Note: Descriptions are shown in the official language in which they were submitted.
CA 02770476 2012-02-21
FLOW METER AND METHOD FOR DETECTING A CABLE FAULT IN A
CABLING OF THE FLOW METER /
Background of the Invention
1. Field of the Invention
The present invention relates to a flow meter and method for detecting a
cable fault in a cabling of the flow meter.
2. Statement of the Problem
Vibrating conduit sensors, such as Coriolis mass flow meters, typically
operate by detecting motion of a vibrating conduit that contains a flowing
material. Properties associated with the material in the conduit, such as mass
flow, density and the like, can be determined by processing measurement
signals received from motion transducers associated with the conduit. The
vibration modes of the vibrating material-filled system generally are affected
by
the combined mass, stiffness and damping characteristics of the containing
conduit and the material contained therein.
A typical Coriolis mass flow meter includes one or more conduits that are
connected inline in a pipeline or other transport system and convey material,
e.g., fluids, slurries and the like, in the system. Each conduit may be viewed
as
having a set of natural vibration modes including, for example, simple
bending,
torsional, radial, and coupled modes. In a typical Coriolis mass flow
measurement application, a conduit is excited in one or more vibration modes
as
a material flows through the conduit, and motion of the conduit is measured at
points spaced along the conduit. Excitation is typically provided by an
actuator,
e.g., an electromechanical device, such as a voice coil-type driver, that
perturbs
the conduit in a periodic fashion. Mass flow rate may be determined by
measuring time delay or phase differences between motions at the transducer
locations. Two such transducers (or pickoff sensors) are typically employed in
order to measure a vibrational response of the flow conduit or conduits, and
are
typically located at positions upstream and downstream of the actuator. The
two
pickoff sensors are connected to electronic instrumentation by cabling, such
as
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two independent pairs of wires. The instrumentation receives signals from the
two pickoff sensors and processes the signals in order to derive a mass flow
rate
measurement.
When the flow conduit or conduits of a Coriolis flow meter are empty, then
the phase difference between the two pickoff signals is ideally zero. In
contrast,
during normal operation, the flow through the flow meter induces a phase shift
between the two pickoff signals due to the Coriolis effect. The phase shift is
directly proportional to the material flow through the conduits. Therefore, by
making an accurate measurement of the signal difference, the flow meter can
accurately measure the mass flow rate.
A Coriolis flow meter typically uses coils to drive a flow conduit(s) and to
measure resulting flow conduit vibrations. In many cases, the flow sensor
apparatus (i.e., the flow conduit(s), pickoff sensors, and driver), is not
integrally
mounted with the transmitter electronics. A typical Coriolis meter includes 9
wires bundled in a cable between the transmitter/meter electronics and the
flow
sensor apparatus. The cabling typically includes 3 wires for a Resistance
Temperature Detector (RTD) sensor, 2 wires for a first pickoff sensor, 2 wires
for
a second pickoff sensor, and 2 wires for a driver.
The cabling is typically connected in the field and by the customer. This
can lead to problems in the cabling. Pairs of wires can be swapped. Wires can
be mixed up. Bad terminal connections or a failed coil can result in an open
circuit. For example, if a first pickoff sensor is connected in a first
orientation and
the second pickoff sensor is connected in a second, opposite orientation, then
a
measured phase shift during a zeroing operation will be excessively large.
Similarly, where the wires connecting to the driver are switched, then an
expected phase characteristic will not be observed and a feedback loop of the
driver circuit may drive the response toward zero instead of driving the
response
to a fundamental frequency.
Another problem that can occur is a broken or unconnected wire between
components. A broken or unconnected wire may not be detected until the unit is
put into operation. Troubleshooting the problem at the customer's location is
costly and time-consuming. In addition, the customer will experience downtime,
expense, and frustration.
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It is desirable for the transmitter to automatically determine if the sensor
is
wired correctly, and if not, correct for the encountered problem.
Additionally, it is
desirable to determine this independently of process variations.
Summary of the Solution
Meter electronics for detecting a cable fault in a cabling of a flow meter is
provided according to an embodiment of the invention. The meter electronics
comprises first and second pickoff sensors and the cabling coupled to the
first
and second pickoff sensors. The cabling includes one or more first pickoff
wires
and one or more second pickoff wires. The meter electronics further comprises
a signal injection device coupled to the cabling. The signal injection device
is
configured to generate an injection signal and communicate the injection
signal
into the cabling and to the first and second pickoff sensors. The meter
electronics further comprises a signal conditioning circuit coupled to the
cabling.
The signal conditioning circuit is configured to receive at least one response
signal from at least one of the first and second pickoff sensors in response
to the
injection signal and determine one or more of a pickoff open wire fault and a
pickoff connection orientation fault in one or both of the one or more first
pickoff
wires and the one or more second pickoff wires of the cabling.
Meter electronics for detecting a cable fault in a cabling of a flow meter is
provided according to an embodiment of the invention. The meter electronics
comprises a driver, first and second pickoff sensors, and the cabling coupled
to
the first and second pickoff sensors and to the driver. The meter electronics
further comprises a driver circuit coupled to the cabling and configured to
generate a drive signal and communicate the drive signal into the cabling and
to
the driver. The meter electronics further comprises a signal conditioning
circuit
coupled to the cabling. The signal conditioning circuit is configured to
receive at
least one response signal from at least one of the first and second pickoff
sensors in response to the drive signal and determine one or more of a driver
open wire fault and a driver connection orientation fault in one or more
driver
wires of the cabling.
A method for detecting a cable fault in a cabling of a flow meter is
provided according to an embodiment of the invention. The method comprises
comparing an injection signal component of a response signal received from at
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least one of a first pickoff sensor and a second pickoff sensor to a
predetermined
pickoff amplitude threshold and determining a pickoff open wire fault in a
corresponding one or more first pickoff wires or in a corresponding one or
more
second pickoff wires if the injection signal component does not exceed the
predetermined pickoff amplitude threshold.
A method for detecting a cable fault in a cabling of a flow meter is
provided according to an embodiment of the invention. The method comprises
comparing a phase difference between a first pickoff response phase of a first
pickoff response signal and a second pickoff response phase of a second
pickoff
response signal to a predetermined pickoff phase difference threshold. The
first
pickoff response signal and the second pickoff response signal are received
from
the first pickoff sensor and the second pickoff sensor via the cabling. The
method further comprises determining a pickoff connection orientation fault if
the
phase difference exceeds the predetermined pickoff phase difference threshold.
A method for detecting a cable fault in a cabling of a flow meter is
provided according to an embodiment of the invention. The method comprises
comparing a drive resistor voltage across a drive resistor RD at an output of
the
driver circuit to a predetermined voltage threshold and determining a driver
open
wire fault in the one or more driver wires if the drive resistor voltage does
not
exceed the predetermined voltage threshold.
A method for detecting a cable fault in a cabling of a flow meter is
provided according to an embodiment of the invention. The method comprises
comparing a response signal phase difference to a predetermined driver phase
difference threshold. The response signal phase difference comprises a
difference between a response signal phase and a drive signal phase. The
response signal phase is received from at least one of a first pickoff sensor
and
a second pickoff sensor. The method further comprises determining a driver
connection orientation fault in the one or more driver wires if the response
signal
phase difference exceeds the predetermined driver phase difference threshold.
A method for detecting a cable fault in a cabling of a flow meter is
provided according to an embodiment of the invention. The method comprises
determining a vibrational response amplitude of a vibrational response and
determining a driver connection orientation fault in the one or more driver
wires if
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the vibrational response amplitude does not substantially track a drive signal
amplitude.
A method for detecting a cable fault in a cabling of a flow meter is
provided according to an embodiment of the invention. The method comprises
testing one or more first pickoff wires and one or more second pickoff wires
of
the cabling for pickoff open wire faults. The one or more first pickoff wires
and
the one or more second pickoff wires are included in the cabling and connect
to
a first pickoff sensor and to a second pickoff sensor respectively. The method
further comprises testing the one or more first pickoff wires and the one or
more
second pickoff wires for a pickoff connection orientation fault if no pickoff
open
wire faults are determined in the one or more first pickoff wires and the one
or
more second pickoff wires. The method further comprises testing one or more
driver wires of the cabling for a driver open wire fault. The one or more
driver
wires connect to a driver. The method further comprises testing the one or
more
driver wires for a driver connection orientation fault if no driver open wire
faults
are determined in the one or more driver wires.
ASPECTS
In one aspect of the meter electronics, the signal conditioning circuit is
configured to compare an injection signal component of the at least one
response signal to a predetermined pickoff amplitude threshold and determine a
pickoff open wire fault in the corresponding one or more first pickoff wires
or in
the corresponding one or more second pickoff wires if the injection signal
component does not exceed the predetermined pickoff amplitude threshold.
In another aspect of the meter electronics, the signal conditioning circuit
receives a first pickoff response signal and a second pickoff response signal
and
the signal conditioning circuit is configured to compare a phase difference
between a first pickoff response phase and a second pickoff response phase to
a predetermined pickoff phase difference threshold and determine a pickoff
connection orientation fault in the corresponding one or more first pickoff
wires or
in the corresponding one or more second pickoff wires if the phase difference
exceeds the predetermined pickoff phase difference threshold.
In yet another aspect of the meter electronics, the signal injection device
comprises a digital-to-analog (D/A) converter configured to receive a digital
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frequency command and output a frequency input, an injection signal generator
that receives the frequency input from the D/A converter and outputs an
injection
signal of a frequency specified by the frequency input, and a transformer that
communicates the injection signal into the cabling.
In yet another aspect of the meter electronics, the signal conditioning
circuit is further configured to invert a received response signal from one
pickoff
sensor if a pickoff connection orientation fault is determined to exist.
In yet another aspect of the meter electronics, the signal conditioning
circuit is configured to compare a drive resistor voltage across a drive
resistor RD
at an output of the driver circuit to a predetermined voltage threshold and
determine a driver open wire fault in the one or more driver wires if the
drive
resistor voltage does not exceed the predetermined voltage threshold.
In yet another aspect of the meter electronics, the signal conditioning
circuit is configured to compare a response signal phase difference to a
predetermined driver phase difference threshold and determine a driver
connection orientation fault in the one or more driver wires if the response
signal
phase difference exceeds the predetermined driver phase difference threshold,
with the response signal phase difference comprising a difference between a
response signal phase and a drive signal phase and with the response signal
phase being received from at least one of the first pickoff sensor and the
second
pickoff sensor.
In yet another aspect of the meter electronics, the meter electronics is
further configured to determine a vibrational response amplitude of a
vibrational
response and determine a driver connection orientation fault in the one or
more
driver wires if the vibrational response amplitude does not substantially
track a
drive signal amplitude.
In yet another aspect of the meter electronics, the driver circuit is further
configured to invert a drive signal if the driver connection orientation fault
is
determined to exist.
In one embodiment of the method, the method further comprises
generating an alarm if the pickoff open wire fault is determined to exist.
In another embodiment of the method, the comparing and determining
further comprise comparing a first injection signal component of a first
response
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signal from the first pickoff sensor to the predetermined pickoff amplitude
threshold, determining a first pickoff open wire fault in the one or more
first
pickoff wires if the first injection signal component does not exceed the
predetermined pickoff amplitude threshold, comparing a second injection signal
component of a second response signal from the second pickoff sensor to the
predetermined pickoff amplitude threshold, and determining a second pickoff
open wire fault in the one or more second pickoff wires if the second
injection
signal component does not exceed the predetermined pickoff amplitude
threshold.
In yet another embodiment of the method, the method further comprises
generating an alarm if the pickoff connection orientation fault is determined
to
exist.
In yet another embodiment of the method, the method further comprises,
after the determining, inverting a received response signal from one pickoff
sensor if a pickoff connection orientation fault is determined to exist.
In yet another embodiment of the method, the method further comprises
generating an alarm if the driver open wire fault is determined to exist.
In yet another embodiment of the method, the method further comprises
generating an alarm if the driver connection orientation fault is determined
to
exist.
In yet another embodiment of the method, the method further comprises,
after the determining, inverting a drive signal from the driver circuit if the
driver
connection orientation fault is determined to exist.
In yet another embodiment of the method, the method further comprises
generating an alarm if the driver connection orientation fault is determined
to
exist.
In yet another embodiment of the method, the method further comprises,
after the determining, inverting a drive signal from the driver circuit if the
driver
connection orientation fault is determined to exist.
In yet another embodiment of the method, the method further comprises
generating an alarm if an open wire fault is determined to exist in the one or
more first pickoff wires, in the one or more second pickoff wires, or in the
one or
more driver wires.
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In yet another embodiment of the method, the method further comprises
generating an alarm if a connection orientation fault is determined to exist
in the
one or more first pickoff wires, in the one or more second pickoff wires, or
in the
one or more driver wires.
In yet another embodiment of the method, the testing the one or more
pickoff sensors for pickoff open wire faults comprises comparing an injection
signal component of a response signal received from at least one of the first
pickoff sensor and the second pickoff sensor to a predetermined pickoff
amplitude threshold and determining a pickoff open wire fault in a
corresponding
one or more first pickoff wires or in a corresponding one or more second
pickoff
wires if the injection signal component does not exceed the predetermined
pickoff amplitude threshold.
In yet another embodiment of the method, testing the one or more first
pickoff wires and the one or more second pickoff wires for pickoff connection
orientation faults comprises comparing a phase difference between a first
pickoff
response phase of a first pickoff response signal and a second pickoff
response
phase of a second pickoff response signal to a predetermined pickoff phase
difference threshold, with the first pickoff response signal and the second
pickoff
response signal being received from the first pickoff sensor and the second
pickoff sensor via the cabling, and determining a pickoff connection
orientation
fault if the phase difference exceeds the predetermined pickoff phase
difference
threshold.
In yet another embodiment of the method, the method further comprises,
after testing for the pickoff connection orientation fault, inverting the
response
signal from one pickoff sensor if a pickoff connection orientation fault is
determined to exist.
In yet another embodiment of the method, testing the driver for open wires
comprises comparing a drive resistor voltage across a drive resistor RD at an
output of the driver circuit to a predetermined voltage threshold and
determining
a driver open wire fault in the one or more driver wires if the drive resistor
voltage does not exceed the predetermined voltage threshold.
In yet another embodiment of the method, testing the one or more driver
wires for a driver connection orientation fault comprises comparing a response
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signal phase difference to a predetermined driver phase difference threshold,
with the response signal phase difference comprising a difference between a
response signal phase and a drive signal phase and with the response signal
phase being received from at least one of the first pickoff sensor and the
second
pickoff sensor, and determining a driver connection orientation fault in the
one or
more driver wires if the response signal phase difference exceeds the
predetermined driver phase difference threshold.
In yet another embodiment of the method, testing the one or more driver
wires for a driver connection orientation fault comprises determining a
vibrational
response amplitude of a vibrational response and determining a driver
connection orientation fault in the one or more driver wires if the
vibrational
response amplitude does not substantially track a drive signal amplitude.
In yet another embodiment of the method, the method further comprises,
after testing the one or more driver wires for the driver connection
orientation
fault, inverting the drive signal from the driver if the driver connection
orientation
fault is determined to exist.
Description of the Drawings
FIG. 1 illustrates a Coriolis flow meter comprising a flow meter assembly
and meter electronics.
FIG. 2 is a diagram of a portion of the flow meter according to an
embodiment of the invention.
FIG. 3 is a flowchart of a method for detecting a cable fault in a cabling of
a flow meter according to an embodiment of the invention.
FIG. 4 is a flowchart of a method for detecting a cable fault in a cabling of
a flow meter according to an embodiment of the invention.
FIG. 5 is a flowchart of a method for detecting a cable fault in a cabling of
a flow meter according to an embodiment of the invention.
FIG. 6 is a flowchart of a method for detecting a cable fault in a cabling of
a flow meter according to an embodiment of the invention.
FIG. 7 is a flowchart of a method for detecting a cable fault in a cabling of
a flow meter according to an embodiment of the invention.
FIG. 8 shows the flow meter according to an embodiment of the invention.
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Detailed Description of the Invention
FIGS. 1-8 and the following description depict specific examples to teach
those skilled in the art how to make and use the best mode of the invention.
For
the purpose of teaching inventive principles, some conventional aspects have
been simplified or omitted. Those skilled in the art will appreciate
variations from
these examples that fall within the scope of the invention. Those skilled in
the
art will appreciate that the features described below can be combined in
various
ways to form multiple variations of the invention. As a result, the invention
is not
limited to the specific examples described below, but only by the claims and
their
equivalents.
FIG. 1 illustrates a Coriolis flow meter 5 comprising a flow meter assembly
10 and meter electronics 20. Meter electronics 20 is connected to meter
assembly 10 via leads 100 to provide density, mass flow rate, volume flow
rate,
totalized mass flow, temperature, and other information over path 26. It
should
be apparent to those skilled in the art that the present invention can be used
by
any type of Coriolis flow meter regardless of the number of drivers, pickoff
sensors, flow conduits, or the operating mode of vibration. A Coriolis flow
meter
structure is described although it is apparent to those skilled in the art
that the
present invention could be practiced as a vibrating tube densitometer without
the
additional measurement capability provided by a Coriolis mass flow meter.
Flow meter assembly 10 includes a pair of flanges 101 and 101',
manifolds 102 and 102', driver 104, pickoff sensors 105-105', and flow
conduits
103A and 103B. Driver 104 and pickoff sensors 105 and 105' are connected to
flow conduits 103A and 103B.
Flanges 101 and 101' are affixed to manifolds 102 and 102'. Manifolds
102 and 102' are affixed to opposite ends of spacer 106. Spacer 106 maintains
the spacing between manifolds 102 and 102' to prevent undesired vibrations in
flow conduits 103A and 103B. When flow meter assembly 10 is inserted into a
pipeline system (not shown) which carries the material being measured,
material
enters flow meter assembly 10 through flange 101, passes through inlet
manifold
102 where the total amount of material is directed to enter flow conduits 103A
and 103B, flows through flow conduits 103A and 103B and back into outlet
manifold 102' where it exits meter assembly 10 through flange 101'.
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Flow conduits 103A and 1036 are selected and appropriately mounted to
inlet manifold 102 and outlet manifold 102' so as to have substantially the
same
mass distribution, moments of inertia, and elastic modules about bending axes
W--W and W'--W' respectively. The flow conduits extend outwardly from the
manifolds in an essentially parallel fashion.
Flow conduits 103A-B are driven by driver 104 in opposite directions
about their respective bending axes W and Wand at what is termed the first out
of bending mode of the flow meter. Driver 104 may comprise one of many well
known arrangements, such as a magnet mounted to flow conduit 103A and an
opposing coil mounted to flow conduit 103B. An alternating current is passed
through the opposing coil to cause both conduits to oscillate. A suitable
drive
signal is applied by meter electronics 20, via lead 110 to driver 104.
Meter electronics 20 receives sensor signals on leads 111 and 111',
respectively. Meter electronics 20 produces a drive signal on lead 110 which
causes driver 104 to oscillate flow conduits 103A and 103B. Meter electronics
processes left and right velocity signals from pickoff sensors 105 and 105' in
order to compute a mass flow rate. Path 26 provides an input and an output
means that allows meter electronics 20 to interface with an operator. The
description of FIG. 1 is provided merely as an example of the operation of a
flow
20 meter and is not intended to limit the teaching of the present invention.
FIG. 2 is a diagram of a portion of the flow meter 5 according to an
embodiment of the invention. The flow meter 5 includes a first pickoff sensor
201 a, a second pickoff sensor 201 b, a driver 204, and the meter electronics
20.
The meter electronics 20 can operate as a mass flow meter or can operate as a
densitometer, including operating as a Coriolis flow meter. The meter
electronics 20 can include, among other things, a driver circuit 220, a signal
injection device 203, and a signal conditioning circuit 202. The meter
electronics
20 is connected to the pickoff sensors 201 and to the driver 204 by cabling
205.
The cabling 205 connects the first pickoff sensor 201 a and the second pickoff
sensor 201 b to a signal conditioning circuit 202 and to a signal injection
device
203. The cabling 205 connects the driver 204 to the driver circuit 220. In one
embodiment, the signal conditioning circuit 202 and the signal injection
device
203 are interconnected by a link 210.
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The cabling 205 can comprise any manner of wires, cables, fibers, etc.,
that electrically connect the first and second pickoff sensors 201 a and 201 b
to
the signal conditioning circuit 202. The cabling 205 in one embodiment
comprises at least a portion of the leads 100 of FIG. 1.
A typical flow meter includes 9 wires bundled in the cabling 205 between
the transmitter/meter electronics 20 and the flow meter assembly 10. The
cabling 205 typically includes 3 wires for a Resistance Temperature Detector
(RTD) sensor, 2 wires for a first pickoff sensor, 2 wires for a second pickoff
sensor, and 2 wires for the driver.
The meter electronics 20 in one embodiment can perform cable fault
determinations for the cabling 205 between the meter electronics 20 and the
pickoff sensors 201 a and 201 b. The meter electronics 20 in one embodiment
can perform cable fault determinations for the cabling 205 between the meter
electronics 20 and the driver 204.
The driver circuit 220 generates a drive signal and communicates the
drive signal to the driver 204. The driver 204 vibrates the flow conduits 103A
and 103B according to the drive signal. The drive signal therefore includes an
amplitude characteristic and a frequency characteristic. Where the meter
electronics 20 implements a closed-loop drive, a difference between a drive
signal and a response signal is employed as feedback for modifying the drive
signal. For example, a phase difference between the drive signal and a
response signal can comprise the feedback. Ideally, under no-flow conditions
the phase difference will be substantially zero if the flow meter is
accurately
calibrated.
The driver circuit 220 can generate a drive signal. The drive signal in one
embodiment comprises an operational drive signal that is generated by the
driver
circuit 220, wherein the signal vibrates a flow conduit(s) 103. A resulting
response signal to the drive signal can be received in the signal conditioning
circuit 202. Alternatively, the drive signal can be generated specifically for
a fault
test according to the invention.
The signal injection device 203 can generate an injection signal and can
communicate the injection signal to one or both of the first pickoff sensor
201 a
and the second pickoff sensor 201 b via the cabling 205. The signal injection
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device 203 can generate an injection signal according to an injection signal
command that can be received from the signal conditioning circuit 202 over the
link 210. The injection signal can comprise any desired frequency or
frequencies. The injection signal can include frequencies above, below, or the
same as a drive signal.
The signal conditioning circuit 202 receives response signals from both
pickoff sensors 201 a and 201 b. The signal conditioning circuit 202 can
detect
and/or process the response signals. The signal conditioning circuit 202 can
process the response signals in order to produce appropriate flow
measurements. In addition, the signal conditioning circuit 202 can process the
response signals in order to detect faults in the cabling 205 according to
embodiments of the invention.
The response signals can be generated by the pickoff sensors 201
according to normal operation of the flow meter 5. Alternatively, the response
signals can be generated by the pickoff sensors 201 in response to any manner
of test vibration of the flow conduits 103. In yet another alternative, the
response
signals can be generated by the pickoff sensor 201 in response to an injection
signal from the signal injection device 203.
The signal conditioning circuit 202 can determine a response signal
amplitude for each pickoff sensor. The signal conditioning circuit 202 can
determine a phase difference between the response signals received from the
first pickoff sensor 201 a and the second pickoff sensor 201 b. The amplitude
and
phase difference can be used to determine a connection orientation faults in
the
cabling 205.
In one embodiment, the meter electronics 20 can include a processor (not
shown) and a cable troubleshooting software routine. The processor can
execute the cable troubleshooting software routine and can initiate and
supervise open wire and connection orientation fault determinations for the
cabling 205. The processor and cable troubleshooting software routine can
initiate signals into the pickoff sensors 201 a and 201 b. The processor and
routine can receive measurements/data from the open wire and connection
orientation fault tests and can perform appropriate fault determinations. The
processor and routine can generate alarms if problems are detected. In
addition,
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the processor and routine can perform compensation techniques, including
inverting signals or signal responses in order to compensate for improper
wiring
orientations. Alternatively, the signal conditioning circuit 202, the signal
injection
device 203, the driver circuit 220, and the processor can include equivalent
circuitry and/or specialized circuit components that perform the above
operations.
FIG. 3 is a flowchart 300 of a method for detecting a cable fault in a
cabling of a flow meter according to an embodiment of the invention. In this
method, a pickoff open wire fault determination is performed. The pickoff open
wire fault test can detect open wire faults such as a wire break or an
unconnected wire in corresponding pickoff wires of the cabling 205.
In step 301, an injection signal is communicated into one or more pickoff
wires of the cabling 205. As a result, the injection signal is communicated to
at
least one of the first pickoff sensor 201 a and the second pickoff sensor 201
b.
The injection signal can be generated by the signal injection device 203, for
example. When an injection signal is generated by the signal injection device
203, the signal conditioning circuit 202 should substantially simultaneously
receive response signals from both pickoff sensors 201 a and 201 b.
In step 302, a response signal is compared to a predetermined pickoff
amplitude threshold. The injection signal sent to the pickoff sensor 201 will
generate two different, returning signals to the signal conditioning circuit
202, but
only if the pickoff wires are not open. The first signal, an injection signal
component, is a reflection of the injection signal and is at substantially the
same
frequency as the injection signal. If the pickoff wires are not open, then
this
injection signal component should be similar in amplitude to the injection
signal
and therefore can be compared to a threshold. The second signal is a response
signal component and differs in frequency from the original injection signal
due
to the effects of vibration of the flow conduit(s) 103 and due to the effects
of a
flow material in the flow conduit(s) 103. However, this response signal
component may vary in amplitude and may be undetectable in some cases.
Therefore, in one embodiment, the injection signal component of the response
signal is used for the comparing.
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In step 303, if the injection signal component does not exceed the
predetermined pickoff amplitude threshold, then the method proceeds to step
304. Here, it is determined that a response signal was not received and that a
wire of the corresponding pickoff sensor is either broken or not connected.
Otherwise, if the injection signal component does exceed the predetermined
pickoff amplitude threshold, then the method branches around step 304.
Therefore, it is determined that a response signal was received and that the
corresponding pickoff wires are not broken or disconnected.
In step 304, because the injection signal component did not exceed the
predetermined pickoff amplitude threshold, the corresponding pickoff wires are
determined to have an open wire fault. Subsequently, the meter electronics 20
can perform other actions, including generating an alarm that indicates the
open
wire fault.
The above steps are discussed in the context of a single pickoff sensor
and a single response signal amplitude. However, it should be understood that
the steps 302-304 can be performed on the response signals from both pickoff
sensors 201 a and 201 b.
FIG. 4 is a flowchart 400 of a method for detecting a cable fault in a
cabling of a flow meter according to an embodiment of the invention. In this
method, a pickoff sensor connection orientation fault determination is
performed.
In step 401, a response signal is received from one or both pickoff
sensors via the cabling 205 in response to a drive signal applied by the
driver
204.
Under no-flow conditions in the flow meter 5, the phase difference
between the left and right (or first and second) pickoff signals will be
substantially
zero. Under flow conditions, the phase of the first pickoff signal will differ
from
the phase of the second pickoff signal by a relatively small amount, according
to
a mass flow rate of flow material through the flow meter 5. However, if the
phase difference between the two pickoff signals is too great, then a
connection
orientation fault exists.
In step 402, a phase difference is compared to a predetermined pickoff
phase difference threshold. The phase difference comprises a difference
between a response signal phase and a drive signal phase.
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In step 403, if the phase difference exceeds the predetermined pickoff
phase difference threshold, then the method proceeds to step 404. If the phase
difference does not exceed the predetermined pickoff phase difference
threshold, then the method branches around step 404.
In step 404, because the phase difference exceeded the predetermined
pickoff phase difference threshold, then it is determined that a connection
orientation fault exists in corresponding pickoff wires. For example, the two
response signals can be around 180 degrees out of phase, plus or minus a
relatively small phase difference portion caused by a response to a flow
material
in the flow conduit(s) 103. As before, an alarm condition can be generated if
the
connection orientation fault is determined to exist. In addition, the meter
electronics 20 can invert all subsequent response signals received from the
affected pickoff sensor. In this manner, the improper connection orientation
can
be remediated.
The above steps are discussed in the context of a single pickoff sensor
and a single phase difference. However, it should be understood that the steps
402-404 can be performed on the response signals from both pickoff sensors
201 a and 201 b.
FIG. 5 is a flowchart 500 of a method for detecting a cable fault in a
cabling 205 of a flow meter according to an embodiment of the invention. In
this
method, a driver open wire fault determination is performed. The driver open
wire fault test can detect open wire faults such as a wire break or an
unconnected wire.
In step 501, a drive signal is communicated into one or more driver wires
of the cabling 205 and to the driver 204. The drive signal can be generated by
the driver circuit 220, as previously discussed. The drive signal can comprise
a
normal operational drive signal or can comprise any generated signal that is
suitable for the wire open fault testing.
Referring back to FIG. 2, the driver circuit 220 includes a drive resistor RD
in the output. An op-amp 221 is connected across the drive resistor R0. In one
embodiment, the op-amp 221 amplifies a voltage across the drive resistor RD
and outputs a drive resistor voltage. The drive resistor voltage can comprise
an
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CA 02770476 2012-02-21
analog voltage signal that can be compared to a predetermined voltage
threshold.
Referring again to FIG. 5, in step 502 the drive resistor voltage across the
drive resistor RD is compared to a predetermined voltage threshold. If the
drive
resistor voltage at the output of the op-amp 221 exceeds the predetermined
voltage threshold, then an expected level of electrical current is flowing
through
the cabling 205 to the driver 204.
In step 503, if the drive resistor voltage does not exceed the
predetermined voltage threshold, then the method proceeds to step 504.
Otherwise, if the drive resistor voltage exceeds the predetermined voltage
threshold, then it can be determined that no open wire condition exists and
therefore the method branches around step 504.
In step 504, because the drive resistor voltage did not exceed the
predetermined voltage threshold, then it can be determined that a driver open
wire fault condition exists in the cabling 205 to the driver 204. This step
can
include generating an alarm condition, as previously discussed.
Alternatively, the op-amp 221 can comprise a comparator device that
compares the voltage at the cabling side of the drive resistor RD to a voltage
(i.e., to the predetermined voltage threshold) and generates a digital true or
false
output. The digital output therefore comprises a first digital output level if
the
drive resistor voltage exceeds the predetermined voltage and a second digital
output level if the drive resistor voltage does not exceed the predetermined
voltage. The comparison of step 502 therefore can comprise a comparison
internal to the comparator device, wherein the predetermined voltage threshold
comprises a voltage input to the comparator device.
FIG. 6 is a flowchart 600 of a method for detecting a cable fault in a
cabling of a flow meter according to an embodiment of the invention. In this
method, a driver connection orientation fault determination is performed.
In step 601, the driver circuit 220 generates a drive signal and
communicates the drive signal to the driver 204 via the cabling 205, as
previously discussed. As a result, the driver 204 generates a physical
excitation
in the flow conduits 103A and 103B using the drive signal. Consequently, the
signal conditioning circuit 202 receives first and second response signals
from
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CA 02770476 2012-02-21
the first and second pickoff sensors 201 a and 201 b via the cabling 205 in
response to the vibration of the flow conduits by the driver 204.
In step 602, a response signal phase difference is compared to a
predetermined driver phase difference threshold. The response signal phase
difference comprises a difference between a response signal phase and a drive
signal phase. The drive signal phase is the phase characteristic provided to
the
driver circuit 220, i.e., it s the drive phase that the driver circuit 220 and
the drive
204 are targeted to achieve. The actual phase of the response should be close
to the phase, and will typically differ in relation to a mass flow rate of
flow
material in the flow conduits 103.
In step 603, if the response signal phase difference exceeds the
predetermined driver phase difference threshold, then a driver connection
orientation fault is determined in the driver wires and the method proceeds to
step 604. Otherwise, if the response signal phase difference does not exceed
the predetermined driver phase difference threshold, then the driver
connection
orientation is determined to be correct and the method branches around step
604.
In step 604, because the response signal phase difference exceeded the
predetermined driver phase difference threshold, then it is determined that a
driver connection orientation fault exists in the driver wires. For example,
the
phase difference can be around 180 degrees, plus or minus a relatively small
phase difference portion caused by a response to a flow material in the flow
conduit(s) 103. As before, an alarm condition can be generated if the
connection
orientation fault is determined to exist. In addition, the meter electronics
20 can
invert the drive signal. For example, the drive signal can be inverted before
it is
sent to the driver 204. In this manner, the improper driver connection
orientation
can be remediated.
It should be understood that either method of FIG. 6 or FIG. 7 can be
used to make a driver connection orientation fault determination.
FIG. 7 is a flowchart 700 of a method for detecting a cable fault in a
cabling of a flow meter according to an embodiment of the invention. In this
method, a driver connection orientation fault determination is performed.
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CA 02770476 2012-02-21
In step 701, a vibrational response amplitude is determined. The
vibrational response amplitude can comprise an amplitude of a response signal
from either pickoff.
In step 702, the vibrational response amplitude is compared to a drive
signal amplitude. The comparison can be a comparison of the two amplitudes at
one or more instantaneous points in time. Alternatively, the comparison can
compare averaged or filtered values, etc.
In step 703, if the vibrational response amplitude is substantially tracking
the drive signal amplitude, then the method exits. If the vibrational response
amplitude is not substantially tracking the drive signal amplitude, then the
method proceeds to step 704.
In step 704, because the vibrational response amplitude is not
substantially tracking the drive signal amplitude, then it is determined that
a
driver connection orientation fault exists in the driver wires. As before, an
alarm
condition can be generated if the driver connection orientation fault is
determined
to exist. In addition, the meter electronics 20 can invert the drive signal.
For
example, the drive signal can be inverted before it is sent to the drive 204.
In
this manner, the improper driver connection orientation can be remediated.
FIG. 8 shows the flow meter 5 according to an embodiment of the
invention. Components in common with FIG. 2 share the same reference
numbers. In this embodiment, the signal injection device 203 comprises a
digital-to-analog (D/A) converter 808, an injection signal generator 806, and
a
transformer 807. The D/A 808 is connected to the signal conditioning circuit
202
and to the injection signal generator 806. The injection signal generator 806
is
further connected to the transformer 807.
The D/A 808 receives a digital frequency command from the signal
conditioning circuit 202. The D/A 808 converts the digital frequency command
into a frequency input into the injection signal generator 806, wherein the
frequency input specifies the frequency of a (single) injection signal to be
generated. The injection signal generator 806 generates the injection signal
and
transmits the injection signal to primary windings 810 of the transformer 807.
The transformer 807 creates the first and second injection signals through
the use of a split transformer secondary, wherein the secondary windings 811
of
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CA 02770476 2012-02-21
the transformer 807 comprise substantially equal pairs of secondary windings.
In this manner, the injection signal at the primary windings 810 of the
transformer
807 is converted into the first and second injection signals at the secondary
windings 811. The two secondary windings 811 are connected to the cabling
205 and to the first and second pickoff sensors 201 a and 201 b, wherein
signals
can be injected into the pickoff sensors. As before, the signal conditioning
circuit
202 receives the first and second response signals that are created as a
result of
the injection of the first and second injection signals.
