INDUSTRIAL PROCESS DEVICE UTILIZING

PIEZOELECTRIC TRANSDUCER

BACKGROUND OF THE INVENTION

The present invention relates to industrial process devices of the type used to couple to industrial process control and monitoring systems.

In industrial settings, control systems are used to monitor and control inventories of industrial and chemical processes, and the like. Typically, a control system performs these functions using field devices distributed at key locations in the industrial process and coupled to the control circuitry located in a control room by a process control loop. The term "field device" refers to any device that performs a function in a distributed control or process monitoring system, including all devices used in the measurement, control and monitoring of industrial processes.

Some field devices include a process variable sensor. Typically, the transducer transforms an input into an output having a different form. Types of transducers include various analytical equipment, pressure sensors, thermistors, thermocouples, strain gauges, flow transmitters, positioners, actuators, solenoids, indicator lights, and others. Other field devices include a control element and are used to control the industrial process. Examples of such process devices include valve controllers, valve position controllers, heater controllers, pump controllers, etc.

In many process installations, process devices experience pulsations. The pulsations can occur during normal operation of the process.

SUMMARY A process device for coupling to an industrial process for use in monitoring or controlling the process includes a device housing configured to physically couple to the industrial process. A process variable sensor is configured to measure a process variable and measurement circuitry coupled to

the process variable sensor provides an output related to the sensed process variable. A piezoelectric transducer provides an electrical output related to pressure pulsations in the industrial process. Electrical circuitry in the housing includes an input configured to receive the electrical output from the piezoelectric sensor. In one configuration, the electrical output provides power to the process device.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a simplified diagram of a process monitoring or control system for monitoring or controlling an industrial process. Figure 2 shows a cutaway view and simplified block diagram of a process device including pulsation sensing circuitry for use in performing diagnostics.

Figure 3 shows a cutaway view and simplified block diagram of a process device including pulsation sensing circuitry for use in generating power for the process device.

Figure 4 is a bottom plan view of a sensor module including an isolation diaphragm for use with a piezoelectric transducer.

Figure 5 is cross sectional view showing an isolation diaphragm for use with a piezoelectric transducer. Figure 6 is a planned view of a process device including a piezoelectric transducer located in a mounting flange.

Figure 7 is a planned view of a process device including a piezoelectric transducer located in a process coupling.

Figure 8 is a simplified diagram of a configuration in which a piezoelectric transducer is coupled to the process fluid at a location remote from the process device.

DETAILED DESCRIPTION

Various prior art techniques exist which utilize mechanical vibrations in processes for diagnostic or harvesting energy. However, these

vibrations are typically received from process components such as piping, mounting brackets, etc rather than from directly receiving pulsations from the process fluid, for example, from process fluid carried in a process pipe. These pressure pulsations may arise from many sources including, for example, pumps, pipe obstructions, etc. In some instances, the internal pressure pulsations do not result in external mechanical vibrations which are transmitted into the piping itself, brackets, or other components. Often, the maximum energy available is inside the process vessel, for example inside the process piping. In one aspect, the present invention includes capturing this energy from the process and using it for diagnostics and/or energy harvesting. As used herein, a "pressure pulsation" is any type of a change in pressure in the process fluid. Pressure pulsations may be carried in the form of waves of pressure, a traveling wavefront, etc. In one configuration, the pressure pulsations may comprise a single pressure pulse and in other configurations, the pressure pulsation can be a periodic or repeating wave form, or other wave form having an extended duration.

Figure 1 is a simplified diagram of an industrial process controller monitoring system 10 including a process device 16 in accordance with the present invention. As discussed in more detail below, process device 10 includes a piezoelectric transducer (not shown in Figure 1 ) configured to move in response to pressure pulsations in system 10 and thereby generate an electrical output.

Process device 16 is shown coupled to process piping 12 which is configured to carry a process fluid 14. A process interface element 18 is configured to couple to the process and is used for input or output to the process device 16. For example, if the process device is configured as a process control transmitter, interface element 18 can comprise some type of a process variable sensor such as a pressure sensor, flow sensor, temperature sensor, etc configured to sense a process variable. On the other hand, if process device 16 is configured

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as a process control device, interface element 18 can be, for example, a valve, a heater, a motor, a pump, etc., which is used to control the process. Process device 16 couples to remotely located circuitry such as control room 20 over a process control loop 22. Process control loop 22 is illustrated as a two wire process control loop and can comprise, for example, a process control loop configured to operate in accordance with industrial standards. Example industrial standards include 4-20 mA protocols, the HART® protocol, FieldBus protocols, and others. In some embodiments, device 16 communicates using a wireless process control loop and may or may not also couple to wired loop 22. Figure 1 also shows a pressure pulse 72 carried in the process fluid.

Figure 2 is a simplified cross-sectional view showing one example embodiment of the present invention in which process device 16 couples to process piping through a process coupling 50 such as a flange or the like. Field device 16 includes interface circuitry 52 which couples to process interface 18. When configured as a transmitter, interface circuitry 52 can perform initial processing and operate with a process variable sensor. Similarly, when configured as a process controller, interface circuitry 52 is used to control the process interface 18. Field device 16 includes a microcontroller 60 which operates in accordance with programming instructions stored in memory 62. Microcontroller 60 also couples to I/O circuitry 64 which itself couples to process control loop 22. In some configurations, I/O circuitry 64 also provides a power output which is used to power some or all of the circuitry of process device 16.

Piezoelectric transducer 68 is mounted in a device housing 70 of the process device 16. Piezoelectric transducer 68 is physically coupled to the process, either directly or indirectly through one or more additional components, such that pressure pulsations 72 emanating from the industrial process 14 are received by piezoelectric transducer 68. These pulsations cause movement of transducer 68 which results in an electrical output signal 74 which is a function

of the received pulsations. In the configuration of Figure 2, piezoelectric transducer 68 provides an electrical output signal 74 to an analog to digital converter 76. The analog to digital converter 76 receives the output signal 74 and provides a digitized signal 80 to the microcontroller 60. The microcontroller 60 can process the digitized signal using any desired technique and is not limited to those discussed herein.

In one example configuration, microcontroller 60 monitors the amplitude, spectral content and/or signature (time and/or frequency) of the pulsation signal 72. The signal 72 can be compared against known signals which are representative of nominal operation of the process 10. Nominal signal values such as amplitude, spectral content and/or signatures can be stored, for example, in memory 62.

In another example configuration, certain levels or thresholds in the output signal 74 may indicate specific failures in the process 10 such as a broken or failing pump or bracket. Similarly, certain frequencies or groups of frequencies may suggest specific failures such as a failing or failed impeller. The pulsation information can also be used to provide prognostic information related to the expected lifetime reduction in the process device 10, or other device in process 10, due to the exposure to pulsations. If, during operation of the process device 16, the pulsation signal 72 varies in a predetermined manner from the stored nominal values, programming instructions executed by microcontroller 60 can be used to make a determination that some type of event has occurred in the process which warrants further investigation. For example, the microcontroller 60 can provide an output signal indicative of component failure or potential failure that should be investigated by an operator. The information can also be used for other purposes such as to provide an indication of operation of other components in the industrial process such as a valve controller or the like. If the process coupling 50 has become loose, the pulsation signal 72 will also change. In another example, if the pulsation signal 72 should

suddenly decrease or even disappear completely, this can be an indication that the process 10 has improperly shut down or is in an undesirable state. Various examples of diagnostic techniques are shown in U.S. Patent No. 6,601,005, issued July 29, 2003 by Eyrurek, which is incorporated herein by reference in its entirety.

Figure 3 is another simplified block diagram of process device 16 showing another example configuration of the present invention. In Figure 3, elements which are similar to those shown in Figure 2 have retained their numbering. In the configuration of Figure 3, the pulsation signal 72 is received by piezoelectric transducer 68. The current output signal 74 from piezoelectric transducer 68 is provided to a power storage circuitry 82. Power storage circuitry 82 can be any appropriate device for storing electrical power and can include, for example, an electrical capacitor and rectifying circuitry, a battery, etc., used to store energy from piezoelectric transducer 68. Power storage circuitry 82 provides a power output signal which can be used to power process device 16. In such a configuration, I/O circuitry 64 may not be required to provide a power output signal. Further, in some configurations process device 16 is configured to operate over a wireless connection and I/O circuitry 64 is used for wireless communication. Power storage circuitry 82 can provide all of the power for process device 16, or can provide supplemental or backup power to the device 16.

In general, power from the process cannot be harvested using this technique unless there is kinetic energy. For example, a pressurized vessel may contain a significant amount of potential energy. However, if the pressure remains constant, the energy cannot be harvested. One solution is to harvest energy created by process pressure noise such as due to a water "hammer" effect, pump pulsations, etc. With the present invention, such energy can be harvested using a piezoelectric effect. Typical piezoelectric elements have a relatively low current output. However, given a sufficient input force, enough

power may be generated to be useful in process control devices. In various configurations, the piezoelectric transducer can be used to harvest power from pressure pulsations in the process fluid. The piezoelectric transducer can be integrated into a pressure sensor module or process connection to thereby eliminate external wiring. A battery capacitor or other power storage device, such as power storage 82 shown in Figure 3, can be included in the configuration. The battery can wholly or partially supplement power provided by the piezoelectric transducer. Further, the piezoelectric transducer can be used to charge the battery when there is sufficient excess energy. This can also extend the life of the battery by reducing discharge. In another example configuration, a control signal can be applied to the piezoelectric transducer 68 from microcontroller 60 to thereby cause movement of the transducer 68 and provide pressure pulsations. In such a configuration, the induced pressure signal can be sensed by a pressure sensor of the process device to diagnose or verify transmitter operation. The magnitude of the signal can also be used to provide an indication of line pressure. Although a single piezoelectric transducer 68 is illustrated, multiple circuits can be used.

Figure 4 shows a bottom plan view of a pressure module 150 for use in one embodiment of the present invention. The pressure module 150 includes an isolation diaphragm 152 for coupling to a high side of a process pressure and an isolation diaphragm 154 for coupling to a low pressure side of a process pressure. A pressure sensor, for example embodied in interface circuitry 52 shown in Figures 2 and 3, can be used and arranged to measure a differential pressure between diaphragms 152 and 154 applied by process fluid. Such differential pressure can be indicative, for example, of flow rate of the process fluid. A isolation diaphragm 156 can be used to couple the piezoelectric transducer 68 to the process fluid. For example, the piezoelectric transducer 68 can mount to the isolation diaphragm 156 such that movement of the isolation

diaphragm 156 causes movement of the piezoelectric transducer 68. This allows transducer 68 to directly sense pulsations in the process fluid.

Figure 5 is a side cross sectional view of module 150 showing diaphragm 156 in greater detail. As illustrated in Figure 5, the piezoelectric sensor 68 is physically coupled to diaphragm 156. The sensor 68 is shown positioned in a cavity 170 formed in module 150. An electrical connection carries the output 74 from transducer 68. In the configuration of Figure 5, as pulsations occur in the process fluid, diaphragm 156 will move. This movement of diaphragm 156 causes a resultant movement of transducer 68 which results in an electrical output. As discussed above, an input signal can be applied to transducer 68 resulting in movement of diaphragm 156 which induces a pulsation in the process fluid.

Figure 6 is a plan view of another example embodiment of the present invention in which the process variable transmitter is shown which includes a transmitter electronics housing 202 and a sensor module 204. A mounting flange 206 is used to mount the transmitter sensor module 204 to piping of an industrial process. The flange 206 may, for example, include valves or the like. In the configuration of Figure 5, the piezoelectric transducer 68 is carried in the flange 206 and can be, for example, coupled to the process fluid using a technique such as that illustrated in Figure 5 which uses the diaphragm 156. An electrical connection 210 extends from flange 206 to the transmitter electronic housing 202 is used to couple electrical signals and/or from the transducer 68.

Figure 7 is a plan view of transmitter 200 configured in a similar manner to that which is shown in Figure 6 and the numbering has been retained accordingly. However, in the configuration of Figure 7, the transmitter 200 includes some type of a process coupling 220 such as a probe for sensing temperature, pressure, etc. The coupling in the configuration of Figure 7, the coupling 220 is illustrated as including the piezoelectric transducer 68. The

transducer 68 can be coupled to the process using any appropriate technique, including, for example, the diaphragm 156 shown in Figure 5.

In the configurations of Figures 6 and 7, the piezoelectric transducer is carried in a "wetted" component. Such configurations may be advantageous because they can be repaired or upgraded in the field without altering the transmitter itself. Further, these configurations do not require additional space within the transmitter housing.

Figure 8 shows another example configuration of the present invention in which the piezoelectric sensor 68 is coupled to process piping 230 through a resonant pipe 232. The transducer 68 couples to a process device, such as those discussed above through electrical connection 234. In the configuration of Figure 8, the piezoelectric transducer is separated from the process device. The transducer 68 may include electronics to provide amplification or signal processing and can be configured to screw, for example into a threaded port on a vessel. In one configuration, the transducer 68, including its associate electronics, is between 1 to 2 inches in diameter and 1 to 2 inches in height and appear as a pipe plug. Such a configuration is advantageous because it may be repaired or upgraded in the field and increases energy harvesting as the process measurement point may be different from the optimum process noise location. The optional resonant in pipe 262 may be configured to take advantage of standing waves that can occur in any closed wave medium. For example, this configuration can be used to amplify or otherwise focus pulsations in the process fluid onto the piezoelectric transducer 68. In the example of a resonated pipe, the equation is L=V s/F where L is the length of the pipe, Vs is the speed of sound and F is the frequency of the sound. In one configuration, pulsation frequencies of interest will generally be in the range of 60 to 80 hertz and the length of resonant pipe 232 may be between 0.5 and one meter.

Although other configurations may be used, in one embodiment, s the circuitry may include a super capacitor to store electrical charge from the piezoelectric transducer. When the energy being scavenged is sufficient to power the device, the scavenged energy can be used rather than energy from a battery. Further, when scavenged energy is still greater, excess charge can be stored in, for example, a super capacitor. However, if the energy generated by the transducer 68 is not sufficient to power the device, energy from a battery may be used. Thus, in such a configuration, the energy scavenging does not replace the battery in the device, but rather extends battery life. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. Although the embodiments of Figures 2 and 3 are illustrated separately, the piezoelectric transducer 68 can be used simultaneously for both diagnostics as well as power generation.