Acoustic transducer assembly for a pressure vessel

A transducer assembly includes an acoustic sensor element and an acoustic waveguide. The acoustic waveguide includes a rotatable acoustic coupler, a tube, and a foot. The foot has a mounting surface that is mountable on a fluid conduit. A circuit assembly couples to acoustic sensor element and provides a diagnostic output.

BACKGROUND

The present application relates to the monitoring of pressure vessels. More particularly, the present application relates to transducing malfunctions in flow control such as leaky valves, stuck valves, liquid or gas phases, or multiple phases associated with flow control in pressure vessels.

Steam traps are commonly used in many industries to remove condensate from steam lines. In a typical plant, thousands of such devices may be deployed. A steam trap is generally a relatively low technology device that is designed to be relatively inexpensive. Often, steam traps are completely mechanical. Adding any electrical wiring for either powering or wiring would be considered cost prohibitive, impractical or labor intensive.

A steam trap is generally designed to allow condensate to escape a steam pipe in order to maintain efficiency and prevent pipe “knocking”. A typical steam trap may have one or more chambers and a movable member that is in physical contact with the condensate. As the level of condensate rises above some threshold, the movable member within the steam trap actuates or otherwise engages one or more valves to allow at least some of the condensate to escape. As the condensate escapes, the level of condensate within the steam trap is reduced to such an extent that the valve is closed.

Malfunctioning steam traps can leak steam which wastes energy or can fail to remove condensate properly. In many instances, the malfunction is not detected by plant control systems and is therefore unknown to plant personnel for extended periods of time.

Other types of flow control devices associated with pressure vessels such as control valves, orifices, nozzles and restrictions are subject to malfunctions.

SUMMARY

A transducer assembly includes an acoustic sensor element and an acoustic waveguide. The acoustic waveguide includes a tube that has a first tube end acoustically coupled to the acoustic sensing element by a rotatable acoustic coupler. The acoustic waveguide further includes a second tube end. The second tube end has a mounting surface that is mountable on a fluid conduit. A circuit assembly is coupled to the acoustic sensor element and provides a diagnostic output that identifies a steam leak based upon a received acoustic signal. A method is also included.

DETAILED DESCRIPTION

In the embodiments described below, a transducer assembly detects malfunctions in flow control such as leaking gasses in pressure vessels such as valves, steam traps, flow restrictors, pressure relief valves and the like. The transducer assembly uses acoustic sensing. In some embodiments, temperature sensing is used as well. In one example, when there is a low level of noise or no acoustic noise detected, and a pressure vessel temperature is near saturation temperature of the steam, then a steam trap is operating normally. When acoustic noise rises above a threshold level and the temperature is near the saturation temperature of the steam, then the transducer assembly senses and indicates that a valve in the pressure vessel is leaking. When the acoustic noise is high and temperature is low, then the transducer assembly senses and indicates that a valve in the pressure vessel is in a start-up condition with air leaking. When there is no acoustic noise and the temperature is low, then the transducer assembly senses and indicates that a valve in the pressure vessel is plugged, jammed or not operational. The invention, however, is not limited to this exemplary diagnostic technique.

The transducer assembly includes an acoustic sensor element and an acoustic waveguide. The acoustic waveguide allows the diagnostic circuitry to be thermally separated from a high temperature vessel. The acoustic waveguide includes a rotatable acoustic coupler, such as a spring or shaft for example, that couples to the acoustic sensor, and includes a tube that couples to the rotatable acoustic coupler and to a foot that has a mounting surface that mounts to a fluid conduit connected to the pressure vessel. In one embodiment, a temperature sensor senses temperature in an internal thermowell cavity in the foot and has an output cable that extends through the tube. A thermowell cavity is a protected cavity in a thermowell. A thermowell is a protecting tube designed to enclose a temperature sensing device in a cavity and protect the temperature sensing device from deleterious effects of the environment. According to one embodiment, an electronics assembly in the transducer assembly receives temperature and acoustic noise data from the sensors and provides a wireless output that couples to a remote monitor.

FIG. 1illustrates an exploded view of a transducer assembly50. The transducer assembly50includes an acoustic sensor element1. According to one embodiment, the acoustic sensor element1includes a piezoelectric force sensor. According to another embodiment, the acoustic sensor element1includes a capacitive force sensor. According to yet another embodiment, the acoustic sensor element1includes a magnetic force sensor.

The transducer assembly50includes an acoustic waveguide4. The acoustic waveguide4includes a spring4A that rotatably couples to the acoustic sensor element1. The acoustic waveguide4includes a tube4B that has a first tube end7coupled to the spring4A.

The acoustic waveguide4includes a foot4C which provides a coupling region that couples to a second tube end9of the tube4B. The foot4C includes a mounting surface11that is mountable in contact with a fluid conduit (not illustrated inFIG. 1).

The acoustic waveguide4couples an acoustic vibration from the mounting surface11of the foot4C to the acoustic sensor element1. It will be understood by those skilled in the arts that the tube4B and the foot4C can be formed of a single tube, and in that case there is no joint between the tube4B and the foot4C. According to one embodiment, acoustic vibration is sensed in the range of 30 kHz to 50 kHz.

According to one embodiment, the tube4B has a length that spaces the acoustic sensor element1a distance away from the foot4C to provide thermal isolation. High temperature at the foot4C, which is typically clamped to a line on a process vessel, is attenuated along the length of the tube4B such that the acoustic sensor element1has a lower temperature that is near the temperature of the surrounding ambient air. The tube4B is hollow, as illustrated, which reduces thermal conduction along the length of the tube4B.

According to one embodiment, the spring4A is positioned adjacent the acoustic sensor element1by an insulating cap13that provides a rotatable joint between the spring4A and the acoustic sensor element1. The insulating cap13couples the acoustic vibration from the spring4A to the acoustic sensor element1. The insulating cap13positions the spring4A in a position where it exerts a force on the acoustic sensor element1.

According to one embodiment, the insulating cap13is formed of electrically insulating material and is dimensioned to provide adequate electrical clearance and creepage distances between the sensor element1and the electrically conducting spring4A to ensure electrical isolation. According to another embodiment, the spring4A is at a pipe electrical potential, and the sensor element1is at an electronic circuit potential, and the insulating cap13provides galvanic isolation to ensure that intrinsic safety requirements are met for circuitry in the transducer assembly50.

According to one embodiment, the transducer assembly50includes an electronic housing mounting flange23that is mounted to the tube4B and that includes a threaded flange portion21adjacent the first tube end7. In this embodiment, the electronic housing mounting flange23is used to mount an electronic housing2adjacent the first tube end7. According to another embodiment, the transducer assembly50includes a sensor support adapter22. The sensor support adapter22includes a printed wiring board26that slides into slots of the adapter22for mounting. In this embodiment, the acoustic sensor element1is mounted on the printed wiring board for mechanical support and electrical connection. The sensor support adapter22is threaded with threads21A that engage the threads21. As thread engagement progresses, the spring4A exerts an increasing force on the acoustic sensor element1and compresses the spring4A, eliminating free play or lost motion in the acoustic waveguide4.

Electrical leads30of the acoustic sensor element1provide an acoustic energy output that is electrical and that couples to electronics. The acoustic energy output on electrical leads30is useful for diagnostic testing of steam traps and other process fluid vessels.

According to one embodiment, the tube4B includes a metal tube having an external diameter of less than 11 millimeters. According to another embodiment, the tube4B includes a tube wall thickness of less than 2.0 millimeter.

The transducer assembly50includes the electronic housing2and a housing cover5. An O-ring6provides a seal between the electronics housing2and the cover5.

The electronic housing2includes frustoconical inner surfaces8,10that have a conic apex12that is common to both frustoconical inner surfaces8,10. A frustoconical outer surface14of the electronic housing mounting flange23is assembled adjacent the frustoconical inner surface10. The transducer assembly50includes a frustoconical washer16that has a frustoconical outer surface18that is assembled adjacent the frustoconical inner surface8. A spring washer (also called a Belleville washer)20is positioned on top of the frustoconical washer16. The threads21A of the sensor support adapter22are threaded onto threads21of the electronic housing mounting flange23, compressing the spring washer20. The arrangement of the frustoconical surfaces8,10,14,18having a common apex12provides a connection between the housing2and the flange23that maintains stable spacing even though the housing2and tube4B are formed of materials with different temperature coefficients of expansion.

An electronics assembly24provides wireless communication through the cover5. A battery27energizes the electronics assembly24. The electronics assembly24includes stored thresholds of acoustic signal level. The stored thresholds are stored in non-volatile memory and are adjustable by wireless communication. The real time levels of acoustic signal level are compared to the respective stored thresholds in order to perform diagnostic decision making in real time. The electronics assembly50also includes a stored identification number or name that is transmitted wirelessly to identify the source of the data or diagnostic decision.

According to one embodiment, the housing2supports an electrical connector32for connection to an external temperature sensor (not illustrated inFIG. 1). In this embodiment, the electronics assembly24makes decisions based on both acoustic signal level and also an external temperature. According to another embodiment, the electronics assembly includes a digital display3that is visible through a window in the cover5.

FIG. 2illustrates a transducer assembly100that is secured to a steam/condensate line150that brings a condensate/steam mixture151to a steam trap152. One or more clamps154secure a foot102of the transducer assembly100to the steam/condensate line150. The clamp or clamps154can be hose clamps, locking pliers, C-clamps or other known types of clamps. As illustrated inFIG. 2, the foot102has a concave rounded surface that is clamped in contact with a convex round outer surface of the steam/condensate line150.

A piping length156between the foot102and the steam trap152is kept short so that a temperature at the foot102is representative of a temperature of the condensate/steam mixture151. A condensate160is separated from the steam and is discharged from the steam trap152. A temperature sensor103is enclosed inside the foot102in a thermowell cavity. The piping length156is sufficiently short that acoustic noise generated by a fluid flow through a valve158in the steam trap152readily couples with low attenuation along the steam/condensate line150from the valve158to the foot102. The foot102of the transducer assembly100is in thermal and acoustic communication with the steam trap152for transducing performance of the steam trap156and for diagnostic testing of the steam trap156such as detection of leaks, plugging and a start-up condition.

The steam trap152couples to the steam/condensate line150. According to one embodiment, the steam/condensate line150carries steam from a steam source (not illustrated inFIG. 2) to a steam utilization device (not illustrated inFIG. 2). Condensate in the steam/condensate line150drains into the steam trap152. Stored condensate164accumulates inside the steam trap152until a sufficient amount of stored condensate164has accumulated to raise a float166and open the valve158. When the valve158opens, condensate164flows into drain line168(as indicated by arrow160) until the float166sinks and closes the valve158with some stored condensate164still present in the steam trap152. The arrangement of the float166, valve158, and stored condensate164traps steam in the steam trap152, while allowing excess condensate to drain. When functioning properly, the steam trap152performs the useful function of draining off undesired excess condensate in the steam/condensate line150, while preventing loss of steam (and an associated loss of energy) through the steam trap152. When the steam trap152malfunctions, there can be a great loss of energy, plugging of the steam/condensate line150with condensate, or other problems.

The foot102of the transducer assembly100is attached to a tube104by a weld106. The tube104has a tube length108. The tube104is welded to an electronic housing mounting flange110by a weld112. According to one embodiment, the tube104has a round cylindrical cross section as illustrated. According to another aspect the tube104has a generally rectangular cross section. The electronic housing mounting flange110supports an electronic housing114. The electronic housing114encloses an acoustic sensor element116. The acoustic sensor element116is acoustically coupled to an end118of the pipe104by a spring120. An electronics assembly122couples by leads124to the acoustic sensor element116and the temperature sensor103. The electronics assembly122communicates using wireless communication signals126with, for example, a remote monitoring station128. A housing cover130is transparent to the wireless communication signals126. According to one embodiment, the housing cover130includes thermoplastic resin. A battery132energizes the electronics assembly122.

The foot102, the tube104and the spring120function as an acoustic waveguide that couples acoustic vibration or an acoustic signal from a mounting surface on steam/condensate line150(at foot102) to the acoustic sensor element116. According to one embodiment, the acoustic vibrations sensed by the acoustic sensor element116are in a range of 30 kHz to 50 kHz. The acoustic vibrations originate in the steam trap152, particularly at the valve158due to gas flow through the valve158. The gas flow through valve158can be steam in the case of a leaky valve, and can be either air or steam in the case of a start-up condition. The electronics assembly122processes acoustic and temperature data from the sensors103,116to calculate diagnostic information concerning the function of the steam trap156. According to one embodiment, the foot102, the clamp154and the steam/condensate line150are wrapped in thermal insulation at the time of installation to reduce a temperature difference between the steam trap152and the temperature sensor103. The operation of the transducer assembly100is described in more detail below by way of an example illustrated inFIG. 3.

FIG. 3illustrates a transducer assembly200. The transducer assembly200includes an acoustic sensor element202. According to one embodiment, the acoustic sensor element202includes a piezoelectric force sensor. According to another embodiment, the acoustic sensor element202includes a capacitive force sensor. According to yet another embodiment, the acoustic sensor element202includes a magnetic force sensor.

The transducer assembly202includes an acoustic waveguide204. The acoustic waveguide204includes a spring204A that rotatably couples to the acoustic sensor element202. The acoustic waveguide204includes a tube204B that has a first tube end206coupled to the spring204A.

The acoustic waveguide204includes a foot204C which provides a coupling region that couples to a second tube end210of the tube204B. The foot204C includes a mounting surface208that is mountable in contact with a fluid conduit212. The foot204C includes an internal thermowell cavity214adjacent the mounting surface208. A temperature sensor216is disposed in the thermowell cavity214and senses a temperature in the internal thermowell cavity214. Space in the thermowell cavity214can be filled with a quantity of heat conducting potting compound215. According to one embodiment, the potting compound215includes a thin layer of inorganic ceramic cement for high temperatures sold by Sauereisen Cements Company of Pittsburgh, Pa. 15238 USA. The heat conducting compound215provides good thermal coupling between the temperature sensor216and the fluid conduit212. The temperature sensor216connects to an output cable218that extends through the tube204B and the first tube end206. According to one embodiment, the temperature sensor216includes a thermistor. According to another embodiment, the temperature sensor216includes a thermocouple junction.

The acoustic waveguide204couples an acoustic vibration from the mounting surface208of the foot204C to the acoustic sensor element202. It will be understood by those skilled in the arts that the tube204B and the foot204C can be formed of a single tube, and in that case there is no joint between the tube204B and the foot204C. According to one embodiment, the acoustic vibration is sensed in the range of 30 kHz to 50 kHz.

According to one embodiment, the tube204B has a length that spaces the acoustic sensor element202a distance away from the foot204C to provide thermal isolation. High temperature at the foot204C, which is typically clamped to a steam trap drain line, is attenuated along the length of the tube204B such that the acoustic sensor element202has a lower temperature that is near the temperature of the surrounding ambient air. The tube204B is hollow, as illustrated, which reduces thermal conduction along the length of the tube204B.

According to one embodiment, the spring204A is positioned adjacent the acoustic sensor element202by an insulating cap220that provides a rotatable joint between the spring204A and the acoustic sensor element202. The insulating cap220couples the acoustic vibration from the spring204A to the acoustic sensor element202. The insulating cap220positions the spring204A in a position where it exerts a force on the acoustic sensor element202. According to one embodiment, the insulating cap220is formed of electrically insulating material and is dimensioned to provide adequate electrical clearance and creepage distances between the sensor element202and the electrically conducting and spring204to ensure electrical isolation. According to another embodiment, the spring204A is at a pipe electrical potential, and the sensor element202is at an electronic circuit potential, and the insulating cap220provides galvanic isolation to ensure that intrinsic safety requirements are met for circuitry in the transducer assembly200.

According to one embodiment, the transducer assembly200includes an electronic housing mounting flange223that is mounted to the tube204B and that includes a threaded flange portion224adjacent the first tube end206. In this embodiment, the electronic housing mounting flange223is used to mount an electronic housing (not illustrated inFIG. 3) adjacent the first tube end206.

According to another embodiment, the transducer assembly200includes a sensor support adapter222. The sensor support adapter222includes a printed wiring board226that slides into slots228of the adapter222for mounting. In this embodiment, the acoustic sensor element202is mounted on the printed wiring board for mechanical support and electrical connection. The sensor support adapter222is threaded with threads221that engage the threaded flange portion224.

Electrical leads230of the acoustic sensor element202and the output cable218of the temperature sensor216provide acoustic energy and temperature outputs and couple to electronics (not illustrated inFIG. 3). The temperature and acoustic energy outputs are useful for diagnostic testing of steam traps and other process fluid vessels. The sensor support adapter222includes a threaded support end225with the threads221that engage the threaded flange portion224. As thread engagement progresses, the spring204A exerts an increasing force on the acoustic sensor element202and compresses the spring204A, eliminating free play or lost motion in the acoustic waveguide204.

According to one embodiment, the tube204B includes a metal tube having an external diameter of less than 11 millimeters. According to another embodiment, the tube204B includes a tube wall thickness of less than 2.0 millimeter. The assembly and operation of the transducer assembly200is described in more detail below in connection with an example illustrated inFIG. 4.

FIG. 4illustrates an exploded view of a transducer assembly300. The transducer assembly300includes a waveguide that includes a spring204A, a tube204B and a foot204C as illustrated inFIG. 3. The transducer assembly300includes an acoustic sensor element202, a sensor support adapter222, and an electronic housing mounting flange223as illustrated inFIG. 3. Reference can be made toFIG. 3and the description ofFIG. 3for a description of the assembly and function of components that are common toFIG. 3andFIG. 4. The transducer assembly300includes an electronic housing302and a housing cover304. An O-ring306provides a seal between the electronics housing302and the cover304.

The electronic housing302includes frustoconical inner surfaces308,310that have a conic apex312that is common to both frustoconical inner surfaces308,310. A frustoconical outer surface314of the electronic housing mounting flange223is assembled adjacent the frustoconical inner surface310. The transducer assembly300includes a frustoconical washer316that has a frustoconical outer surface318that is assembled adjacent the frustoconical inner surface308. A spring washer (also called a Belleville washer)320is positioned on top of the frustoconical washer316. The sensor support adapter222is threaded onto threads322of the electronic housing mounting flange223, compressing the spring washer320. The arrangement of the frustoconical surfaces308,310,314,318having a common apex312provides a connection between the housing302and the flange223that maintains stable spacing even though the housing302and tube204B are formed of materials with different temperature coefficients of expansion.

An electronics assembly324provides wireless communication through the cover304. In other respects, the transducer assembly300is similar to the transducer assembly100inFIG. 2. A battery326energizes the electronics assembly324. The electronics assembly324includes stored thresholds of temperature and acoustic signal level. The stored thresholds are stored in non-volatile memory and are adjustable by wireless communication. The real time levels of temperature and acoustic signal level are compared to the respective stored thresholds in order to perform diagnostic decision making real time temperate and level data, decision, or both are transmitted by wireless communication. The electronics assembly324also includes a stored identification number or name that is transmitted wirelessly to identify the source of the data or diagnostic decision. The electronics assembly324includes a digital display303that is visible through a window in the cover304.

FIG. 5Aillustrates temperature sensing locations on a transducer assembly400. The transducer assembly400includes a foot408secured to a condensate drain pipe402by clamps404,406. During normal operation, the condensate drain pipe402carries heated condensate. Heat flows from the condensate drain pipe402through the transducer assembly400to the surrounding ambient, which is at a lower temperature. There is therefore a temperature gradient in the transducer assembly400. The temperature gradient is beneficial in that it provides a lower operating temperature for an electronics assembly (such as assembly122inFIG. 2). The temperature gradient is problematic in that it becomes difficult to find a location on the transducer assembly400where a temperature sensor can be located to obtain a temperature reading from which a temperature of the condensate drain pipe can be inferred accurately.

For purposes of measuring temperatures during a design test, thermocouple junctions are compressed under the clamp404at locations indicated by TOE near a toe end of the foot408. Thermocouple junctions are compressed under the clamp406at locations indicated by HEEL at a heel end of the foot408.

Readings from the thermocouple junctions under the toe clamp404are averaged to provide a recorded TOE temperature reading as illustrated inFIG. 5B. Readings from the thermocouple junctions under the heel clamp406are averaged to provide a recorded HEEL temperature reading as illustrated inFIG. 5B.

Two thermocouple junctions are attached to the condensate drain pipe402at locations indicated by PIPE. Readings from the thermocouple junctions at the pipe locations are averaged to provide a PIPE temperature reading as indicated inFIG. 5B. A SENSOR which is part of the transducer assembly400provides a SENSOR temperature reading inFIG. 5B.

FIG. 5Billustrates a graph of temperatures for the temperature sensing locations ofFIG. 5Aduring a design test. As illustrated inFIG. 5B, the condensate drain pipe is heated starting at time zero. After approximately 100 minutes from time zero, recorded temperatures stabilize. After approximate 115 minutes from time zero, the foot408and the adjacent portion of the condensate drain pipe402are wrapped with thermal insulation. After approximately 200 minutes from time zero, recorded temperatures again stabilize. It can be seen by inspection ofFIG. 5B, that the temperature recorded at location TOE is closest to the PIPE temperature. Based on the these results, the temperature sensor (such as temperature sensor216inFIG. 3) which is used in the transducer assembly400is advantageously placed near a TOE end of a foot408in order to provide improved accuracy of temperature reading. Based on these test results, thermal insulation can be wrapped around the foot408and adjacent condensate drain pipe402to reduce a temperature difference between the PIPE and the SENSOR, improving temperature measurement accuracy as illustrated inFIG. 5B.

According to one embodiment, temperature errors that remain in the temperature reading of the sensor are corrected electronically as described in more detail below in connection withFIG. 9.

FIG. 6illustrates a rotation of a main antenna lobe502of a transducer assembly504. The transducer assembly504includes an electronics housing506(similar to electronics housing302inFIG. 4) and an electronics assembly508(similar to electronics assembly324inFIG. 4). The electronics assembly508is mounted to the electronics housing508by mounting screws510,512. The electronics housing506(and the attached electronics assembly508) are rotatable as indicated by arrow514. A directional antenna516on the electronics assembly508produces the main antenna lobe502. That directional antenna516can also produce less salient antenna lobes. Rotation of the electronic housing506rotates the main antennal lobe502, allowing an operator to aim the main antenna lobe502toward an antenna520of a remote monitoring station522.

As illustrated above inFIG. 4, an electronic housing302is rotatable on frustoconical bearing surfaces314,318. A spring washer320provides a compressive force to the frustoconical bearing surfaces314,318. According to one embodiment, an electronic data display303is mounted to the electronics assembly324. The rotatable frustoconical bearing surfaces314,318are rotatable to orient the electronic data display303in a preferred direction for convenient reading by field service personnel. The rotatability of the display303overcomes a problem in which an electronic data display in a fixed position may by installed so that the electronic data display is not oriented for convenient reading.

Normally, the tube204B (FIGS. 3-4) is installed in a horizontal orientation to avoid heat from a steam trap convecting toward the electronics. The electronic data display303mounted on the circuit board can be oriented for proper reading by rotating the electronics housing302. According to one aspect, the electronic data display303is oriented on the electronics assembly324in relationship to an antenna on the electronics assembly324so that the antenna is preferentially oriented for transmission and reception when the display303is properly oriented for reading. Typically, the display303is oriented to read from left to right horizontally for reading of English letters and numbers by service personnel.

FIGS. 7A and 7Billustrate torque required for rotation as a function of temperature for rotation of the main antenna lobe502. The torque is controlled by the compressive force of the spring washer320to provide torques in the range of 8 to 22 foot pounds. According to one aspect, the adjustable, controlled compressive force provided by the spring washer320in combination with the use of frustoconical bearing surfaces308,310,314,316as rotational sliding surfaces provides for a desired controlled torque that is also adjustable. The torque range (in both clockwise and counterclockwise directions) is sufficiently high that vibration will not change the direction of the main antenna lobe502. The torque range is sufficiently low (in both clockwise and counterclockwise directions) that the main antenna lobe502can be easily rotated by hand. The torque range is sufficiently stable over a temperature range of −40 degrees Centigrade to +80 degrees Centigrade because of the use of frustoconical bearing surfaces308,310and the spring washer320.

FIG. 8illustrates a circuit assembly700for use in a transducer assembly such as transducer assembly300inFIG. 4or transducer assembly50inFIG. 1. The circuit assembly700couples to a temperature sensor702which provides temperature data, and to an acoustic sensor element704that provides acoustic data. According to one embodiment illustrated inFIG. 1, the temperature sensor704is external. According to another embodiment illustrated inFIG. 3, the temperature sensor704is part of the transducer assembly. The circuit assembly700couples to a battery706that energizes the circuit assembly700.

The circuit assembly700includes an antenna708for communication with an antenna710that couples to a monitoring station712. According to one aspect, the antenna708comprises a directional antenna. According to another aspect, the antenna708comprises a pattern of printed conductors on a printed circuit board.

The circuit assembly comprises a processor circuit720. According to one aspect, the processor circuit720makes decisions as described in more detail below in connection with a logic flow chart inFIG. 9. The processor circuit provides decision outputs to a communication circuit722. The communication circuit722encodes the decisions and stored identification data according to a standard communication protocol and transmits the decisions and identification data using the antenna708.

Threshold settings for decision making and an identification number for the circuit assembly700are stored in a non-volatile storage circuit724. According to one aspect, the non-volatile storage circuit724comprises EEPROM memory. As part of commissioning or startup operations, the monitoring station712transmits threshold setting to the circuit assembly700for storage in the non-volatile storage circuit724.

FIG. 9illustrates a diagnostic flow chart that illustrates an example of decisions that can be performed by the processor circuit720ofFIG. 8. Processing begins at START802and continues along a line804to an action block801. At action block801, an optional temperature error correction algorithm is performed. After optional completion of the temperature error correction algorithm, processing continues along line803to decision block806.

According to one embodiment, the temperature error correction algorithm in the action block801performs a static error correction routine:
TPC=TW+(K×(TW−TC))
where:
TPCrepresents a corrected pipe temperature;
TWrepresents a sensor temperature;
TCrepresents a circuit board temperature; and
K represents a static correction coefficient determined by tests.
According to another embodiment, the temperature error correction algorithm in the action block801performs a dynamic error correction routine:

TPC=TW+(K×(TW-TC))+M×ⅆ(TW-TC)ⅆt
where:
TPCrepresents a corrected pipe temperature;
TWrepresents a sensor temperature;
TCrepresents a circuit board temperature;
K represents a static correction coefficient determined by tests;
M represents a dynamic correction coefficient determined by tests; and
d/dt represents mathematical differentiation.

At decision block806, temperature data is compared to a stored temperature threshold. If the temperature is higher than the stored temperature threshold, then processing continues along line808to a decision block810. If the temperature is lower than the stored temperature threshold, then processing continues along line812to decision block814.

At decision block814, if acoustic noise is higher than a stored acoustic noise threshold, then processing continues along line816to an action block818. At action block818, a decision is recorded that the monitored device is in a start up condition or leaking air. If acoustic noise is lower than the stored acoustic noise threshold, the processing continues along line820to an action block822. At action block822, a decision is recorded that the monitored device is jammed or not operating.

At decision block810, if acoustic noise is higher than the stored acoustic noise threshold, then processing continues along line830to an action block832. At action block832, a decision is recorded that the monitored device is leaking steam. If acoustic noise is lower than the stored acoustic noise threshold, then processing continues along line834to an action block836. At action block836, a decision is recorded that the monitored device is in normal operation.

At action block840, a most recent decision from one of actions blocks818,822,832or836is transmitted to a communication circuit for wireless transmission along with an identification number. After transmission, processing continues along line842to action block844. At action block844, decisions in blocks832,836,818,822are reset, and processing returns to start802.

FIG. 10illustrates an alternative embodiment of a rotatable acoustic coupler900. The rotatable acoustic coupler900comprises a central shaft902and a socket904. The central shaft902has a first shaft end906that is acoustically coupled to an acoustic sensor element908. The central shaft902has a second shaft end910that is coupled to the socket904. A length of the central shaft between the first shaft end906and the socket904is sufficiently long to permit flexing of the central shaft902to allow for small misalignments between the central shaft902and the socket904. The socket904has a tapered opening912to allow for small misalignments.

According to one embodiment, the socket904is held in placed in a tube914by retainer rings916,918. According to another embodiment, the tapered opening912of the socket904tapers to an interference fit with the central shaft902. The socket904contacts the central shaft902to provide acoustic coupling between the tube914and the central shaft902. According to one aspect, the socket904is formed of an elastic material to provide contact. According to another aspect, the socket904is formed of heat-stabilized type6polyamide available from Professional Plastics Inc., Fullerton, Calif., USA 92831. The gripping joint between the central shaft902and the socket904is rotatable.

According to one aspect the socket904includes one or more radial openings920through which electrical leads922of a temperature sensor can be threaded.

FIG. 11Aillustrates a graph of an exemplary temperature error without use of error correction routines. As shown in the graph inFIG. 11A, uncompensated static temperature errors are approximately 12 degrees Centigrade without the use of insulation, and approximately 7 degrees Centigrade with the use of insulation. Uncompensated dynamic temperature errors range up to approximately 14 degrees without the use of insulation and 7 degrees with the use of insulation.

FIG. 11Billustrates a graph of exemplary temperature error using a static error correction routine. As shown in the graph inFIG. 11B, static compensated static temperature errors are approximately 3 degrees Centigrade without the use of insulation, and approximately −2 degrees Centigrade with the use of insulation. Static compensated dynamic temperature errors range up to approximately 12 degrees without the use of insulation and −2 degrees with the use of insulation.

FIG. 11Cillustrates a graph of temperature error using a dynamic error correction routine. As shown in the graph inFIG. 11C, dynamically compensated static temperature errors are approximately 2 degrees Centigrade without the use of insulation, and approximately −2.5 degrees Centigrade with the use of insulation. Dynamically compensated dynamic temperature errors range up to approximately −2 degrees without the use of insulation and −2.5 degrees with the use of insulation.

The data inFIGS. 11A, B, C illustrate that static and dynamic compensation can reduce temperature measurement error significantly. According to one aspect, the temperature compensation is adjustable by service personnel at the installation site to adapt to the use or lack of use of insulation in the installation.

FIG. 12illustrates a transducer assembly950coupled to an outlet of an actuatable control valve960. The control valve960includes a valve seat961and a valve plug962that is movable relative to the valve seat961. According to one embodiment, when the control valve960is nominally closed, but there is leakage past the seal between the valve seat961and the valve plug962, acoustic noise is generated by the leakage that is sensed and diagnosed by the transducer assembly950. According to another embodiment, when control valve960operates normally with liquid flow, but the valve is instead filled with air, and air is flowing through the valve960, acoustic noise is generated by the air flow and is sensed and diagnosed by the transducer assembly950.

FIG. 13illustrates a transducer assembly970mounted to a flow control arrangement980that includes a flow restriction981. According to one aspect, a high pressure side of process cooling system provide liquid refrigerant984to a flow restriction981that comprises a capillary tube as illustrated. As the liquid refrigerant984flows along the flow restriction981toward a low pressure side986of the process cooling system, the pressure of the liquid refrigerant984drops, and the refrigerant vaporizes into a gas as it exits the flow restriction981into the low pressure side986, providing cooling. In the event that the process cooling system leaks refrigerant, and gas is flowing through the flow restriction981instead of liquid, acoustic noise is generated. According to one aspect, the transducer assembly970senses the associated acoustic noise and diagnoses the loss of refrigerant. According to another aspect, in the event the flow restrictor981is plugged, the normal noise associated with liquid flow is lost, and the transducer assembly970diagnoses plugging of the flow restriction981.

Various aspects shown in theFIGS. 1-13can be appropriately combined. According to one embodiment, the acoustic sensor202includes a piezoelectric element that includes a piezoelectric crystal disc that is mounted in a metal can with a force sensitive surface of the piezoelectric crystal disc facing the spring204A as illustrated. The piezoelectric crystal disc acts as a diaphragm and receives sound from the spring204A, the surrounding air, or both. The compression of the spring204A maintains contact between the spring204A and the piezoelectric crystal disc. The acoustic sensor202and the spring204A provide filtering of the acoustic signal. According to one embodiment, circuitry in the electronics assembly324is tuned to a resonant frequency range of filtering provided by the spring204A and the acoustic sensor202. While a coil spring is illustrated inFIGS. 2-4, it will be understood by those skilled in the art that other shapes such as the shaft shown inFIG. 10can be used to conduct acoustic signals and maintain contact with an acoustic sensor element.

It is to be understood that even though numerous aspects of various embodiments of the invention have been set forth in the foregoing description, this disclosure is illustrative only, and changes may be made in form and detail, without departing from the scope and spirit of the present invention. The present invention is not limited to the specific transducer assemblies shown herein and is applicable to other transducer assemblies as well as other pressure vessels.