EP1234191A1 - Procede et appareil d'essai d'un capteur capacitif - Google Patents

Procede et appareil d'essai d'un capteur capacitif

Info

Publication number
EP1234191A1
EP1234191A1 EP00975031A EP00975031A EP1234191A1 EP 1234191 A1 EP1234191 A1 EP 1234191A1 EP 00975031 A EP00975031 A EP 00975031A EP 00975031 A EP00975031 A EP 00975031A EP 1234191 A1 EP1234191 A1 EP 1234191A1
Authority
EP
European Patent Office
Prior art keywords
sensor
test
signal
output signal
frequency range
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP00975031A
Other languages
German (de)
English (en)
Other versions
EP1234191A4 (fr
Inventor
Arnim Holger Littek
Michael Jouhannes Pot
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Med-Dev Ltd
Med Dev Ltd
Original Assignee
Med-Dev Ltd
Med Dev Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Med-Dev Ltd, Med Dev Ltd filed Critical Med-Dev Ltd
Publication of EP1234191A1 publication Critical patent/EP1234191A1/fr
Publication of EP1234191A4 publication Critical patent/EP1234191A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass

Definitions

  • the present invention relates to a method and apparatus for testing a capacitive sensor.
  • the output of the sensor is critical to the operation of a device. Therefore a need exists for an efficient method of testing the operation of the sensor, and at least providing an indication if abnormal operation is detected.
  • I S JP-A-0631 8744 describes a sensor comprising a piezoelectric material affixed on both surfaces with a pair of electrodes. Each electrode is formed in a U-shape with a pair terminals, one at each end. Discontinuities in each electrode can be detected by measuring the resistance between a respective pair of terminals.
  • JP-A-0631 8744 A problem with the arrangement of JP-A-0631 8744 is that the electrodes must be formed into a special shape. Another problem is that it is not possible to detect discontinuities between the electrodes, for instance due to a breakdown in the piezoelectric material.
  • An object of the invention is to address these problems, or at least to provide the public with a useful alternative.
  • apparatus for testing a capacitive sensor including: means for applying a test input signal to the sensor, the test input signal having a predetermined signal characteristic; and means for monitoring a sensor output signal from the sensor and generating a test output signal which varies in accordance with the presence or absence of the predetermined signal characteristic in the monitored sensor output signal.
  • a method of testing a capacitive sensor including the steps of: applying a test input signal to the sensor, the test input signal having a predetermined signal characteristic; and monitoring a sensor output signal from the sensor and generating a test output signal which varies in accordance with the presence or absence of the predetermined signal characteristic in the monitored sensor output signal.
  • test input signal can be applied across the sensor without creating unwanted interference with sensing signals which are generated by the sensor during normal operation (and which will not, in general, possess the predetermined signal characteristic) .
  • the test signal lies within a test frequency range, and the means for monitoring blocks signals outside the test frequency range (typically employing a band-limiting filter such as a high-pass, low-pass, comb, notch or band-pass filter) .
  • a band-limiting filter such as a high-pass, low-pass, comb, notch or band-pass filter
  • the test signal is substantially sinusoidal.
  • the apparatus further includes means for extracting a sensing signal from the sensor outout signal by blocking signals outside a sensing frequency range (typically a band-limiting filter such as a high- pass, low-pass, comb, notch or band-pass filter) Typically there is no overlap between the two frequency ranges. In other words the test frequency range lies completely above or completely below the sensing frequency range.
  • a sensing frequency range typically a band-limiting filter such as a high- pass, low-pass, comb, notch or band-pass filter
  • test input signal is encoded with a predetermined code sequence (such as a psuedo-random sequence), and the test output signal is generated by correlating the predetermined code sequence with the sensor output signal.
  • a predetermined code sequence such as a psuedo-random sequence
  • the test input signal is applied to the sensor via an impedance element (eg. a capacitor, resistor, inductor or combination thereof).
  • an impedance element eg. a capacitor, resistor, inductor or combination thereof.
  • the impedance element has an impedance at least 1 0- 1 00 times greater than the impedance of the sensor, at the frequency of the test signal.
  • the apparatus may simply be used to check the presence or absence of the sensor.
  • the sensor will present a known impedance to the test input signal. However if a fault exists the sensor will present a higher or lower impedance to the test signal. This can be detected and used to generate a two-level test output signal (le. a signal with one level during normal operation and another level when the impedance measurement lies outside predetermined performance criteria) .
  • a fault signal is generated when the impedance of the sensor lies outside predetermined performance criteria.
  • the test output signal has more than two output values, if for example the capacitive sensor can significantly vary its capacitance value as a part of its normal operation.
  • the apparatus is used to monitor a movement sensor comprising a piezoelectric material which generates sensing signals by movement of the piezoelectric material
  • the invention may be employed in a variety of applications.
  • the sensor may acquire signals from a human or animal subject.
  • a biomedical system is an infant apnoea monitoring system which employs a capacitive piezoelectric sensor to acquire cardiac, respiratory and/or large motor movement data from an infant during sleep.
  • Another example is an automobile driver monitoring system in which a capacitive piezoelectric sensor mounted in an automobile seat acquires cardiac, respiratory and/or large motor movement signals from a driver of the automobile.
  • Figure 1 is a schematic circuit diagram of a single-ended piezoelectric sensor system incorporating a sensor testing circuit with the test frequency above the sensor system frequency bands of interest;
  • Figure 2 is a schematic circuit diagram of a differential piezoelectric sensor system incorporating a first sensor testing circuit with the test frequency above the sensor system frequency bands of interest
  • Figure 3 is a schematic circuit diagram of a differential piezoelectric sensor system incorporating a second sensor testing circuit
  • Figure 4 is a schematic circuit diagram of a differential piezoelectric sensor system incorporating a third sensor testing circuit
  • Figure 5 is a schematic circuit diagram of a piezoelectric sensor system incorporating a fourth sensor testing circuit which includes a pseudorandom noise generator; and Figure 6 is a schematic circuit diagram of a linear feedback shift register.
  • a piezoelectric sensor 1 comprises a sheet of polyvinyhdene fluoride (PVDF) film with a pair of electrodes arranged on opposite sides of the film. One electrode is connected to ground and the other electrode is connected to a sensor output line.
  • PVDF film can be made in quite large sizes. For the purposes of this example, we can assume that a standard A4 sheet size would have a capacitance of somewhere between 1 0 nF and 40 nF, depending on the thickness of the film. Deformation of the film results in the generation of a sensing signal on the sensor output line.
  • the relatively high capacitance of the film means that the sensing signal lies in a relatively low frequency band, below 35 Hz for instance.
  • the sensor output signal on the sensor output line is amplified by an amplifier 2, filtered by a lowpass filter 3 which rolls off at 35 Hz, passed on to electronics 4 (eg. analog-to-digital converter etc), and processed by a microprocessor 9.
  • An oscillator 5 generates an oscillating test input signal at a frequency of 1 0 KHz.
  • the test input signal is applied to the sensor output line via a small capacitor 6 (or a high-valued resistor or resistor/inductor combination) with an impedance 10-1 00 times greater than the impedance of the sensor 1 (at the test frequency) so as not to load the sensor 1 .
  • the relatively low impedance sensor 1 effectively short-circuits the 1 0KHz signal to ground.
  • a bandpass filter 7 is coupled to the output of the amplifier 2 via a capacitor (not labelled).
  • the filter 7 has a bandpass region centred on the 1 0KHz test signal frequency
  • any signals at the 10KHz test frequency are passed onto a diode 8 and the microprocessor 9, and any signals in the 0-10Hz sensing signal frequency band are blocked
  • the test signal voltage output by the bandpass filter 7 will lie below a predetermined threshold.
  • the microprocessor 9 generates a fault detection signal.
  • the microprocessor can simultaneously monitor the detected test signal from diode 8 and process the sensing signal from electronics 4.
  • a sensor 10 comprises a film sheet and electrodes (not labelled) encased in a grounded electrostatic shield 1 1 .
  • Differential outputs 1 2, 1 3 of the sensor 10 are coupled to positive and negative input terminals of a differential amplifier 1 6.
  • the output of the differential amplifier 1 6 is input to electronic circuitry (not shown) similar to items 3,4,7,8 and 9 shown in Figure 1 .
  • a high frequency oscillator 1 5 is coupled to one output 1 2 of the sensor 1 0 via a capacitor (not labeled) with an impedance at least 10- 1 00 times greater than the impedance of the sensor 1 (at the test frequency) .
  • a high frequency decoupling capacitor 1 4 (with a relatively high impedance at the sensor measurement frequency band, but with a relatively low impedance at the test frequency) is connected between the other differential output 1 3 and ground to complete the shunt to ground.
  • Figure 3 shows the differential sensing circuit of Figure 2 but with a different sensor testing circuit. In this case the ground shunt capacitor 1 4 is omitted.
  • the test input signal is applied to one differential output of the sensor and a test signal detection circuit 1 8 (comprising a capacitor, bandpass filter and diode) is coupled to the other differential output of the sensor.
  • test signal detection circuit 1 8 outputs a signal to the microprocessor (not shown) which generates a fault detection signal when the test signal output by the bandpass filter falls below a predetermined threshold.
  • Figure 4 shows the differential sensing circuit of Figures 2 and 3 but with a third different sensor testing circuit.
  • the test input signal is applied by a differential oscillator drive 1 9 via a pair of capacitors (not labelled) each with an impedance at least 10-1 00 times greater than the sensor 1 .
  • a differential oscillator drive 1 9 via a pair of capacitors (not labelled) each with an impedance at least 10-1 00 times greater than the sensor 1 .
  • capacitors not labelled
  • testing circuits of Figures 1 -4 all simply illustrate an out-of-band single-frequency detection circuit much higher in frequency than the sensor's target frequency range. It will be appreciated that the same principles apply to a sensor configuration where the test frequency is below the frequency bands of interest from the sensor. Under these circumstances, the sensor frequency bands are isolated instead with highpass filtering.
  • test input signal may also be used to provide a more accurate measurement of the impedance of the capacitive sensor, and hence the sensor integrity.
  • the microprocessor 9 monitors the test signal level from the bandpass filter by means of an analogue to digital converter and provides the measurement for display, recording, or other indication.
  • the accurate impedance measurement can be used to determine whether the sensor 1 has been partially damaged, for instance by being cut.
  • the multi-level output may be useful in applications in which the capacitance of the sensor is varied as part of the normal operation of the sensor.
  • a further extension of the same principle can utilize instead of single- frequency signals for monitoring of the impedance of the sensor, a band of such frequencies.
  • a pseudo-random sequence is one example that lends itself to simple generation and detection.
  • a pseudo-random sequence can be used not only above or below the sensor frequency bands, but may also be used directly in the sensor's frequency range of interest, as is applied in spread spectrum techniques. Given that the applied Pesudo Random Sequence test signal is known, it may be detected by means of correlation, and thereby separated from the sensor measurement signal. The detected level is then processed as in the previous examples.
  • Figures 5 and 6 An example of a system embodying this principle is shown in Figures 5 and 6.
  • Figure 5 is identical to Figure 1 except the oscillator 5 has been replaced with a pseudo-random noise generator 25, the bandpass filter 7 has been replaced by a correlator 26 and the diode 8 has been replaced by an averager 27.
  • the generator 25 may be implemented in the form of a linear feedback shift register shown in Figure 6 (although many different forms of implementation are known in the literature) .
  • a clock signal 20 is supplied to a chain of series-connected f pflops 23. Selected taps of the shift register are summed together with exclusive-OR gates 24 in order to provide a maximal-length sequence of 2 " N - 1 , where N is the number of fhpflops 23 in the shift register.
  • the actual tap points for a maximal length sequence vary with the length of the shift register, but are well known and published in the literature or are relatively easily determined.
  • PRBS pseudo-random binary sequence
  • the pseudo-random binary sequence is also fed to a correlator 26 which generates an output with a DC level (measured by averager 27) which is indicative of the degree of correlation between the output of the sensor and the PRBS.
  • the correlation function implemented by the correlator 26 might, for instance, be carried out by way of a simple phase sensitive detector and low pass filter to both block the sensing signal and recover the test signal.
  • the broad spectral nature of the PRBS may mean that the PRBS may be sufficiently removed from the sensing signal by the LPF 3.
  • the PRBS may be completely removed from the sensing signal by correlation and subtraction utilising digital signal processing techniques.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Resistance Or Impedance (AREA)
  • Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Abstract

L'invention concerne un appareil d'essai d'un capteur capacitif, comprenant des moyens (5, 15, 17, 19) permettant d'appliquer au capteur un signal d'entrée d'essai, lequel présente une caractéristique de signal prédéterminée, ainsi que des moyens (7, 18) permettant d'extraire du capteur un signal de sortie d'essai par la sélection de signaux ayant ladite caractéristique de signal prédéterminée, et le blocage des signaux ne possédant pas cette caractéristique.
EP00975031A 1999-11-03 2000-11-03 Procede et appareil d'essai d'un capteur capacitif Withdrawn EP1234191A4 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
NZ50077099 1999-11-03
NZ50077099 1999-11-03
PCT/NZ2000/000217 WO2001033245A1 (fr) 1999-11-03 2000-11-03 Procede et appareil d'essai d'un capteur capacitif

Publications (2)

Publication Number Publication Date
EP1234191A1 true EP1234191A1 (fr) 2002-08-28
EP1234191A4 EP1234191A4 (fr) 2003-02-19

Family

ID=19927604

Family Applications (1)

Application Number Title Priority Date Filing Date
EP00975031A Withdrawn EP1234191A4 (fr) 1999-11-03 2000-11-03 Procede et appareil d'essai d'un capteur capacitif

Country Status (5)

Country Link
EP (1) EP1234191A4 (fr)
AU (1) AU1313901A (fr)
BR (1) BR0015288A (fr)
CA (1) CA2390176A1 (fr)
WO (1) WO2001033245A1 (fr)

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1392585A1 (fr) * 2001-06-05 2004-03-03 Siemens Aktiengesellschaft Rouleau de mesure et de detection
US6714070B1 (en) * 2002-02-07 2004-03-30 Bei Technologies, Inc. Differential charge amplifier with built-in testing for rotation rate sensor
FR2912814A1 (fr) * 2007-07-06 2008-08-22 Siemens Vdo Automotive Sas Procede et dispositif de detection de defaillance de capteur capacitif passif
US20090241634A1 (en) * 2008-03-28 2009-10-01 Cenk Acar Micromachined accelerometer and method with continuous self-testing
US9791494B2 (en) * 2012-01-20 2017-10-17 Lear Corporation Apparatus and method for diagnostics of a capacitive sensor
CN103235277B (zh) * 2013-03-29 2016-01-06 国家电网公司 智能化变电站容性设备在线监测系统集成化调试装置
US10260983B2 (en) 2014-01-20 2019-04-16 Lear Corporation Apparatus and method for diagnostics of a capacitive sensor with plausibility check
WO2017109520A1 (fr) * 2015-12-24 2017-06-29 Cloudtag Inc Système portatif de surveillance du rythme et de l'activité cardiaques

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2253487A (en) * 1991-03-07 1992-09-09 Rover Group A method of detecting malfunction of a piezoelectric sensor
EP0523732A2 (fr) * 1991-07-19 1993-01-20 Mitsubishi Petrochemical Co., Ltd. Capteur d'accélération avec auto-test, et circuit pour celui-ci
EP0704706A1 (fr) * 1994-09-30 1996-04-03 MAGNETI MARELLI S.p.A. Système diagnostique pour un capteur capacitif
WO1999013345A1 (fr) * 1997-09-11 1999-03-18 Robert Bosch Gmbh Dispositif capteur

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5220519A (en) * 1990-12-28 1993-06-15 Endevco Corporation Method and apparatus for self-testing a transducer system
DE4133426A1 (de) * 1991-10-09 1993-04-15 Bosch Gmbh Robert Schaltungsanordnung zur auswertung und zum test eines kapazitiven sensors

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2253487A (en) * 1991-03-07 1992-09-09 Rover Group A method of detecting malfunction of a piezoelectric sensor
EP0523732A2 (fr) * 1991-07-19 1993-01-20 Mitsubishi Petrochemical Co., Ltd. Capteur d'accélération avec auto-test, et circuit pour celui-ci
EP0704706A1 (fr) * 1994-09-30 1996-04-03 MAGNETI MARELLI S.p.A. Système diagnostique pour un capteur capacitif
WO1999013345A1 (fr) * 1997-09-11 1999-03-18 Robert Bosch Gmbh Dispositif capteur

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of WO0133245A1 *

Also Published As

Publication number Publication date
BR0015288A (pt) 2002-07-09
EP1234191A4 (fr) 2003-02-19
CA2390176A1 (fr) 2001-05-10
AU1313901A (en) 2001-05-14
WO2001033245A1 (fr) 2001-05-10

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