, it
is e.g. also possible to use, instead of a single measuring tube, two bent or
straight measuring tubes. Other suitable forms of embodiment for such
vibration-type measurement pickups are described comprehensively e.g.
CA 02656329 2012-08-10
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32
in US-B 6,711,958, US-B 6,691,583, US-B 6,666,098, US-A 5,301,557,
US-A 5,357,811, US-A 5,557,973, US-A 5,602,345, US-A 5,648õ616 or
US-A 5,796,011. Especially suited as material for the straight measuring
tube 13 of Figs. 3 and 4 are e.g. titanium alloys. Instead of titanium alloys,
however, also other materials usually used also for such, especially also
bent, measuring tubes, can be used, such as e.g. stainless steel, tantalum
or zirconium.
The measuring tube 13, which communicates in the usual manner at its
inlet and outlet ends with the pipeline conveying the medium into, and out
of, the measuring tube, is held oscillatably in a rigid, especially bending-
and twisting-stiff, support frame 14 surrounded by the measurement
pickup housing 100. The support frame 14 is affixed to the measuring
tube 13 on the inlet end by means of an inlet plate 213 and on the outlet
end by means of an outlet plate 223, with these two plates being, in each
case, pierced by corresponding extension pieces of the
measuring tube 13. Furthermore, the support frame 14 has a first side-
plate 24 and a second side-plate 34, both of which plates 24, 34 are
affixed, in each case, in such a manner to the inlet plate 213 and to the
outlet plate 223, that they extend practically parallel to measuring tube 13
and are arranged spaced from this tube, as well as from each other;
compare Fig. 3. Consequently, mutually facing side surfaces of the two
side plates 24, 34 are likewise parallel to one another. A longitudinal strut
is fixed on the side plates 24, 34, spaced from the measuring tube 13,
25 to serve as a balancing mass absorbing the oscillations of the measuring
tube. The longitudinal strut 25 extends, as shown in Fig. 4, essentially
parallel to the entire oscillatable length of measuring tube 13; this is,
however, not obligatory, since the longitudinal strut 25 can, of course, if
necessary, also be made shorter. The support frame 14, with the two side
plates 24, 34, the inlet plate 213, the outlet plate 223 and the longitudinal
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strut 25, thus has a longitudinal line of centers of gravity extending
essentially parallel to a measuring tube central axis 13B virtually
connecting the inlet end 11 and the outlet end 12. The heads of the
screws shown in Figs. 3 and 4 are to indicate that the mentioned
securement of the side plates 24, 34 to the inlet plate 213, to the outlet
plate 223 and to the longitudinal strut 25 can occur by threaded
connections; however, other suitable securement systems known to those
skilled in the are can be used as well. For the case in which the
measurement pickup 10 is to be assembled releasably with the pipeline,
the measuring tube 13 is provided v ith a first flange 119 on the inlet end
and a second flange 120 on the outlet end; compare Fig. 1. Instead of the
flanges 119, 120, also other pipeline connecting pieces can be provided for
the releasable connection with the pipeline, such as indicated e.g. in Fig. 3
in the form of so-called triclamp connectors. In case required, the
measuring tube 13 can also be connected directly with the pipeline, e.g. by
means of welding, hard-soldering or brazing, etc..
For producing the mentioned reaction forces in the medium, the measuring
tube 13 is caused, during operation of the measurement pickup 10, to
vibrate, and, thus, to elastically deform in predeterminable manner, at a
predetermined oscillation frequency, especially a natural resonance
frequency, in the so-called wanted mode, driven by an electromechanical
exciter mechanism 16 coupled with the measuring tube. As already
mentioned, this resonance frequency is also dependent on the
instantaneous density of the fluid. In the illustrated example of an
embodiment, the vibrating measuring tube 13, as is usual for such
vibration-type measurement pickups, is spatially, especially laterally,
deflected out of a static, rest position; the same is essentially true also
for
those measurement pickups, in which one or more bent measuring tubes
execute cantilever oscillations about a corresponding, imaginary,
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longitudinal axis virtually connecting the in- and out-let ends, or also for
those measurement pickups, in which one or more straight measuring
tubes execute planar, bending oscillations about a measuring tube
longitudinal axis. In another case, in which the measurement pickup 10
executes, as described e.g. in the mentioned WO-A 95/16 897, peristaltic,
radial oscillations, so that the cross section of the vibrating measuring tube
is, in the usual manner therefor, symmetrically deformed, the longitudinal
axis of the measuring tube remains in its static, rest position.
The exciter mechanism 16 serves for producing an exciter force Fexc acting
on the measuring tube 13, the exciter force being produced by converting
an electric exciter power Pexc fed from the operating and evaluating circuit
50 in the form of an electric driver signal. The exciter power Pexc serves in
the case of exciting a natural resonance frequency essentially solely for
compensation of the power fraction removed from the oscillation system
by mechanical and fluid-internal friction. For achieving a highest possible
efficiency, the exciter power is, therefore, adjusted as accurately as
possible, such that essentially the oscillations of the measuring tube 13 in
the desired, wanted mode, e.g. in a fundamental resonance frequency, are
maintained. For the purpose of transferring the exciter force Fexc onto the
measuring tube, the exciter mechanism 16 includes, as shown in Fig. 4, a
rigid, electromagnetically and/or electrodynamically driven, lever
arrangement 15 having a cantilever 154 affixed rigidly on the measuring
tube 13 and having a yoke 163. Yoke 163 is, likewise rigidly, affixed on
one of the ends of cantilever 154 spaced from the measuring tube 13, and,
indeed, in such a manner that it is located above the measuring tube 13
and transverse to it. Cantilever 154 can be e.g. a metal disk, or washer,
which accommodates the measuring tube 13 in a bore. Other suitable
embodiments of the lever arrangement 15 are disclosed in the already
mentioned US-A 6,006,609. Lever arrangement 15 is T-
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shaped and so arranged (compare Fig. 4) that it acts on the measuring
tube 13 about at the half-way point, between inlet end 11 and outlet end
12, whereby the measuring tube experiences, during operation, its
greatest lateral deflection at such half-way point. For driving the lever
arrangement 15, the exciter mechanism 16 of Fig. 4 includes a first
magnet coil 26 and an associated, first, permanently magnetic, armature
27, as well as a second magnet coil 36 and an associated, second,
permanently magnetic, armature 37. The two magnet coils 26, 36, which
are preferably connected in series, are affixed, especially releasably, on
both sides of the measuring tube 13, to the support frame 14, beneath the
yoke 163, such that they can interact with their respectively associated
armatures 27, 37 during operation. The two magnet coils 26, 36 can, if
required, of course also be connected in parallel with one another. As
shown in Figs. 3 and 5, the two armatures 27, 37 are affixed to yoke 163,
mutually spaced from one another, in such a manner that, during operation
of the measurement pickup 10, armature 27 is essentially permeated by a
magnetic field of coil 26 and armature 37 essentially permeated by a
magnetic field of coil 36, and on the basis of corresponding electrodynamic
and/or electromagnetic forces, they are moved, especially in a manner
involving plunging in their associated magnet coils. The movements of the
armatures 27, 37 (especially in their functioning as plunging armatures)
produced by the magnetic fields of the magnet coils 26, 36 are transferred
by the yoke 163 and by the cantilever 154 to the measuring tube 13.
These movements of the armatures 27, 37 are so developed relative to the
respectively associated magnet coils that the yoke 163 is deflected from its
rest position alternately in the direction of the side plate 24 or in the
direction of the side plate 34. A corresponding axis of rotation, parallel to
the already mentioned measuring tube central axis 13B can extend e.g.
through the cantilever 154. The support frame 14 serving as support
element for the exciter mechanism 16 includes, additionally, a holder 29
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connected, especially releasably, with the side plates 24, 34, for holding
the magnet coils 26, 36, and, as required, individual components of a
magnet brake mechanism 217 discussed below.
In the case of the measurement pickup 10 of the example of an
embodiment, the lateral deflections of the vibrating measuring tube 13 held
clamped securely at the inlet end 11 and the outlet end 12 effect,
simultaneously, an elastic deformation of the lumen 13A of the measuring
tube. This deformation develops over practically the entire length of the
measuring tube 13. Furthermore, simultaneously to the lateral deflections,
twisting about the measuring tube central axis 13B is caused in the
measuring tube 13, due to the torque acting on such via the lever
arrangement 15, so that the measuring tube 13 oscillates essentially in a
mixed bending-torsional mode of oscillation serving as wanted mode. The
twisting of the measuring tube 13 can, in such case, be so developed, that
a lateral deflection of an end of the cantilever 154 spaced from the
measuring tube 13 is either equally, or oppositely, directed, compared to
the lateral deflection of the measuring tube 13. The measuring tube 13
can, thus, execute torsional oscillations in a first bending-torsional mode
corresponding to the equally-directed case or in a second bending-
torsional mode corresponding to the oppositely directed case. Then, in the
case of the measurement pickup 10 according to the example of an
embodiment, the natural, fundamental resonance frequency of the second
bending-torsional mode of oscillation is approximately, at e.g. 900 Hz,
twice as high as that of the first bending-torsional mode. For the case in
which the measuring tube 13 is to execute, during operation oscillations
solely in the second bending-torsional mode, a magnetic brake
mechanism 217, operating on the eddy current principle, is integrated into
the exciter mechanism 16, for stabilizing the position of the mentioned axis
of rotation. The magnetic brake mechanism 217 can thus assure that the
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measuring tube 13 always oscillates in the second bending-torsional mode
and, consequently, possible external disturbances on the measuring tube
13 do not lead to a spontaneous switching into another bending-torsional
mode, especially not into the mentioned, first mode. Details of such a
magnetic braking arrangement are described comprehensively in US-A
6, 006, 609.
For causing the measuring tube 13 to vibrate, the exciter mechanism 16 is
fed during operation by means of a likewise oscillating exciter current iexc,
especially one of adjustable amplitude and adjustable exciter frequency
fexc, in such a manner that this current flows through the magnet coils 26,
36 during operation and, in corresponding manner, the magnetic fields
required for moving the armatures 27, 37 are produced. The exciter
current ieXC is, as schematically shown in Fig. 5, supplied from a driver unit
50B additionally provided in the field-device electronics 20 and can be, for
example, a harmonic, alternating current. The exciter frequency fexc of the
exciter current fexc is, in the case of the example of an embodiment shown
here, preferably so selected, or it adjusts itself, such that the laterally
oscillating measuring tube 13 torsionally oscillates, to the extent possible,
exclusively in the second bending-torsional oscillation mode.
It is to be noted here, in this connection, that, although in the example of
an embodiment shown here, the field-device electronics 20 has only one
variable inductive impedance - in this case a magnet coil of variable
inductance - fed by the driver unit 50B, the driver unit 50B can also be
designed to excite other electrical impedances, for example a measuring
capacitor of variable capacitance, or the like. In the case of a capacitive
pressure sensor as measurement pickup, its electrical impedance would
then change during operation also as a function of the at least one
parameter to be measured and/or monitored, with, as is known, a signal
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voltage falling across the changing electrical impedance and/or a signal
current flowing through the changing electrical impedance serving as
measurement signal.
For detecting the deformations of the measuring tube 13, the
measurement pickup 10 further includes a sensor arrangement, which, as
shown in Figs. 2 and 3, produces, by means of at least a first sensor
element 17 reacting to vibrations of the measuring tube 13, a first
oscillation measurement signal for representing these vibrations and
serving as measurement signal si. Sensor element 17 can be formed e.g.
by means of a permanently magnetic armature, which is affixed to the
measurement tube and which interacts with a magnet coil held by the
support frame 14. Especially suited as sensor element 17 are especially
those, which, based on the electrodynamic principle, register a velocity of
the deflection of the measuring tube 13. However, also acceleration-
measuring, electrodynamic or even distance-measuring, resistive, or
optical sensors can be used. Of course, also other sensors known to
those skilled in the art and suitable for the detection of such vibrations can
be used, such as e.g. sensors registering strains of the measuring tube 13.
The sensor arrangement further includes a second sensor element 18,
especially one identical to the first sensor element 17, by means of which it
delivers a second oscillation measurement signal likewise representing
vibrations of the measurement tube 13 and, to such extent, serving as a
second measurement signal s2. The two sensor elements 17, 18 are, in
25' the measurement pickup illustrated in the example of an embodiment,
arranged mutually separated along the measuring tube 13, especially at
equal distances from the half-way point along the length of the measuring
tube 13, such that the sensor arrangement 17, 18 locally registers both
inlet- and outlet-end vibrations of the measuring tube 13 and presents
them in the form of corresponding oscillation measurement signals.
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Fig. 5 shows, schematically in the form of a block diagram, an embodiment
of a field-device electronics 20 suitable for the field device of Figs. I to
4.
On the right of Fig. 5, the above described vibration-type measurement
pickup is schematically illustrated, with exciter mechanism 16 and sensor
arrangement 17, 18, with the magnet coils required for the measurement
principle of the pickup being shown symbolically.
The first measurement signal Si, and the second measurement signal s2,
which may, or may not, be present, both usually have a signal frequency
corresponding to the instantaneous oscillation frequency of the measuring
tube 13. These signals are, as shown in Fig. 2, fed to a, preferably digital,
evaluation unit 50A of the operating and evaluating circuit provided in the
field-device electronics 20. Evaluation unit 50A serves for determining,
especially numerically, a measured value, XM, instantaneously
representing the process variable to be registered, here e.g. the mass flow
rate, density, viscosity, etc., and to convert such into a corresponding
measured-value signal xM available at the output of the operating and
evaluating circuit. While, in the case of the measurement pickup illustrated
here, the density or also viscosity are readily determinable on the basis of
just one of the measurement signals s,, s2i for the determining of mass
flow rate, both measurement signals s,, s2 are used, in manner known to
those skilled in the art, for ascertaining, for example in the signal time
domain or in the signal frequency domain, a phase difference
corresponding with the mass flow rate.
In an embodiment of the invention, the evaluation unit 50A is implemented
using a microcomputer iJC provided in the field-device electronics 20. The
microcomputer is so programmed that it digitally determines the measured
value XM on the basis of the measurement signals delivered from the
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sensor arrangement 17, 18. For implementing the microcomputer, e.g.
suitable microprocessors and/or also modern signal processors can be
used. As also shown in Fig. 5, the evaluation unit 50A further includes at
least one A/D converter, via which one of the sensor signals s,, s2 or, as
usual especially in the case of Coriolis mass flow pickups, a signal
difference derived previously from the two sensor signals s,, s2, is supplied
digitized to the microprocessor. The measurement or operational data
produced and/or received by the evaluation unit 50A can, furthermore, be
stored volatilely and/or persistently in corresponding digital data memories
RAM, EEPROM.
As already mentioned, the operating and evaluating circuit 50 further
contains a driver unit 50B serving for feeding the exciter mechanism 16
with the mentioned exciter current iexc. Driver unit 50B forms, together
with the measuring tube 13, essentially a control loop. This control loop is
so designed that it electrically tunes both to the mechanical resonance
frequency of the excited vibrations of the measuring tube 13 as well as
also to the amplitude of these vibrations predetermined by means of the
reference signal Sr. Driver unit 50B can, in such case, be constructed in
the usual manner by means of a phase-locked loop, a so-called PLL, for
electrical control of the resonance frequency as well as also the phase
position of the driver signal and by means of a corresponding amplitude
control stage for electrical control of the amplitude of the driver signal,
and,
as a result, also the amplitude of the vibrations.
As shown in Fig. 5, driver unit 50B is also in contact with the evaluating
unit, especially the already mentioned microprocessor pC, from which the
driver unit 50B receives e.g. the required operating data, such as e.g. the
exciter frequency instantaneously to be set and/or the amplitude and, as
required, phase, instantaneously to be set for the exciter current, or to
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which the driver unit 50B sends internally produced tuning signals and/or
parameters, especially also information concerning the set exciter current
iexc and/or the exciter power Pexc fed into the measurement pickup. The
operating data for the driver unit 50B, exciter frequency, amplitude and/or
phase, can, in such case, be both absolute values as well as also relative
values. Alternatively or in supplementation thereto, the operating data
transmitted to the driver unit 50B can also represent incremental, or
decremental, changes of exciter frequency, amplitude and/or phase. In
addition to the microprocessor pC, the operating and evaluating circuit 50
can also include a signal generator serving for producing the driver signal,
for example a digital signal processor or a programmable logic component,
especially a FPGA, configured correspondingly as a signal generator.
Figs 6 to 12 show block diagrams of examples of embodiments of the
driver unit 50B suited especially also for use in a field device designed as
an intrinsically safe measuring device and/or as a 2L-measuring-device.
In a first variant, one of the sensor signals delivered from the sensors 17,
18 or e.g. also their sum is fed to an amplitude demodulation stage pd as
input signal. Thus, the amplitude demodulation stage pd is connected at
its input with one of the sensors 17, 18. In Fig. 6, that is the sensor 17.
The amplitude demodulation stage pd serves for determining continuously
an oscillation amplitude of the measuring tube vibrations. Additionally, the
amplitude demodulation stage pd serves for delivering an output signal,
e.g. a simple direct-current signal representing this registered oscillation
amplitude. To this end, in a preferred embodiment of the invention, a peak
value detector is provided for the input signal in the amplitude
demodulation stage pd. Instead of this peak value detector, also e.g. a
synchronous rectifier can be used for registering the oscillation amplitude.
The rectifier is clocked by a reference signal of equal phase to the input
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signal. A first input of a comparison stage sa is connected with an output
of the amplitude demodulation stage pd; a second input of the comparison
stage sa receives an adjustable reference signal Sr, which specifies an
amplitude of vibration of the measuring tube 13. The comparison stage sa
determines a deviation of the output signal of the amplitude demodulation
stage pd from the reference signal Sr and issues this as a corresponding
output signal. This deviation can be determined and forwarded on the
basis of a simple difference between the registered oscillation amplitude
and that specified by the reference signal Sr in the form of an absolute
amplitude error or e.g. also on the basis of a quotient of registered and
specified oscillation amplitudes in the form of a relative amplitude error.
To a first input of an amplitude modulation stage amt is supplied the input
signal of the amplitude demodulation stage pd and, to a second input the
output signal of the comparison stage sa. The amplitude modulation stage
amt serves for modulating the input signal of the amplitude demodulation
stage pd with the output signal of the comparison stage sa. In such case,
e.g. one of the sensor signals s,, the sum of the two sensor signals s,, s2
or also a signal essentially proportional thereto, produced synthetically, for
example, by means of an appropriate signal generator, can serve as input
signal, which, to such extent, is a carrier signal which can be quite variable
as to frequency. Onto this carrier signal is modulated the error signal of
variable amplitude, as produced by means of the comparison stage sa.
The error signal represents, namely, the deviation of the instantaneous
vibration amplitude of the measuring tube 13 from its, or their, desired
oscillation amplitude represented by the reference signal Sr. Additionally,
the amplitude modulation stage amt serves to deliver the driver signal
carrying the driving energy for the exciter mechanism 16. For such
purpose, the amplitude modulation stage has a corresponding end stage
ps for amplifying the carrier signal modulated with the modulation signal.
For the purpose of the amplitude modulation of the carrier signal with the
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modulation signal, a multiplier ml is additionally provided in the amplitude
modulation stage amt; compare Fig. 6.
Fig. 7 shows, corresponding to the second variant of the invention, partly
in the form of a block diagram, the circuit of a second variant for the driver
unit 50B. The example of an embodiment in Fig. 7 differs from that in Fig.
6 essentially in that, instead of its amplitude modulation stage amt, a
pulse-width modulation stage pwm is provided, having a pulse-length
modulator pm clocked by an external alternating current signal. The
pulse-length modulator pm is, as shown in Fig. 7, driven by a constant,
positive, first, direct voltage +U1 and lies at circuit ground, or zero point,
SN. Supplied to a first input of the pulse-length modulator pm - that is the
carrier signal input - is the input signal of the amplitude demodulation
stage pd. Thus, this first input is connected with one of the sensors - in
Fig. 7 this is again the sensor 17. Supplied to a second input of the pulse-
length modulator pm - this is the modulation signal input - is the error
signal proportional to the determined amplitude error. The output of the
pulse-length modulator pm is, in turn, connected with the input of an end
stage ps', which feeds, on its output side, the exciter mechanism 16 with a
corresponding driver signal. The driver signal delivered from the end
stage ps' is, in this case, a rectangular signal, which is clocked with a
signal frequency of the input signal of the amplitude demodulation stage
pd and which has a pulse width modulated with the output signal of the
comparison stage sa.
Fig. 8 shows, partly in the form of a block diagram, the circuit of a third
variant of the driver unit 50B. The example of an embodiment shown in
Fig. 8 differs from that of Fig. 6 in that, instead of its multiplier ml, a
comparator kk and a DC-DC converter dc are provided, which delivers at
least one driver voltage driving the exciter current iexc. The amplitude of
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this driver voltage is, in turn, dependent on the output signal of the
comparison stage sa and, therefore, is to be considered as non-constant.
Depending on the driver voltage, the exciter current iexc can, as already
mentioned, be bi-polar or, however, also unipolar. Consequently, the DC-
DC converter dc delivers, in a preferred embodiment of the invention
according to Fig. 8, a driver voltage having a positive first potential +u and
a negative second potential -u, with a control input of the DC-DC converter
dc serving for adjusting of the potentials and receiving the output signal of
the comparison stage sa. The driver voltage delivered by the DC-DC
converter dc, appropriately adapted in its amplitude, is applied to an end
stage ps" of the pulse width modulation stage pwm as operating voltage
and the end stage ps", in turn, feeds the exciter mechanism 16. Moreover,
the end stage ps" is connected on its input side with an output of the
comparator kk. Comparator kk is operated by the constant, positive, first
direct voltage +U1 and lies at circuit ground SN. Supplied to an input of
the comparator kk is the input signal of the peak value detector pd.
Consequently, comparator kk is connected on its input side with one of the
sensors - in Fig. 8 this is again the sensor 17.
In Figs. 6 to 7, it is indicated in each case by dashed lines that, instead of
one of the sensor signals of the sensors 17, 18, also their sum can be
supplied to the peak value detector pd and to the multiplier ml, or to the
pulse-length modulator pm, or to the comparator kk, as the case may be;
then, these sensor signals have to be passed through a summing unit.
Alternatively, however, as already mentioned, a synthetic signal can be
used, produced by means of a digital signal processor and a D/A converter
connected to its output, and correspondingly adapted to the sensor signal
in its frequency and phase position. In Figs. 6 to 7, still other circuit
portions are shown in dashed representation, to indicate preferred further
developments of the preferred exciter circuit. In one further development
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of the driver unit 50B, a pre-amplifier vv is provided, which is placed in
front of the peak-value detector pd or, as required, the synchronous
rectifier. In another further development of the driver unit 50B, an amplifier
v is provided, which amplifies the output signal of the comparison stage,
before it reaches the amplitude modulation stage as error signal. Such an
amplifier can be an operational amplifier op, whose non-inverting input lies
at circuit ground SN, whose inverting input is connected via a series
resistor wv with the output of the comparison stage sa and via a shunt
resistor ws with the amplifier output. The operational amplifier connected
in this manner is, in each case, shown at the right top in Figs. 6 to 7. In a
next further development of the driver unit 50B, an integrating amplifier vi
is provided, which amplifies and integrates the output signal of the
comparison stage sa, before it reaches the multiplier m as error signal.
Such an amplifier can be an operational amplifier op', whose non-inverting
input lies at circuit ground SN, and whose inverting input is connected with
the output of the comparison stage sa via a series resistor wv' and, via a
series circuit formed of a shunt resistor ws' and a capacitor k, with the
output of the amplifier. The operational amplifier op' connected in this
manner is shown in each case in the right-middle of Figs. 6 and 7.
Another further development of the driver unit 50B utilizes a differentiating
and integrating amplifier vd, which amplifies, differentiates and integrates
the output signal of the comparison stage sa, before it reaches multiplier
ml as error signal. Such an amplifier can be an operational amplifier op",
whose non-inverting input lies at circuit ground SN, and whose inverting
input is connected via a parallel circuit of a series resistor wv" and a first
capacitor k1 with the output of the comparison stage sa and via a series
circuit of a shunt resistor ws" and a second capacitor k2 with the amplifier
output. The operational amplifier op" connected in this manner is shown in
Figs. 6 and 7 in each case at the right-bottom of the figure. The arrows in
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Figs. 6 and 7 indicate that the relevant amplifier v, vi, vd is to be placed
in
the box q (shown in dashed representation), which lies either between the
output of the comparison stage sa and the second input of the amplitude
modulation stage am, or, however, between the output of the comparison
stage sa and the modulation signal input of the pulse-width modulation
stage pwm.
Quite within the framework of the invention is to have the functions of the
individual circuit portions of Figs. 6 and 7 implemented by corresponding
analog or digital circuit portions, in the latter case, thus e.g. by means of
a
suitable programmed microprocessor, with the signals going to such being
first passed through an analog/digital conversion and its output signals, if
required, being subjected to a digital/analog conversion.
Fig. 9 shows a circuit of a first example of an embodiment of an end stage
ps, which can be inserted, for example, in the amplitude modulation stage
am of Fig. 6. An operational amplifier ov is powered by a positive and a
negative, in each case constant, direct voltage +U, -U and is connected as
follows. An inverting input lies, via a first resistor w1, at circuit ground
SN
and a non-inverting input is connected via a second resistor w2 to the
output of the multiplier ml. An output of the operational amplifier ov is
connected through a third resistor w3 with a first terminal ppl of a primary
winding of a transformer tf; a second terminal pp2 of the primary winding
lies at circuit ground SN. The secondary winding of transformer tf is
connected by means of its two terminals sp1, sp2 to the exciter
mechanism 16.
The primary winding has a primary winding number N1 and the secondary
winding a secondary winding number N2. The transformer tf is a current
step-up transformer and has a transformation ratio of e.g. 20:1. The
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inverting input of the operational amplifier ov is connected through a fourth
resistor w4 to the first terminal ppl of the primary winding. The non-
inverting input is connected with the output through a fifth resistor w5. The
five resistors w1, w2, w3, w4, w5 have corresponding resistance values
R1, R2, R3, R4, R5. The resistance value R1 is selected equal to the
resistance value R2, and the resistance value R4 is selected equal to the
resistance value R5. The alternating current i flowing into the exciter
mechanism 16 is as follows, where urn is the output voltage of the
multiplier m: R5N1 1 =um m R1 R3 N2.
Fig. 10 shows a circuit of a preferred, second example of an embodiment
of an end stage ps', which can be inserted, for example, in the pulse-width
modulation stage pwm of Fig. 7. The "core" of this embodiment of the end
stage, which is a complementary push-pull end stage, is a series
connection of the controlled current path of a p-channel-enhancement,
insulating layer, field-effect transistor P with an n-channel-enhancement,
insulating layer, field effect transistor N, which will be referenced in the
following as "transistors" for short. The exciter mechanism 16 is
connected to the junction point of the controlled current paths. On each
controlled current path, a protective diode dn, dp is connected in parallel,
with each cathode lying on the positive point of the associated transistor.
The end of the series connection on the p-transistor-side lies at a constant,
positive, second direct voltage +U2 and its end on the n-transistor-side lies
at a corresponding, negative direct voltage -U2. The gates of the
transistors N, P are connected together and with an output of the
comparator W. The non-inverting input of the comparator kk' lies on the
output of the pulse-length modulator pm; compare Fig. 7. The inverting
input of the comparator kk' is connected with a tap of a voltage divider
composed of a resistor r1 and a resistor r2. The resistors r1, r2 have the
same resistance values and lie between the positive, direct voltage +U1
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and circuit ground SN. The resistors r1, r2 and the comparator kk' serve
for making the output signal of the pulse-length modulator pm symmetrical
with reference to the half-value of the direct voltage +U1. The exciter
mechanism 16 receives, consequently, at every positively directed edge
through zero for the output signal of the sensor 17, or the sum of the
output signals of the sensors 17, 18, as the case may be, a positive
current pulse and, at every negatively directed edge through zero for the
output signal of the sensor 17, or the sum of the output signals of the
sensors 17, 18, as the case may be, a negative current pulse. The
respective durations of these current pulses are adjusted automatically,
such that the oscillation amplitude of the measuring tube 13, as specified
by the reference signal Sr, is achieved.
Fig. 11 shows a circuit diagram of another example of an embodiment of
an end stage ps", which can be inserted, for example, in the amplitude
modulation stage amt of Fig. 8. The "core" of this embodiment of the end
stage, which again is a complementary push-pull end stage, is, also here,
as in the case of Fig. 10, a series connection of the controlled current path
of a p-channel-enhancement, insulating layer, field-effect transistor P with
an n-channel-enhancement, insulating layer, field effect transistor N',
which will again be referenced in the following as "transistors" for short.
The exciter mechanism 16 is connected to the junction point of the
controlled current paths. On each controlled current path, a protective
diode dn', dp' is connected in parallel, with each cathode lying on the
positive point of the associated transistor. The end of the series
connection on the p-transistor-side lies at a positive, second direct voltage
+u dependent on the output signal of the comparison stage sa and its end
on the n-transistor-side lies at a negative direct voltage -u dependent on
the output signal of the comparison stage sa. The gates of the transistors
N', P' are connected together and with an output of the comparator kk".
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The non-inverting input of the comparator kk" lies on the output of the
comparator kk; compare Fig. 8. The inverting input of the comparator kk"
is connected with a tap of a voltage divider composed of a resistor r3 and
a resistor r4. The resistors r3, r4 have the same resistance values and lie
between the positive, direct voltage +U1 and circuit ground SN. The
resistors r3, r4 and the comparator kk" serve for making the output signal
of the comparator kk symmetrical with reference to the half-value of the
direct voltage +U1. The exciter mechanism 16 receives, consequently, at
every positive half-wave of the output signal of the sensor 17, or of the
sum of the output signals of the sensors 17, 18, as the case may be, a
positive current pulse and, at every negative half wave of the output signal
of the sensor 17, or of the sum of the output signals of the sensors 17, 18,
as the case may be, a negative current pulse. The respective amplitudes
of these current pulses are dependent on the direct voltages +u, -u, which
are themselves dependent on the output signal of the comparison stage
sa, so that the oscillation amplitude of the measuring tube 13, as specified
by the reference signal Sr, is achieved automatically.
Finally, Fig. 12 shows schematically in the form of a block diagram an
example of an embodiment for a hybrid (thus, operating partly digitally and
partly analogly) driver circuit 50B. Driver circuit 50B includes a digital
signal generator, which serves for converting default values, especially
numerical default values, produced by the microcomputer 50A for
individual parameters of the exciter signal, for example an amplitude of the
exciter current iexc, a phase of the exciter signal and/or an oscillation
frequency of the same, into a corresponding, digital, oscillation signal. The
individual parameters can, as already mentioned, in such case, be
transmitted, for example, as absolute values and/or incremental, or
decremental, values, as the case may be, to the driver unit 50B.
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As already mentioned, the field-device electronics, and, to such extent,
also the field device, are fed from an external, electrical energy supply 70,
for example a remotely located measurement transmitter supply device or
the like, which is connected with the field device, or, more accurately, with
the field-device electronics 20, via the at least one pair of electric lines
2L.
The measurement transmitter supply device, in turn, can, for example, be
connected via a field bus system with a superordinated process control
system stationed in a process control room. In the example of an
embodiment shown here, the field-device electronics, as usual in a
multitude of measurement and automation technology applications, is
electrically connected with the external electrical energy supply solely via a
single pair of electric lines 2L. Accordingly, the field-device electronics is
thus, on the one hand, supplied with electric energy via this one pair of
lines. On the other hand, it is provided that the field-device electronics
transmits the measured value XM, produced at least at times, to an
external evaluating circuit 80 located in the external electric energy supply
70 and/or electrically coupled with the energy supply, likewise via the
single pair of electric lines 2L. The pair of electric lines 2L, in this case,
the single pair, connecting the measurement transmitter supply device and
the field device can, for example, for such purpose, be connected in series
with an energy source 71 feeding the supply current I, e.g. a battery or a
direct voltage source fed via an installation-internal supply network, and
with measuring resistor RM. Energy source 70 drives the supply current I
and supplies, therefore, the field-device electronics 20 with the electric
energy required for its operation. The measuring resistor RM is additionally
provided with two measuring terminals 72, 73, on which the supply current
instantaneously representing the measured value XM can be sensed in the
form of a current-proportional, measured voltage UM. The measured
voltage UM can be visualized on-site or fed to a superordinated, measured
value processing unit. The - here, single - pair of electric lines 2L can be
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embodied, for example, as a so-called two-wire, current loop, especially a
4 mA - 20 mA current loop, or as a connecting line to an external, digital
field bus, for example, a PROFIBUS-PA or a FOUNDATION-FIELDBUS.
In a further embodiment of the invention, it is, therefore, further provided
that the instantaneous measured value XM is modulated onto the supply
current I. For example, the measured value instantaneously determined
by means of the field device can be represented by an instantaneous
current level (especially an electrical current level adjusted to a value
lying
between 4 mA and 20 mA) of the supply current I flowing in the pair of
electric lines 2L embodied as a two-wire, or two-conductor, current loop.
In another embodiment of the invention, it is provided that the field device
communicates, for example exchanges field-device-specific data, via a
data transmission system, at least at times, with an external control and
review unit, for example, a handheld operating device or a programmable
logic controller. For this purpose, there is additionally provided in the
field-
device electronics 20 a communication circuit COM, which reviews and
controls the communication via the data transmission system. Especially,
the communication circuit serves for converting, besides the measured
value XM, e.g. also internal field-device parameters, into signals, which are
transmittable over the pair of electric lines 2L, and for then coupling these
signals into such lines. Alternatively or in supplementation thereof, the
communication circuit COM can, however, also be designed for
correspondingly receiving field-device parameters sent from the outside
over the pair of electric lines 2L. The communication circuit COM can be,
especially for the above-described case in which the field device is
connected during operation solely via a two-wire current loop to the
external supply circuit, e.g. an interfacing circuit working according to the
HART@-Field-Communication-Protocol of the HART Communication
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Foundation, Austin, TX, which uses FSK-coded, high-frequency,
alternating voltages as signal carrier.
As is evident from the combination of Figs. 1 and 5, the field-device
electronics has, for the adjusting and control of voltages and/or currents
internally in the field device, further, at least one current adjuster IS1,
through which the supply current I flows, for adjusting and/or modulating,
especially clocking, of the supply current I. Additionally provided in the
field-device electronics 20 is an internal supply circuit 40, which lies at an
internal input voltage Ue of the field-device electronics 20 derived from the
terminal voltage UK and which serves for the electrical feeding of the
internal operating and evaluating circuit 50.
For registering and regulating voltages instantaneously dropping in the
field-device electronics 20 and/or instantaneously flowing currents, the
supply circuit further includes a corresponding measuring and control unit
60. Moreover, the measuring and control unit 60 serves, especially for the
above-mentioned case in which the measured value XM is modulated onto
the supply current I, also for converting a measured-value signal xM, as
supplied from the operating and evaluating circuit 50 and representing the
instantaneously produced, measured value XM, into a correspondingly
controlling, first current control signal (control controlling the current
adjuster
IS1 and, to such extent, also the supply current. To this end, the
measuring and control unit 60 includes a corresponding current control
circuit 60A, which converts the measured value signal xM delivered by the
internal operating and evaluating circuit 50 to the measuring and control
unit 60 appropriately into the current control signal lcontrol. The control
circuit 60A of the measuring and control unit 60 thus forms, together with
the current adjuster IS1, for practical purposes, a current controller (in
this
case, a so-called linear, longitudinal controller) for the supply current I.
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The current control signal Icontrol is, in an embodiment of the invention, so
adapted that the current adjuster IS1 becomes able to control the supply
current I on the basis of the instantaneously determined measured value
XM proportionally thereto. Alternatively, or in supplementation thereof, the
current control signal (control is so developed that the current adjuster IS1
strobes the supply current, for example binary coded for the purpose of
communication according to the standard PROFIBUS-PA. For producing
correspondingly current-representing, especially essentially current-
proportional, sense voltages I1_ actual, 12_actual, 13-actual, corresponding
sense
resistors R1, R2, R3 are additionally provided in the supply circuit 40. At
least at times, the supply current, or current components I1, 12, 13 derived
therefrom, flow through the respective resistors R1, R2, R3.
At least for the above-described case, in which the supply current is
modulated in its amplitude for the purpose of representing the measured
value XM, and, due to the limited electric power of the external energy
supply, the supply voltage Uv delivered therefrom and, consequently,
associated therewith, also the terminal voltage UK correspondingly sink
with increasing supply current I, or, the reverse, with sinking supply current
I they again increase, the supply voltage Uv and, to such extent, also the
terminal voltage UK are to be considered fluctuating in voltage level in, at
first, non-determinable manner and, to such extent, variable during
operation in significant measure. When the field device works according
to the above-mentioned, in industrial measurement technology long-
established standard of 4 mA to 20 mA, the only available current range
for energy supply in normal operation is that beneath 4 mA, and,
depending on the level of the supply voltage, the permanently available
electric power is then only around 40 to 90 mW (= milliwatts).
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The supply circuit 40 therefore has, as also schematically shown in Fig. 5,
additionally, at the input, a voltage adjuster 30, which, controlled by the
measuring and control unit 60, is provided for the purpose of adjusting an
internal input voltage Ue (serving as primary, or base, voltage for the
internal energy supply) of the field-device electronics as accurately as
possible to a predetermined voltage level (which, on occasion, can also be
varied during operation) and for maintaining such at this, for the moment
selected, voltage level also as constantly at the same level as possible, at
least for the undisturbed, normal operation, wherein, among other things,
the terminal voltage UK is at least equal to a minimum voltage value UKmin.
The measuring and control unit 60 forms, as a result, together with the
voltage adjuster 30, an input voltage controller for the internal input
voltage
Ue and serves, especially, for adjusting and stabilizing this as accurately
as possible.
The voltage level of the internal, input voltage Ue is, in an embodiment of
the invention, so maintained, that the internal input voltage Ue is, as also
shown schematically in Fig. 13, always lower than the terminal voltage UK.
In such case, the voltage level, at which the internal input voltage Ue is
held by means of the aforementioned input voltage controller 30, 60, can,
during operation, be, for example, essentially continuously changed as a
function of the instantaneously flowing, supply current I. Alternatively
thereto, however, it is also possible to hold the voltage level constant over
a certain current-strength range of the supply current and, as a result, also
over a corresponding voltage range of the terminal voltage UK, and, as
indicated in Fig. 13 by means of the dash-dotted line, to change stepwise,
for example at exceeding or falling beneath predetermined threshold
values for the supply current I and/or the terminal voltage UK. In a further
embodiment of the invention, the input voltage controller 30, 60 is so
designed, that the voltage level is held constant after the reaching of a
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predetermined or predeterminable, maximum voltage level Ue max, for
example in an order of magnitude of 15 V, despite possibly further
increasing terminal voltage UK to values, for example, over 20 V. As a
result, the input voltage controller 30, 60 thus acts not only as a voltage
stabilizer for the internal input voltage Ue but also as a voltage limiter
therefor.
For the further, internal, distribution of the electric energy to individual
components or groups of the field-device electronics, such further
includes, for converting the stabilized, internal, input voltage Uei a first
useful-voltage controller UR1, which, at least at times, is flowed-through by
an, especially variable, first current component I, of the supply current and
which serves for providing a first internal, useful voltage UN1 in the field-
device electronics 20. This voltage UN1 is essentially constantly controlled
to a predetermined, as required also parameterable, desired first voltage
level UN1 desired.
Additionally provided in the supply circuit 40 is a second voltage controller
UR2 likewise converting the stabilized, internal input voltage Ue. This
second voltage controller UR2 is flowed-through, at least at times, by an
especially variable, second current component 12 of the supply current I.
The second voltage controller UR2, in turn, serves for making available in
the field-device electronics 20 a second internal useful voltage UN2, which
is variable over a predetermined voltage range. The voltage level for the
useful voltage UN2 best-suited for the instantaneous situation as regards
consumption in the field-device electronics can be determined, for
example, by the measuring and control unit 60 with regard to an
instantaneous consumption situation in the field-device electronics and
then forwarded correspondingly to the useful-voltage controller UR2 in the
form of a voltage control signal UN2_desired. The voltage control signal
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UN2_desired can, as also shown in Fig. 2, be produced, for example, by
means of the, as required present, power control circuit 60B of the
measuring and control unit 60.
Useful-voltage controllers UR1, UR2 can be, for example, so-called
switching controllers, or regulators, and/or unclocked linear controllers, or
regulators, while the voltage adjuster and, as a result, the input voltage
controller, can be formed, for example, by means of a shunt-regulator IS2
lying in a bypass to the internal input voltage Ue, for example one
implemented by means of a transistor and/or an adjustable Zener diode.
Beyond this, the input voltage regulator is, as also shown in Fig. 5, so
designed that a third, especially variable, current component 13 of the
supply current I flows through it, at least at times, during normal operation,
with the measuring and control unit 60 delivering a second current control
signal 13_control appropriately controlling the voltage adjuster 30 - here the
shunt regulator IS2 - and, to such extent, also determining the third
electrical current component. The current control signal 13 control is, in
such
instance, so designed, at least for the case in which the electrical power
instantaneously available in the field-device electronics 20, resulting from
internal input voltage Ue, which is maintained essentially constant, and
from the instantaneously set supply current I, exceeds the electrical power
actually instantaneously needed on the part of the operating and
evaluating circuit 50, that it causes a transistor provided in the input
voltage controller to become conductive to a sufficient degree that a
sufficiently high current component 13 is caused to flow for the stabilization
of the input voltage Ue. For this purpose, the input voltage controller (here
voltage adjuster 30) has, in a further embodiment of the invention, also
components, especially a semiconductor element with cooling fin, or the
like, serving for the dissipation of electric energy and for getting rid of
heat
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energy associated therewith. On the other hand, however, the current
control signal 13_control is also so designed that, in the case in which the
need for power in the operating and evaluating circuit 50 becomes greater,
it again lessens the current component 13 instantaneously flowing in the
voltage adjuster 30. For producing the control signal 13 control actuating the
voltage adjuster 30 during operation and, as a result, also at least partially
regulating the division of the electrical power instantaneously available in
the field device electronics, the measuring and control unit 60 additionally
includes, in a further embodiment of the invention, a corresponding power
control circuit 60B.
As also shown in Fig. 5, it is further provided in the field-device
electronics
of the invention, and, to such extent, also in the field device of the
invention, that the operating and evaluating circuit 50 is flowed-through, at
15 least at times, both by a first useful current INl, especially such a
current
which is variable, driven by the first useful voltage UN1, which is kept
essentially constant, at least in normal operation, and by a second useful
current IN2, especially such a current which is variable, driven by the
second useful voltage UN2, which is allowed to vary during operation. This
20 has the advantage that at least the assemblies and circuits of the field-
device electronics 20, especially the mentioned at least one
microprocessor pC, controlling the field device during normal operation
and, to such extend, keeping the field device operational, can always be
supplied with the electrical energy that they actually instantaneously need.
Accordingly, it is provided in an embodiment of the invention, that the
above-mentioned microprocessor pC and/or the mentioned signal
processor are/is operated, at least partially, with first useful voltage UN1
largely held constant during normal operation, or with a secondary voltage
derived therefrom. In a further development of this embodiment of the
invention, the first useful voltage UNI, or a secondary voltage derived
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therefrom, serves further, at least partially, also as operating voltage for
the at least one A/D-converter provided in the operating and evaluating
circuit. In a further embodiment of the invention, it is provided that at
least
also the components of the field-device electronics controlling and
maintaining the communication with the mentioned, superordinated control
and review unit, thus, here, besides the microprocessor pC, also the
communication circuit COM, are, at least partially, supplied by means of
the first useful voltage UN1 or by a secondary voltage derived therefrom.
Depending on which power can actually be made available during
operation on the part of the external supply circuit 70 and as a function
also of the actual power requirement of the consumers fed already, in the
above-described manner, by the first useful voltage UN1, also individual
components of the driver unit 50B, especially such which serve for
producing the driver signal iexCi for example amplifiers, D/A-converters
and/or signal generators, etc., provided therein, can, additionally, be fed,
at least partially, by means of the first useful voltage UN1 or a secondary
voltage derived therefrom; compare, in this connection, also Fig. 12.
However, it has been found that, alone already with currently obtainable
microprocessors pC and/or A/D-converters and the peripheral circuits
required therefor, one must already reckon with a permanent power
requirement of about 30 mW in normal operation, so that, at least in the
case of applications having a permanently available power of only about
40 mW, thus with terminal voltages of 12 V (= volt) or less, the
aforementioned components of the driver unit 50B can only still be
connected to the first useful voltage UN1 to a very limited extent, without
endangering the desired, high stability. To such extent, an embodiment of
the invention further provides that individual components of the driver unit
50B are operated, especially for longer periods of time, only using the
second useful voltage UN2. Especially, the second useful voltage UN2 is
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suitable, as also shown representatively in Fig. 12, as operating voltage for
the operational amplifier provided in the driver unit 50B. Accordingly then,
the exciter current iexc for the magnetic field coils are driven essentially
by
the second useful voltage UN2 or a secondary voltage derived therefrom.
For bridging-over transient voltage fluctuations on the part of the supply
voltage and/or for buffering possible short-time "overloadings" of the
internal field-device voltage supply due to a momentarily higher internal
power requirement, for example in the case of start-up of the
measurement pickup or during writing of the mentioned, persistent
memory EEPROM, a further development of the invention provides in the
operating and evaluating circuit a storage circuit, especially a capacitive
storage circuit, serving for the temporary storage of electric energy. The
energy buffer C is shown as part of the voltage adjuster in the example of
an embodiment illustrated here, so that it lies essentially permanently at
the internal input voltage Ue. However, in order to be able to prevent,
safely, a collapse of the useful voltage UN1, at least in normal operation, it
is, of course, important to make certain, at the beginning, in the design of
the assemblies and circuits supplied by means of the first useful voltage
UNI, that their maximum consumed electrical power is, at most, equal to a
minimum available electric power in normal operation and/or its
instantaneously consumed electric power is at most equal to an
instantaneously available power.
In a further embodiment of the invention, it is provided, additionally, that
the second useful voltage UN2 is controlled during operation as a function
of an instantaneous voltage level of the internal input voltage Ue of the
field-device electronics. Alternatively or in supplementation thereto, it is
provided that the second useful voltage UN2 is controlled as a function of
an instantaneous voltage level of a terminal voltage UK derived from the
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supply voltage and falling from the input, across the field-device
electronics. It has, furthermore, been found to be advantageous, in this
connection, to control the internal input voltage Ue such that a voltage
difference existing between this and the terminal voltage UK is held as
constant as possible, for example at about 1 V, at least during normal
operation. This makes it possible, among other things, to adjust the input
voltage Ue relatively accurately, even in the case of changing operating
temperature of the current adjuster IS1, or also of the total current
controller, and a change of the pertinent transfer characteristic associated
therewith and so, in simple manner, to achieve a very robust control of the
internal input voltage Ue. The control can, in such case, be implemented,
for example, by means of a difference amplifier provided in the mentioned
measuring and control unit 60. The difference amplifier subtracts a sense
voltage correspondingly derived from the internal input voltage Ue from a
sense voltage correspondingly derived from the terminal voltage UK.
Alternatively or in supplementation thereto, the second useful voltage UN2
can also be controlled as a function of an instantaneous electrical current
level of at least one of the three current components I,, 12, 13. For example,
the second useful UN2 can be controlled as a function of the instantaneous
electrical current level of the third current component 13, which, taking into
consideration the instantaneous input voltage Uei essentially represents an
excess power instantaneously present in the field-device electronics.
Suitable as measured quantity, in this case, is especially also the second
current control signal 13_control controlling the voltage adjuster and, to
such
extent, also determining the third current component 13.
For determining and/or monitoring an instantaneous operating state of the
field-device electronics, a further development of the invention additionally
provides means for comparing electric voltages falling in the field-device
electronics and/or electric currents flowing in the field-device electronics
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with predetermined, especially adjustable, threshold values. Such means
for comparing voltages and/or currents can, for example, be embodied as
integral component(s) of the already mentioned, measuring and control
unit of the supply circuit. In an embodiment of this further development of
the invention, the means for comparing are so designed that, on the part of
the field-device electronics, an alarm signal xpwr fail signaling an under-
supplying of the field-device electronics is produced, at least when a
subceeding, or falling beneath, of a minimum useful voltage limit value,
predetermined for the second useful voltage UN2, by the second useful
voltage UN2 and a subceeding of a minimum electrical current component
limit value, predetermined for the third current component 13, by the third
current component 13 are detected. Serving for registering the third current
component 13 can be e.g. a sense-resistor R3 provided in the input voltage
controller 30, 60 and correspondingly flowed-through by the current
component 13, to yield an essentially current-proportional sense-voltage.
In a further embodiment of the invention, the measuring and control unit 60
controls the voltage adjuster 30 by means of the current control signal
is control, such that the third current component 13 flows, especially only
when the comparator comparing the second useful voltage with at least
one associated reference voltage signals an exceeding by the second
useful voltage UN2 of a maximum useful voltage limit value predetermined
for the second useful voltage. The means for comparing voltages and/or
currents can be, for example, simple comparators, which compare, in each
case, the sense voltage with an associated reference voltage, internally
produced, for example, by means of the input voltage Ue and being, in
each case, proportional to the threshold value.
In the field device electronics of the invention, it is further provided, as
already indicated above, that at least parts of the internal operating and
evaluating circuit 50, especially, however, the whole internal operating and
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evaluating circuit, is galvanically separated at least from current adjuster
IS1. Moreover, it can, however, be quite advantageous to maintain the
internal operating and evaluating circuit 50, as directly evident from Fig. 5,
galvanically separated both from the current adjuster IS1 and also from the
voltage adjuster 30. As a result, in this embodiment of the invention, also
the, on occasion, present, microprocessor pC and/or the also, on
occasion, present signal processor are, as components of the operating
and evaluating circuit 50, equally galvanically separated from the current
adjuster IS1 and/or from the voltage adjuster 30. In another embodiment
of the invention, it is further provided that the first useful-voltage
controller
UR, is held galvanically separated from the driver circuit 60B, especially
from the at least one amplifier provided therein, and/or from the at least
one D/A converter and/or from the at least one A/D converter. For
implementing the galvanic separation between operating and evaluating
circuit 50 and at least the current adjuster IS,, in an advantageous further
development, it is further provided that already also the second useful-
voltage controller UR2 is galvanically separated from the current adjuster
IS1 and/or from the voltage adjuster 30.
In a further embodiment of the invention, it is provided that the first useful-
voltage controller UR, and the internal operating and evaluating circuit 50
are galvanically separated from one another. For example, the useful-
voltage controller UR, and the internal operating and evaluating circuit 50
can, for this purpose, be coupled with one another by means of a
transformer 91. Instead of the single transformer 91 shown here, it is also
possible, in case required, to use two or more of such transformers for the
coupling of useful-voltage controller UR, and internal operating and
evaluating circuit 50. It is here recognizable for those skilled in the art
and
requires, as a result, no detailed explanation, that, in the case of use of
transformers for the galvanically separated coupling of two electrical
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components operating on the basis of DC voltage, there must first on the
primary side of the transformer be a conversion of the DC to AC voltage,
and on the secondary side of the transformer accordingly a corresponding
conversion from AC to DC voltage. Accordingly, at least for the case in
which the useful voltage UN1 to be transmitted is a DC voltage, the
transformer 91 is coupled on the primary and secondary sides,
respectively, to electronic components modulating the DC voltage in
suitable manner and to, in turn, electronics demodulating the modulated
and transmitted voltage, so that, with these components, the transformer
91 interacts as a direct voltage converter or also a DC/DC converter for
the useful voltage UN1 delivered from the first useful-voltage controller UR,
situated on the primary side. The electronic components correspondingly
modulating the DC voltage can be, for example, rectangular modulators
acting as choppers, while, for example, passive or synchronously clocked
rectifiers can serve as correspondingly demodulating electronic
components.
In a further development of the invention, the current adjuster IS1 and at
least parts of the internal operating and evaluating circuit 50 are, in very
simple and effective manner, maintained galvanically separated from one
another by already inserting a galvanic separation between both useful-
voltage controllers UR1, UR2. For this, the transformer 91 is, as shown in
Fig. 5, inserted between the two useful-voltage controllers UR1, UR2, so
that they are coupled together, especially exclusively, by the, here, single
transformer 91, optionally coupled with formation of a suitable DC
converter. In an advantageous embodiment of the invention, it is provided
for this purpose that the second useful-voltage controller UR2 is fed by the
useful voltage UN1 delivered from the first useful-voltage controller UR,
and/or at least by a secondary voltage UN1' derived from the first useful
voltage UN1. The second useful-voltage controller UR2 acts, as a result,
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thus as a consumer supplied by the first useful-voltage controller UR, with
the, in the above sense constant, internal, useful voltage UN1.
As already mentioned, the second useful-voltage controller UR2 is
controlled during operation by the measuring and control unit 60, at least
in so far as the voltage level to be set instantaneously for the second
useful voltage UN2 is specified by the measuring and control unit 60. For
this purpose, the measuring and control unit 60 delivers during operation,
at least at times, a voltage control signal UN2-desired correspondingly
controlling the second useful-voltage controller UR2 and representing the
voltage level instantaneously to be set for the second useful voltage UN2.
In a further embodiment of the invention, it is further provided in such case
that the measuring and control unit 60 and the second useful-voltage
controller UR2 are maintained galvanically separated from one another.
The measuring and control unit 60 can, in such case, as also shown
schematically in Fig. 5, be coupled to the second useful-voltage controller
UR2, for example, by means of at least one transformer 92 connected, at
least at times, into the signal path of the voltage control signal UN2 desired
and/or by means of at least one optocoupler connected, at least at times,
into the signal path of the voltage control signal UN2 desired.
Additionally, it is provided in a further embodiment of the invention that the
measuring and control unit 60 and the internal operating and evaluating
circuit 50 are held galvanically separated from one another. The
measuring and control unit 60 and the internal operating and evaluating
circuit 50 can, in such case, as also shown schematically in Fig. 5, be
coupled together for example, by means of at least one transformer 93
and/or by means of at least one optocoupler. As a result, in the case of
this embodiment of the invention, the internal operating and evaluating
circuit 50 is kept galvanically separated also from the, on occasion,
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December 15, 2008
present, at least one comparator for the third current component 13 and/or
from the, on occasion, present, at least one comparator for the second
useful voltage UN2. In a further development of this embodiment of the
invention, for this purpose, the second useful-voltage controller UR2 is
already kept galvanically separated from the at least one comparator for
the third current component 13 and/or from the at least one comparator for
the second useful voltage UN2. Depending on the number of signal
outputs of the operating and evaluating circuit 50 as well as of the
measuring and control unit 60, which, in particular, are each to be coupled
galvanically separatedly directly with a corresponding signal input of the
operating and evaluating circuit 50 or the measuring and control unit 60, it
can be quite necessary to provide, in addition to transformer 93,
appropriately more transformers in the field device electronics. For
example, the transformer 93 can serve for transmitting the alarm signal
xpwrfail from the measuring and control unit 60 to the operating and
evaluating circuit 50, while, as shown in Fig. 5, a corresponding
transformer 94 is used for transmission of the measured value signal xM.
For the above-described case, in which the field device electronics
includes a communications circuit COM, a further advantageous
embodiment of the invention provides that at least the communications
circuit COM is maintained galvanically separated from the current adjuster
IS1. For this purpose, the field device electronics includes at least one
further optocoupler, or, as shown in Fig. 5, at least one additional
transformer 95.
Of course, in the case of the above-explained variants of the galvanic
separation, it is to be understood that the transformers 92, 93, 94, 95 can
each be components of suitable DC/DC converters, at least for those
cases in which DC voltages/currents are transformed in this way. For the
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case in which clocked signals, such as e.g. digital signals, are to be
transmitted via transformer or optocoupler, for example the alarm signal
xpwrfail, or, as shown schematically in Fig. 5, the measured value signal xM
delivered from the internal operating and evaluating circuit 50 to the
measuring and control unit 60, the particularly used transformers, or
optocouplers, can, in case required, be supplemented with appropriate
circuit components, which convert the signals to be transmitted in suitable,
known manners known per se to those skilled in the art. Examples of such
circuits serving for the transmission of digital signals through locations of
galvanic separation are disclosed in, among others, US-B 6,853,685, US-
A 5,952,849 and DE-A 102 51 504.
In the above-explained variants of galvanic separation, it can additionally
be quite advantageous, when the, on occasion, used, at least one
transformer is installed in multiplex operation in such a manner that, on the
primary side, two or more circuit portions are connected, whose respective
output signals are then each transmitted via this one transformer, for
example displaced in time, sequentially and/or on different frequency
bands. Alternatively or in supplementation thereto, the, on occasion, used,
at least one transformer can also be installed in demultiplex operation
such that, on the secondary side, two or more circuit portions are
connected, which each selectively receive signals transmitted via this one
transformer, for example clocked, displaced in time, sequentially and/or,
again, on different frequency bands. Moreover, it is also possible to use
one and the same transformer bidirectionally in duplex operation or half-
duplex operation. Equally, additionally, also possibly used optocouplers
can be installed, on occasion, unidirectionally or bidirectionally in
multiplex
and/or in demultiplex operation.
