Transducer in-situ testing apparatus and method

• US 20030024298A1
• Filed: 04/24/2002
• Published: 02/06/2003
• Est. Priority Date: 04/27/2001
• Status: Active Grant

• Current Assignee: Oceana Sensor Technologies, Inc.
• Original Assignee: Oceana Sensor Technologies, Inc.
• Inventors: Simmons, William, Pegg, Joseph E., Bocko, Mark F., Baber, Isaak
• Granted Patent: US 6,698,269 B2
• Time in Patent Office: Days
• US Class Current: 73/1.82
• CPC Class Codes: G01D 3/08 with provision for safeguarding the apparatus, e.g. against abnormal operation, against breakdown
• CPC Class Codes: G01H 3/005 Testing or calibrating of detectors covered by the subgroups of G01H3/00 calibrating geophysical instruments, e.g. seismic receivers G01V13/00
• CPC Class Codes: G01L 25/00 Testing or calibrating of apparatus for measuring force, torque, work, mechanical power, or mechanical efficiency
• CPC Class Codes: G01L 9/08 by making use of piezoelectric devices , i.e. electric circuits therefor
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

The present invention provides an apparatus and method for in-situ testing of transducers, and more particularly to the testing of piezoelectric transducers including piezoelectric accelerometers. Circuits, measurement techniques, and interpretative algorithms to enable in-situ testing of piezoelectric accelerometers are described. Accelerometers that employ a piezoelectric material to convert mechanical strains into electronic signals are reciprocal electromechanical transducers. In such transducers the electrical output impedance of the sensor is dependent upon the electrical and mechanical parameters of the sensor. The procedure described in this disclosure includes methods of measuring the transducer electrical output impedance as a function of frequency and the extraction of the electrical and mechanical transducer parameters from the measured data. The measured values of the transducer parameters may be interpreted to provide an indication of the operational status of the transducer. In addition to allowing verification of correct transducer performance, a range of failure conditions and degradations may be inferred from the transducer parameter values.

Claims

1. A self-testing transducer circuit comprising:

a transducer characterized by a self-resonant frequency;

an amplifier connected to the transducer amplifying the output of the transducer;

a signal source generating a test signal having a spectrum at least overlapping the self-resonant frequency of the transducer, connected to the amplifier; and

an analyzer connected to an output of the amplifier for measuring the response of the transducer to the test signal and characterizing at least one parameter of the transducer.

3. The self-testing transducer circuit of claim 1 in which the amplifier comprises a charge mode amplifier, the transducer is connected to a sense node of the amplifier, and the test signal source is connected to a reference node of the amplifier.

4. The self-testing transducer circuit of claim 1 in which the amplifier comprises a voltage mode amplifier, the transducer is connected to a non inverting input of the amplifier, and the test signal source is connected to the non inverting input of the amplifier;

and a reference signal is connected to an inverting input of the amplifier.

5. The self-testing transducer circuit of claim 1 in which the amplifier comprises a single ended transistor amplifier and the transducer and the test signal generator are connected to an input of the amplifier.

11. The self-testing transducer circuit of claim 1 in which the test signal comprises a swept frequency test signal.

12. The self-testing transducer circuit of claim 1 in which the test signal comprises a white noise test signal.

2. A method of testing a sensor connected to an amplifier for amplifying an output of the sensor comprising;

coupling a test signal from a signal source having an output spectrum overlapping a self-resonant frequency of the transducer to the sensor;

amplifying a signal created by the sensor in response to the test signal; and

analyzing the signal created by the sensor and characterizing at least one parameter of the sensor.

6. The sensor testing method of claim 2 in which the step of analyzing the signal comprises determining the resonant frequency of the transducer from the signal.

7. The sensor testing method of claim 2 in which the step of analyzing the signal comprises determining the Q of the signal created by the sensor.

8. The sensor testing method of claim 2 in which the step of analyzing the signal comprises storing a reference signal, and comparing a later obtained signal to the reference signal.

9. The sensor testing method of claim 2 in which the test signal comprises a swept frequency test signal.

10. The sensor testing method of claim 2 in which the test signal comprises a white noise test signal.

13. A transducer circuit comprising:

(a) a transducer in communication with an amplifier;

(b) a signal generator at a sense node between the sensor and the amplifier and in communication with the sensor, capable of generating a signal at the sense node;

(c) an analog to digital converter that produces a digitized signal with a spectrum;

(d) a digital signal processor that is in communication with the analog to digital converter and capable of analyzing the spectrum of the digitized processor output signal; and

(e) a microcomputer that is in communication with the digital signal processor and is capable of analyzing the spectrum of the digitized signal or other digital processor output.

14. The transducer circuit of claim 13 in which the amplifier comprises a charge mode amplifier, the transducer is connected to the sense node of the amplifier, and the signal generator is connected to a reference node of the amplifier.

15. The transducer circuit of claim 13 in which the amplifier comprises a voltage mode amplifier, the transducer is connected to a non inverting input of the amplifier, and the signal generator is connected to the non inverting input of the amplifier;

and a reference signal is connected to an inverting input of the amplifier.

16. The transducer circuit of claim 13 in which the amplifier comprises a single ended transistor amplifier and the transducer and the signal generator are connected to an input of the amplifier.

17. The self-testing transducer circuit of claim 13 in which the amplifier comprises a single ended transistor amplifier and the transducer and the signal generator are connected to an input of the amplifier.

18. The transducer circuit of claim 13 in which the signal generator generates a test signal comprising a swept frequency test signal.

19. The transducer circuit of claim 13 in which the signal generator generates a test signal comprising a white noise test signal.

20. A sensor testing method comprising:

coupling a test signal from a signal source having an output spectrum overlapping a self-resonant frequency of the sensor;

amplifying a signal created by the sensor in response to the test signal; and

analyzing the signal created by the sensor and characterizing at least one parameter of the sensor.

21. The sensor testing method of claim 20 in which the step of analyzing the signal comprises determining the resonant frequency of the transducer from the signal.

22. The sensor testing method of claim 20 in which the step of analyzing the signal comprises determining the Q of the signal created by the sensor.

23. The sensor testing method of claim 20 in which the step of analyzing the signal comprises storing a reference signal, and comparing a later obtained signal to the reference signal.

24. The sensor testing method of claim 20 in which the test signal comprises a swept frequency test signal.

25. The sensor testing method of claim 20 in which the test signal comprises a white noise test signal.

26. The sensor testing method of claim 20 in which the parameter comprises a range of failure conditions.

27. The sensor testing method of claim 20 in which the parameter comprises a range of degradation conditions.

28. The sensor testing method of claim 20 in which analyzing the signal created by the sensor and characterizing at least one parameter of the sensor further comprises analyzing a sensor'"'"'s total output impedance as a function of frequency.

29. The sensor testing method of claim 28 in which the parameter comprises one or more parameters corresponding to and derived from the total output impedance.