Patent Description:
Industrial process pressure sensing devices, such as pressure transmitters and flow measurement devices, are used in industrial process control systems to monitor pressures of process media using a pressure sensor that provides an output in response to process media pressures. One well known type of pressure transmitter is the Model <NUM> transmitter available from Rosemount Inc. of Chanhassen, Minn. Pressure transmitters are also shown in <CIT>, for example.

Exposure of the pressure sensor to the process medium can damage the process sensor and adversely affect pressure measurements. An isolation arrangement is used to separate the pressure sensor from the process medium while allowing the pressure sensor to detect the pressure of the process medium. The isolation arrangement typically includes an isolation diaphragm that is exposed to the process medium. The isolation diaphragm is typically a very thin and compliant member that flexes in response to the pressure of the process medium. The flexing of the isolation diaphragm, which represents the pressure of the process medium, is coupled to the pressure sensor through an isolation or fill fluid that is contained in an isolation cavity, such as a fluid line. Thus, the pressure sensor is able to measure the process pressure by measuring the pressure of the isolation fluid without being exposed to the process medium.

The seal of the isolation cavity may be breached due to a rupture of the isolation diaphragm from exposure to corrosive or abrasive process media or a seal failure, for example. The breach of the seal of the isolation cavity can result in an isolation fluid leak, which can lead to a degradation to pressure measurements. Additionally, the process medium may enter the isolation cavity, which can damage the pressure sensor due to the process fluid and further degrade pressure measurements.

The patent <CIT> discloses a transmitter with fill fluid loss detection. The transmitter comprises a housing with two isolation cavities, which are filled with a fill fluid. Two isolation diaphragms seal a process interface of the isolation cavities from a process medium. A differential pressure sensor exposed to the two sensor interfaces of the isolation cavities outputs a differential pressure signal that is indicative of a difference in pressure between the fill fluids in the two isolation cavities. In order to conveniently and reliably detect fluid loss in the isolation cavities, two position sensors disposed proximate the isolator diaphragms monitor the position of the isolator diaphragm. The relative position of the isolator diaphragm is measured and compared with thresholds to detect a substantial loss of fluid.

The patent <CIT> discloses a differential pressure transducer with a pair of interior chambers filled with the process fluid. The chambers are separated by an electrically conductive diaphragm. A magnetic position sensor is positioned on the diaphragm. When the diaphragm is displaced from its nominal plane in response to an applied pressure differential, the changed inductance is measured by the magnetic position sensor. Thus, the differential pressure is indirectly magnetically measured via the position of the diaphragm.

The present invention consists of an industrial process differential pressure sensing device as defined in claim <NUM> and a method of detecting a loss of a seal of an isolation cavity of an isolation arrangement in an industrial process differential pressure sensing device as defined in claim <NUM>. Embodiments of the present disclosure generally relate to an industrial process differential pressure sensing device, a method for detecting a loss of seal condition of an isolation cavity of an isolation arrangement in a differential pressure sensing device, and a differential pressure sensor isolation arrangement. One embodiment of the industrial process differential pressure sensing device includes a housing having first and second isolation cavities that are respectively sealed by first and second diaphragms, a differential pressure sensor, a static pressure sensor, an eddy current displacement sensor, and a controller. The static pressure sensor is configured to output a static pressure signal that is based on a pressure of fill fluid in the first isolation cavity. The differential pressure sensor is configured to output a differential pressure signal that is indicative a pressure difference between the first and second isolation cavities. The eddy current displacement sensor is configured to output a position signal that is indicative of a position of the first isolation diaphragm relative to the housing. The controller is configured to detect a loss of a seal of the isolation cavity based on the position signal, the static pressure signal and the differential pressure signal.

One embodiment of the method relates to an isolation arrangement in an industrial process differential pressure sensing device that includes a housing having first and second isolation cavities, a differential pressure sensor, a static pressure sensor, a first isolation diaphragm sealing a process interface of the first isolation cavity from an industrial process medium, and a second isolation diaphragm sealing a process interface of the second isolation cavity from the process medium. In the method, a position of the first isolation diaphragm relative to the housing is detected using a first eddy current displacement sensor. A static pressure of the fill fluid within the first isolation cavity is obtained using the static pressure sensor, and differential pressure between the first and second isolation cavities is obtained using the differential pressure sensor. An expected position of the first isolation diaphragm relative to the housing from memory is obtained based on the static pressure and the differential pressure using a controller. A loss of seal of the first isolation cavity is detected when a difference between the detected position of the first isolation diaphragm and the expected position of the first isolation diaphragm exceeds a threshold value. A notification is generated when the loss of seal is detected using the controller.

Embodiments of the present disclosure are described more fully hereinafter with reference to the accompanying drawings. Elements that are identified using the same or similar reference characters refer to the same or similar elements. The various embodiments of the present disclosure may be embodied in many different forms and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

<FIG> is a simplified diagram of an exemplary industrial process measurement system <NUM>, in accordance with embodiments of the present disclosure. The system <NUM> may be used in the processing of a material to transform the material from a less valuable state into more valuable and useful products, such as petroleum, chemicals, paper, food, etc. For example, the system <NUM> may be used in an oil refinery that performs industrial processes that can process crude oil into gasoline, fuel oil, and other petrochemicals.

The system <NUM> includes a transmitter <NUM> that utilizes a pressure sensor to measure or sense a pressure (e.g., static or differential pressure) relating to a process medium <NUM>. In some embodiments, the process medium <NUM> may be a fluid (i.e., liquid or gas) that is contained or transported through a process vessel <NUM>, such as a pipe (shown), a tank, or another process vessel. The transmitter <NUM> may be coupled to the vessel <NUM> through an adapter <NUM>, a manifold <NUM> and a process interface <NUM>, for example.

The transmitter <NUM> may communicate process information with a computerized control unit <NUM>. The control unit <NUM> may be remotely located from the transmitter <NUM>, such as in a control room <NUM> for the system <NUM>, as shown in <FIG>. The process information may include, for example, a static pressure, a differential pressure or a related process parameter, such as a flow rate of a fluid flow through the vessel that is based on the differential pressure.

The control unit <NUM> may be communicatively coupled to the transmitter <NUM> over a suitable physical communication link, such as a two-wire control loop <NUM>, or a wireless communication link. Communications between the control unit <NUM> and the transmitter <NUM> may be performed over the control loop <NUM> in accordance with conventional analog and/or digital communication protocols. In some embodiments, the control loop <NUM> includes a <NUM>-<NUM> milliamp control loop, in which a process variable may be represented by a level of a loop current I flowing through the control loop <NUM>. Exemplary digital communication protocols include the modulation of digital signals onto the analog current level of the two-wire control loop <NUM>, such as in accordance with the HART® communication standard. Other purely digital techniques may also be employed including FieldBus and Profibus communication protocols.

The transmitter <NUM> may also be configured to communicate wirelessly with the control unit <NUM> using a conventional wireless communication protocol. For example, the transmitter <NUM> may be configured to implement a wireless mesh network protocol, such as WirelessHARTO (IEC <NUM>) or ISA <NUM>. 11a (IEC <NUM>), or another wireless communication protocol, such as WiFi, LoRa, Sigfox, BLE, or any other suitable protocol.

Power may be supplied to the transmitter <NUM> from any suitable power source. For example, the transmitter <NUM> may be wholly powered by the current I flowing through the control loop <NUM>. One or more power supplies may also be utilized to power the transmitter <NUM>, such as an internal or an external battery. An electrical power generator (e.g., solar panel, a wind power generator, etc.) may also be used to power the transmitter <NUM>, or to charge a power supply used by the transmitter <NUM>.

As discussed above, pressure sensors of industrial process pressure transmitters <NUM> may be coupled to the process medium <NUM> through an isolation arrangement to prevent exposure of the pressure sensor to the process medium. <FIG> is a simplified diagram of an exemplary industrial process pressure sensing device <NUM>, such as a pressure transmitter, having an isolation arrangement <NUM> in accordance with embodiments of the present disclosure. The isolation arrangement <NUM> includes a housing <NUM> having an isolation cavity <NUM>, which is sealed at a process interface <NUM> by an isolation diaphragm <NUM> that is exposed to the process medium <NUM>. The isolation diaphragm <NUM> may be formed of metal (e.g., stainless steel) and flexes in response to the pressure of the process medium <NUM>. The flexing of the isolation diaphragm <NUM>, which represents the pressure of the process medium <NUM>, is communicated to a pressure sensor <NUM> through an isolation fluid <NUM> (e.g., silicone oil, hydraulic fluid, etc.) that is contained in the cavity <NUM>. The pressure sensor <NUM> may generate a pressure signal <NUM> that is indicative of the pressure (e.g., static pressure) of the isolation fluid <NUM> and the process medium <NUM>.

In some embodiments, the device <NUM> includes a controller <NUM> (<FIG>), which may represent one or more processors (i.e., microprocessor, central processing unit, etc.) that control components of the device <NUM> to perform one or more functions described herein in response to the execution of instructions, which may be stored locally in any suitable patent subject matter eligible computer readable media or memory <NUM> that does not include transitory waves or signals, such as, for example, hard disks, CD-ROMs, optical storage devices, or magnetic storage devices.

The processors of the controller <NUM> may be components of one or more computer-based systems. In some embodiments, the controller <NUM> includes one or more control circuits, microprocessor-based engine control systems, one or more programmable hardware components, such as a field programmable gate array (FPGA), that are used to control components of the device <NUM> to perform one or more functions described herein.

The controller <NUM> may also represent other device circuitry, such as communications circuitry that is configured to communicate information <NUM> to the control unit <NUM>, in accordance with a conventional communications protocol. The information may include pressure information <NUM> derived from the pressure signal <NUM>. The pressure information <NUM> may also be based on a temperature signal <NUM> generated by a temperature sensor <NUM>, which may be indicative of a temperature of housing <NUM>, the fill fluid <NUM>, and/or the process medium <NUM>, for example.

The pressure sensor <NUM> may take on any suitable form. <FIG> is a simplified diagram of an exemplary pressure sensor <NUM> and isolation arrangement <NUM> in accordance with the prior art. In some embodiments, the pressure sensor <NUM> may include a pressure sensing diaphragm <NUM> that seals a reference pressure cavity <NUM> having a reference pressure. For an absolute pressure sensor, the reference pressure is a vacuum, for a gauge pressure sensor the reference pressure is at atmospheric pressure, and for a differential pressure sensor the reference pressure is another selected pressure, such as a different pressure of the process being monitored, for example.

The pressure sensing diaphragm <NUM> may be much stiffer than the isolation diaphragm <NUM>. As a result, the pressure drop across the isolation diaphragm <NUM> may be very small compared to the pressure drop across pressure sensing diaphragm <NUM>. As the hydrostatic pressure of the process medium <NUM> increases, the isolation diaphragm <NUM> deflects (dashed line) into the cavity <NUM> and the hydrostatic pressure of the fill fluid <NUM> within the cavity <NUM> increases causing the pressure sensing diaphragm <NUM> to deflect into the reference cavity <NUM>. The amount of deflection of the pressure sensing diaphragm <NUM> (dashed line) may be measured by deflection gauges <NUM> that are attached to the pressure sensing diaphragm <NUM>. The gauges <NUM> generate the pressure signal <NUM> (<FIG>) that indicates the hydrostatic pressure of the process medium <NUM>.

The volume swept by the deflection of the pressure sensing diaphragm <NUM> is filled with the fill fluid <NUM>, so a similar volume of fill fluid is swept by the deflection of the isolation diaphragm <NUM>. In practice, the isolation diaphragm <NUM> may sweep a slightly greater volume than the pressure sensing diaphragm <NUM> due to an expansion of the isolation cavity <NUM> and compression of the fill fluid <NUM>.

The deflected positions of the diaphragms <NUM> and <NUM> (dashed lines) in response to the pressure of the process medium <NUM> are, thus, coupled together. That is, both diaphragms <NUM> and <NUM> deflect in proportion to the pressure applied by the process medium <NUM>.

Over time, the isolation diaphragm <NUM> may become damaged to the point of developing a hole or crack resulting in a loss of the seal of the isolation cavity <NUM>. This may occur due to corrosive or abrasive process media <NUM>, physical damage from the process media <NUM>, such as particles in the process media, or other mechanical interference. Initially, the impact of a rupture of the isolation diaphragm <NUM> may be very subtle. Instead of transferring the process pressure across the isolation diaphragm <NUM>, the pressure is transferred directly to the pressure sensor <NUM> through the fill fluid <NUM>. Thus, the pressure drop across the previously sealed isolation diaphragm <NUM> goes to zero due to the rupture. As discussed above, the lost pressure drop may be a very small positive or negative pressure compared to the pressure of the process medium <NUM>. As a result, while the small increase or decrease in the pressure sensed by the process sensor <NUM> caused by the loss of the pressure drop across the diaphragm <NUM> may affect the accuracy of the pressure measurement, it may not be a sufficient trigger for a warning that the seal of the isolation cavity <NUM> has been breached.

When the process medium <NUM> is a liquid, it will eventually replace the fill fluid <NUM> over time. In the case of a gas or vapor process medium <NUM>, the fill fluid <NUM> will gradually drain from the isolation cavity <NUM>. In either case, the pressure sensor <NUM> becomes exposed to the process medium <NUM>, which may cause damage to the pressure sensor <NUM> and/or degradation of the sensor signal <NUM>.

Some pressure sensors <NUM> have impedance levels that make them very sensitive to galvanic leakage. If the process medium <NUM> (liquid or gas) creates such a leakage into the isolation cavity <NUM>, such high impedance level pressure sensors will likely produce compromised pressure signals <NUM>. For example, salt water is electrically conductive and will destroy the ability of a pressure sensor <NUM> having exposed high impedance nodes to produce an accurate pressure signal <NUM>.

Embodiments of the present disclosure operate as a diagnostic tool for detecting a breach of the seal of the isolation cavity <NUM>, such as a breach of the seal formed by the isolation diaphragm <NUM>, for example. This allows for early notification of possible pressure measurement degradation and the need for servicing of the industrial process pressure sensing device <NUM>.

<FIG> is a flowchart illustrating the method for detecting a loss of the seal of the isolation cavity, in accordance with the present disclosure. At step <NUM> of the method, a position of the isolation diaphragm <NUM> is detected using a position sensor <NUM> (<FIG>). In some embodiments, the position sensor <NUM> detects a position of the isolation diaphragm <NUM> relative to a reference, such as the housing <NUM>, and generates a position signal <NUM> that is indicative of the position of the diaphragm <NUM> relative to the housing <NUM>. Alternatively, a mechanical architecture may be used, in which the position sensor <NUM> is not leveled with the housing <NUM> or the cavity <NUM>, but is imbedded further into the housing <NUM> or cavity <NUM>. As used herein, the detected position of the diaphragm <NUM> corresponds to a position of a portion of the diaphragm <NUM>, such as a central portion of the diaphragm <NUM>, for example. The detected position of the diaphragm <NUM> may be determined by the controller <NUM> based on the position signal <NUM>, and used as an indication of the condition of the seal of the isolation cavity <NUM>.

In some embodiments, the position sensor <NUM> is displaced from the isolation diaphragm <NUM>, as shown in <FIG>. That is, the position sensor <NUM> does not contact the isolation diaphragm <NUM>. In some embodiments, this displacement of the position sensor <NUM> from the isolation diaphragm <NUM> results in a portion of the isolation cavity <NUM> extending between the isolation diaphragm <NUM> and the position sensor <NUM>, as shown in <FIG>. In some embodiments, the gap between the position sensor and the isolation diaphragm is about <NUM>-<NUM> mils.

one example, not forming part of the claimed invention the position sensor <NUM> comprises an optical displacement sensor that measures a time of flight for electromagnetic radiation <NUM> discharged from an emitter <NUM> to reflect from the isolation diaphragm <NUM> and be received by a receiver <NUM> of the sensor <NUM>, as illustrated schematically in <FIG>. Alternatively, the position sensor <NUM> not forming part of the claimed invention may comprise a capacitance displacement sensor that detects a capacitance between the isolation diaphragm <NUM> and an electrode <NUM> that is electrically insulated from the isolation diaphragm <NUM>, as schematically shown in <FIG>. The position sensor <NUM> not forming part of the claimed invention may also comprise a surface acoustic wave (SAW) sensor that is mounted to the isolation diaphragm <NUM> and has an output that changes in response to flexing of the diaphragm <NUM>. The SAW sensor could be interrogated remotely from a position on the housing <NUM>. The uf deposition sensor <NUM> not forming part of the claimed invention may comprise an acoustic sensor that uses a time of flight of an acoustic signal between a transmitter and receiver to detect the position of the isolation diaphragm <NUM> relative to the housing <NUM>. Another exemplary position sensor <NUM> may include a thermal conductivity sensor that senses a thermal conductivity between two points of the housing <NUM> that changes with the position of the isolation diaphragm <NUM> relative to the housing <NUM>.

The position sensor <NUM> according to the claimed invention comprises an eddy current displacement sensor <NUM>, an example of which is shown in the simplified diagram of <FIG>. Note that the housing <NUM> and other components are not shown in <FIG> to simplify the drawing. The sensor <NUM> includes a coil <NUM> supported in a reference position relative to the isolation diaphragm <NUM>, and a coil driver <NUM>. In one embodiment, the reference position of the coil <NUM> is fixed to the housing <NUM>. The coil driver <NUM> is configured to drive an alternating current through the coil <NUM> to produce an alternating current magnetic field <NUM>. The isolation diaphragm <NUM>, which is formed of metal, is in close proximity to the coil <NUM> so that it is exposed to the magnetic field <NUM>. The magnetic field <NUM> induces eddy currents <NUM> in the isolation diaphragm <NUM>, which in turn create magnetic fields <NUM> (dashed lines) that oppose the incident magnetic field <NUM>. The magnitude of the eddy currents <NUM> and the impedance of the coil varies with the position of the isolation diaphragm <NUM> relative to the coil <NUM>. Thus, the position of the isolation diaphragm <NUM> (e.g., central portion of the isolation diaphragm) relative to the housing <NUM> (<FIG>) may be inferred by the impedance of the coil. As the isolation diaphragm moves closer to the coil, the impedance of the coil decreases, and as the isolation diaphragm moves away from the coil, the impedance of the coil increases. Accordingly, a measurement of the impedance of the coil <NUM> may be used as the position signal <NUM>.

The coil <NUM> of the eddy current displacement sensor <NUM> may have a diameter that is at least twice the gap <NUM> between the coil <NUM> and the isolation diaphragm <NUM>. In some embodiments, the gap varies with movement of the isolation diaphragm over a range of approximately <NUM>-<NUM> mils. Thus, in some embodiments, the coil has a diameter of at least <NUM> mils.

At <NUM> of the method, an expected position of the isolation diaphragm <NUM> relative to the housing <NUM> is obtained by the controller <NUM> based on the static pressure of the fill fluid <NUM> contained in the isolation cavity <NUM> detected by the pressure sensor <NUM> and indicated by the pressure signal <NUM>. As discussed below, when the pressure sensor <NUM> is in the form of a differential pressure sensor, the static or line pressure may be obtained using a dedicated static pressure sensor, for example. In some embodiments, the controller <NUM> uses the static pressure of the fill fluid as an index to the expected position data <NUM> stored in the memory <NUM> to obtain the expected position of the isolation diaphragm <NUM> relative to the housing <NUM>, and complete step <NUM> of the method.

The expected position of the isolation diaphragm <NUM> during normal operation when the isolation cavity <NUM> is properly sealed may be empirically determined. For example, the estimated or expected position of the isolation diaphragm <NUM> relative to the housing <NUM> over a range of pressures of the isolation fluid <NUM> may be determined through measurements of the isolation diaphragm position over a range of pressures of the isolation fluid <NUM> of the isolation arrangement <NUM>, or a similar isolation arrangement. The resultant expected position data <NUM> may be defined by an algorithm, such as a polynomial, to compute the expected position of the isolation diaphragm <NUM> relative to the housing <NUM> based on the static pressure of the isolation fluid. Such a polynomial may also account for temperature and differential pressure (if applicable). Alternatively, a look-up table or another suitable data storage index may be used, that links the static pressure of the isolation fluid <NUM> within the cavity <NUM>, and possibly a differential pressure (if applicable) and temperature, to the measured deflection or position.

The expected position of the isolation diaphragm <NUM> for a given pressure of the isolation fluid <NUM> may be based on additional environmental factors, such as temperature. Fill fluids <NUM>, such as silicone oil, generally have a positive coefficient of thermal expansion. The expansion of the fill fluid may dominate other thermal expansions so that isolation diaphragm <NUM> position tends to deflect away from the pressure sensor <NUM> as the isolation arrangement <NUM> is heated. This influence may be determined during the empirical analysis of the isolation arrangement <NUM> by measuring the position of the isolation diaphragm <NUM> relative to the housing <NUM> over a range of static pressures of the fill fluid <NUM> and a range temperatures at each pressure. This results in expected position data <NUM> that indexes the position of the diaphragm <NUM> to a pressure and a temperature of the fill fluid <NUM>. Thus, in some embodiments of step <NUM>, the controller <NUM> uses the temperature signal <NUM> output by the temperature sensor <NUM> and the static pressure indicated by the pressure signal <NUM> to estimate the temperature of the fill fluid <NUM> and obtain the expected position of the isolation diaphragm <NUM> relative to the housing <NUM> using the expected position data <NUM>.

At <NUM> of the method, the controller <NUM> detects a loss of seal of the isolation cavity <NUM> when a difference (absolute value) between the detected position (step <NUM>) and the expected position (step <NUM>) exceeds a threshold value <NUM>, which may be retrieved from the memory <NUM>, as indicated in <FIG>. The threshold value <NUM> may be set empirically for a given pressure of the fill fluid <NUM> or combination of pressure and temperature of the fill fluid <NUM>. Additionally, different threshold values may be indexed over a range of pressures or combination of pressures and temperatures for the fill fluid <NUM>. A breach of the seal of the isolation cavity <NUM> is indicated when the difference between the expected and detected positions of the isolation diaphragm <NUM> relative to the housing <NUM> exceed the threshold value <NUM>.

<FIG> is a diagram illustrating deflection of the isolation diaphragm <NUM> over a range of static pressures of the fill fluid <NUM> with sealed and unsealed isolation cavity conditions. The vertical scale is normalized to the deflection range of the isolation diaphragm <NUM>. The solid line <NUM> represents the deflection of the isolation diaphragm <NUM> for a properly sealed isolation cavity <NUM> and corresponds to the expected deflection or position of the diaphragm <NUM> defined by the expected position data <NUM>.

The dashed line <NUM> represents the deflection of a ruptured isolation diaphragm <NUM>. Here, the isolation diaphragm <NUM> moves to a neutral position, which is shown as being at <NUM>, but could be a different value. The position of the isolation diaphragm <NUM> is independent of the pressure of the fill fluid <NUM>, so it will deviate from the expected position for a given pressure and/or pressure and temperature of the fill fluid <NUM>, except where the position line <NUM> intersects the position line <NUM> for normal operation. Accordingly, for a vast majority of the pressure range, the ruptured isolation diaphragm <NUM> is detectable in step <NUM> of the method, due to the difference between the expected position and the detected position being greater than the threshold value <NUM>.

The dashed line <NUM> of <FIG> represents a partial loss of the fill fluid <NUM> from the isolation cavity <NUM> due to a leak. Here, the isolation diaphragm <NUM> still responds to pressure changes of the process medium <NUM>, however the measured position of the isolation diaphragm (line <NUM>) will be offset from the expected position (line <NUM>) due to the partial loss of the fill fluid <NUM>. After a sufficient amount of the fill fluid <NUM> has leaked from the isolation cavity <NUM>, the difference between the measured and expected positions of the isolation diaphragm <NUM> will exceed the corresponding threshold value <NUM>, and the controller <NUM> will detect the fault in step <NUM> of the method.

In some embodiments of the method, the controller <NUM> is configured to generate a notification of the loss of seal condition of the cavity <NUM> detected in step <NUM>, as indicated at <NUM> of the method. The notification may take on any suitable form. In some embodiments, the notification comprises an alarm including a visible alarm and/or an audible alarm issued by a suitable output device <NUM> (e.g., strobe, LED, speaker, etc.) of the device <NUM>, which is shown in <FIG>. Some embodiments of the notification include a communication of notification information <NUM> to an external computing device, such as the control unit <NUM>. The notification <NUM> may include information regarding the type of breach of the isolation cavity seal that has occurred. For example, the notification <NUM> may indicate that the isolation diaphragm <NUM> has ruptured or that the isolation cavity <NUM> has a leak, based on the measured position of the isolation diaphragm <NUM> relative to its expected position, such as using information that distinguishes these conditions, such as that presented in <FIG>.

<FIG> is a simplified cross-sectional view of a portion of an exemplary industrial process differential pressure sensing device <NUM>, in accordance with embodiments of the present disclosure. The illustrated device <NUM> may comprise the differential pressure transmitter <NUM> mounted to the adapter <NUM> (<FIG>). The transmitter <NUM> may include a housing <NUM> that encloses and protects electronics of the transmitter <NUM> from environmental conditions, and a differential pressure sensor <NUM>. The housing <NUM> includes a base <NUM> that may include one or more process openings <NUM>, such as process openings 236A and 236B. The process openings <NUM> may be coupled to the process medium <NUM> through suitable connections, such as through the adapter <NUM>, the manifold <NUM>, and/or process interface <NUM>, as shown in <FIG>.

The exemplary transmitter <NUM> essentially includes two isolation arrangements 132A and 132B. The isolation arrangement 132A utilizes an isolation diaphragm 140A that is exposed to the process pressure P1 presented to the process opening 236A, and the isolation arrangement 132B utilizes an isolation diaphragm 140B that is exposed to the process pressure P2 presented to the process opening 236B. As discussed above, the isolation diaphragms 140A and 140B each flex in response to the pressures P1 and P2, which are communicated to the differential pressure sensor <NUM> through corresponding isolation cavities 136A and 136B comprising lines 238A and 238B, which are filled with an isolation fluid <NUM>.

The differential pressure sensor <NUM> generates a differential pressure signal <NUM> in response to the difference between the pressures P1 and P2. The differential pressure signal <NUM> may be delivered to the controller <NUM> through lead wires or another suitable connection, and the controller <NUM> may be used to communicate the differential pressure measurement indicated by the signal <NUM> to the control unit <NUM> using any suitable technique.

Some embodiments of the present disclosure operate to detect a loss of seal condition of the isolation cavity 136A of the isolation arrangement 132A and/or the isolation cavity 136B of the isolation arrangement 132B. <FIG> is a flowchart of a method of detecting such a loss of a seal, in accordance with embodiments of the present disclosure.

In some examples the isolation arrangement 132A includes a position sensor 172A, and/or the isolation arrangement 132B includes a position sensor 172B. In one embodiment, the position sensors 172A and 172B are eddy current displacement sensors, such as that discussed above with reference to <FIG>.

At <NUM> of the method, a position of the isolation diaphragm 140A relative to the housing <NUM> is detected using the position sensor 172A, such as described above with regard to step <NUM> of the method of <FIG>. The position sensor 172A outputs a position signal 174A to the controller <NUM> that is indicative of the sensed position of the isolation diaphragm 140A. In some embodiments, a position of the diaphragm 140B relative to the housing <NUM> is detected using the position sensor 172B, which outputs a position signal 174B to the controller <NUM> that is indicative of the detected position.

The device <NUM> includes at least one static or line pressure sensor <NUM>, such as static pressure sensors 242A or 242B, which are respectively configured to measure the static pressure of the fill fluid <NUM> in the isolation cavities 136A and 136B, and generate static pressure signals 246A and 246B indicating the measured pressures. Only one of the static pressure sensors 242A or 242B may be necessary to establish the static pressures in both cavities 136A and 136B when the differential pressure between the cavities 136A and 136B is known. For example, when the differential pressure (DP=P1-P2) and the static pressure P1 are known, the static pressure P2 may be calculated by subtracting the differential pressure from the pressure P1. For some industrial process applications, the static pressure may be quite extreme and range from zero to several thousand pounds per square inch (psi). Some industrial process differential pressure sensing devices are rated to withstand static pressures up to <NUM>,<NUM> psi (same as <NUM> Bar or <NUM> MPa).

At <NUM> of the method, the controller <NUM> obtains a static pressure of the fill fluid within the isolation cavities 136A and 136B is obtained using a static pressure sensor, such as sensor 242A or 242B. The controller <NUM> also obtains a differential pressure between the isolation cavities136A and 136B using the differential pressure sensor <NUM>, at <NUM> of the method. For example, the controller <NUM> may receive a signal <NUM> that is indicative of the differential pressure between the cavities 136A and 136B.

At <NUM> of the method, the controller <NUM> obtains an expected position for the isolation diaphragm 140A based on the obtained static and differential pressures. The controller <NUM> may also obtain an expected position of the isolation diaphragm 140B based on the obtained static and differential pressures. Additionally, as discussed above, the expected positions for the isolation diaphragms 140A and 140B may further be based on a temperature signal <NUM> output from the temperature sensor <NUM>.

At <NUM> of the method, the controller <NUM> detects a loss of seal condition of the isolation cavity 136A when the difference between the measured and expected positions of the isolation diaphragm 140A exceed a corresponding threshold <NUM> (<FIG>). Likewise, the controller <NUM> can detect a loss of seal condition of the isolation cavity 136B when the difference between the measured and expected positions of the isolation diaphragm 140B exceed a corresponding threshold <NUM>.

When a loss of seal condition is detected, the controller <NUM> may generate a notification at <NUM> of the method, such as described above with regard to step <NUM> of the method of <FIG>. In addition to the information mentioned above, some embodiments of the notification include information that identifies the isolation arrangement 132A or 132B or the corresponding isolation cavity 136A or 136B whose seal has been breached.

The effects on the change in position of the isolation diaphragms 140A and 140B due to the differential pressure between the cavities 136A and 136B measured by the sensor <NUM>, the temperature of the fill fluid <NUM> measured by the temperature sensor <NUM>, and the static pressure of the fill fluid <NUM> measured by the static pressure sensor 242A or 242B, may be determined for a particular differential pressure sensing device using empirical techniques. For example, the position of the diaphragm 140A on the high pressure side P1 measured by the position sensor 172A may decrease and the position of the diaphragm 140B on the low pressure side P2 measured by the position sensor 172B may increase from a differential pressure of zero to the maximum differential pressure (e.g., about <NUM> psi). The positions of the isolation diaphragms 140A and 140B measured by the sensors 172A and 172B may increase as the fill fluid temperature measured by the sensor <NUM> increases. The positions of the diaphragms 140A and 140B measured by the sensors 172A and 172B may decrease over a static pressure range of <NUM> to <NUM> psi. Thus, an accurate determination of the expected positions of the isolation diaphragm 140A or 140B in step <NUM> of the method, depends on the accurate prediction of the isolation diaphragm positions in the presence of these influences of the differential pressure, the temperature of the fill fluid <NUM>, and the static pressure of the fill fluid <NUM> in the cavity 136A or 136B.

The effect the static pressure has on the compression of the fill fluid <NUM> and the position of the isolation diaphragms 140A or 140B may involve measuring the static pressure using the sensor 242A and/or 242B and using either empirically-derived family characteristics of a population of the pressure sensing devices <NUM> or an empirically-derived factory characterization of the pressure sensing device <NUM>, to form a characterization (e.g., look-up table, polynomial, correction algorithm), from which a measured static pressure of the fill fluid <NUM> can be used to determine an expected change in position of the diaphragm 140A and/or 140B for a given differential pressure and/or temperature measurement. The controller <NUM> may use characterization to identify a position change of the diaphragm 140A and/or 140B based upon the static pressure detected by the sensor 242A or 242B, and take this position change into account when determining the expected positions of the diaphragms 140A or 140B in step <NUM> of the method.

The use of the family characteristics of the device <NUM> to establish the effects of the static pressure of the fill fluid on the position of the diaphragms 140A or 140B is generally preferred when the devices <NUM> perform substantially the same from unit to unit. The empirically established family characteristics for the population of devices <NUM> may be used in each of the devices <NUM> to account for the influence the static pressure of the fill fluid <NUM>, and optionally, the temperature of the fill fluid <NUM>, have on the expected position of the isolation diaphragms 140A and 140B. The advantage of the use of the family characteristics is that each individual device <NUM> is not required to be factory characterized, resulting in lower manufacturing cost.

The use of an empirically-derived factory characterization of the pressure sensing device <NUM> is preferably used when a population of the devices <NUM> have substantially dissimilar characteristic responses to the static pressure of the fill fluid <NUM>. In this case, each device <NUM> is factory characterized for the influence of the static pressure of the fill fluid <NUM> on the position of the isolation diaphragms 140A and/or 140B. In some embodiments, this characterization is determined for each temperature in the characterization profile. This allows the controller <NUM> to account for the influence of the static pressure of the fill fluid <NUM> measured by the sensor 242A or 242B at all pressures and temperatures that the device <NUM> is likely to be subjected to. This process is more expensive than when the family characteristics are used because each device <NUM> must be analyzed to determine the effects of exposure to the static pressure and temperature conditions to form the look-up table for the device <NUM>.

The characterization of a device <NUM> or a family of devices <NUM> may involve a characterization over a range of differential pressures, temperatures and static pressures that the device <NUM> is likely to be subjected to. For example, a characterization profile may be established using: <NUM> differential pressure (DP) points, such as [-<NUM>, -<NUM>, -<NUM>, -<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>] percent of the upper range limit (URL); <NUM> temperature points [-<NUM>, -<NUM>, <NUM>, <NUM>, <NUM>] degrees Celsius; and <NUM> static pressure or line pressure (LP) points [<NUM>, <NUM>, <NUM>] psi. Note that the negative percentages of the URL may operate to cover the lower range limit (LRL) of the device <NUM>. For example, the URL of a device <NUM> may be <NUM> psi and the LRL of the device <NUM> may be -<NUM> psi. Conditions of the device <NUM> are stabilized at each point, and the position of the diaphragms 140A and/or 140B are measured at each point, such as using the position sensors 172A and 172B. The position measurements may be recorded along with the corresponding differential pressure, temperature and static pressure raw data in a look-up table or mapping. A full set of points may include all of the differential pressure and temperature points combination, which, for the above example, results in <NUM> measurement points. Additionally, the full set of points may include the zero differential pressure and non-zero static pressure points at all temperatures, which, for the above example, results in <NUM> measurement points. Alternatively, the impact of the static pressure on the position of the diaphragm 140A and/or 140B may be determined for multiple differential pressures. Exemplary data representing the characterization of a device <NUM> or family of devices <NUM> having all <NUM> measurement points is provided below in Table <NUM>.

The collected characterization data may be used to form a look-up table or to calculate coefficients for correction algorithms that may be used by the controller <NUM> to estimate the expected position of the isolation diaphragms 140A and 140B. The correction algorithms may be based on multivariate polynomials, or lookup tables, or a combination of polynomials and lookup tables. Such correction algorithms use the coefficients to calculate a corrected differential pressure, a corrected temperature, a corrected static pressure, an estimated or expected position for the diaphragm 140A, and an estimated or expected position for the diaphragm 140B. The corrected differential pressure is the estimated differential pressure compensated for temperature and static pressure influences. A curve fitting process may use the differential pressure in the data table above as the independent variable. The corrected temperature may be an estimate of the fill fluid temperature compensated for differential pressure and static pressure, if necessary. A curve fitting process may use the test station temperature from the table above as the independent variable. The corrected static or line pressure may be an estimate of the static pressure that is compensated for temperature and differential pressure, if necessary. A curve fitting process may use the test station measured static pressure from the table above as the independent variable. The estimated or expected position of the diaphragm 140A may be calculated based on the corrected differential pressure, the corrected static pressure and the corrected temperature. A curve fitting process may use the measured position of the diaphragm 140A, such as by the position sensor 172A, from the characterization data in the table above as the independent variable. The estimated or expected position of the diaphragm 140B may be calculated based on the corrected differential pressure, the corrected static pressure and the corrected temperature. A curve fitting process may use the measured position of the diaphragm 140B, such as by the position sensor 172B, from the characterization data in the table above as the independent variable. The correction algorithms may also remove linearity errors from the native sensor signals generated by the pressure sensor <NUM>, the differential pressure sensor <NUM>, the temperature sensor <NUM> and the position sensor <NUM>, using conventional techniques.

Claim 1:
An industrial process differential pressure sensing device comprising:
a housing (<NUM>) including a first isolation cavity (136A) and a fill fluid (<NUM>) contained in the first isolation cavity (136A), and a second isolation cavity (136B) and a fill fluid (<NUM>) contained in the second isolation cavity (136B);
a first isolation diaphragm (140A) configured to seal a process interface (<NUM>, <NUM>) of the first isolation cavity (136A) from a process medium (<NUM>);
a second isolation diaphragm (140B) configured to seal a process interface (<NUM>, <NUM>) of the second isolation cavity (136B) from the process medium (<NUM>);
a static pressure sensor (<NUM>) configured to output a static pressure signal (246A) that is based on a pressure of the fill fluid (<NUM>) in the first isolation cavity (136A);
a first eddy current displacement sensor (<NUM>) configured to output a first position signal (174A) indicative of a position of the first isolation diaphragm (140A) relative to the housing (<NUM>);
a differential pressure sensor (<NUM>) exposed to sensor interfaces of the first and second isolation cavities (<NUM>) and configured to output a differential pressure signal (<NUM>) that is indicative of a difference in pressure between the fill fluids (<NUM>) in the first and second isolation cavities (<NUM>); and
a controller (<NUM>) configured to detect a loss of a seal of the first isolation cavity (136A) based on the first position signal (174A), the static pressure signal (246A) and the differential pressure signal (<NUM>).