Pressure Sensitive Thermowell

Abstract

A process fluid multivariable measurement system is provided. The multivariable measurement system includes a thermowell (100, 200, 300) configured to couple to a process fluid conduit (504) and extend through a wall (506) of the process fluid conduit (504). The multivariable measurement system also includes a temperature sensor assembly (110, 210, 310) disposed within the thermowell (100, 200, 300), the temperature sensor assembly (110, 210, 310) also including at least one temperature-sensitive element (114, 214, 314) disposed therein. The multivariable measurement system also includes a pressure sensor assembly (118, 218, 318) coupled to the thermowell (100, 200, 300), the pressure sensor assembly (118, 218, 318) having at least one pressure-sensitive element (120, 220, 320) disposed therein. The multivariable measurement system further includes a transmitter circuit (400) communicatively coupled to the temperature sensor assembly (110, 210, 310) and the pressure sensor assembly (118, 218, 318) and configured to receive a temperature sensor signal from the at least one temperature sensitive element (114, 214, 314) and responsively generate a temperature measurement output based on the temperature sensor signal. The transmitter circuit (400) is further configured to receive a pressure sensor signal from the at least one pressure sensitive element (120, 220, 320) and responsively generate a pressure measurement output based on the pressure sensor signal.

Description

[Technical field]

[0001] background Many industrial processes transport process fluids through pipes or other conduits. Such process fluids may include liquids, gases, and in some cases, entrained solids. These process fluids may be found in any of a variety of industries, including, but not limited to, sanitary food and beverage production, water treatment, high purity pharmaceutical production, chemical processing, hydrocarbon extraction and processing, and the hydrocarbon fuels industry, including hydraulic fracturing techniques that utilize abrasive and corrosive slurries.

[0002] Industrial process transmitters and sensor assemblies are used to sense properties of process fluids flowing through conduits or contained within vessels and transmit information about these process properties to control, monitoring and / or safety systems located remotely from the process measurement location. Process transmitters are typically electrically connected to the sensor assemblies via sensor wires that are used to transmit current or voltage based analog sensor output signals that reflect the process parameters. Transmitters read and convert these sensor output signals into measurements of the process parameters. Finally, the transmitters transmit the information to a control system.

[0003] It is common to place a temperature sensor in a thermowell and insert it into the process fluid flow through an opening in a conduit. In a typical industrial process environment, the ability to add additional measurement points to obtain measurements of different process characteristics is difficult due to the complex nature of the process environment. For example, in a typical industrial process environment, measuring different process characteristics typically requires significant changes to the infrastructure of the process environment along with significant financial costs to modify the infrastructure of the process environment. Thus, the use of thermowells in industrial process environments, while useful for providing accurate process fluid temperatures, has many limitations. Summary of the Invention

[0004] A process fluid multivariable measurement system is provided. The multivariable measurement system includes a thermowell coupled to a process fluid conduit and configured to extend through a wall of the process fluid conduit. The multivariable measurement system also includes a temperature sensor assembly disposed within the thermowell, the temperature sensor assembly having at least one temperature sensitive element disposed therein. The multivariable measurement system also includes a pressure sensor assembly coupled to the thermowell, the pressure sensor assembly having at least one pressure sensitive element disposed therein. The multivariable measurement system further includes a transmitter circuit communicatively coupled to the temperature sensor assembly and the pressure sensor assembly and configured to receive a temperature sensor signal from the at least one temperature sensitive element and responsively generate a temperature measurement output based on the temperature sensor signal. The transmitter circuit is further configured to receive a pressure sensor signal from the at least one pressure sensitive element and responsively generate a pressure measurement output based on the pressure sensor signal. [Brief description of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic diagram of a multivariable thermowell for implementation in a multivariable process fluid measurement system, to which embodiments of the present invention are particularly applicable. [Diagram 2] FIG. 13 is a schematic diagram of a multivariable thermowell for implementation in a multivariable process fluid measurement system according to another embodiment of the present invention. [Diagram 3] FIG. 1 is a schematic diagram of a multivariable thermowell for implementation in a multivariable process fluid measurement system according to an embodiment of the present invention. [Figure 4] 1 is a circuit block diagram of a process fluid multivariable measurement system to which embodiments of the present invention are particularly applicable; [Figure 5A] 1 is a schematic diagram of a process fluid multivariate measurement system to which embodiments of the present invention are particularly applicable; [Figure 5B]1 is a schematic diagram of a process fluid multivariate measurement system to which embodiments of the present invention are particularly applicable; [Figure 6] FIG. 2 is a schematic diagram of a multivariable thermowell with a strain-gauge based pressure sensor according to an embodiment of the present invention. [Figure 7] FIG. 2 is a schematic diagram of a multivariable thermowell with a capacitive pressure sensor according to an embodiment of the present invention. [Figure 8] 1 is a schematic diagram of a multivariable sensor for implementation in a multivariable process fluid measurement system according to an embodiment of the present invention. [Figure 9] FIG. 13 is a schematic diagram of a multivariable thermowell for implementation in a multivariable process fluid measurement system according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] As noted above, due to the complex nature of industrial process environments, it is difficult to add additional measurement points to obtain measurements of different process characteristics. For example, adding a system capable of detecting pressure in an industrial process environment typically requires significant intervention and modification to the process environment infrastructure, such as creating new access points in the infrastructure for the measurement of the new process characteristic. Furthermore, such modifications are difficult due to the high temperature conditions present in the conduits of an industrial process environment.

[0007] FIG. 1 is a schematic diagram of a multivariable thermowell for implementation into a process fluid multivariable measurement system, to which embodiments of the present invention are particularly applicable. As shown, the thermowell 100 is configured to couple to a process fluid conduit (such as the process fluid conduits depicted in FIGS. 5A-5B) and extend through a wall of the process fluid conduit. The thermowell 100 is further configured to generally contact a process fluid within the process fluid conduit to obtain measurements of the process fluid, such as temperature and / or pressure. In one embodiment, the thermowell 100 is a threaded thermowell. However, in other embodiments, the thermowell 100 can be a flanged thermowell or other thermowell design that is coupleable to a process fluid conduit. The thermowell 100 generally further includes a temperature sensor assembly 110 disposed therein and a sensor capsule 112. The term "capsule" is not intended to imply a particular structure or shape, and thus can be formed in a variety of shapes, sizes, and configurations. The temperature sensor assembly 110 typically includes one or more temperature sensing elements 114, such as a resistive temperature device (RTD). The temperature sensing elements 114 are configured to be electrically connected to a transmitter circuit (not shown) via an access hole 116 to obtain one or more temperature measurements. The access hole 116 is typically configured to allow a coupling 140 of the temperature sensor assembly to pass therethrough. The sensor capsule 112 can be electrically connected to the transmitter circuit via a transmission loop, a fiber optic cable, a wireless link, or some other connection.

[0008] The thermowell 100 also generally includes a pressure sensor assembly 118 configured to be disposed within the thermowell 100 and obtain one or more pressure measurements and including one or more pressure sensitive elements 120 disposed therein. In one embodiment, the pressure sensor assembly 118 includes a strain gauge based sensor. In another embodiment, the pressure sensor assembly 118 can include a capacitance based pressure sensor. Of course, in other embodiments, the pressure sensor assembly 118 can include different types of pressure sensors, such as potentiometer sensors, resonant wire sensors, or other pressure sensors capable of obtaining pressure measurements. Additionally, in one embodiment, the pressure sensor assembly 118 can include a multivariable sensor, as described below in FIG. 8, configured to simultaneously obtain both pressure and temperature measurements and responsively generate temperature and pressure sensor signals in a process fluid multivariable measurement system. By incorporating a multivariable sensor into the pressure sensor assembly 118, additional temperature measurements can be obtained. The additional temperature measurements obtained by the multivariable sensor provide an alternative mode of measuring temperature in the event of any equipment errors. For example, redundant temperature measurements provided by both the multivariable sensor and the temperature sensor assembly 110 can provide backup temperature measurements in the event the other fails.

[0009] The pressure sensitive element 120 can be disposed within the sensor capsule 112 in one embodiment. However, in alternative embodiments, the pressure sensitive element 120 can be disposed outside the sensor capsule 112. The pressure sensitive element 120 is electrically connected to a transmitter circuit (not shown) via an access hole 122 that is configured to allow the pressure sensor assembly 118 to be coupled therethrough (not shown). As shown, the access hole 122 is disposed adjacent to the temperature sensor assembly 110 and is generally disposed within the wall of the thermowell 100. In particular, the access hole 122 is disposed adjacent to, but separate from, the access hole 116. As further shown, the access hole 122 is parallel to the temperature sensor assembly 110. As further shown, the access hole 122 is parallel to the temperature sensor assembly 110. However, in alternative embodiments, the access hole 122 can be disposed adjacent to the temperature sensor assembly 110 in other ways that allow the pressure sensitive element 120 to be coupled to the transmitter circuit.

[0010] The access holes 122 can be incorporated into the walls of the thermowell 100 in a number of ways. For example, the access holes 122 can be incorporated by utilizing EDM machining or gun-bore drilling techniques. By incorporating the access holes 122 into the thermowell 100, the pressure sensor assembly 118 can be added without significantly modifying the process environment infrastructure.

[0011] FIG. 2 is a schematic diagram of a multivariable thermowell for implementation into a process fluid multivariable measurement system according to another embodiment of the present invention. The system illustrated in FIG. 2 has some similarities to FIG. 1, with similar components being similarly numbered. As shown, the thermowell 200 is configured to couple to a process fluid conduit, such as the process fluid conduits described in FIGS. 5A-5B, and extend through a wall of the process fluid conduit. The thermowell 200 is further configured to generally contact the process fluid within the process fluid conduit to obtain measurements of the process fluid, such as temperature and / or pressure. In one embodiment, the thermowell 200 is a threaded thermowell. However, in other embodiments, the thermowell 200 can be a flanged thermowell or other thermowell design that can couple to a process fluid conduit.

[0012] The thermowell 200 further typically includes a temperature sensor assembly 210 and a pressure sensor assembly 218 disposed therein, as well as a sensor capsule 212. The sensor capsule 212 typically includes one or more temperature sensing elements 214 and / or one or more pressure sensing elements 220. In one embodiment, the temperature sensor assembly 210 and / or the pressure sensor assembly 218 may include a strain gauge based sensor. However, in other embodiments, a different type of pressure sensor may be utilized (e.g., a capacitive pressure sensor). Additionally, in one embodiment, the pressure sensor assembly 218 may include a multivariable sensor, as described below in FIG. 8, configured to obtain both pressure and temperature measurements simultaneously in a process fluid multivariable measurement system. By incorporating a multivariable sensor into the pressure sensor assembly 218, additional temperature measurements may be obtained.

[0013] The temperature sensing element 214 and the pressure sensing element 220 are electrically connected to a transmitter circuit (not shown) via an access hole 216 to allow one or more temperature measurements and / or one or more pressure measurements to be obtained. The access hole 216 is generally configured to allow the couplings 240 of the temperature sensor assembly 210 and the pressure sensor assembly 218 to pass therethrough. The temperature sensing element 214 and the pressure sensing element 220 can be electrically connected to the transmitter circuit via a transmission loop, a fiber optic cable, a wireless link, or some other connection. As shown in FIG. 2, in one embodiment, the pressure sensor assembly 218 shares the same access hole 216 as the temperature sensor assembly 210. By incorporating the pressure sensor assembly 218 into the same access hole 216 as the temperature sensor assembly 210, no additional modifications, such as adding an additional access hole to the thermowell 200, are required. For example, a thermowell embodiment having a limited thermowell wall thickness may utilize the same access holes for pressure sensor assembly 218 as temperature sensor assembly 210 to enable multivariate sensing of process fluid properties. In one embodiment, pressure sensing element 220 is incorporated into the end of sensor capsule 212 by boring the tip of thermowell 200 so that the pressure sensing element can be coupled, such as by welding, to sensor capsule 212.

[0014] FIG. 3 is a schematic diagram of a multivariable thermowell for implementation into a process fluid multivariable measurement system, according to an embodiment of the present invention. The system illustrated in FIG. 3 has some similarities to FIGS. 1 and 2, with similar components being similarly numbered. As illustrated, the thermowell 300 is configured to couple to a process fluid conduit, such as the process fluid conduits described in FIGS. 5A-5B, and extend through a wall of the process fluid conduit. The thermowell 300 is further configured to generally contact a process fluid within the process fluid conduit to obtain measurements of the process fluid, such as temperature and / or pressure. In one embodiment, the thermowell 300 is a threaded thermowell. However, in other embodiments, the thermowell 300 can be a flanged thermowell or other thermowell design that is coupleable to a process fluid conduit. The thermowell 300 further generally includes a temperature sensor assembly 310 disposed within the thermowell 300. The temperature sensor assembly 310 typically includes one or more temperature sensing elements 314, such as a resistive temperature device (RTD). The temperature sensing elements 314 are configured to be electrically connected to a transmitter circuit (not shown) via an access hole 316 to obtain one or more temperature measurements. The access hole 316 is typically configured to allow a coupling 340 of the temperature sensor assembly therethrough. The temperature sensor assembly 310 can be electrically connected to the transmitter circuit via a transmission loop, a fiber optic cable, a wireless link, or some other connection.

[0015] The thermowell 300 generally includes a pressure sensor assembly 318 disposed within the thermowell 300 and including one or more pressure sensitive elements 320 disposed therein. As shown, the pressure sensor assembly 318 further includes an access hole 322. In one embodiment, the access hole 322 is filled with a pressure transmitting material 324, and the pressure sensitive element 320 includes a membrane 326 that fluidly couples the process fluid in the process fluid conduit to the pressure transmitting material 324. The pressure transmitting material 324 can be, for example, an oil. However, in other embodiments, the pressure transmitting material 324 can be another fluid capable of transmitting an indication of pressure. The access hole 322 further includes a tube 328 that allows the pressure transmitting material 324 to couple to a pressure sensor 330 via a pressure deflection diaphragm, generally indicated at 332. The pressure deflection diaphragm can be, for example, a thin film diaphragm, a corrugated diaphragm, or other diaphragm that can couple the pressure sensor 330 to the pressure transmitting material 324. Thus, as shown, pressure sensor 330 can be located remotely from the thermowell and can generate a pressure sensor signal via a pressure reading transmitted through pressure transmitting material 324 in access hole 322 and received by a transmitter circuit (not shown). This can prevent harsh process conditions, such as high temperature processes, from interfering with the pressure sensing functionality of multivariable thermowell 300.

[0016] FIG. 4 is a block diagram of a circuit of a process fluid multivariable measurement system to which embodiments of the present invention are particularly applicable. System 400 has some similarities to the elements of the multivariable thermowells described in FIGS. 1-3, with like components being similarly numbered. System 400 may also include other items as well, as indicated by block 436. System 400 includes a communication circuit 422 coupled to a controller 424. Communication circuit 422 may be any suitable circuit capable of communicating information regarding process fluid temperature and / or pressure obtained at a multivariable thermowell, such as those described in FIGS. 1-3 and 9. Communication circuit 422 allows a multivariable thermowell disposed within the process fluid multivariable measurement system to communicate an output of the process fluid temperature and / or pressure over a process communication loop or segment, such as a transmission loop. Suitable examples of process communication loop protocols include the 4-20 milliamp protocol, the Highway Addressable Remote Transducer (HART®) protocol, the FOUNDATION® Fieldbus protocol, and the Wireless HART protocol (IEC 62591).

[0017] The system 400 also includes a power supply module 426 that provides power to all components of the system 400, as indicated by arrow 428. For embodiments in which the system 400 is coupled to a wired process communication loop, such as a HART® loop or a FOUNDATION® Fieldbus segment, the power supply module 426 may include appropriate circuitry for conditioning power received from the loop or segment to operate the various components of the system 400. Thus, for such wired process communication loop embodiments, the power supply module 426 may provide appropriate power conditioning to allow the entire device to be powered by the loop to which it is coupled. For other embodiments, where wireless process communication is used, the power supply module 426 may include a power source, such as a battery, and appropriate conditioning circuitry.

[0018] The controller 424 is communicatively coupled to the communication circuitry 422 and includes any suitable arrangement capable of using measurements from the temperature sensor assembly 410 and the pressure sensor assembly 418 to generate a heat flow based process fluid temperature output and a process fluid pressure output. For example, the controller 424 can receive a temperature sensor signal from the temperature sensing element 414 in the temperature sensor assembly 410 and responsively generate a temperature measurement output based on the temperature sensor signal. Alternatively, or additionally, the controller 424 can receive a pressure sensor signal from the pressure sensing element 420 in the pressure sensor assembly 418 and responsively generate a pressure measurement output based on the pressure sensor signal. The output can be provided to an operator, a machine, or other device. Additionally, the output can be a visual output, an audio output, or other output that can be indicative of the temperature and / or pressure measurements in the process fluid multivariable measurement system. As an example, the controller 424 is a microprocessor.

[0019] Measurement circuitry 430 is coupled to controller 424 and provides digital representations of measurements obtained from temperature sensor assembly 410 and pressure sensor assembly 418. Measurement circuitry 430 may include one or more analog-to-digital converters and / or appropriate multiplexing circuitry for interfacing the one or more analog-to-digital converters to temperature sensor assembly 410 and pressure sensor assembly 418. Additionally, measurement circuitry 430 may include appropriate amplification and / or linearization circuitry appropriate for the various types of sensors used.

[0020] The temperature sensor assembly 410 illustratively includes a temperature sensing element 414 and may include other items as indicated by block 432. One example of such other items is a vibration sensor. The temperature sensing element 414 is coupled to the electronic circuitry of the system 400 via an access hole (not shown) and is used to generate a temperature sensor signal indicative of the temperature of the process fluid in the process fluid multivariable measurement system. The pressure sensor assembly 418 illustratively includes a pressure sensing element 420 and may include other items as indicated by block 434. One example of such other items is a vibration sensor. The pressure sensing element 420 is coupled to the electronic circuitry of the system 400 via an access hole (not shown) and is used to generate a pressure sensor signal indicative of the pressure of the process fluid multivariable measurement system. In one embodiment, the pressure sensing element 420 is coupled to the electronic circuitry of the system 400 via the same access hole as the temperature sensing element. However, in other embodiments, the pressure sensing element uses an additional access hole separate from the access hole used by the temperature sensor assembly 410. For example, the access hole may be located adjacent to the temperature sensor assembly, parallel to the temperature sensor assembly, or otherwise disposed within the wall of the thermowell.

[0021] 5A-5B are schematic diagrams of a process fluid multivariable measurement system to which embodiments of the present invention are particularly applicable. The system illustrated in FIG. 5A has several similarities to FIG. 5B, with like components being similarly numbered. As illustrated, the system 500 generally includes a thermowell 502 configured to couple to a process fluid conduit 504 and extend through a wall 506 of the process fluid conduit. The thermowell 502 is further configured to contact a process fluid 508 within the process fluid conduit 504 to obtain measurements of the process fluid, such as temperature and / or pressure. The thermowell 502 further generally includes a temperature sensor assembly 510 disposed within the thermowell 502, and further includes a sensor capsule as shown in FIGS. 1-3. The system 500 generally includes one or more temperature sensing elements (not shown) disposed within the thermowell 502, such as the temperature sensing element 114 described above with respect to FIG. 1. The temperature sensing elements are configured to obtain one or more temperature measurements and are electrically connected to a transmitter circuit, as illustrated in FIG. 4.

[0022] The process fluid multivariable measurement system 500 also includes a pressure sensor assembly 518 coupled to the thermowell 502. The pressure sensor assembly 518 typically has one or more pressure sensing elements (not shown) disposed therein, such as the pressure sensing element 120 described above with respect to FIG. 1. Upon contact with the process fluid 508 within the process fluid conduit 504, the temperature and pressure sensor assemblies are configured to generate and transmit a temperature and / or pressure sensor signal to the transmitter circuitry using the temperature and pressure sensing elements, respectively, disposed within the thermowell 502. As described above with respect to FIG. 4, the transmitter circuitry receives the temperature and / or pressure sensor signal and responsively generates a temperature measurement output and / or a pressure measurement output based on the received signals. The output is generally indicative of the temperature and / or pressure of the process fluid 508 within the process fluid conduit 504. Alternatively, or additionally, the output can be indicative of the temperature and / or pressure of the environment within the process fluid conduit 504.

[0023] As shown in Figure 5A, the thermowell 502 includes a flanged fitting. However, in Figure 5B, the thermowell 502 includes a threaded fitting. As shown in Figure 5A, the flanged fitting 524 generally includes bolts 526 configured to couple the thermowell 502 to a nozzle 530 of the process fluid conduit 504. The flanged fitting 524 further includes a sealing ring 528 configured to prevent flow of process fluid therethrough. The sealing ring 528 can be an O-ring seal or any other seal capable of sealing the process fluid 508 to the process fluid conduit 504.

[0024] 5B, the thermowell 502 may alternatively include a threaded fitting 532 configured to couple to threads (not shown) on the thermowell 502 to couple the thermowell 502 to the process fluid conduit 504. The threaded fitting 532 includes a weld 534 configured to couple the threaded fitting 532 to the wall 506 of the process fluid conduit 504. The use of a multivariable thermowell in either a threaded or flanged embodiment can allow for the installation of a variety of thermowells, thereby allowing for temperature and / or pressure sensing functions within the process fluid environment.

[0025] 6 is a schematic diagram of a multivariable thermowell with a strain gauge based pressure sensor, according to an embodiment of the invention. A thermowell body 600 generally includes an access hole 602 disposed within the thermowell body and configured to allow a pressure sensor assembly to be coupled therethrough. The thermowell body 600 further includes a strain gauge based sensor 604 configured to generate a pressure sensor signal in response to pressure detected within the process fluid conduit. The strain gauge based sensor includes an adaptive collar 606 configured to couple the strain gauge based sensor 604 to the thermowell body 600. The strain gauge based sensor 604 is coupled to the adaptive collar 606 with a coupling mechanism 608. The coupling mechanism 608 can be, for example, a weld that couples the adaptive collar 606 to the strain gauge based sensor 604.

[0026] The strain gauge based sensor 604 further includes a pressure sensor element 610 configured to sense a pressure in the process fluid conduit and generate a pressure signal indicative of the sensed pressure. In one embodiment, the strain gauge based sensor 604 further generally includes a pressure transmitting material disposed within the channel 614. The pressure transmitting material is fluidly isolated from the process fluid by an isolation diaphragm 620 and communicates an indication of the pressure to the pressure sensor element 610. In this manner, the indication of the pressure can be communicated from the process fluid through the pressure transmitting material to the pressure sensor element 610 to responsively generate a pressure sensor signal. The pressure transmitting material can be, for example, oil. However, in other embodiments, the pressure transmitting material can be other fluids capable of transmitting an indication of pressure.

[0027] An isolation diaphragm 620 is coupled to the pressure sensor 604 via a latching point 616 and configured to isolate the process fluid from the pressure transmitting material and the pressure sensor element 610. In one embodiment, the latching point 616 is a weld. The strain gauge based sensor 604 further includes a screen 612. By incorporating the screen 612 at the tip of the strain gauge based sensor 604, the strain gauge based sensor can be encapsulated and protected from passing debris while simultaneously being limited from wake frequencies. In other words, the flow characteristics are optimized, potentially resulting in improved pressure and / or temperature measurements.

[0028] 7 is a schematic diagram of a sensor capsule in a multivariable thermowell with a capacitive pressure sensor, according to an embodiment of the present invention. The thermowell body 700 generally includes an access hole 702 configured to allow a coupling 704 of a pressure sensor assembly therethrough. As shown, the coupling 704 includes a cable wire. However, in other embodiments, the coupling 704 can be a pressure transmitting material, a two or more wire cable, or a wireless link. The thermowell body 700 further includes a capacitive pressure sensor 714 configured to generate a pressure sensor signal in response to a detected pressure in the process fluid conduit. By using a capacitive pressure sensor assembly, the coupling of the pressure sensor assembly can be located in various locations within the thermowell body 700, such as within the access hole 702.

[0029] The capacitive pressure sensor 714 further includes a capacitive plate 708 disposed near an end of the thermowell configured to couple to a process fluid in a process fluid conduit. The capacitive plate 708, in one embodiment, includes an electrode 710 and a pressure biasing diaphragm 712 configured to generate and communicate an indication of pressure in the process fluid conduit. In one embodiment, the capacitive plate 708 is formed of a glass material. In this manner, a vacuum can be formed in a cavity 714 between the pressure biasing diaphragm 712 and the electrode 710 to enable the generation and communication of an indication of pressure. In one embodiment, the pressure biasing diaphragm 712 is a corrugated diaphragm. However, in other embodiments, the pressure biasing diaphragm 712 can be a thin film diaphragm.

[0030] FIG. 8 is a schematic diagram of a multivariable sensor for implementation in a multivariable process fluid measurement system, according to an embodiment of the present invention. The sensor 800 is generally configured to obtain one or more temperature measurements and / or one or more pressure measurements. In particular, the sensor 800 can be configured to obtain both pressure and temperature measurements simultaneously in a process fluid multivariable measurement system. In one embodiment, the sensor 800 is a strain gauge based sensor. As shown, the sensor 800 includes resistors 802-808 whose resistances are both strain and temperature dependent. As the temperature (correlated to Vref) changes, the resistors 802-808 change their resistances in a similar direction and by a similar amount. Furthermore, as the pressure (correlated to Vout) increases, the resistors 802 and 806 increase their resistances by a similar amount, while the resistors 804 and 808 decrease their resistances by a similar amount. In this manner, the sensor 800 can obtain pressure and temperature measurements simultaneously in a process fluid measurement system.

[0031] FIG. 9 is a schematic diagram of a multivariable thermowell for implementation into a process fluid multivariable measurement system according to another embodiment of the present invention. The system illustrated in FIG. 9 has some similarities to FIG. 1, with similar components being similarly numbered. As shown, the thermowell 900 is configured to couple to a process fluid conduit, such as the process fluid conduits described in FIGS. 5A-5B, and extend through a wall of the process fluid conduit. The thermowell 900 is further configured to generally contact a process fluid within the process fluid conduit to obtain measurements of the process fluid, such as temperature and / or pressure. In one embodiment, the thermowell 900 is a threaded thermowell. However, in other embodiments, the thermowell 900 can be a flanged thermowell or other thermowell design that is coupleable to a process fluid conduit.

[0032] Thermowell 900 further includes a multi-variable sensor 920 generally disposed within a sensor capsule 912 of thermowell 900. Sensor capsule 912 may include a multi-variable sensor 920 similar to the multi-variable sensor described above with respect to FIG. 8, for example. In one embodiment, multi-variable sensor 920 is a strain gauge-based sensor. However, in other embodiments, different types of multi-variable sensors may be utilized. Multi-variable sensor 920 is electrically connected to a transmitter circuit (not shown) via access hole 916 and configured to obtain one or more temperature measurements and / or one or more pressure measurements. In particular, multi-variable sensor 920 may be configured to simultaneously obtain both pressure and temperature measurements in a process fluid multi-variable measurement system and responsively generate temperature and pressure sensor signals. Multi-variable sensor 920 may, for example, generally include one or more multi-variable sensitive elements disposed therein and configured to obtain one or more temperature and pressure measurements. The access hole 916 is generally configured to allow a coupling 940 of the multi-variable sensor 920 therethrough. The multi-variable sensor 920 can be electrically connected to a transmitter circuit, such as that described above with respect to FIG. 4, via a transmission loop, a fiber optic cable, a wireless link, or some other connection. In operation, the transmitter circuit can receive temperature and pressure sensor signals from at least one multi-variable sensitive element and responsively generate temperature and pressure measurement outputs based on the received sensor signals. By incorporating a multi-variable sensor similar to that described above with respect to FIG. 8, both the temperature and pressure of a process environment can be determined without the need for separate sensor assemblies.

[0033] Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, although embodiments of the present invention have been described with reference to thermowells having pressure sensing capabilities, other process variable sensors, including but not limited to flow, level, pH, vibration, and erosion, may also be implemented within the thermowells.

Claims

1. 1. A process fluid multivariate measurement system comprising: a thermowell configured to couple to a process fluid conduit and extend through a wall of the process fluid conduit; a temperature sensor assembly removably disposed within said thermowell, said temperature sensor assembly having at least one temperature sensitive element disposed therein; a pressure sensor assembly coupled to the thermowell, the pressure sensor assembly having at least one pressure sensitive element disposed therein and fluidly isolated from the process fluid conduit; a transmitter circuit communicatively coupled to the temperature sensor assembly and the pressure sensor assembly, receiving a temperature sensor signal from the at least one temperature sensitive element and responsively generating a temperature measurement output based on the temperature sensor signal; and receiving a pressure sensor signal from the at least one pressure sensitive element and responsively generating a pressure measurement output based on the pressure sensor signal; and the transmitter circuit communicates the temperature measurement output and the pressure measurement output using a process communication protocol. The transmitter circuit is configured as follows: A process fluid multivariable measurement system comprising:

2. The process fluid multivariable measurement system of claim 1 , wherein the transmitter circuit is configured to couple to the pressure sensor assembly through an access hole in the thermowell.

3. The process fluid multivariable measurement system of claim 2 , wherein the access hole is located adjacent to the temperature sensor assembly.

4. The process fluid multivariable measurement system of claim 3 , wherein the access hole is disposed parallel to the temperature sensor assembly.

5. The process fluid multivariable measurement system of claim 3 , wherein the access hole is disposed in a wall of the thermowell.

6. The process fluid multivariable measurement system of claim 1 , wherein the pressure sensitive element comprises a capacitive pressure sensor configured to generate the pressure sensor signal in response to a detected pressure in the process fluid conduit.

7. The process fluid multivariable measurement system of claim 2 , wherein the pressure sensitive element comprises a pressure biasing diaphragm communicatively coupled to a pressure sensor, the pressure sensor being located remotely from the thermowell.

8. 8. The process fluid multivariable measurement system of claim 7, wherein the pressure deflection diaphragm is communicatively coupled to the pressure sensor by a pressure transmitting material disposed within the access hole.

9. The process fluid multivariable measurement system of claim 8 , wherein the pressure transmitting material is oil.

10. 1. A multivariable thermowell comprising: a temperature sensor assembly having at least one temperature sensitive element disposed therein and removably mounted within said thermowell; a pressure sensor assembly having at least one pressure sensitive element disposed therein, the pressure sensitive element being configured to be fluidly isolated from a process fluid conduit; and an access hole disposed within the thermowell, the access hole configured to permit coupling of the pressure sensor assembly therethrough; Multivariable thermowells including.

11. The multivariable thermowell of claim 10 , wherein the access hole is located adjacent to the temperature sensor assembly.

12. The multivariable thermowell of claim 10 , wherein the pressure sensor assembly is configured to couple to a transmitter circuit through the access hole in the thermowell.

13. The multivariable thermowell of claim 10 , wherein the pressure sensitive element comprises a pressure biasing diaphragm communicatively coupled to a pressure sensor located remotely from the multivariable thermowell.

14. 14. The multivariable thermowell of claim 13, wherein the pressure deflection diaphragm is communicatively coupled to the pressure sensor by a pressure transmitting material disposed within the access hole.

15. 1. A process fluid multivariate measurement system comprising: a thermowell configured to couple to a process fluid conduit and extending through a wall of the process fluid conduit; a temperature sensor assembly disposed within the thermowell, the temperature sensor assembly having at least one temperature sensitive element disposed therein; a multivariable sensor disposed within said thermowell, said multivariable sensor having at least one multivariable sensitive element disposed therein, said multivariable sensor configured to be fluidly isolated from said process fluid conduit; a transmitter circuit communicatively coupled to the temperature sensor assembly and the multivariable sensor, receiving a temperature sensor signal from the at least one temperature sensitive element and responsively generating a temperature measurement output based on the temperature sensor signal; receiving a pressure sensor signal from the at least one multivariable sensitive element and responsively generating a pressure measurement output based on the pressure sensor signal; and receiving an additional temperature sensor signal from the at least one multivariable sensitive element and responsively generating an additional temperature measurement output based on the additional temperature sensor signal; The transmitter circuit is configured to A process fluid multivariable measurement system comprising:

16. The process fluid multivariable measurement system of claim 15 , wherein the additional temperature sensor signal is configured to provide a back-up temperature measurement.

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