Piezoelectric transducer condition monitoring

Patent metadata

Field	Value
Publication number	US-11293790-B2
Application number	US-201916652478-A
Country	US
Kind code	B2
Filing date	Sep 25, 2019
Priority date	Sep 25, 2019
Publication date	Apr 5, 2022
Grant date	Apr 5, 2022

Abstract

An industrial process field device includes a piezoelectric transducer, a sensor circuit, a test circuit, a controller and a communications circuit. The sensor circuit generates a sensor signal indicating a process variable based on a voltage across the piezoelectric transducer. The test circuit is configured to apply a voltage pulse having a pulse voltage to the piezoelectric transducer that induces a response signal, and capture peak positive and negative voltages of the response signal. The controller calculates a current condition value of the piezoelectric transducer based on the peak positive voltage, the peak negative voltage and the pulse voltage, and generates 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. The communications circuit communicates the process variable and the diagnostic test result to an external control unit over a process control loop.

First claim

What is claimed is:

1. An industrial process field device for sensing a process variable comprising:
a piezoelectric transducer;
a sensor circuit configured to operate the piezoelectric transducer in a sensing mode, in which the sensor circuit generates a sensor signal indicating the process variable based on a voltage across the piezoelectric transducer;
a test circuit configured to operate the piezoelectric transducer in a testing mode, in which the test circuit:
applies a voltage pulse having a pulse voltage to the piezoelectric transducer that deforms the piezoelectric transducer and induces a response signal from the piezoelectric transducer;
captures and stores a peak positive voltage of the response signal; and
captures and stores a peak negative voltage of the response signal;

a controller configured to:
calculate a current condition value of the piezoelectric transducer based on the peak positive voltage, the peak negative voltage and the pulse voltage; 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; and

a communications circuit configured to communicate the process variable and the diagnostic test result to an external control unit over a process control loop.

2. The device of claim 1 , wherein:
the peak positive voltage of the response signal corresponds to a rise time of the voltage pulse; and
the peak negative voltage of the response signal corresponds to a fall time of the voltage pulse.

3. The device of claim 1 , wherein the test circuit comprises:
a pulse generator configured to generate the voltage pulse;
a reference resistance through which the response signal travels;
a peak positive voltage detector configured to capture the peak positive voltage across the reference resistance; and
a peak negative voltage detector configured to capture the peak negative voltage across the reference resistance.

4. The device of claim 3 , wherein the current condition value is calculated based on a ratio of the sum of the absolute values of the peak positive and negative voltages and the pulse voltage.

5. The device of claim 4 , wherein the testing circuit comprises:
an inverter configured to invert the peak negative voltage; and
an adder configured to add the peak positive voltage to the inverted peak negative voltage.

6. The device of claim 4 , wherein the diagnostic test result indicates that the condition of the piezoelectric transducer is abnormal when a difference between the current condition value and the reference condition value exceeds a threshold value.

7. The device of claim 6 , wherein the threshold value and the reference condition value are stored in a computer-readable medium that is accessible by the controller.

8. The device of claim 3 , further comprising a switch configured to transition the device between the sensing and testing modes, wherein:
the switch couples a first terminal of the piezoelectric transducer to the sensor circuit, and couples a second terminal of the piezoelectric transducer to electrical ground, when in the sensing mode; and
the switch couples the first terminal of the piezoelectric transducer to the pulse generator, and couples the second terminal of the piezoelectric transducer to the reference resistance, the peak positive voltage detector, and the peak negative voltage detector, when in the testing mode.

9. The device of claim 1 , wherein the process variable of the industrial process includes a flow rate of a process medium.

10. A method for testing a condition of a piezoelectric transducer in an industrial process field device, the method comprising:
operating the piezoelectric transducer in a sensing mode using a sensing circuit of the field device comprising generating a sensor signal indicating a process variable based on a voltage across the piezoelectric transducer;
operating the piezoelectric transducer in a testing mode using a test circuit of the field device including:
applying a voltage pulse having a pulse voltage to the piezoelectric transducer that deforms the piezoelectric transducer;
generating a response signal from the piezoelectric transducer in response to the voltage pulse;
capturing and storing a peak positive voltage of the response signal using the test circuit; and
capturing and storing a peak negative voltage of the response signal using the test circuit;

generating a diagnostic test result for the piezoelectric transducer using a controller of the field device comprising:
calculating a current condition value of the piezoelectric transducer based on the peak positive voltage, the peak negative voltage and the pulse voltage; and
generating the diagnostic test result based on a comparison of the current condition value to a reference condition value corresponding to a properly operating piezoelectric transducer; and

communicating the process variable and the diagnostic test result to an external control unit over a process control loop using communications circuitry of the field device.

11. The method of claim 10 , wherein:
the peak positive voltage of the response signal corresponds to a rise time of the voltage pulse; and
the peak negative voltage of the response signal corresponds to a fall time of the voltage pulse.

12. The method of claim 10 , wherein operating the piezoelectric transducer in a testing mode using a test circuit comprises:
generating the voltage pulse using a pulse generator;
directing the response signal through a reference resistance;
capturing the peak positive voltage across the reference resistance using a peak positive voltage detector; and
capturing the peak negative voltage across the reference resistance using a peak negative voltage detector.

13. The method of claim 12 , wherein calculating the current condition value of the piezoelectric transducer comprises calculating the current condition value based on a ratio of the sum of the absolute values of the peak positive and negative voltages and the pulse voltage.

14. The method of claim 13 , wherein operating the piezoelectric transducer in a testing mode using a test circuit comprises:
inverting the peak negative voltage using an inverter; and
adding the peak positive voltage to the inverted peak negative voltage using an adder.

15. The method of claim 13 , wherein:
generating a diagnostic test result for the piezoelectric transducer using the controller comprises comparing a difference between the current condition value and the reference condition value to a threshold value; and
the diagnostic test result indicates that the condition of the piezoelectric transducer is abnormal when the difference exceeds the threshold value.

16. The method of claim 15 , further comprising obtaining the threshold value and the reference condition value from a computer-readable medium using the controller.

17. The method of claim 12 , further comprising switching between the sensor mode and the test mode using a switch comprising:
coupling a first terminal of the piezoelectric transducer to the sensor circuit, and coupling a second terminal of the piezoelectric transducer to electrical ground, when in the sensing mode; and
coupling the first terminal of the piezoelectric transducer to the pulse generator, and coupling the second terminal of the piezoelectric transducer to the reference resistance, the peak positive voltage detector, and the peak negative voltage detector, when in the testing mode.

18. The method of

Assignees

• Rosemount Inc

Inventors

• Bogdanov Vladimir D

Classifications

• B06B2201/55

  Piezoelectric transducer · CPC title

• G01P21/025

  for measuring speed of fluids; for measuring speed of bodies relative to fluids (for measuring volume flow G01F25/10) · CPC title

• B06B1/0215

  for generating pulses, e.g. bursts of oscillations, envelopes · CPC title

• B06B2201/40

  with testing, calibrating, safety devices, built-in protection, construction details · CPC title

• G05B23/0256 Primary

  injecting test signals and analyzing monitored process response, e.g. injecting the test signal while interrupting the normal operation of the monitored system; superimposing the test signal onto a control signal during normal operation of the monitored system · CPC title