Note: Descriptions are shown in the official language in which they were submitted.
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SUPPLY BIASED PNEUMATIC PRESSURE RELAY
This invention relates to electro-pneumatic
converter devices and in particular to current to
pressure transducer/positioner devices.
Background of the Invention
Electro-pneumatic converters, such as current
to pressure transducers are in common use as field
instruments mounted in pipeline systems for controlling
the process fluid. Subsequently these devices are
installed in potentially hazardous explosive environ-
ments. Such devices receive, for example, a variable
current input signal of between 4-20 mA and eventually
provide a variable pressure output to an actuator for a
fluid control valve. Since these devices can be
employed in a potentially explosive environment, to
provide an explosion proof device the electrical and
pneumatic components are isolated within an explosion
proof portion of the transducer/positioner unit, except
for the pressure gauges which are normally located on
the unit exterior.
With presently available electro-pneumatic
converters operating in a potentially explosively
hazardous area, in the event either service of the unit
or normal maintenance is required, the electric power
must be disconnected and/or the entire unit must be
removed from the potentially hazardous area in order to
be worked on. Occasionally, for instance, the pneumat-
is elements must be adjusted or removed and replaced.
In present units, if the seal of the explosion proof
portion of the unit is removed,in order to get access
to these pneumatic elements, then a potentially unsafe
condition is created where any spark caused in the
electrical elements could ignite potentially explosive
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gases. Accordingly, shutting down the electrical power
in order to service or remove the unit from the
hazardous area is time consuming, costly, and wasteful.
In addition, with the electrical and pneumat-
is components maintained within an explosion proof
portion of the transducer/positioner unit, the mounting
of the pressure gauges on the portion outside the
explosion proof portion of the unit is required.
However, this exposes the pressure gauges to the atmos-
phere as well as to physical damage from unintentional
blows to the pressure gauges protruding even slightly
from the transducer/positioner exterior surface.
Accordingly, it is desired to provide an
electro-pneumatic converter which can be used in a
potentially explosive environment and wherein pneumatic
components can be serviced without requiring electrical
shutdown or removal of the entire unit from the hazard-
ous area.
In addition, it is desired to provide an
electro-pneumatic converter where the pressure gauges
can be protected from the atmosphere as well as from
any unintentional physical damage.
Currently available pressure transducer
instruments contain a pressure to current sensor to
convert a pressure signal to a current signal in
supplying feedback to the instrument. Analog pressure
transducer units are available, as well as respective
digital pressure transducer units. Also currently
available are separate valve positioner units which
incorporate feedback from the valve supplied from a
mechanical linkage with the valve stem. Both analog
valve positioner units and digital valve controller
units are separately available.
Typically, the customer chooses the type of
instrument needed in order to fit within his present
system. Thus, a customer may initially choose to
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purchase a pressure transducer instrument in analog
form as most conveniently adaptable to his present
system. If the customer s system changes or he wishes
to modify his system to operate in digital form, the
customer must then purchase the required separate
instruments. Also, if the customer wants to change to
a valve positioner configuration when he initially
purchased a pressure transducer instrument, he must
purchase a new valve positioner device in the proper
data format to fit his changed system.
It is therefore further desired to provide an
electro-pneumatic instrument which is usable and readi-
ly convertible from a pressure transducer to a valve
positioner or vice versa. In addition, it is desired
to enable a user to readily convert from an analog data
handling capability to a digital data handling capabil-
ity or vice versa. Furthermore, it is desired to
enable the instrument user to incorporate and to change
to any desired communications data protocol.
In existing electro-pneumatic instruments,
the instrument housing is usually formed of a casting.
The casting must then be drilled with precise holes to
form passageways and interconnected passageways to
enable the desired communication of fluid between
components. Forming of the desired passageways by
drilling intersecting holes in the casting requires
time consuming precision drilling and set up of the
housings for drilling. Present instruments also
utilize many individual sub-assembly components requir-
ing stocking and assembly time. The instrument covers,
for instance, normally require two or more pins and
locks or other multi-part fasteners to mount the cover
to the instrument. This requires an inventory of the
several parts and an inordinate amount of assembly time
to assemble the cover to the instrument.
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Pneumatic relays, used extensively in posi-
tioners and transducers, normally have been made from
aluminum based materials. Machine screws are used to
assemble the aluminum relay body components together
while clamping rubber diaphragms and o-rings to provide
the pressure seals. Assembly of these numerous sub-
assembly components of present pneumatic relays is
tedious and costly in the manufacturing environment.
It is desired therefore to eliminate compon-
ents or at least reduce the number of components
required for an electro-pneumatic instrument.
Summary of the Invention
In accordance with the present invention
there is provided a versatile modular configuration for
an electro-pneumatic instrument that can serve as a
platform of construction for a wide range of output
devices which includes, for example: a digital pres-
sure transducer; a digital valve controller; an analog
valve positioner; and an analog pressure transducer.
All of the aforementioned output devices available from
the present invention can provide the following
features:
1. A modular configuration with a field
termination compartment, an electronics compartment,
and a pneumatic compartment which are all environmen-
tally segregated from each other;
2. A modular configuration which is
explosion proof, and allows maintenance and service-
ability of the pneumatic elements without interfering
with the electrical components; and
3. A modular configuration permitting user
selected variations in feedback and mountings to accom-
modate both sliding stem valve actuators and rotary
shaft valve actuators.
In accordance with the principles of the
present invention, there is provided an electro-
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pneumatic instrument of modular construction which is
readily convertible from a pressure transducer to a
valve positioner and vice versa. In the preferred
embodiment of the invention, the convertible instrument
includes an enclosure having a housing defining a
hollow interior, and a modular base containing electri-
cal and pneumatic components, where the modular base is
removably insertable into the housing. A housing
portion-is included on the housing and is adapted for
receiving and mounting therein a potentiometer and
shaft in converting the instrument to a valve position-
er. The housing portion communicates with the hollow
interior to enable the potentiometer output to be
connected to the electrical components on the modular
base via the housing portion and the housing hollow
interior.
The housing portion may be formed of an
elongated cylindrical boss extending along the housing
and which includes a pocket interior to receive the
potentiometer at one end. The pocket interior inter-
sects with the housing hollow interior and a bushing is
threadably mounted on the elongated cylindrical boss to
supportably mount the potentiometer shaft.
In converting a valve positioner utilizing
the present electro-pneumatic instrument of the present
invention to a pressure transducer, this can be readily
provided by removing the potentiometer from the housing
portion, disconnecting the potentiometer output cable
from the main printed circuit board mounted on the
modular base, and replacing the main circuit board to
accommodate the signals appropriate to a pressure
" transducer as is known in the art.
The preferred embodiment also includes an
electrical terminal box mounted on the housing with a
passageway between the housing interior and the termin-
al box. An electrical terminal board is replaceably
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mounted in the terminal box which includes a removable
cover for access thereto. A cable harness is connected
to the electrical terminal board in the terminal box
and extends through the passageway and the housing
hollow interior for connection to the main circuit
board on the modular base. The terminal board and
cable harness are replaceable to accommodate
corresponding desired formats and functions, such as
analog, digital, communication or data protocols.
In accordance with another aspect of the
present invention, a housing is provided with a sub-
stantially flat housing mounting surface with open
channels or slots within the surface. A modular base
has a modular base mounting surface opposite to the
housing mounting surface. A gasket is provided inter-
mediate the housing mounting surface and the modular
base mounting surface. The gasket covers the open
channels so as to define the housing fluid passageways,
and further includes apertures for communicating the
housing fluid passageways to the modular base fluid
passageways. A distinct advantage of this aspect of
the invention is the elimination of the need to drill
precise holes through the housing or to precisely
locate and drill intersecting holes to form the desired
fluid communicating passageways.
In accordance with still another aspect of
the present invention, there is provided a cover with
self-contained mounting ears shaped for ease of insert-
ing the ears into the module base so the cover is
retained on the module base in a closed configuration
and yet can be readily removed from the module base if
desired in an open configuration.
In accordance with a further aspect of the
present invention, there is provided a pneumatic relay
with plastic molded structural body components. These
components are ultrasonically welded together in a
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manner that clamps the diaphragm to provide the pres-
sure seals, thus eliminating the need for machine
screws. Thus, the number of sub-assembly components
are minimized and the assembly costs for the pneumatic
relay are drastically reduced by almost one-half.
There is also provided an electro-pneumatic
converter in the form of a current to pressure
transducer/positioner unit having an enclosure which
includes a housing and module base for electrical and
pneumatic components with a compartmented portion of
the unit forming two segregated compartments for the
respective electrical and pneumatic components. A
dividing interior wall between opposite sides of the
module base defines a segregated compartment between
the dividing interior wall and a first portion of the
module base opposite the dividing interior wall in a
first direction. This segregated compartment prefer-
ably contains the electrical components. Another
segregated compartment is defined between the dividing
interior wall and a second portion of the module base
opposite the dividing interior wall in a second direc-
tion opposite from the first direction for preferably
containing the pneumatic components isolated from the
electrical components.
A removable cover is preferably provided for
the segregated compartment containing the pneumatic
components. Accordingly, removing the cover enables
access to the pneumatic component segregated compart-
ment for servicing the pneumatic components while
maintaining the electrical components isolated. There-
fore, with the present invention, the explosion proof
'. electronic compartment remains isolated and undisturbed
and all of the explosion proof elements can remain
intact while one services the pneumatic elements in the
unit of the present invention. Thus, there is no need
to disconnect the electrical power while working on the
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pneumatic elements in the unit of the present
invention.
The significant advantage of this aspect of
the invention includes the ability to adjust or remove
and replace the pneumatic elements while the power is
connected without breaking the seal of the explosion
proof portion of the transducer/positioner. Other
significant advantages include the ability to provide
additional maintenance features, such as stroking the
pneumatic elements fully opened or closed to perform
maintenance diagnosis of the unit. The pneumatic
elements can also be adjusted to change pneumatic zero
during maintenance or troubleshooting. Also, access to
the supply pressure primary restriction which may be-
come clogged and requires cleanout is readily provided
in accordance with this invention.
In accordance with another aspect of the
present invention, an electro-pneumatic converter unit
includes an enclosure having a housing defining a hol-
low interior and a modular base removably insertable
into the housing hollow interior so as to be surrounded
by the enclosure. Electrical and pneumatic converter
components are mounted on the modular base including
one or more pressure gauges so that the pressure gauges
are located within the enclosure and thereby protected
from the environment and any physical damage. The
gauges, which are mounted in the pneumatic compartment
are in an atmosphere which is constantly being purged
by the supply pressure medium, thus affording them
additional protection to corrosive atmospheres not seen
with devices with externally mounted pressure gauges.
The pressure gauges are preferably threadably mounted
on the modular base for ease in servicing and
replacement.
In accordance with still another aspect of
the present invention, the modular base includes a
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dividing interior wall. First means are provided for
mounting the electrical components on one side of the
dividing interior wall. Second means are provided for
mounting the pneumatic components including pressure
gauges on the opposite side of the dividing interior
wall. Accordingly, as the modular base is insertably
mounted into the housing interior, segregated compart-
ments are defined for respectively isolating the
electrical components from the pneumatic components.
In accordance with still another aspect of
the invention there is provided an improved pneumatic
pressure relay for a fluid actuator control valve
assembly. The supply pressure is communicated to a
supply bias cavity through a capillary hole to maintain
a substantially constant supply pressure of the relay.
Pressure transients in response to load changes are
isolated from the supply bias cavity by the capillary
hole.
Brief Description of the Drawinas
The features of this invention which are
believed to be novel are set forth with particularity
in the appended claims. The invention may be best
understood by reference to the following description
taken in conjunction with the accompanying drawings, in
which like reference numerals identify like elements in
the several figures and in which:
Figure 1 is a front elevational view illus-
trating a current to pressure transducer having an
enclosure with a housing and a removable module base in
accordance with the present invention;
Figure 2 is a cross-sectional view taken
along section lines 2-2 of the current to pressure
transducer shown in Figure 1, with certain components
removed for clarity;
Figure 3 is a sectional view of the module
taken along section lines 3-3 of the current to
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pressure transducer shown in Figure 1, with certain
components removed for clarity;
Figure 4 is a sectional view taken along
section lines 4-4 of the current to pressure transducer
shown in Figure 2, with certain components removed for
clarity;
Figure 4A is a fragmentary sectional view
taken along section lines 4A-4A of the current to
pressure transducer shown in Figure 1;
Figure 5 is a fragmented sectional view taken
along section lines 5-5 of the current to pressure
transducer shown in Figure 1, with certain components
removed for clarity;
Figure 6 is an elevational view showing an
interconnect board for connecting electrical terminals;
Figure 7 is an elevational view showing the
interior of the housing with the interconnect board
floatably mounted therein;
Figure 8 is a schematic sectional view
showing a shoulder screw mounting the interconnect
board in a floating manner;
Figure 9 is a sectional view showing a supply
biased pneumatic pressure relay;
Figure l0 is a perspective view of a
preferred embodiment of the invention illustrating a
valve positioner in modular configuration which can be
readily converted to a pressure transducer;
Figure 11 is a sectional view of the prefer-
red embodiment of the invention taken along section
lines il-11 of the valve positioner shown in Figure 10;
Figures 12 and 12A are exploded perspective
views of the modular configured valve positioner of
Figure 10, the two figures being consecutively locat-
able along the same central reference axis along the
direction indicated by the respective arrowheads;
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Figure 13 is an elevational view showing a
modular base with some components removed for clarity;
Figure 14 is a sectional view taken along
section lines 14-14 of the modular base shown in Figure
13;
Figure 15 is a fragmented view partly in sec-
tion showing a pressure sensor sensing the output
pressure;
Figure 16 is an elevational view of the
instrument housing portion showing channels in the
surface for fluid passageways;
Figure 17 is an elevational view of the
modular base showing the modular base surface facing
the housing surface of Figure 16; and
Figure 18 is a schematic block diagram illus-
trating the electro-pneumatic converter instrument
readily convertible from a valve positioner to a
pressure transducer and vice versa.
Detailed Description
The modular and convertible aspect of the
invention illustrated in Figures 1-9 will be described
in connection with an embodiment comprising a current
to pressure transducer. It is to be understood that
the teachings herein can as well be applied to other
electro-pneumatic converter devices to solve problems
similar to those which are solved by the present inven-
tion. As an example, while this description is in
connection with a current to pressure transducer, it is
well-known in the art that such devices can readily be
converted to a current to pressure positioner following
the teachings herein.
The flexible modular and convertible aspect
of the invention illustrated in Figures 10-18 will be
described in connection with a preferred embodiment
comprising a current to pressure positioner which is
more readily convertible to a current to pressure
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transducer and vice versa than the embodiment of
Figures 1-9. Accordingly, the present description is
to be understood to be for purposes of describing the
preferred embodiment and is not meant to limit the
scope of the invention and the claims. Thus, the
invention and the claims are to be given a broad
interpretation consistent with the teachings herein.
I. Convertible Current To Pressure Transducer
Referring now to Figures 1 and 2, there is
illustrated a current to pressure transducer 10 having
an enclosure which includes a housing 12 with one
portion defining a hollow interior 14. The housing 12
includes a field terminal box portion 16 including a
field terminal strip 18 for suitable connection to an
electrical signal cable for receiving a current control
signal from a distributing control system, so as to for
instance monitor a process. End cap 20 is removable
from the housing so that the appropriate cable wiring
connections can be made to terminal 18.
Housing 12 also includes an inlet 22 for
receiving a supply pressure from a pneumatic supply
source, and an outlet port 24 through which the output
pressure can be suitably coupled to a positioner or
directly to a valve actuator. Typically, in response
to a variable 4-20 mA current control signal, current
to pressure transducer 10 provides a variable pressure
output at outlet 24.
A modular base 26 (see Figure 3) contains the
electrical components and the pneumatic components for
current to pressure transducer l0. Typically, this
will consist of a current to pressure converter device
such as a I/P nozzle block having a flapper for
converting the variable current control signal input
into a variable nozzle pressure signal; a pressure
relay receiving the variable nozzle pressure signal and
providing a variable pressure output on outlet 24; a
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pressure gauge monitoring the supply pressure coupled
to inlet port 22; a second pressure gauge monitoring
the pressure output on outlet 24; and electronic equip-
ment such as a pressure sensor and a printed circuit
board with circuitry to process the electrical signals
as required.
Modular base 26 includes a metal base 28 hav-
ing a threaded ring 30 and O-rings 32 so that modular
base 26 can be inserted into housing 12 by threadable
engagement. Reference may be made to Figure 2, wherein
modular base 26 is shown in its complete threadable
mounting position when fully inserted within housing
12.
The modular base also includes a modular wall
34 which provides the mounting of the pressure compon-
ents on one side and the electrical components on the
other side. In the modular base 26, and opposite wall
34, there is provided a masking plate 36 and a clear
cover plate 38 forming a pressure compartment 40 in the
modular base and defined between modular wall 34 and
cover plate 38. With reference to Figure 2, it can be
seen that when the modular base is insertably mounted
into the housing, an electrical compartment 42 is
defined as part of housing interior 14 and is
specifically defined between modular wall 34 and a
housing side 44.
With reference to Figures 1-3 it can be seen
that the pressure components are mounted in the modular
base on one side of modular wall 34 and the electrical
components are mounted on the other side of wall 34.
For example, an I/P nozzle block-flapper unit 46, a
. pneumatic relay 48, and pressure gauges 50, 52 are all
mounted in pneumatic compartment 40 on one side of wall
34. A printed circuit board 54 containing electrical
components and a pressure sensor 56 are mounted on the
opposite side of modular wall 34 so that they are
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confined within electrical compartment 42 when the
modular base is inserted into the housing.
Accordingly, as can be seen from Figure 2,
the electronic components are isolated within segregat-
ed electrical compartment 42 and the pressure compon-
ents are isolated in segregated pressure compartment 40
on opposite sides of modular wall 34. All of the
electrical and pneumatic components, including the
pressure gauges, are maintained within the instrument
enclosure. It is understood, of course, that suitable
explosion preventing devices are inserted in the
orifices through wall 34 which may otherwise inter-
connect compartments 40 and 42. As an example, with
reference to Figure 3, aperture 58 through wall 34
interconnects pressure gauge 52 and pressure sensor 56.
A commercially available item known as a flame arrester
60 is inserted in aperture 58. The flame arrester 60
may comprise a porous metal plug which allows pressure
to pass through the plug but which will cool and lower
the temperature of any flame in aperture 58 to prevent
ignition of potentially hazardous environments.
Threaded ring 30 is free to rotate with
respect to metal base 28. The threaded ring is secure-
ly captured between metal base 28 on one side and two
stanchions 62 mounted to metal base 28 and having a
projecting ledge 64 slightly spaced from a rim 66 of
threaded ring 30.
This enables the threaded ring to rotate and
threadably engage a threaded housing portion 68 so as
to securely mount and seal the metal base 28 through
O-rings 32 with respect to housing 12.
In accordance with one aspect of the present
invention, it may be noted that while the pressure
components and the electrical components have been
isolated within the enclosure formed by housing 12 and
modular base 26 to prevent any inadvertent spark from
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the electrical components to ignite potentially
hazardous environments which may be present in the
pressure components, yet the pressure components can be
serviced and maintained without shutting down the power
or requiring removal of unit l0 from the potentially
hazardous area. With respect to this aspect of the
present invention, note that removal of cover 38 and
mask 36 from the enclosure provides access to the
pressure components within pressure compartment 40
while still maintaining the isolation of the electrical
components in electrical compartment 42.
Thus, the I/P nozzle block 46 can be serviced
without turning off the electrical power. For
instance, the pneumatic elements can be adjusted to
pneumatic zero during maintenance or troubleshooting by
affording access to a zero adjustment nut 70 on the I/P
nozzle block unit. Also, access is permitted to a
cleanout wire 72 to permit the wire to be used to
cleanup the pneumatic restriction or orifice in the air
supply line which can become clogged. In a similar
manner, the pressure gauges can be threadably removed
from the module and replaced, if necessary, without
shutting off the power supply. Servicing of the pneu-
matic relay can also be performed with the complete
isolation of the electrical components in electrical
compartment 42.
In accordance with another aspect of the
present invention, it may be noted that pressure gauges
50 and 52 are mounted totally within the enclosure
formed by housing 12 and modular base 26 so they are
not subject to the environment or to any physical
. damage from actions outside of the housing. Yet, the
pressure gauges can be removed or are subject to repair
by removing replaceable cover 38 and mask 36 to provide
access to pressure compartment 40.
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Figure 4 illustrates the modular wall 34
which contains a longitudinal passageway to communicate
the inlet pneumatic supply at an inlet end 76 into I/P
nozzle block 46 and to communicate the I/P nozzle block
variable pressure output into the pneumatic relay 48.
Referring now to Figure 4A, there is illustrated
modular wall 34 and the passageways through the modular
base for connecting the supply pressure from inlet end
76 to passageways 77 and 79 to the I/P nozzle block 46
from the main supply passage 81. The variable pressure
output of nozzle block 46 is supplied through a
passageway 83 to interconnecting passageway 74 to the
pneumatic relay 48.
With reference to Figure 3, it can be seen
that passageway 81 connects to a transverse passageway
85 at the inlet end 76 for eventual communication with
inlet port 22 for receiving the pneumatic supply pres-
sure when the modular unit is mounted in the housing.
With reference to Figure 4, apertures 78 are
shown in the modular wall to permit the electrical con-
nections from printed circuit board 54 through the
modular wall to the I/P nozzle block. As indicated
previously, these apertures also contain suitable
explosion proof seals to isolate and prevent any sparks
in electrical compartment 42 from causing ignition of
potentially hazardous environment through the wall 34
and into pressure compartment 40.
In accordance with another aspect of the
present invention, the mating of connections between
the housing terminals and the modular terminals is
provided by a blind connection, i.e. automatically as
modular base 26 is insertably mounted into housing 12.
The electronic components on printed circuit board 54
are electrically connected to a modular terminal strip
80 containing modular terminals 82, which as shown in
Figure 5 consist of a plurality of male terminal pins.
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Printed circuit board 54 is mounted within a plastic
cover 84, preferably by epoxy molding of all of the
units within the plastic cover. Cover 84 is in turn
mounted to modular wall 34 through the use of appro-
priate threaded screws 86. As shown in Figure 5,
modular terminals 82 protrude through cover 84 for
engagement with female housing terminals 88 contained
on a housing terminal strip 90 which in turn is mounted
to a housing interconnect board 92.
With reference to Figures 6 and 7, there is
indicated the manner in which the housing interconnect
board is floatably mounted so as to permit self-
aligning of the board with the modular terminal pins.
Housing side 44 includes a pair of upright ribs 94 each
having a threaded aperture for receiving a respective
mounting screw 96. Preferably, mounting screws 96 are
shoulder screws so that the bottom of the shoulder
butts against the rib and prevents further penetration
of the shoulder screw into the threaded aperture of the
rib.
Referring to the schematic illustration of
Figure 8, this configuration is illustrated in more
detail. Threaded aperture 98 within rib 94 receives a
threaded portion 100 of screw 96 until a shoulder 102
compressingly abuts against rib 94. As seen in Figure
8, the length of shoulder 102 is greater in dimension
than the width of housing interconnect board 92.
Therefore, the housing interconnect board can float
longitudinally along screw 96 and between the screw
head and the top of rib 94. If desired, screw head 96
can be sized for this purpose or, a larger washer 106
~ may be utilized. In addition, apertures 104 in housing
interconnect board 92 are made slightly larger in
diameter than the diameter of shoulder 102. This
permits the interconnect board to slightly move trans
versally with respect to the screw. Thus, housing
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interconnect board is securely captured by screw 96 and
ribs 94 but is allowed to float in position between the
screw and the rib so that the housing terminals are
self-aligned with the modular terminals during the
insertable mounting of modular base 26 into the
housing.
To guide the modular terminals in the correct
orientation with respect to the housing terminals, a
longitudinal groove 108 is provided on the inside sur-
face of the housing. Groove 108 matches an indexing
pin 110 which is fixed within the outer surface of
metal base 28. Thus, in inserting modular base 26 into
the housing, the modular base is rotated until indexing
pin 110 is fitted within longitudinal groove 108 to
correctly position modular terminals 82 with the hous-
ing terminals 88. Thereafter, as threaded ring 30 is
rotated to move the modular base into the housing,
because of the floating mounting of housing inter-
connect board 92, the female housing terminals 88
become self-aligned with the male modular terminals 82
to achieve the final electrical interconnection of the
modular base with the housing interconnect board as
shown in Figure 5.
A flexible electrical cable 112 interconnects
the housing interconnect board 92 with a small printed
circuit board 114 which in turn is connected to a
series of RFI filters 116 with the filters 116 connec-
ted through housing 12 to appropriate field terminals
18.
Since the transducer unit can readily be
converted to a positioner as known in the art, housing
interconnect board 92 also includes suitable connec-
tions 118 for connection to a potentiometer. For a
transducer unit, a plug 120 is threadably mounted into
housing side 44 to close off electrical compartment 42.
When the unit is to be used as a positioner, a poten-
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tiometer can be mounted in the electrical compartment
for electrical connection to connectors 118 and with
the potentiometer shaft extending through an aperture
with suitable flame arresting devices in a plug.
Referring now to Figure 9, there is
illustrated an improved pneumatic pressure relay 48
which receives a variable control pressure on inlet 122
and delivers a variable output pressure on outlet 124
coupled to pneumatic outlet 24 of housing 12 (see
Figure 1) for communication with a valve actuator.
Relay 48 also includes a supply pressure inlet 126
coupled to the inlet 22 of housing 12 (see Figure 1)
for connection to a source of pneumatic supply pres-
sure. Relay 48 also includes an exhaust outlet 128.
Pneumatic pressure relay 48 includes a supply
bias portion for establishing the start point of the
pneumatic pressure input range at inlet 122 for a given
supply pressure at inlet 126. The start point input
pressure will change with changing supply pressures and
therefore allows the relay 48 to operate at different
supply pressures without hardware changes, such as bias
springs. With reference to Figure 9, it may be seen
that relay 48 includes an input signal diaphragm 130,
an input supply port 132, and an exhaust port 134. The
movement of diaphragm 130 in response to the variable
pressure input on inlet 122 controls the opening and
closing of the input supply and exhaust ports. A valve
rod 136 includes a supply valve plug 138 at one end and
an exhaust valve plug 140 at the other end.
A valve spring 142 seated against plug 138
and cap 144 normally maintains plug 138 seated against
input supply port 132 as shown in Figure 9. This
blocks the supply pressure from inlet 126 from reaching
the actuator outlet 124 which supply pressure otherwise
would communicate through passageways 146, 148, through
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an open input supply port 132 and through a passageway
150 to actuator outlet 124.
The drive coupling between input signal
diaphragm 130 and valve rod 136 is provided through
three intermediate diaphragm mounting bodies, namely an
upper body 152, a middle body 154 and a lower body 156.
An upper supply bias diaphragm 158 is captured between
bodies 152, 154 and a lower supply bias diaphragm 160
is captured between middle block 154 and lower block
156.
A supply bias cavity 162 is defined between
diaphragms 158, 160, middle block 154 and an outer
casing 155. A small capillary hole 164 through casing
155 communicates the supply bias cavity with supply
pressure inlet 126 so that the supply bias cavity is
substantially always under the supply pressure. Thus,
the supply pressure is not only channeled to input
supply port 132, but also enters supply bias cavity 162
via capillary hole 164. It is desirable that once the
supply pressure is established in cavity 162, that it
not change during the operation of relay 48. Momentary
fluctuations in the supply pressure can result when
supply port 132 is opened and closed. The capillary
hole isolates the supply bias cavity from pressure
transients created when valve plug 138 opens or closes
supply port 132 in response to load changes. This
effectively stabilizes the valve assembly when brief
pressure fluctuations occur due to input signal changes
thereby resulting in improved performance.
Figure 9 illustrates relay 48 in its normal
position. When an increasing variable pressure is
coupled to inlet 122, input signal diaphragm 130 is
flexed upwardly in Figure 9 to move bodies 156, 154,
152, exhaust plug 140, rod 136 and valve plug 138 also
upwardly to unseat the supply port 132. Exhaust port
134 remains closed. Supply pressure is thereby coupled
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from inlet 126 through passageways 146, 148 and through
open supply input port 132 and passageway 150 to actua-
for outlet 124 and eventually to the valve actuator.
It may be noted that lower supply bias diaphragm 160
contains a greater diaphragm area than the upper supply
bias diaphragm 158. This enables biasing the relay to
form an output start point commensurate with the input
signal based on the given supply pressure.
II. Convertible Current To Pressure Positioner
Reference may now be made to Figures 10-18
wherein there is illustrated a preferred embodiment of
an electro-pneumatic instrument which is readily con-
vertible from a current to pressure positioner to a
current to pressure transducer and vice versa. The
assembled views of Figures 10 and 11, for instance,
illustrate a preferred electro-pneumatic convertible
instrument 200 providing optimum flexibility in con-
figuration over such presently available devices. In
particular, the configuration is modular with respect
to several main instrument components, thereby provid-
ing the following advantages:
(1) Enabling a ready conversion of the
instrument from a valve positioner to a pressure trans-
ducer in a manner not available with prior instruments;
and
(2) Enabling different types of terminal
boxes to be replaceably mounted on the housing for
accommodating a variety of field connections and
configurations.
The electro-pneumatic convertible instrument
200 shown in the assembled views of Figures 10 and 11
is in the form of a valve positioner which includes
several basic enclosure components in modular form,
i.e., a housing 202, a field terminal box 204 separable
from and replaceably mounted on housing 202, and a
modular base 206 also replaceably mounted onto housing
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202. A removable cover 208 for the instrument enclos-
ure is rernovably mounted on modular base 206. A
terminal box cover 210 is mounted on field terminal box
204 to protect the contents from the environment.
Instrument 200 is in the form of a valve
positioner which includes a bushing 212 mounted into an
elongated cylindrical boss 214 which extends along the
housing for mounting a potentiometer assembly 216.
Elongated cylindrical boss 214 is formed integrally
with housing 202 as a cast unit so as to extend along
housing back wall 218 (see Figure 11). Boss 214 is
hollow and includes an interior pocket 220 which
intersects and communicates with the hollow interior
222 of housing 202. As can be seen in the exploded
view of Figure 12, potentiometer assembly 216 is
inserted with potentiometer 224 being placed into the
interior pocket 220 and with the potentiometer leads
226 and connector plug 228 extending through interior
pocket 220 and into the housing hollow interior 222 to
connect to a printed circuit board 230 mounted within
the modular base 206. Bushing 212 is then slipped over
potentiometer shaft 232 and threadably engaged into the
boss 220 so as to supportably mount the potentiometer
shaft 232 and maintain potentiometer assembly 216
mounted within housing 202.
Referring to the assembled view of Figure 11
and the exploded view of Figure 12, there is illustrat-
ed the manner in which the various components including
the potentiometer assembly 216 are mounted to housing
202. In particular, field terminal box 204 includes a
male threaded end portion 233 which is threadably
engaged with a corresponding female threaded portion
234 on housing 202. Terminal box 204 includes an
interior portion 236 which leads to a tubular passage-
way 238 which extends from interior 236 and at right
angles through terminal 204 to the other terminal end
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240 which communicates with the hollow interior 222 of
housing 202.
A field terminal block 242 is mounted to a
printed wiring board 244 and which in turn is mounted
to a cable harness 246 ending in a connector plug 248.
As is seen from Figure 12, the terminal block, printed
wiring board, cable harness and connector plug have all
been combined into one assembly. In particular, it may
be noted that the cable harness includes radio frequen-
cy interference (RFI) filter feedthroughs 250 (see
Figure 11).
A significant advantage of this configuration
is that it reduces manufacturing costs required for
installing threaded RFI filters into the housing and
then soldering the printed wiring board and terminal
block assembly to the RFI filters. Furthermore, the
terminal assembly shown in Figure 12 can be more easily
replaced and is more reliable in installation and
operation. In installing the field terminal block 242,
and associated cable harness, connector plug 248 is
inserted into the interior 236 and then into tubular
passageway 238, continuing beyond terminal end 240 and
into the hollow interior 222 of housing 202. Plug 248
may then be connected to main printed circuit board 230
on the modular base 206. Within terminal box 204,
printed wiring board 244 is moved against one end of
tubular passageway 238 until the board butts against an
O-ring 252 and the printed wiring board 244 is main-
tained in position by means of screws 254. O-ring 252
acts as a seal to maintain the housing interior 222 and
the main circuit board 230 sealed off from the environ-
ment. Terminal box cover 210 is then threadably mount-
ed on the terminal box so as to aid in maintaining the
electrical components free from the environment.
Modular base 206 contains a main electrical
compartment 256 segregated on one side of a dividing
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wall 258 with pneumatic components on the other side of
wall 258. In particular, a current to pressure
converter device such as an IJP nozzle block - flapper
unit 260, a pressure relay 262, and pressure gauges
264, 266 are all mounted to modular base 206 on one
side of dividing wall 258 so as to be physically
isolated and segregated from the electrical components
on the other side of wall 258. The electrical
components are thus maintained within an explosion
proof portion of the instrument enclosure. Also, all
of the electrical and pneumatic components, including
the pressure gauges are maintained within the
instrument enclosure. Cover 208 contains respective
transparent viewing windows to permit visual reading of
gauges 264, 266.
Electrical connections from main printed
circuit board 230 to the I/P converter are supplied
through electrical contacts 268 coupled through
suitable apertures 270 to the I/P converter 260.
Aperture 272 in wall 258 is for coupling the supply
pressure to the IjP converter 260. Aperture 274 is for
coupling the variable pressure from the I/P converter
to the instrument output as will be described in more
detail hereinafter.
Figure 16 is a front view of the housing face
showing the supply pressure coupled to input port 276
with a passageway 278 connecting the supply pressure to
open channels 280 in housing surface 282. Surface 282
also includes another set of open channels 284 which
connect to a passageway 286 communicating with the
instrument output port 288. Accordingly, open channels
280 and housing surface 282 are associated with the
pressure on the input side or supply pressure side of
the system and open channels 284 in surface 282 are
associated with the variable output pressure side of
the instrument.
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Figure 17 illustrates a rear view of modular
base 206, i.e. viewing the modular base from the direc-
tion of reference arrow 290 in Figure 12A with the
electrical compartment 256 removed for ease of
illustrating the rear surface 292 of modular base 206.
Figure 17 shows several passageways which are provided
in modular base 206 to communicate with the fluid
passageways and channels in housing 202 for fluidly
interconnecting the various components on the
instrument. As an example, in Figure 17, passageway
294 is the relay exhaust passageway, passageway 296
communicates supply pressure to the relay, and
passageway 298 communicates the variable pressure
output of the relay and therefore comprises the
instrument output. Passageway 300 communicates with
the output pressure gauge 264 and passageway 302
communicates with the input pressure gauge 266.
Passageway 304 is coupled to the output pressure sensor
354, and passageway 306 is connected to the I/P
converter supply pressure input (see Figure 14j.
As can be seen from the illustrated position
of the components in the exploded views of Figures 12
and 12A, and with specific reference to Figures 16 and
17, the input supply pressure on input port 276 which
is coupled to passageway 278 and channel 280 communi-
cates with passageway 296 to supply pressure to relay
262. Relay exhaust passageway 294, communicating
through passageway 318 (see Figure 16j, exhausts out
the relay exhaust port 308 as shown in Figure il. A
plastic vent assembly 309 prevents dirt and debris from
access to relay exhaust port 308.
Intermediate surface 282 of the housing 202
and surface 292 of modular base 206 there is provided a
gasket 310 which can be formed of flexible rubber
material. Gasket 310 covers the open channels 280 and
284 so as to form fluid passageways in the housing 202.
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Furthermore, gasket 310 includes a series of apertures
for desirably coupling fluid channels between the
modular base and the housing. Note for instance
apertures 312, 314, 316 which are respectively aligned
with passageways 294, 296, 298 on modular base 206 as
well as with respective passageway 318, channel 280,
and 284.
Removable cover 208 includes transparent
sections 320, 322 for viewing the pressure gauges 264,
266 when the cover is closed in position. As can be
seen from Figure 12A, cover 208 includes a pair of
curved ears 324. Cover 208 is mounted onto modular
base 206 by first elevating cover 208 until leading
edge 326 of each ear 324 is directly facing a
respective cover mounting slot 328 in modular base
upper wall 330. This places the curved ear portions
324 substantially in line with the longitudinal slot so
that they can be inserted into the slot until the cover
front edge 332 abuts the modular base upper wall 330.
At this point the cover 208 may now be rotated
downwardly to the closed position with the curved ears
324 aiding in maintaining the cover in the downward
closed position.
Referring now to Figures 13-16, there is
illustrated the details of mounting of the pressure
components on modular base 206 and their fluid
interconnections through appropriate passageways. For
convenience, in Figure 13, the input pressure side has
been labeled "IN" and the output pressure side has been
labeled "OUT". Referring to Figure 14, supply pressure
through passageway 306 is supplied from input port 276
~ (see Figures 16 and 17), channels 280, hole 309 in
gasket 310 (see Figure 12), through passageway 306.
Passageway 306 interconnects with intersecting
passageway 336 which in turn communicates with
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passageway 272 which provides the input supply pressure
to I/P converter 260.
The pressure output side of I/P converter 260
is coupled to passageway 274 and then to a vertical
passageway 338 in dividing wall 258, the passageway 338
coupling in turn with the variable pressure input to
the input diaphragm of pressure relay 262 as shown in
Figure il. Input pressure gauge 266 is mounted to an
upstanding ledge 340 containing a passageway 342 which
communicates with passageway 302 (see Figure 17) so as
to couple input supply pressure from channel 280 and
input port 276 to pressure gauge 266.
With reference to Figure 15, it can be seen
that in a similar manner the output pressure gauge 264
is mounted on an upstanding ledge 344. Ledge 344 in
turn includes passageway 346 which communicates with
passageway 300 which in turn passes through hole 315 in
gasket 310 so as to communicate with channel 284 in
housing 202. This enables gauge 264 to sense and
indicate the output pressure of the instrument.
The instrument variable output pressure
developed by pressure relay 262 is coupled from the
output chamber of pressure relay 262 to passageway 348
and through a flame arrester 350 to an intersecting
passageway 304, which in turn communicates the pressure
through hole 313 on gasket 310 to channel 284 on
housing 202. A pressure sensor 354 may be provided for
sensing the output pressure through passageway 348 as
shown on Figure 14. When this instrument is used as a
valve positioner, pressure sensor 354 can be used for
diagnostic purposes. When the instrument is used as a
current to pressure transducer, the pressure sensor 354
acts as the feedback mechanism for the system as will
be described more particularly hereinafter.
Reference may now be made to Figure 18
wherein there is illustrated a schematic block diagram
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of instrument 200 with the major components shown in a
functional block diagram as used for either a valve
positioner or as a pressure transducer. As illustrated
with respect to the preferred embodiment of the
invention shown in Figures 10-17, there is shown a
current to pressure positioner in the form of a valve
positioner which includes an I/P converter 260 and
pressure relay 262 mounted on modular base 206. Also,
housing 202 contains a housing portion, i.e. integral
hollow boss 214 and an interior pocket 220 for
receiving a potentiometer assembly 216 including a
position potentiometer 224. When used as a valve
positioner, instrument 200 includes a feedback arm 356
which includes screw attachment means 358 for attaching
the feedback arm 356 (see Figures 10 and 11) to
potentiometer shaft 232 so that the shaft 232 is
rotated by the feedback arm 356.
With reference to Figure 18, there is
schematically illustrated a fluid control valve 360 and
a sliding valve stem actuator 362 with the valve
actuator containing a pin 364 connected to move with
the valve stem during linear valve stem movements.
Accordingly, as valve stem 362 is moved vertically up
or down as shown by the reference arrows in Figure 18,
pin 364 also moves with the valve stem, and with the
pin being coupled to feedback arm 356, the feedback arm
is rotated in the manner illustrated by the rotational
reference arrows. Rotation of feedback arm 356 rotates
the potentiometer shaft 232 and changes the position of
the potentiometer 224 so that the changed position is
sensed by position sensor 366 to couple a variable
current to the input of the I/P converter 260. Rather
than the potentiometer, other feedback elements with
capacitors, inductors, or active elements can be used.
Figure 11 illustrates the pin 364 maintained
in a biased position in a slot 368 in feedback arm 356.
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A spring clip 370 is biased to maintain pin 364 against
the side of slot 368. Accordingly, as the pin 364 is
moved in movements following the valve stem 362, pin
364 also moves linearly within slot 368 so as to rotate
feedback arm 356 and register the valve position change
into a change in the position of potentiometer 224.
The signal indicating the change in potentiometer
position is carried by potentiometer leads 226 to the
position sensor 366 which is mounted on the main
circuit board 230 within electrical compartment 256.
The corresponding variable current signal input to the
I/P converter 260 is carried on input leads 268 from
the circuit board 230 through apertures 270 and into
the I/P converter 260.
Accordingly, in the illustrated preferred
embodiment of the invention where the instrument is
acting as a valve positioner 200, a variable pressure
output on output port 288 moves valve stem 362 and pin
364 in a certain manner. This movement is translated
by feedback arm 356 into a changed position in
potentiometer 224. The changed position is sensed by
position sensor 366 and transformed into a variable
current supplied on leads 268 into the I/P converter
260 to provide a variable pressure on line 274.
In accordance with one significant advantage
of the present invention, the instrument can readily be
converted to a pressure transducer. In order to
accomplish this conversion, electrical compartment 256
may need to be replaced in order to provide a new main
circuit board 230. That is, it is preferred that the
circuit board 230 and the electrical components within
~ electrical compartment 256 are potted within the hollow
structure. However, the electrical compartment can
readily be changed by removing four screws 372 to
separate modular base 206 from housing 202, and then
removing plugs 248 and 228 from the main circuit board
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230 before removing electrical compartment 256 and
replacing it with one suitable for use as a pressure
transducer. Also, the potentiometer assembly 16 and
bushing 212 could be removed from housing boss 214 and
replaced by a suitable plug, or these components can
simply be left in position but not connected with the
main circuit board. In any event, in the current to
pressure transducer mode, the feedback of variable
pressure on output port 288 is coupled through pressure
sensor 354 to provide a variable current signal
supplied on input lead 268 to the I/P converter 260.
It is understood of course that if the
original instrument had been set up as a current to
pressure transducer, to convert the instrument to a
i5 current to pressure positioner would simply have
required placement of a potentiometer assembly 216 with
a bushing 212 into the interior pocket 220 of housing
boss 214; changing the main circuit board 230 and
preferably the entire electrical compartment 256 with a
new one adapted for valve positioner operations; and
mounting of feedback arm 356 to the potentiometer shaft
232 and placing pin 364 in slot 368 for a sliding stem
valve operation. It is also understood of course that
if a rotary shaft actuator is used for a fluid valve
instead of a sliding stem situation, then a suitable
feedback arm like feedback arm 356 would be coupled to
potentiometer shaft 232 and also coupled to a suitable
rotary movement feedback link from the rotary actuator
so that movements of the feedback link generate
rotations of potentiometer shaft 232. Other types of
feedback elements, instead of a potentiometer, can be
utilized and incorporated into instrument 200 in
accordance with. the teachings herein. For example,
feedback elements using capacitors, inductors, or
active elements could be used in place of a
potentiometer, or in combination.
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It is preferred that feedback arm 356 is
stabilized with respect to housing 202 during transit
and initial system calibrations, by means of a pin 374
passing through a suitable aperture in feedback arm 356
as shown for instance in Figure 10. During operation
of the instrument 200 the pin 374 is removed.
Referring now to Figures 11 and 12A, there is
illustrated an improved pressure relay which utilizes
plastic molded structural body components which can be
ultrasonically welded together in a manner to clamp the
diaphragms to provide the pressure seals so as to
eliminate the need for machine screws. In accordance
with this aspect of the invention, assembly costs for
the pressure relay are drastically reduced and loose
parts are minimized. In particular, the plastic body
components are formed of a glass filled polyphenylene
oxide; the diaphragms are formed of a nitrile with a
polyester fabric; and the O-rings are formed of Buna-N
rubber material. In particular, input diaphragm 380,
supply bias diaphragm 382, and feedback diaphragm 384
are maintained spacially separated by the relay body
parts and to form the required chambers in the relay.
Exhaust body 386, diaphragm retainer 388, diaphragm
spacer 390, and supply body 392 are plastic components
which maintain the diaphragms separated and form
respective relay chambers. The respective relay
chambers as formed in relay 262 are shown in Figure 11
as an input pressure chamber communicating with
passageway 338, exhaust chamber 394, supply pressure
chamber 396, and output pressure chamber 398.
All of the aforementioned relay components
may be ultrasonically welded together using
conventional ultrasonic welding equipment and
technique. Thus, the main relay body components are
readily assembled with ultrasonic welding and without
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the need for any metal screws or other metal
attachments.
The remaining metal components may then be
inserted into the relay, such as valve plug 400, and
the conventional supply port and exhaust port. A metal
cap 402 and Belleville springs 404 along with suitable
screws 406 are used to secure relay 262 to modular base
206. A series of O-rings 408 are used on the perimeter
of relay 262 in order to seal the various relay
chambers from each other when installed within modular
base 206. Also, within relay 262, supply pressure from
chamber 396 is supplied to formed chamber 410 so that
the chamber 410 between cap 402 and supply body 392 is
maintained at the supply pressure. Accordingly, this
improved pneumatic relay also includes the
substantially constant supply bias pressure improvement
described above in connection with the embodiment of
Figures 1-9.
The foregoing detailed description has been
given for clearness of understanding only, and no
unnecessary limitations should be understood therefrom,
as modifications will be obvious to those skilled in
the art.
