Patent Description:
<CIT>describes an apparatus for detecting the malfunctioning of an accelerometer. A a test signal in form of a pulse is transmitted from a test signal generator to the accelerometer by means of a change-over switch capable of performing a change in such a manner that the response signal from the accelerometer can be transmitted to an analyzing circuit so as to be subjected to a malfunction detection. The change-over switch is adapted to alternately connect the accelerometer either to the test signal generator or to the analyzing circuit. <CIT>describes a functional self-test for a piezoelectric element deployed in an end-product. An excitation signal is applied to a unit under test (UUT), the excitation signal including a cyclical signal for a first interval and substantially zero signal for a second interval. A frequency content of a UUT response signal is determined, and a fail result is generated in response to the frequency content below a predetermined threshold. <CIT> describes an ultrasonic wave flowmeter detecting measurement errors and failures caused by changes in characteristics of ultrasonic wave oscillators.

Industrial process field devices used in industrial process control and monitoring systems typically include a sensing element or transducer that responds to a process variable, and signal conditioning and processing circuitry to convert the sensed variable into a transmitter output that is a function of the sensed process variable. The term "process variable" refers to a physical or chemical state of matter or conversion of energy. Examples of process variables include pressure, temperature, flow, conductivity, PH, and other properties. Process transmitters are typically used to monitor process variables and send measurement values back to a control room in a chemical, petroleum, gas, pharmaceutical, or other fluid processing plant.

One common transducer used in industrial process field devices is a piezoelectric transducer. Piezoelectric transducers may be used to detect an applied force, such as one produced by motion or vibration of an object, to which the piezoelectric transducer is attached. Movement of the object causes the piezoelectric transducer to generate a voltage across terminals of the transducer, the magnitude of which corresponds to the degree of force applied to the transducer. Sensors formed using piezoelectric transducers may be configured to detect industrial process variables such as, for example, fluid flow rates.

Piezoelectric transducers have the potential to malfunction or fail. Such a malfunction could result in faulty process variable measurements. Routine testing of the field device by a skilled technician could potentially assist in detecting a failing piezoelectric transducer of the device, but such testing may require the field device to be removed from service and transported to a testing facility.

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.

<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 (e.g., process medium) 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 field device <NUM> (e.g., a process transmitter) that utilizes a piezoelectric transducer <NUM> to sense a process variable, such as a variable relating to a process medium <NUM>. The field device <NUM> includes communications circuit <NUM> for communicating with an external computerized control unit <NUM> over a suitable process control loop. The control unit <NUM> may be remotely located from the device <NUM>, such as in a control room <NUM> for the system <NUM>, as shown in <FIG>.

In some embodiments, the process control loop includes a physical communication link, such as a two-wire control loop <NUM>, or a wireless communication link. Communications between the control unit <NUM>, or another external computing device, and the field device <NUM> may be performed over the control loop <NUM> in accordance with conventional analog and/or digital communication protocols. In some embodiments, the two-wire 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 two-wire 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.

Exemplary wireless versions of the process control loop include, for example, a wireless mesh network protocol, such as WirelessHART® (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 field device <NUM> from any suitable power source. For example, the field device <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 field device <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 field device <NUM>, or charge a power supply used by the field device <NUM>.

The device <NUM> includes a controller <NUM>, which may represent one or more processors (i.e., microprocessor, microcontroller, 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 piezoelectric transducer <NUM> may be used to perform any conventional function relating to industrial process field devices <NUM>, such as a sensing function, in which the piezoelectric transducer <NUM> is used to sense a process variable relating to an industrial process, such as a process variable associated with a process medium <NUM>. This sensing function may be facilitated using a sensor circuit <NUM> that operates the piezoelectric transducer <NUM> in a sensing mode, and generates a sensor signal <NUM> indicating the process variable based on a signal output from the piezoelectric transducer, such as a voltage across terminals of the piezoelectric transducer. The sensor signal <NUM> may be processed by the controller <NUM> and communicated to the control unit <NUM> or another external computing device using the communications circuit <NUM>.

As discussed above, piezoelectric transducers may degrade and fail, which can result in faulty process variable measurements. In order to detect a degrading or failing piezoelectric transducer, conventional field devices require direct testing of the field device by a technician, which may include transporting the field device to a testing facility. As a result, such periodic testing of the field devices can be costly and lead to significant downtime.

According to the invention, test circuit <NUM> is used to operate the piezoelectric transducer <NUM> in a testing mode, in which one or more diagnostic tests may be performed on the piezoelectric transducer <NUM> to determine whether it is operating properly. The test circuit <NUM> outputs diagnostic information <NUM>, which may be used by the controller <NUM> to determine a current condition of the piezoelectric transducer, and generate a diagnostic test result for the piezoelectric transducer <NUM>. The diagnostic test result may indicate whether the piezoelectric transducer <NUM> is operating properly (e.g., within a normal operating range) or abnormally. The controller may also communicate the diagnostic test result to the control unit <NUM> or another external computing device using the communications circuit <NUM> over the process control loop (e.g., physical or wireless communication link).

<FIG> is a flowchart illustrating an exemplary method for testing a condition of a piezoelectric transducer <NUM> of an industrial process field device <NUM>, in accordance with embodiments of the present disclosure. Embodiments of the method may refer to <FIG> and <FIG>, which are simplified diagrams of circuitry comprising an exemplary sensor circuit <NUM> and an exemplary test circuit <NUM>, with the piezoelectric transducer respectively operating in sensing and testing modes, in accordance with embodiments of the present disclosure.

At <NUM> of the method, the piezoelectric transducer <NUM> is operated in a sensing mode (<FIG>) using the sensor circuit <NUM> of the field device <NUM>. This involves generating the sensor signal <NUM> that indicates the process variable based on a voltage across the piezoelectric transducer <NUM>, such as across terminals <NUM> and <NUM> of the piezoelectric transducer <NUM>.

In some embodiments, when the piezoelectric transducer <NUM> is operating in the sensor mode, the terminal <NUM> of the piezoelectric transducer <NUM> is connected to electrical ground <NUM>, and the terminal <NUM> is connected to a sensor signal amplifier <NUM> of the sensor circuit <NUM>, as indicated in <FIG>. The sensor signal amplifier <NUM> may be any suitable amplifier for use with piezoelectric transducers to amplify the voltage signal (sensor signal) across the piezoelectric transducer <NUM> that indicates the sensed process variable. For example, the sensor signal amplifier <NUM> may include signal amplifying circuits, analog-to-digital converters, and other conventional components for translating the voltage signal across the piezoelectric transducer <NUM> into a form that may be used by a microcontroller <NUM> or the controller <NUM> to discern the process variable measurement. When the microcontroller <NUM> is separate from the controller <NUM> of the device <NUM>, the microcontroller <NUM> may communicate the sensor signal <NUM>, or the value represented thereby, through a suitable input/output component <NUM>, as indicated in <FIG>. Thus, in one example of operating the piezoelectric transducer <NUM> or the device <NUM> in the sensing mode, the piezoelectric transducer <NUM> generates the sensor signal based on the process variable being detected. The sensor signal may be amplified by the sensor signal amplifier <NUM> and provided to the microcontroller <NUM>. The microcontroller <NUM> may perform additional processing of the sensor signal <NUM>, and may communicate the sensor signal <NUM>, or a corresponding value indicated by the sensor signal <NUM>, to the controller <NUM> of the device <NUM>, as indicated by the sensor signal <NUM> in <FIG>. The controller <NUM> may then communicate the sensor signal <NUM>, or the value indicated by the sensor signal <NUM>, to the control unit <NUM> or another external computing device.

At <NUM> of the method, the piezoelectric transducer <NUM> or the device <NUM> is operated in a testing mode (<FIG>) using the test circuit <NUM> of the field device <NUM>. In some embodiments, when the piezoelectric transducer <NUM> is operated in the testing mode, the terminal <NUM> of the piezoelectric transducer <NUM> is coupled to a pulse generator <NUM> of the test circuit <NUM>, and the terminal <NUM> is coupled to a node <NUM> of the test circuit <NUM>, as indicated in <FIG>.

At <NUM> of the method, the pulse generator <NUM> applies a voltage pulse to the piezoelectric transducer <NUM>, such as in response to a signal <NUM> from the microcontroller <NUM>. The voltage pulse deforms the piezoelectric transducer <NUM> and causes the piezoelectric transducer <NUM> to generate a response signal, at <NUM> of the method.

<FIG> is a chart of voltage over time illustrating an exemplary voltage pulse <NUM> and a corresponding response signal <NUM> from the piezoelectric transducer <NUM>, in accordance with embodiments of the present disclosure. The voltage pulse <NUM> includes a pulse voltage <NUM>, a rise time <NUM>, a fall time <NUM> and a pulse duration <NUM>.

The response signal <NUM> generated by the piezoelectric transducer <NUM> may be measured using any suitable technique. In some embodiments, a current from the piezoelectric transducer <NUM> is delivered through a reference resistance, and the measured response signal <NUM> corresponds to a voltage generated across the reference resistance <NUM> in response to the current. In one example, the test circuit <NUM> includes a reference resistance <NUM> (<FIG>) that is connected between the node <NUM> and electrical ground <NUM>. Thus, the response signal <NUM> corresponds to a voltage across the reference resistance <NUM>, such as the voltage at node <NUM> of the test circuit <NUM>.

At <NUM> of the method, a peak positive voltage <NUM> and a peak negative voltage <NUM> (<FIG>) of the response signal <NUM> are captured using the test circuit <NUM>. In some embodiments, the peak positive voltage <NUM> of the response signal <NUM> is sampled during the rise time <NUM> of the voltage pulse <NUM>, and the peak negative voltage <NUM> of the response signal <NUM> is sampled during the fall time <NUM> of the voltage pulse <NUM>, as indicated in <FIG>.

The test circuit <NUM> may include a peak positive voltage detector <NUM> and a peak negative voltage detector <NUM> that are each coupled to the node <NUM> of the test circuit <NUM>. For example, the peak positive voltage detector <NUM> may include a diode <NUM>, and a capacitor <NUM> that is coupled to electrical ground <NUM> and captures the peak positive voltage <NUM> of the response signal <NUM>. Likewise, the peak negative voltage detector <NUM> may include a diode <NUM> and a capacitor <NUM> that is attached to electrical ground <NUM> and captures the peak negative voltage <NUM> of the response signal <NUM> at the node <NUM>.

In some embodiments, the test circuit <NUM> may include components of the sensor circuit <NUM>. For example, the test circuit <NUM> may use the sensor signal amplifier <NUM> or components thereof (e.g., an analog-to-digital converter), to form the detectors <NUM> and <NUM> and capture the peak positive and negative voltages <NUM>, <NUM>, for example.

At <NUM> of the method, a current condition value of the piezoelectric transducer <NUM> is calculated using the controller <NUM> of the device <NUM>. The current condition value of the piezoelectric transducer <NUM> is calculated based on the peak positive voltage <NUM>, the peak negative voltage <NUM> and the pulse voltage <NUM>. The controller <NUM> stores the detected peak positive voltage <NUM> and peak negative voltage <NUM> in the memory <NUM>, as indicated in <FIG>. The pulse voltage <NUM> may be predefined and stored in the memory <NUM>.

According to the invention, the controller <NUM> calculates the current condition value of the piezoelectric transducer <NUM> based on a ratio of the sum of the absolute values of the peak positive voltage <NUM> and the peak negative voltage <NUM> (voltage <NUM> in <FIG>) and the pulse voltage <NUM>. For example, in one embodiment, the current condition value is calculated based on the pulse voltage <NUM> divided by the absolute value of the sum of the peak positive voltage <NUM> and the peak negative voltage <NUM> or voltage <NUM>. Thus, when the pulse voltage is <NUM>,<NUM> millivolts and the sum of the absolute values of the peak positive and negative voltages is <NUM> millivolts, the current condition value may be calculated as <NUM>,<NUM>/<NUM> or <NUM>.

In some embodiments, the test circuit <NUM> includes an inverter <NUM> and an adder <NUM>. The inverter <NUM> is coupled to the output of the peak negative voltage detector <NUM> that operates to invert the peak negative voltage <NUM> detected by the detector <NUM>. The adder <NUM> is coupled to the output of the peak positive voltage detector <NUM> and the output from the inverter <NUM>. Thus, the adder outputs the sum (<NUM>) of the peak positive voltage <NUM> and the absolute value of the peak negative voltage <NUM> to the microcontroller <NUM>, as indicated in <FIG>. The test circuit <NUM> may also include analog-to-digital converters and other components that are used to process signals from the detectors <NUM>, <NUM>, the inverter <NUM>, and/or the adder <NUM> before presenting the voltage sum <NUM> to the microcontroller <NUM>.

The microcontroller <NUM> may be used to determine a value of the voltage sum <NUM> and output the value to the controller <NUM> of the device <NUM> through the input/output component <NUM>. The controller <NUM> may then calculate the current condition value based on the ratio of the pulse voltage <NUM> to the voltage sum <NUM>. The calculated current condition value may be stored in the memory <NUM>, as indicated at <NUM>, and may be an entry in a condition values log <NUM>, for example.

The condition values log <NUM> may also include previously calculated current condition values for the piezoelectric transducer <NUM>. Trends in the condition of the piezoelectric transducer <NUM> can be monitored using the condition values stored in the log <NUM>, and used to provide additional diagnostic analysis of the transducer <NUM>.

At <NUM> of the method, the controller <NUM> generates a diagnostic test result <NUM> for the piezoelectric transducer <NUM>, which may be stored in the memory <NUM>, based on the current condition value and a reference condition value <NUM>, which may also be stored in the memory <NUM>, as indicated in <FIG>. The reference condition value <NUM> may be calculated in the same or similar manner as the current condition value, and corresponds to a condition value of the piezoelectric transducer when it is operating properly. The reference condition value <NUM> may be based upon empirical studies of one or more piezoelectric transducers that are similar to the piezoelectric transducer <NUM> of the device <NUM>, or one or more empirical studies of the piezoelectric transducer <NUM> taken at the time of manufacture of the piezoelectric transducer <NUM> or the device <NUM>.

In some embodiments of step <NUM> of the method, the diagnostic test result <NUM> is generated based on a comparison of a difference between the calculated current condition value <NUM> and the reference condition value <NUM> to a threshold value <NUM>, which may be retrieved by the controller <NUM> from the memory <NUM> of the device <NUM>, as indicated in <FIG>. In some embodiments, the diagnostic test result <NUM> indicates that the condition of the piezoelectric transducer <NUM> is abnormal when the difference exceeds the threshold value <NUM>.

The method may also include a step of communicating information to the control unit <NUM> or another external computing device using the communications circuit <NUM>. The information may include, for example, the detected process variable value indicated by the sensor signal <NUM>, the diagnostic test result <NUM>, and/or other information.

In some embodiments, the device <NUM> includes a switch <NUM> (<FIG> and <FIG>) for transitioning the device <NUM> between the sensing and testing modes, such as in response to a signal <NUM> from the microcontroller <NUM>. In some embodiments, the switch <NUM> is configured to couple the terminal <NUM> of the piezoelectric transducer <NUM> to the sensor circuit <NUM> (e.g., sensor signal amplifier <NUM>), and couple the terminal <NUM> of the piezoelectric transducer <NUM> to electrical ground <NUM>, when in the sensing mode, as shown in <FIG>. Thus, in some embodiments, the switch <NUM> disconnects the piezoelectric transducer <NUM> from the test circuit <NUM> when in the sensing mode. Additionally, the switch <NUM> is configured to couple the terminal <NUM> of the piezoelectric transducer <NUM> to the test circuit <NUM> (e.g., the pulse generator <NUM>), and couple the terminal <NUM> of the piezoelectric transducer <NUM> to the node <NUM>, the reference resistance <NUM>, the peak positive voltage detector <NUM> and the peak negative voltage detector <NUM>, when in the testing mode, as shown in <FIG>. Thus, in some embodiments, the switch <NUM> disconnects the piezoelectric transducer <NUM> from the sensor circuit <NUM> when in the testing mode.

One exemplary industrial process field device that uses a piezoelectric sensor to detect or measure a process variable is a vortex flow meter, an example of which is illustrated in <FIG> is a simplified front view of an exemplary vortex flowmeter <NUM>, and <FIG> is a top cross-sectional view of the vortex flowmeter <NUM> of <FIG> taken generally along line <NUM>-<NUM>, in accordance with embodiments of the present disclosure.

The vortex flowmeter <NUM> includes a piezoelectric transducer for detecting a flow rate of a process medium fluid flow <NUM> (<FIG>) traveling through a process vessel <NUM>, such as a pipe, for example. Some embodiments of the vortex flowmeter <NUM> include a housing <NUM>, a vortex shedder <NUM> and a vortex frequency sensor <NUM>. The housing <NUM> includes an interior cavity <NUM>, such as a tubular interior cavity having a central axis <NUM>. The housing <NUM> may be connected in line with the pipe <NUM>, such that the central axis <NUM> is substantially coaxial to a central axis <NUM> of the pipe <NUM>, as shown in <FIG>.

The vortex shedder <NUM> is supported by the housing <NUM> and extends into the tubular interior cavity <NUM> along an axis <NUM> that is oblique to the central axis <NUM>. In some embodiments, the vortex shedder <NUM> has a conventional cross-sectional shape that is configured to shed vortices <NUM> in response to the fluid flow <NUM>, as indicated in <FIG>. In one exemplary embodiment, the vortex shedder <NUM> has a trapezoidal cross-sectional shape, as shown in <FIG>. The vortex shedder <NUM> may extend through the center of the tubular cavity <NUM>, such that the axis <NUM> intersects the axis <NUM>, as shown in <FIG>. In some embodiments, both ends of the vortex shedder <NUM> are attached to the housing <NUM>, as indicated in <FIG>. Alternatively, the vortex shedder <NUM> may be secured to the housing <NUM> at only one of its ends.

The vortex frequency sensor <NUM> is supported by the housing <NUM> on a downstream side <NUM> from the vortex shedder <NUM> relative to the fluid flow <NUM>, as shown in <FIG>. In some embodiments, the sensor <NUM> includes a beam <NUM> that extends from a wall <NUM> of the housing <NUM> into the tubular interior cavity <NUM>, and a piezoelectric transducer <NUM>, which is indicated in phantom lines in <FIG>. The piezoelectric transducer <NUM> is used to sense motion of the beam <NUM> in response to the vortices <NUM> flowing past the beam <NUM>. Specifically, the beam <NUM> oscillates in response to the vortices <NUM> and the piezoelectric transducer <NUM> produces a sensor signal (e.g., voltage) indicating the oscillatory movement of the beam <NUM> and, thus, the frequency at which the vortices <NUM> flow past the beam <NUM>. This vortex frequency may be used to estimate the flow rate of the fluid flow <NUM>, in accordance with conventional techniques.

The vortex flowmeter <NUM> also includes embodiments of the sensor and test circuits <NUM>, <NUM> described above. Thus, the vortex flowmeter <NUM> and the piezoelectric transducer <NUM> may be operated in a sensing mode using the sensor circuit <NUM>, in accordance with embodiments of the method step <NUM> described above. For example, when in the sensing mode, the controller <NUM> estimates the flow rate of the fluid flow <NUM> based on the vortex frequency that is obtained from the sensor signal output from the piezoelectric transducer <NUM> (e.g., voltage across the terminals <NUM> and <NUM> shown in <FIG>). The controller <NUM> may communicate the flow rate to the control unit <NUM> or another external computing device using the communications circuit <NUM>.

Claim 1:
An industrial process field device (<NUM>) for sensing a process variable comprising:
a piezoelectric transducer (<NUM>);
a sensor circuit (<NUM>) configured to operate the piezoelectric transducer (<NUM>) in a sensing mode, in which the sensor circuit (<NUM>) generates a sensor signal indicating the process variable based on a voltage across the piezoelectric transducer (<NUM>);
a test circuit (<NUM>) configured to operate the piezoelectric transducer (<NUM>) in a testing mode, in which the test circuit (<NUM>):
applies a voltage pulse having a pulse voltage to the piezoelectric transducer (<NUM>) that deforms the piezoelectric transducer (<NUM>) and induces a response signal from the piezoelectric transducer (<NUM>);
captures a peak positive voltage of the response signal; and
captures a peak negative voltage of the response signal;
a memory (<NUM>);
a controller (<NUM>) configured to:
store the captured peak positive voltage of the response signal in the memory (<NUM>);
store the captured peak negative voltage of the response signal in the memory (<NUM>);
calculate a current condition value of the piezoelectric transducer (<NUM>) based on a ratio of the sum of the absolute values of the peak positive voltage (<NUM>) and the peak negative voltage (<NUM>) to the pulse voltage (<NUM>); and
generate a diagnostic test result based on a comparison of the current condition value to a reference condition value corresponding to a properly operating piezoelectric transducer (<NUM>); and
a communications circuit (<NUM>) configured to communicate the process variable and the diagnostic test result to an external control unit (<NUM>) over a process control loop (<NUM>).