Differential pressure transmitter with intrinsic verification

Abstract

A differential pressure transmitter is disclosed, which comprises a body for housing a high-pressure sensor and a low-pressure sensor, a plurality of high-pressure process connectors formed in said body and fluidly coupled to said high-pressure sensor for transmitting a first pressure of a process fluid to said high-pressure sensor, each of said high-pressure process connectors comprising a conduit having an opening for receiving the process fluid, a plurality of low-pressure process connectors formed in said body and fluidly coupled to said low-pressure sensor for transmitting a second pressure of a process fluid to said low-pressure sensor, each of said low-pressure process connectors comprising a conduit having an opening for receiving the process fluid, wherein said second pressure is equal to or less than said first pressure, wherein said openings of the high-pressure connectors are spaced relative to said openings of the low-pressure connectors to allow a plurality of pair-wise connections to the process fluid.

Claims

1. A differential pressure transmitter, comprising: a body for housing a high-pressure sensor and a low-pressure sensor, a plurality of high-pressure input process connectors formed in said body and fluidly coupled to said high-pressure sensor for transmitting a first pressure of a process fluid to said high-pressure sensor, each of said high-pressure input process connectors comprising a conduit having an opening for receiving the process fluid independent of any of the other high-pressure input process connectors and transmitting said first pressure of the process fluid to said high-pressure sensor, a plurality of low-pressure input process connectors formed in said body and fluidly coupled to said low-pressure sensor for transmitting a second pressure of a process fluid to said low-pressure sensor, each of said low-pressure input process connectors comprising a conduit having an opening for receiving the process fluid independent of any of the other low-pressure input process connectors and transmitting said second pressure of the process fluid to said low-pressure sensor, wherein said second pressure is equal to or less than said first pressure, wherein said openings of the high-pressure connectors and the low-pressure connectors are arranged so as to allow a plurality of pair-wise connections of the high-pressure and the low-pressure connectors to the process fluid such that spacing between the high-pressure and the low-pressure connectors of each pair is different than the respective spacing of another pair.

2. The differential pressure transmitter of claim 1, wherein said process fluid is a flowing fluid.

3. The differential pressure transmitter of claim 1, wherein a spacing between the high-pressure and the low-pressure connectors of at least one of said pair-wise connections is about 2 inches.

4. The differential pressure transmitter of claim 1, wherein a spacing between the high-pressure and the low-pressure connectors of at least one of said pair-wise connections is about 2⅛ inches.

5. The differential pressure transmitter of claim 1, wherein a spacing between the high-pressure and the low-pressure connectors of at least one of said pair-wise connections is about 2¼ inches.

6. The differential pressure transmitter of claim 1, wherein said body has at least two lateral opposed side surfaces.

7. The differential pressure transmitter of claim 1, wherein said openings of the high-pressure connectors and said openings of the low-pressure connectors are formed on only one of a plurality of lateral sides of the body.

8. The differential pressure transmitter of claim 1, wherein at least one opening of said high-pressure connectors and at least one opening of said low-pressure connectors is formed on one of said lateral surfaces of said body.

9. The differential pressure transmitter of claim 1, wherein at least one of said conduits of said high-pressure connectors is substantially parallel to at least one of said conduits of said low-pressure connectors.

10. The differential pressure transmitter of claim 1, wherein said body comprises one enclosure for receiving said high-pressure sensor and another enclosure for receiving said low-pressure sensor.

11. The differential pressure transmitter of claim 10, further comprising a first vent valve coupled to said high-pressure sensor enclosure for exposing said sensor to an external environment different from the enclosure in which the high pressure sensor is disposed, when said first vent valve is opened and a second vent valve coupled to said low-pressure sensor for exposing said sensor to an external environment different from the enclosure in which the low pressure sensor is disposed, when said second vent valve is opened.

12. The differential pressure transmitter of claim 11, wherein said external environment is ambient atmosphere.

13. The differential pressure transmitter of claim 1, wherein each of said high-pressure and low-pressure sensors is coupled to a respective fluid-filled conduit.

14. The differential pressure transmitter of claim 1, further comprising a first isolation valve for isolating said high-pressure sensor from the process fluid when closed and a second isolation valve for isolating said low-pressure sensor from the process fluid when closed.

15. The differential pressure transmitter of claim 1, further comprising a pressure equalization valve disposed between said high-pressure sensor and said low-pressure sensor.

16. The differential pressure transmitter of claim 1, further comprising two pressure equalization valves, wherein one of said valves is fluidly coupled to the high-pressure sensor and the other valve is fluidly coupled to the low-pressure sensor and wherein said equalization valves are coupled via a fluid-filled conduit.

17. The differential pressure transmitter of claim 16, further comprising a vent valve fluidly coupled to both of said equalization valves to expose one or both of said equalization valves to an external environment.

18. A differential pressure transmitter, comprising: a body for housing two pressure sensors, at least two sets of process connectors formed in said body, wherein each set comprises at least two connector, and wherein the connectors of the first set are configured for transmitting pressure of a process fluid to one of said sensors and the connectors of the second set are configured for transmitting pressure of the process fluid to another one of said sensors, each of said process connectors comprising a conduit having an input opening for receiving said process fluid, wherein the process connectors of the first and the second set can be pairwise coupled to said sensors for obtaining a pressure differential of a process fluid as it flows through a conduit fluidly coupled to the transmitter.

19. The differential pressure transmitter of claim 18, wherein at least one of the connectors of the first set is spaced from at least one of the connectors of the second set by about 2 inches.

20. The differential pressure transmitter of claim 18, wherein at least one of the connectors of the first set is spaced from at least one of the connectors of the second set by about 2⅛ inches.

21. The differential pressure transmitter of claim 18, wherein at least one of the connectors of the first set is spaced from at least one of the connectors of the second set by about 2¼ inches.

22. The differential pressure transmitter of claim 18, wherein said each of said process connectors is configured to be plugged or used as a vent when that process connector is not employed to transmit pressure of the process fluid to one of the sensors and at least another pair of the process connectors is employed to transmit pressure of the process fluid to said sensors.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an isometric view of the differential pressure transmitter.

(2) FIG. 2 is a cross sectional view of the proposed differential pressure sensor of the differential pressure transmitter.

(3) FIG. 3 is an isometric view of the premium differential pressure transmitter with integrated three-position valve and valve operator and gravitational reference with operator.

(4) FIG. 4 is a schematic view illustrating the three position hydraulic connections.

(5) FIG. 5 is a view showing the three-position valve components in the normal position.

(6) FIG. 6 is an isometric view of the three position valve components in the equilibrate position.

(7) FIG. 6A is a cross sectional view of the three position valve in the equilibrate position with center piston positioned in center position.

(8) FIG. 7 is a cross sectional view of the gravitational pressure reference with the actuator in the normal run position.

(9) FIG. 8 is a cross sectional view of the gravitational pressure reference with the actuator having raised the weight and cylinder assembly and prepared to initiate development of the gravitational pressure reference.

(10) FIG. 9 schematically depicts a conventional approach for connecting a differential pressure transmitter to a process fluid conduit.

(11) FIG. 10A schematically depicts a differential pressure transmitter according to an embodiment of the present teachings, illustrating the process connectors, valves and pressure sensors.

(12) FIG. 10B is a partial isometric view of the differential transmitter depicted in FIG. 10A, illustrating a pair of enclosures in which the high-pressure and the low-pressure sensors of the differential pressure transmitter are disposed.

(13) FIG. 10C is a partial schematic view of the differential pressure transmitter depicted in FIG. 10A (differential pressure transmitter 900), depicting some of the internal conduits thereof.

(14) FIG. 10D is a schematic view of the process-connectors and internal connections of the differential pressure transmitter depicted in FIG. 10A.

(15) FIG. 11 schematically depicts a process connector of the differential pressure transmitter depicted in FIG. 10A connected to a pipe containing a process fluid.

(16) FIG. 12 schematically depicts the internal connections of another implementation of the differential pressure transmitter depicted in FIG. 10A according to the present teachings

DETAILED DESCRIPTION OF THE INVENTION

(17) The proposed dual sensor, single fill fluid volume differential pressure transmitter (1) is illustrated in FIG. 1 with the major components shown as a body (2), two process interface assemblies (3A) and (3B), high pressure process port (12) and low pressure process port (13).

(18) The dual sensor, single fill fluid volume differential pressure transmitter (1) of FIG. 1. is very compact and optimized to accommodate present impulse line spacing of 2⅛″ between high-pressure process port (12) and low-pressure process port (13). The flexible element assembly (3A) of FIG. 2, is composed of a flexible element end (8A) and two convolutions (9AA) and (9AB). The flexible element assembly (3A) is attached to a base (15A) having an isolation groove (16A) that minimizes influences from distortion of the body (2) due to process pressure or process/environmental temperature. Additional components are the fill fluid (14), fill fluid connecting tube (11) and fill fluid filling ports (10A) and (10B).

(19) The dual sensor measures the differential pressure by sensing the capacitance change due to the deflection of flexible element end (8A) with respect to the fixed electrode (4A) as shown in cross section 2-2 of FIG. 2. and simultaneously the deflection of flexible element end (8B) with respect to the fixed electrode (4B). The flexible element assemblies (3A) and (3B) thereby provide process isolation and a differential pressure sensing capability.

(20) The flexible element assembly (3A) has an electrode (4A) mounted upon an insulator (5A) that is attached to the base (15A). The electrode (4A) has an electrical conductor (6A) providing electrical continuity from the electrode (4A) to an electrical termination (17A) of hermetic seal (7A). The electrical conductor (6A) has a stress relief (not shown) that minimizes thermal expansion and pressure expansion influences to assure reliable connectivity between electrode (4A) and the electrical termination (17A) of the hermetic seal (7A). Additionally, the electrical conductor (6A) is contained within an insulator (18A) to minimize undesirable capacitive coupling and restrict relative motion between the conductor (6A) and the body (2).

(21) A fill fluid (14) hydraulically couples the flexible element assembly (3A) of the high side to the flexible element assembly (3B) of the low side. Thus a high pressure applied to a flexible element assembly (3A) of the high side causes an inward deflection while the opposing flexible element assembly (3B) experiences an outward deflection.

(22) The equations predicting the differential pressure considering the position of the flexible element ends (8A) and (8B) and the ratio of spring rate to effective area of the flexible elements (9AA), (9AB), (9BA), and (9BB) of FIG. 2. are developed as follows:

Definitions

(23) PHS=Pressure sensed on high side

(24) PI=Internal pressure of fill fluid

(25) P=Process pressure on high and low side

(26) KH=Spring rate flexible element assembly high side

(27) KL=Spring rate flexible element assembly low side

(28) AH=Effective area flexible element assembly high side

(29) AL=Effective area flexible element assembly low side

(30) DHR=Position of high side flexible element end with PHS

(31) DHZ=Position of high side flexible element end without differential pressure

(32) DLR=Position of low side flexible element end with PHS applied to high side

(33) DLZ=Position of low side flexible element end with no differential pressure

(34) The summation of the forces applied to flexible element ends are determined as follows:

(35) ${\mathrm{AH}}^{*}\left(\mathrm{PHS}+P-\mathrm{PI}\right)-{\mathrm{KU}}^{*}\left(\mathrm{DHR}-\mathrm{DHZ}\right)=0\mathrm{Sum}\mathrm{of}\mathrm{forces}\mathrm{on}\mathrm{high}\mathrm{side}\mathrm{flexible}\mathrm{elements}$$\mathrm{PHS}+P-\mathrm{PI}=\frac{\mathrm{KH}*\left(\mathrm{DHR}-\mathrm{DHZ}\right)}{\mathrm{AH}}$
d/p of high side flexible element

(36) ${\mathrm{AL}}^{*}\left(\mathrm{PI}-P\right)-{\mathrm{KL}}^{*}\left(\mathrm{DLR}-\mathrm{DLZ}\right)=0$$\mathrm{Sum}\mathrm{of}\mathrm{forces}\mathrm{on}\mathrm{low}\mathrm{side}\mathrm{flexible}\mathrm{element}$$\mathrm{PI}-P=\frac{\mathrm{KL}*\left(\mathrm{DLR}-\mathrm{DLZ}\right)}{\mathrm{AL}}$
d/p of low side flexible element

(37) $\mathrm{PHS}=\frac{\mathrm{KH}}{\mathrm{AH}}*\left(\mathrm{DHR}-\mathrm{DHZ}\right)+\frac{\mathrm{KL}}{\mathrm{AL}}\left(\mathrm{DLR}-\mathrm{DLZ}\right)$
Desired equation for differential pressure

(38) Thus the sum of the deflections of the flexible element ends is proportional to the differential pressure.

(39) This equation requires the actual value of each ratio of spring rate to effective areas of the flexible element assemblies be known. Alternatively, an innovative procedure has been developed. In this procedure, a high process pressure is applied to the high process pressure port (12) and simultaneously to the low process pressure port (13) thereby compressing the fill fluid volume (14). The compression of the fill fluid is sensed by the deflection of each flexible element end. The ratio of these deflections provides a means of compensating the ratios of spring rate to effective area of the two flexible element assemblies. The compensation is developed as follows:

Definitions

(40) PI=Process pressure internal

(41) P=Process pressure high and low side

(42) DLP=Position of low side

(43) DHP=Position of high side

(44) T=Temperature difference from a reference temperature

(45) a=Coefficient of thermal change in volume

(46) b=Bulk Modulus Coefficient of pressure change to volume change

(47) A force balance summation of each flexible element assembly provides the desired relation to be used in the compensation.

(48) ${\left(P-\mathrm{PI}\right)}^{*}\mathrm{AH}-{\mathrm{KH}}^{*}\mathrm{DHP}=0$${\left(P-\mathrm{PI}\right)}^{*}\mathrm{AL}-{\mathrm{KL}}^{*}\mathrm{DLP}=0$$P-\mathrm{PI}=\frac{\mathrm{KH}*\mathrm{DHP}}{\mathrm{AH}}$$P-\mathrm{PI}=\frac{\mathrm{KL}*\mathrm{DLP}}{\mathrm{AL}}$$\mathrm{DHP}=\frac{\mathrm{DLP}}{\frac{\mathrm{KH}*\mathrm{AL}}{\mathrm{AH}*\mathrm{KL}}}$
Equating pressures and solving for desired ratio

(49) $K=\frac{\mathrm{KH}*\mathrm{AL}}{\mathrm{AH}*\mathrm{KL}}$$\mathrm{DHP}=\frac{\mathrm{DLP}}{K}$
Abbreviate

(50) The ratios of spring rate to effective area of the two flexible element assemblies can now be compensated using this factor. Compensation is achieved by arbitrarily selecting the high side flexible element assembly as a reference and applying the compensation factor to the low side flexible element assembly. Thus the compensated equation becomes:

(51) $\mathrm{PHS}=\frac{\mathrm{KH}}{\mathrm{AH}}*\left(\mathrm{DHR}-\mathrm{DHZ}\right)+\frac{\mathrm{KL}}{\mathrm{AL}}*\frac{\mathrm{DLR}-\mathrm{DLZ}}{K}$

(52) The compensation also requires a change in reference from KL/AL to KH/AH for the low side.

(53) Thus, the desired differential pressure can be sensed from the deflection of the compensated flexible element assemblies without a need to determine the actual value of the spring rate or effective area of each flexible element assembly. An overall calibration coefficient would include the ratio of spring rate to effective area and an additional factor for setting the output for a given input.

(54) It will now be shown how the compensated equation intrinsically eliminates the detrimental influences of process and environmental influences. A change in the common fill fluid volume will cause an equal and opposing change in the differential pressure applied upon each of the flexible element assemblies but will not cause any change in the total differential pressure sensing. This is an important and basic benefit, for process temperature, process pressure, environmental temperature and enclosure distortion will change the common fill fluid volume. Therefore the detrimental performance influences are intrinsically eliminated.

(55) An equation considering the detrimental influences will illustrate the manner in which they are intrinsically eliminated. The deflection associated with the detrimental differential pressure due to an increased process pressure compressing the fill fluid volume can be determined from the following equations:

(56) $\mathrm{DPH}=\frac{P*\beta *V}{2*\mathrm{AH}}$$\mathrm{DPL}=\frac{P*\beta *V}{2*\mathrm{AL}}*\frac{\mathrm{AL}}{\mathrm{AH}}$$\mathrm{DPH}=\mathrm{DPL}$

(57) Similarly, the deflection associated with the detrimental differential pressure due to due to an increased temperature expanding the fill fluid volume can be determined from the following equations:

(58) $\mathrm{DTH}=\frac{T*\alpha *V}{2*\mathrm{AH}}$$\mathrm{DTL}=\frac{T*\alpha *V}{2*\mathrm{AL}}*\frac{\mathrm{AL}}{\mathrm{AH}}$$\mathrm{DTL}=\mathrm{DTH}$
Including these influences within the basic equation provides:

(59) $\mathrm{PHS}=\frac{\mathrm{KH}}{\mathrm{AH}}*\left(\mathrm{DHR}-\mathrm{DHZ}\right)+\mathrm{DPH}-\mathrm{DTH}+\frac{\mathrm{KH}}{\mathrm{AH}}*\frac{\mathrm{DLR}-\mathrm{DLZ}}{K}-\mathrm{DPL}+\mathrm{DTL}$

(60) This complete, compensated equation reveals that the detrimental influences are equal and opposing and are therefore intrinsically eliminated. The need to continually sense the process pressure and process temperature and apply an instantaneous compensation is eliminated.

(61) AH and AL can be verified with the three-position valve in the equilibrate position. With the addition of a temperature and pressure sensors, an awareness of the thermal coefficient of volumetric change and the bulk modulus of the fill fluid, the fill fluid volume and the sensed total deflection DTPH and DTPL provides a means to determine AH and AL.

(62) 0$\mathrm{DTPH}=\mathrm{DTH}=\mathrm{DPH}\mathrm{and}\mathrm{DTPL}=\mathrm{DTL}+\mathrm{DPL}$$\mathrm{DTH}=\frac{T*\alpha *V}{2*\mathrm{AH}}\mathrm{DPH}=\mathrm{DPH}=\frac{P*\beta *V}{2*\mathrm{AH}}*\mathrm{AH}=\frac{V}{2*\mathrm{DTPH}}*\left(T*\alpha *P*\beta \right)$$\mathrm{AL}=\frac{V}{2*\mathrm{DTPH}}*\left(T*\alpha *P*\beta \right)$$\mathrm{Ancillary}\mathrm{Devices}$

(63) The ancillary devices providing the desired enhancements of the differential pressure transmitter (1) are the three-position valve, valve actuator, gravity pressure reference and the gravity reference actuator. All ancillary devices are contained within an assembly (14) of FIG. 3. They will be described sequentially in the following description.

(64) The three-position valve configures the proposed differential pressure transmitter (1) for normal, equilibrated or reverse operation and are shown schematically in FIG. 4. The main components of the proposed three-position valve and valve operator (20) are shown in FIG. 5 and now considered.

(65) The normal position of FIG. 4. connects a high-pressure process port to a high-pressure differential pressure transmitter port and a low-pressure port to a high-pressure differential pressure transmitter with a normal flow direction.

(66) Equilibrate position of FIG. 4. connects a high-pressure differential pressure transmitter port to a low-pressure differential pressure transmitter port equilibrating pressures and no differential pressure being applied to the differential pressure transmitter.

(67) Reverse position of FIG. 4. connects a high-pressure process port to a high-pressure differential pressure transmitter port and a low-pressure process port to a low-pressure differential pressure transmitter port providing reverse flow measurement capability. Although the differential pressure transmitter (1) remains in the same position, the high-pressure and low-pressure ports of the reverse position of the differential pressure transmitter (1) are opposite the high-pressure and low-pressure ports of the normal position.

(68) The three position valve and operator (20) as shown in FIG. 5 is composed of a fixed valve seat (21) that is restricted from rotation by a matching key way in the body (2) that is not shown and provides the ports for communication with the differential pressure transmitter (1), a selector disc (22) that is rotated to configure the desired positions of FIG. 4, a compensation plate that is not shown, provides axial compensation for thermal and pressure deflections and torsionally couples selector disc (22) to rotor (24), an axial spring (23) that provides a load to selector disc (22) and rotor (24) assuring that selector disc (22) achieves a seal with valve seat (21) while compensating for thermal and pressure deflections, rotor (24) is driven by a crank (26) of three position actuator.

(69) The novel three-position actuator of the three-position valve (20) is shown in cross section 2-2 of FIG. 6A for the equilibrate position. The center piston (29) is driven to the equilibrate position by applying pressure to port (33) that acts upon piston (30) forcing it to the right until arrested by stop (35) in cylinder of lower molding (32) and simultaneously applying pressure to port (34) that acts upon piston (31) forcing it to the left until arrested by stop (36) in the cylinder of lower molding (32).

(70) The normal and reverse positions of the valve actuator are achieved by motion of three pistons (30), (31) and (32) having an innovative sequence. Referring to FIG. 6A, when the pneumatic port (33) on the left is pressurized, the left piston (30) travels to the right and engages the center piston (29) and sequentially engages the right piston (31) and continues to the right until piston (30) is limited by a stop (35) at this time the pressure is applied to center piston (29) through path (38A) and piston (31) is then driven to the right termination of the cylinder. Similarly, when the pneumatic port (34) on the right is pressurized, the right piston (31) travels to the left and engages the center piston (29) and sequentially engages the left piston (30) and continues to the left until piston (31) is limited by a stop (36) at this time the pressure is applied to center piston (29) through path (38B) and piston (30) is then driven to the left termination of the cylinder.

(71) Motion of piston (29) of FIG. 6A actuates the valve. A post (37) of the center piston (29) is attached to valve plate (28) and valve plate (28) is coupled to a crank (26). As post (37) is positioned to the left, center and the right, it rotates the crank (30) of the three-position valve (20). The crank (26) turns the rotor (24) that positions the selector disk (22) to the desired valve position. The valve may also be operated manually by positioning valve plate (28) by hand. Valve plate (28) provides an indication of the position of the valve.

(72) The three-position valve (20) provides the ability to determine and remove the influence of level or density in impulse lines. With a constant flow or ideally no flow, the three position valve (20) is first positioned in the normal position and the normal value of the differential pressure transmitter (1) is determined. Then the three-position valve (20) is positioned in the reverse position and the reverse value of the differential pressure transmitter (1) is determined. The results are compared and a correction made to minimize any level or density differences in the impulse lines.

(73) The gravity pressure reference (40) shown in cross section 3-3 of FIG. 7, functions is described in detail in U.S. Pat. No. 6,321,585 Sgourakes for a Differential Pressure Generator. However, the basic operation is as follows:

(74) The weight and cylinder assemblies (43A) and (43B) are raised with respect to fixed spherical pistons (41A) and (41B) and then allowed to descend under the action of gravity thereby producing a traceable, reliable reference pressure within the cylinders (42A) and (42B) that is applied to the differential pressure transmitter (1).

(75) The principle of operation is simple. The weight and cylinder assembly (43A) on the high side has the same volume as the weight and cylinder assembly (43B) on the low side. The desired reference differential pressure is developed by a density difference of the weight and cylinder assembly (43A) with respect to the weight and cylinder assembly (43B). The density of the fill fluid changes significantly due to volume changes with respect to pressure or temperature. However, the fill fluid changes produce equal influences upon the assemblies and therefore do not influence the desired reference differential pressure. Thus the reference differential pressure is not influenced by fill fluid density variations that occur with temperature or process pressure.

(76) Innovative concepts have now been provided to enhance the raising and the descent of the weight and cylinder assemblies (43A) and (43B) of FIG. 7. Located within the enclosure are internal magnets (45A) and (45B) that are raised by an opposing magnet field or lowered by an attractive magnetic field. These magnet fields are produced externally.

(77) Positioning an external magnet (48) having an opposing magnetic orientation to the internal magnet (45) produces an opposing magnetic field that raises the internal magnet. Positioning an external magnet (48) having an attractive magnetic orientation to the internal magnet (45) produces an attractive magnetic field that lowers the internal magnet.

(78) The positioning of the external magnets with respect to the internal magnets is simply done by shuttling the external magnets horizontally left or right a distance equal to the one half the horizontal distance between the internal magnets (45A) and (45B). This motion is illustrated in FIG. 7 illustrating the relationship in normal operation desiring to capture the internal magnets by providing an attractive field and reduce vibration of the internal magnets. Fewer magnets could be used but the desired advantage of capturing the internal magnets in normal operation thereby reducing pressure pulsations would not be achieved.

(79) In the moment prior to the descent of the weight and cylinder assemblies (43A) and (43B) the internal magnets are held in a position illustrated in FIG. 8. To initiate a descent the external magnets (48) are quickly returned to the normal position. At this time the weight assemblies (43A) and (43B) experience a gravitational force that is applied upon the effective area defined by the sphere within the cylinder thereby producing the desired differential pressure.

(80) The positioning of the external magnets is achieved by pneumatic pressure applied to either end of the piston (47) carrying the external magnets (48).

(81) In another aspect, the present teachings provide improved connectors for connecting a differential pressure transmitter according to the present teachings to a process fluid. By way of background, conventional differential pressure transmitters are configured to provide three standardized process connector spacings of 2 inches, 2⅛ inches, and 2¼ inches (or metric equivalents thereof) using a process connection adapter having an eccentric connection port with respect to two bolt holes of the connection adapter. For the 2-inch spacing, the eccentricities are positioned toward each other, for the 2¼-inch spacing, the eccentricities are positioned away from one another, and for the 2⅛-inch spacing, the eccentricities are positioned in the same direction. By way of illustration, FIG. 9 schematically depicts a conventional approach for connecting a sensor (S) to a process fluid conduit (PFC) using an adaptor (A).

(82) Such conventional connectors suffer from a number of shortcomings. In particular, such connectors typically require significant material for their adaptors and for mating requirements of an isolation manifold and sensor. For example, many such conventional adapters require four bolts for attachments to their isolation manifolds and/or sensors, and increased material in the differential pressure transmitter to provide eight threaded bolt holes to capture the four bolts in either of two transmitter positions. Furthermore, many such conventional connectors require two process compatible elastomeric seals for adapters but as many as six seals for complete installation of adapters, isolation manifolds and sensors. When the connector position is changed, the process compatible elastomeric seals must be replaced to assure reliable sealing. Moreover, many conventional connectors require an inventory of process compatible seals for accommodating the process fluid at temperature and pressure requirements of different process fluid environments.

(83) For example, some conventional process connectors were introduced with a differential pressure transmitter having a sensor clamped between two covers. The covers had increased material to provide eight threaded bolt holes for fastening the adapters. The eight threaded bolt holes were required to provide four bolts for mounting process connectors on either of the two sides of the differential pressure transmitter for different installation positions.

(84) FIGS. 10A and 10B schematically depict a differential pressure transmitter 900 according to an embodiment, which provides flexibility for connecting the transmitter to a process fluid in a plurality of different coupling configurations and solves the above-shortcomings of conventional process connectors. The differential transmitter 900 includes a body 902 that is configured to house a high-pressure sensor 904 and a low-pressure sensor 906. In particular, in this embodiment, the body 902 has a generally parallelepiped shape, with a rectangular cross-sectional profile, and includes two enclosures 908 and 910 for housing, respectively, the high-pressure sensor 904 and the low-pressure sensor 906.

(85) In this embodiment, the high-pressure and low-pressure sensors are capacitive sensors implemented in a manner discussed above (See, e.g., FIG. 2 and the associated description).

(86) The differential transmitter 900 includes three high-side process connectors 912, 914, and 916 that are fluidly coupled to the high pressure sensor 904, and three low-side process connectors 918, 920, and 922 that are fluidly coupled to the low pressure sensor 906. In this embodiment, each of the process connectors is in the form of a conduit having a threaded opening. As discussed in more detail below, these process connectors can be pair-wise utilized to connect the differential transmitter to a process fluid (e.g., a process liquid, gas or steam). For example, in this exemplary implementation, the process connectors 912 and 918 are employed to fluidly connect the differential transmitter to a process fluid, via tubings 917 and 919, respectively, and the other process connectors (i.e., process connectors 914, 916, 920 and 922) are sealed, e.g., by using plugs 914a, 916a, 920a, and 922a.

(87) With continued reference to FIG. 10A as well as FIG. 10C, each of the process connectors 912, 914, 916, 918, 920, and 922 includes a fluid conduit having a threaded opening that allows coupling the process connector (e.g., via appropriate tubing or pipe) to the process fluid. For example, in this embodiment, the process connector 912 includes a conduit 912a having a threaded opening 912b. The threaded opening 912b allows coupling the process connector 912 to the process fluid, and the conduit 912a allows the process fluid to reach the high-pressure sensor 904. The other process connectors can be fluidly coupled to the process fluid in a similar fashion. More specifically, the process connectors 914, 916, 918, 920, and 922 include, respectively, fluid conduits 914a, 916a, 918a, 920a, and 922a and threaded openings 914b, 916b, 918b, 920b, and 922b. FIG. 11 schematically depicts pipes 917 and 919 coupled, respectively, to the high-pressure process connector 912 and the low-pressure processor connector 918 to allow fluidly coupling a process fluid to the differential pressure transmitter.

(88) Referring to FIG. 10A, while in this embodiment, all of the process connectors 912, 914, 916, 918, 920, and 922 are disposed on a single lateral side (900a) of the body 902, in other embodiments, one or more of the process connectors can be disposed on different lateral surfaces of the body 902.

(89) With reference to FIG. 10C, FIG. 10D as well as FIG. 10A, in this embodiment, each of the high-pressure process connectors 912, 914, and 916 is fluidly connected via a high side connection manifold 1000 to a central conduit 1002 that couples the process fluid to the high-pressure sensor 904. Further, each of the low-pressure process connectors 918, 920, and 922 is coupled via a low side connection manifold 1004 to a central conduit 1006 that couples the process fluid to the low-pressure sensor 906. In this embodiment, the conduits of the process connectors are substantially parallel to one another (i.e., any deviation from being parallel is less than 5 degrees). In other embodiments, the conduits of the process connectors may not be parallel to one another.

(90) In this embodiment, the openings of the process connectors 912 and 918 are separated (laterally separated) by 2 inches, and the openings of process connectors 914 and 920 are separated by 2⅛ inches and the openings of the process connectors 916 and 922 are separated by 2¼ inches. Thus, the process connectors provide three standardized process connector spacings and allow fluidly coupling the differential pressure transmitter to a process fluid using pair-wise process connectors corresponding to any of these spacings with a highly reliable metal-to-metal pipe thread seal without a need for adapters, bolts and process compatible seals.

(91) With continued reference to FIG. 10C, in this embodiment, the differential pressure transmitter 900 further includes a vent valve 2000 for coupling the high-pressure sensor 904 to an external environment, e.g., ambient atmosphere or an external device, for example for venting the high-pressure sensor 904. The differential pressure transmitter 900 further includes an isolation valve 2002 for isolating the high-pressure sensor 904 from the pressure of the process fluid. In other words, the isolation valve 2002 can be closed to isolate the high-pressure sensor 904 from the process fluid. A valve 2006 allows isolating the low-pressure sensor from the process fluid. Another valve 2004 allows equalizing the pressure between the high-pressure sensor and the low-pressure sensor when isolation valve 2002 and isolation valve 2006 are closed.

(92) Furthermore, a vent valve 2008 allows coupling the low-pressure sensor 906 to an external environment, e.g., ambient atmosphere or an external device, for example, to vent the low-pressure sensor. In use, prior to performing pressure measurements, the isolation valves 2002 and 2006 can be closed to isolate the high-pressure as well as the low-pressure sensors from the process fluid. The valve 2004 can then be opened to equalize the pressure between the high-pressure and the low-pressure sensors so as to calibrate the system. Subsequently, in order to return to service, the isolation valves 2002 and 2006 can be opened to expose the high-pressure and the low-pressure sensors to the process fluid followed by closing the equalizing valve 2004.

(93) FIG. 12 schematically shows the internal connections of another embodiment of a differential pressure transmitter that includes two isolation valves 1200 and 1201 coupled, respectively, to the high-pressure sensor 904 and the low-pressure sensor 906. In some embodiments, the configuration shown in FIG. 12 can be used when the process fluid is natural gas. In this embodiment, two equalizer valves 1202 and 1203 couple the high-pressure sensor 904 and the low-pressure sensor 906 to a single vent valve 1204, which can be used to couple the high-pressure sensor, the low-pressure sensor, or both to an external environment (e.g., ambient atmosphere).