A process fluid temperature measurement system is provided. The process fluid temperature measurement system includes a thermowell configured to couple to a process fluid conduit and extend through a wall of the process fluid conduit. The process fluid temperature measurement system also includes a temperature sensor assembly disposed within the thermowell, the temperature sensor assembly including a sensor capsule having at least one temperature sensitive element disposed therein. The temperature sensor assembly also includes a vibration sensor coupled to the sensor capsule, the vibration sensor being configured to produce a vibration signal in response to detected vibration. The process fluid temperature measurement system further includes transmitter circuitry coupled to the vibration sensor and configured to receive the vibration signal and produce an output based on the received vibration signal.

BACKGROUND

The present invention relates generally to process sensor systems, and more particularly to thermowell sensor housings for fluid sensors in industrial process monitoring systems.

Many industrial processes convey process fluids through pipes or other conduits. Such process fluids can include liquids, gasses, and sometimes entrained solids. These process fluids may be found in any of a variety of industries including, without limitation, hygienic food and beverage production, water treatment, high-purity pharmaceutical manufacturing, chemical processing, the hydrocarbon fuel industry, including hydrocarbon extraction and processing as well as hydraulic fracturing techniques utilizing abrasive and corrosive slurries.

Industrial process transmitters and sensor assemblies are used to sense various characteristics of process fluids flowing through a conduit or contained within a vessel, and to transmit information about those process characteristics to a control, monitoring and/or safety system remotely located from the process measurement location. Sensor assemblies may sense a variety of process parameters, including pressure, temperature, pH, or flow rate. Process transmitters are typically electrically connected sensor assemblies via sensor wires used to transmit current- or voltage-based analog sensor output signals reflecting at least one such process parameter. Each transmitter reads these sensor output signals and converts them into measurement of the process parameter. Finally, the transmitter sends the information to the control system.

It is common to place a temperature sensor within a thermowell, which is then inserted into the process fluid flow through an aperture in the conduit. When being inserted into the process fluid, the thermowell may experience dynamic stress imposed by varying conditions of process fluid flow. To aid in design, wake frequency calculations are typically performed for thermowell installations in order to keep the thermowell from being exposed to process conditions that would ultimately lead to fatigue due to vibration. However, this approach may not always be practical in that process characteristics or thermowell structure can change over time, resulting in premature failure. Accordingly, thermowells, while useful for providing a process seal for temperature sensors, have a number of limitations.

SUMMARY

A process fluid temperature measurement system is provided. The process fluid temperature measurement system includes a thermowell configured to couple to a process fluid conduit and extend through a wall of the process fluid conduit. The process fluid temperature measurement system also includes a temperature sensor assembly disposed within the thermowell, the temperature sensor assembly including a sensor capsule having at least one temperature sensitive element disposed therein. The temperature sensor assembly also includes a vibration sensor coupled to the sensor capsule, the vibration sensor being configured to produce a vibration signal in response to detected vibration. The process fluid temperature measurement system further includes transmitter circuitry coupled to the vibration sensor and configured to receive the vibration signal and produce an output based on the received vibration signal.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

As set forth above, wake frequency calculations may be performed for thermowell installations to aid in its design. These calculations are implemented generally in order to keep the thermowell from being exposed to process conditions that would ultimately lead to fatigue due to vibration. Such systems generally utilize a process condition standard, wherein typical process conditions are loaded into the calculation at the time of calculating the wake frequency from varying process fluid flow.

The wake frequency calculation described above generally relies upon the assumption that process conditions within thermowell installations do not change over time. However, over time, changes in process characteristics or thermowell structure may occur, resulting in calculation error and/or premature failure. Additionally, when a process condition changes, vortices may be created within the process fluid. Vortices produced in the process fluid, if significant, can fatigue and/or fracture components of the thermowell installation. For example, if the created vortices reach a vortex-shedding frequency, that is, a frequency level capable of causing potential damage to the thermowell, the thermowell may fatigue, resulting in permanent damage. Further, if vortices reach the natural frequency of the thermowell, the thermowell may be significantly fatigued to the point where fracture may occur. The natural frequency may be specific to the particular type of thermowell employed and can thus be a broad range of different vibrational frequencies. Additionally, in some instances, the magnitude of the vortices is at a level significant enough to cause damage to components of the thermowell installation.

Implementing a sensor within the thermowell to sense vibration is difficult due to the high temperature conditions that exist within the conduit. Ideally, a vibration sensor would be mounted in a transmitter housing that is attached to the thermowell to allow for more measurement flexibility. However, in many applications, the transmitter is remotely mounted from the thermowell.

FIG.1is a diagrammatic view of a process fluid temperature measurement system with which embodiments of the present invention are particularly applicable. As illustrated, system100generally includes a thermowell102configured to couple to a process fluid conduit104and extend through a wall106of the process fluid conduit. Thermowell102is further configured to contact process fluid108within process fluid conduit104in order to obtain measurements of the process fluid, such as temperature. Thermowell102has a temperature sensor assembly110generally disposed therein. The temperature sensing assembly110comprises a sensor capsule112. The term “capsule” is not intended to imply any particular structure or shape and can thus be formed in a variety of shapes, sizes and configurations. Sensor capsule112generally includes one or more temperature sensitive elements (not shown), such as resistance temperature devices (RTDs) or thermocouples. Sensors within sensor capsule112are electrically connected to transmitter circuitry114within housing116, which is configured to obtain one or more temperature measurements from sensor capsule112. As shown, in one embodiment, sensor capsule112is electrically connected to transmitter circuitry114via measurement wiring130, which can include a two or more conductor cable. Also, as shown, transmitter circuitry114is electrically connected to a host system within a control room124via a transmission loop118illustrated as a wire cable. Alternatively, transmission loop118may be a two or more wire cable, a fiber optic cable, or a wireless link.

Temperature sensor assembly110also includes vibration sensor120coupled to sensor capsule112. Vibration sensor120is generally configured to sense vibration of thermowell102in response to conditions of the process fluid and produce a vibration signal in response to the detected vibration. For example, if vortices are produced within the process fluid and cause vibration of the thermowell, vibration sensor120is configured to sense the vibration and produce a vibration signal indicative of the vibration of the thermowell. As shown inFIG.1, in one embodiment, vibration sensor120is disposed on sensor capsule112and located at the base of thermowell102. By disposing vibration sensor120at the base of thermowell102, vibration of thermowell102may be sensed at a point where fracture is likely to occur as a result of the vibration. Alternatively, vibration sensor120may be positioned at other locations of the thermowell such that vibration may be detected. Further, while it is shown inFIG.1that vibration sensor120is disposed in sensor capsule112, vibration sensor120may, in other embodiments, be embedded within the thermowell and disposed proximate the sensor capsule.

FIG.2is a block diagram of circuitry within housing216of process fluid temperature measurement system200, with which embodiments of the present invention are particularly applicable. System200bears some similarities to system100(shown inFIG.1) and like components are numbered similarly. System200can also include other items as well, as indicated by block236. System200includes communication circuitry222coupled to controller224. Communication circuitry222can be any suitable circuitry that is able to convey information regarding the process fluid temperature and/or vibration of the thermowell, such as thermowell102(shown inFIG.1). Communication circuitry222allows process fluid temperature measurement system200to communicate a process fluid temperature output over a process communication loop or segment, such as transmission loop118(shown inFIG.1). Suitable examples of process communication loop protocols include the 4-20 milliamp protocol, Highway Addressable Remote Transducer (HART®) protocol, FOUNDATION™ Fieldbus Protocol, and the WirelessHART protocol (IEC 62591). Communication circuitry222also allows vibration sensor220within temperature sensor assembly210to communicate vibration signals in response to thermowell vibration over a process communication loop or segment, such as transmission loop118and/or measurement wiring130.

System200also includes power supply module226that provides power to all components of system200as indicated by arrow228. In embodiments where system200is coupled to a wired process communication loop, such as a HART® loop or FOUNDATION™ Fieldbus segment, power module226may include suitable circuitry to condition power received from the loop or segment to operate the various components of system200. Accordingly, in such wired process communication loop embodiments, power supply module226may provide suitable power conditioning to allow the entire device to be powered by the loop to which it is coupled. In other embodiments, when wireless process communication is used, power supply module226may include a source of power, such as a battery and suitable conditioning circuitry.

Controller224is communicatively coupled to communication circuitry222and includes any suitable arrangement that is able to generate a temperature output using measurements from sensor(s) within sensor capsule212. In one example, controller224is a microprocessor. Additionally, controller224includes any suitable arrangement that is able to generate a vibration output indicative of thermowell vibration detected and measured from vibration sensor220, such as a vibration that meets the natural frequency of the thermowell. The output may be provided to a control room, such as control room124(shown inFIG.1). Alternatively, or additionally, the output may be provided to an operator, machine, or other device. In one embodiment, the output is a visual output indicative of thermowell vibration. However, in other embodiments, the output may be an auditory output.

Measurement circuitry230is coupled to controller224and provides digital indications with respect to measurements obtained from sensors232and vibration sensor220. Measurement circuitry230can include one or more analog-to-digital converters and/or suitable multi-plexing circuitry to interface the one or more analog-to-digital converters to vibration sensor220. Additionally, measurement circuitry230can include suitable amplification and/or linearization circuitry as may be appropriate for the various types of vibration sensors and other sensors employed.

Temperature sensor assembly210illustratively includes sensor capsule212, vibration sensor220, and can include other items as well, as indicated by block234. Vibration sensor220is coupled to the electronic circuitry of system200and is used to sense thermowell vibration in response to process conditions within the process fluid and produce a vibration signal in response to detected vibration of the thermowell. For example, if vortices produced by the process fluid within the conduit meet a particular frequency or magnitude, a vibration signal is produced and communicated to the electronic circuitry of system200to produce an output based on the vibration signal indicative of the vibration. In one embodiment, a vibration signal is produced only when a frequency threshold is met by the thermowell vibration. The frequency threshold may comprise a broad range of frequency signals indicative of thermowell vibration. For example, the frequency threshold may be the vortex-shedding frequency, that is, a frequency level capable of causing potential damage to the thermowell. Alternatively, or additionally, the frequency threshold may be the natural frequency of the thermowell under vibration or may be an alternative vibration frequency capable of being detected by vibration sensor220.

FIG.3is a diagrammatic view of a temperature sensor assembly in accordance with an embodiment of the present invention. Assembly310bears some similarities to temperature sensor assembly110(shown inFIG.1) and like components are numbered similarly. In particular, temperature sensor assembly310includes sensor capsule312that is urged against an outer surface of the process fluid temperature measurement system via adapter322. As shown inFIG.3, adapter322is a threaded adapter. However, in alternative embodiments, adapter322may be a spring adapter or other suitable mechanical element. Additionally, sensor capsule312is electrically coupled to electronic circuitry of the process fluid temperature measurement system in order to generate an output indicative of process fluid temperature and/or detected vibration. Sensor capsule312is electrically coupled to electronic circuitry via measurement wiring330.

Sensor assembly310includes one or more temperature sensor element324, such as one or more resistance temperature devices (RTDs). Temperature sensor element324is coupled to sensor capsule312, which is configured to obtain one or more temperature measurements within the process fluid conduit. The one or more temperature measurements are responsively sent as signals to the electronic circuitry of the process fluid temperature measurement system (not shown) to be produced as a temperature measurement output.

Also included in temperature sensor assembly310is vibration sensor320. Vibration sensor320is coupled to sensor capsule312and is configured to produce a vibration signal in response to detected vibration of the thermowell. As shown inFIG.3, vibration sensor320is disposed on sensor capsule312near the base of the sensor capsule, and accordingly, near the base of the thermowell. However, in other embodiments, vibration sensor may be disposed on different areas of sensor capsule312or disposed within the thermowell proximate sensor capsule312. Vibration sensor320may alternatively be embedded at other locations of the thermowell where vibration may be detected. For example, vibration sensor320may be placed in a housing (not shown) in installations where the electronic circuitry is coupled to adapter322.

By placing vibration sensor320at the base of the thermowell, where the majority of vibrational stress is located and where fracture is likely to occur, vibration sensor320may sense certain vibrational frequencies and magnitudes that could be potentially damaging to the thermowell, for example a vortex-shedding frequency produced by process fluid within the conduit. In response to detected vibration, vibration sensor320may provide a vibration signal to be used to provide an output. Additionally, embodiments described herein may also sense different vibrational frequencies of the thermowell, such as when the vibration equates to the natural frequency of the thermowell or an alternative frequency. In one embodiment, a vibration signal is produced only when the detected vibration meets a frequency threshold.

Vibration sensor320is further configured to sense vibration at an initial frequency, corresponding to normal process fluid flow. When process conditions change and cause significant vibration to the thermowell, vibration sensor320detects the vibration at the higher harmonic frequency, indicative of the vibration. In this way, vibration sensor320can sense vibration at a first frequency and sense vibration at a higher harmonic frequency corresponding to a vibration of the thermowell, the higher harmonic frequency being indicative of a different vibration state. For example, in one embodiment, the higher harmonic frequency detected may correspond to a change in vibration state from an in-line to a transverse direction. When the vibration state undergoes this transition, indicative of thermowell vibration, vibration sensor320may detect the transition to the transverse direction and produce a vibration signal in response.

Vibration sensor320is configured to produce a vibration signal over measurement wiring330indicative of detected vibration. In one embodiment, vibration sensor320includes a piezoelectric material, for example a piezoelectric film. When vibration of the thermowell occurs within the process fluid temperature measurement system, the piezoelectric material will stress in response to the thermowell under vibration, causing it to be excited and couple noise along measurement wiring330at the frequency of the detected vibration. The signal corresponding to the frequency of the detected vibration is, in turn, received by electronic circuitry (not shown) to produce an output indicative of the vibration.

In another embodiment, vibration sensor320includes a triboelectric mechanism, for example a triboelectric wire. When vibration of the thermowell occurs within the process fluid temperature measurement system, two insulators included within the triboelectric mechanism will responsively rub against one another, developing a charge. As vibration of the thermowell increases in magnitude and/or frequency, the rate at which the two insulators move increases, thereby generating a higher charge quantity sufficient to produce a signal indicative of the detected vibration.

FIGS.4A-4Billustrate a schematic diagram of a vibration sensor for the process fluid temperature measurement system ofFIG.1in accordance with an embodiment of the present invention. As shown inFIGS.4A-4B, vibration sensor420illustratively includes a piezoelectric material. In another embodiment, however, vibration sensor420may include a triboelectric mechanism, or other sensor capable of detecting vibration of a thermowell within the process fluid temperature measurement system.

FIG.4Aparticularly illustrates vibration sensor420coupled to existing measurement wiring of the process fluid temperature measurement system (not shown), and resistor422. Resistor422may be, for example, a resistance temperature device (RTD). As shown inFIG.4A, a4wire RTD is utilized. However, in other embodiments, resistor422may be a3wire RTD. Because temperature changes slowly over time in a process fluid conduit, temperature signals acquired by sensors within the sensor capsule are nearly direct current (DC) signals. In contrast, vibration detected by thermowells within the process fluid temperature measurement system and the vibration signals produced by vibration sensor420are presented as an alternating current (AC) signal. The difference in signal production between vibration sensor420and sensors within the sensor capsule allows the electronic circuitry within the temperature measurement system to distinguish measurements and signal outputs for both the one or more temperature sensor elements and vibration sensor420. In this way, vibration sensor420may produce a vibration signal along the existing measurement wiring typically used for the one or more temperature sensor element.

FIG.4Bparticularly illustrates vibration sensor420coupled to separate measurement wiring of the process fluid temperature measurement system, and resistor422. Resistor422may be, for example, a resistance temperature device (RTD). In this example, a3wire RTD is utilized. As shown, a separate wire may couple vibration sensor420to electronic circuitry within the temperature measurement system (not shown). Because the vibration signal produced by vibration sensor420is generally low in magnitude, the use of additional wiring may be utilized to eliminate the possibility of the vibration signal from being impacted by a low impedance from the signals produced by sensors within the sensor capsule. In this way, vibration sensor420may couple to measurement wiring separate from the measurement wiring used for the one or more temperature sensor element.

FIG.5is a chart showing thermowell tip displacement as velocity of process fluid flow varies. The data shown inFIG.5is illustrative of a condition when process fluid is flowing. The data shows a difference between a first vibration state, as indicated at reference numeral502, and a second vibration state, as indicated at reference numeral504, with respect to process fluid velocity. As shown, as fluid velocity increases, thermowell tip displacement generally increases, indicative of a change in vibration state. For example, when the velocity of process fluid flow reaches 15 ft/s, the conversion of vibration state from an in-line to transverse direction is shown. The sudden shift in vibration state in turn significantly increases thermowell tip displacement, thereby increasing thermowell vibration and producing a vibration at a higher harmonic frequency. The change in thermowell vibration, corresponding to a different vibration state, is therefore detectable by a vibration sensor, such as vibration sensor320described above with regard toFIG.3. Additionally, while the change of vibration state is illustratively shown at 15 ft/s, it is expressly contemplated that the change in vibration state may occur at varying process fluid velocity, and such a conversion may be detected by vibration sensor320.

FIGS.6A-6Fillustrate a series of frequency domain plots at various process fluid flow rates for the signal output of a vibration sensor consistent with an embodiment of the present invention. The data shown inFIGS.6A-6Fare illustrative of a condition when process fluid flow is flowing at varying flow rates. As shown, as the flow rate increases, the vibration magnitude at the natural frequency of the thermowell increases. For example, as shown inFIG.6A, the signal output at a flow rate of 5 feet per second (ft/sec) is indicated generally at reference numeral602. As the flow rate increases, for example to 7 ft/sec, as shown inFIG.6B, the vibration magnitude and output signal of the vibration sensor increases, indicated generally by reference numeral604. As flow rate continues to increase, the vibration magnitude at the natural frequency increases, and therefore the signal output by the vibration sensor responsively increases. As shown generally inFIGS.6C-6Fat reference numerals606-616, the output signal of the vibration sensor corresponding to a higher vibration magnitude at the natural frequency increases with an increasing flow rate, for example to 10 ft/sec, 15 ft/sec, and 17 ft/sec. Finally, as shown inFIG.6F, the magnitude of vibration detected and the output signal are most significant, indicated by reference numerals614and616, corresponding to, respectively, 1 mV and 5 mV at a flow rate of 20 ft/sec. Additionally, while varying flow rates of 5 ft/sec, 7 ft/sec, 10 ft/sec, 15 ft/sec, and 20 ft/sec are used in this example, it is expressly contemplated that the detection of thermowell vibration and production of a vibration signal output may occur at different process fluid flow rates.