SU1643968A1 - Device for testing of piezoelectric pickups - Google Patents

Abstract

This invention relates to a measurement technique. The goal is to increase the reliability of monitoring the characteristics of piezoelectric sensors — sensitivity, resonance frequency and switching on polarity. The device for calibrating piezoelectric sensors contains a controlled piezoelectric sensor 1, a connecting cable 2, an electric pulse generator 6, a response signal display unit 7, and an exemplary piezoelectric sensor 3, adjustable compensating capacitor 4 and the switching unit 5. Using the display unit 7, both the recording of the main signal-response parameters from the sample piezoelectric sensor 3, shunted by the adjustable compensating capacitor 4, and the signal-response from the piezo sensor being monitored 1 via the connecting cable 2, and the comparison of the main parameters of the indicated response signals 2 or 2 are performed.

Description

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About 4 SO ch)

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The invention relates to a measurement technique, in particular, to devices for calibrating piezoelectric sensors under operating conditions and can be used to determine operability, sensitivity and its change. the resonant frequency and its change, the polarity of the piezodgtchik included on the test object.

The aim of the invention is to increase the reliability of monitoring sensitivity and resonance frequency while simultaneously determining the polarity of switching on a piezoelectric sensor.

FIG. 1 shows a diagram of a device for calibrating piezoelectric sensors; in fig. 2 - excitation signals and response of the piezoelectric sensors of the model (curve IJ, controlled (curve II), controlled reverse polarity (curve III).

A device for calibrating piezoelectric sensors (Fig. 1) contains a controlled piezo sensor 1 installed at the test object (for example, for measuring impact processes), a connecting cable 2 that serves to connect a controlled piezo sensor to the device elements, each cable core is shielded, a model piezo sensor 3, in which the sensitivity of the AO is normalized, the resonant frequency f0, the signal form of the response when an electric pulse is applied (normalized in magnitude, duration, polarity and frequency is repeated ) to the corresponding outputs of the piezo sensor (for example, the polarity and shape of the first three half waves of the response signal), an adjustable compensating capacitor 4 connected in parallel to the exemplary piezo sensor 3 and used to compensate for the capacitive impedance of the connecting cable 2, switching unit 5, through which a certain program is implemented the connection between the generator 6 electric pulses, piezoelectric sensors 3 exemplary, shunting adjustable compensating capacitor 4, and controlled 1 through the connection The power cable 2, as well as the unit 7 for displaying the response signals from the indicated sensors, the switching unit 5 can be implemented on toggle switches, buttons (with manual control), relays, and electronic circuits (for example, controlled by a pulse generator 6).

The device works as follows

In the initial state, the capacitance of the adjustable compensating capacitor 4 is set equal to

the capacitance of the connecting cable 2, which is used when checking the piezoelectric sensor 1.

Before work (checking piezo sensor

1 through the connecting cable 2) the device is monitored: the necessary parameters of the excitation pulse from the generator 6 and the gain factor of the block 7 are set, which are set at

arriving at the display 7 unit directly of the response signal from the sample piezoelectric sensor 3, shunted by the compensating capacitor 4. For this, in the switching unit 5, the corresponding switchings must be made, providing both excitation pulses from the generator 6 to the piezoelectric model 3, shunted by the compensating capacitor 4, and connecting the display signal display unit 7 to the exemplary piezoelectric sensor 3.

As a result of the monitoring, the dependence U2 (t), (oscillogram I, Fig. 2), the magnitude of the excitation pulse UB, which is subsequently kept constant, the magnitude of the maximum amplitude of the response signal Umo from the sample piezoelectric sensor 3, shunting by a compensating capacitor 4, the magnitude of the period T0 of the oscillation of the response signal and, accordingly, the resonant frequency fpo of the exemplary piezo-sensor 3. the shape and polarity of the response signal.

The repetition rate fe

Tv

im0

five

0

five

The excitation pulses and the magnitude of their duration TUB are determined from the condition of obtaining the maximum magnitude of the response signal Umo from the exemplary piezoelectric transducer 3 and are subsequently kept constant.

The verification of the piezoelectric sensor 1 installed at the test object is carried out after controlling the device when working with a sample piezo sensor 3, shunted by an adjustable compensating capacitor 4, the capacitance of which must be equal to the capacitance of the connecting cable 2.

In the switching unit 5, the contacts, through which, when monitored, the pulse excitation signal from generator 6 is applied to a standard piezo sensor 3, shunted by a compensating capacitor 4, is disconnected from the exemplary piezo sensor 3 and switched through a connecting cable 2 to a controlled piezo sensor 1. Generator 6 through connecting cable 2 is fed to the controlled piezosensor 1 (Fig. 2, U1 (t)). The response signal at the resonant frequency from the controlled piezoelectric sensor 1, due to the inverse piezoelectric effect, is small (several millivolts) through the connecting cable 2 and unit 5 is fed to the input of the response signal display unit 7. The vibrational response signal is amplified by the amplifying channel of the display unit 7, recorded (Fig. 2, Ua (t), H waveform) and compared with the response signal from the exemplary piezoelectric sensor 3 (Fig. 2, U2 (t), NI waveform) registered by the display unit 7 either earlier or simultaneously.

The sensitivity of AK controlled piezoelectric sensor 1 can be determined from the ratio

Umk

Ak JSC

U

that

where AO is the sensitivity of the standard piezoelectric sensor 3 (according to passport data, laboratory calibration); 25

Umo - the maximum amplitude of the response signal from the standard piezoelectric sensor 3, shunted by a compensating capacitor 4;

Otk - maximum amplitude of the response signal 30 from the controlled piezoelectric transducer 1.

The resonant frequency fpK of the controlled piezo sensor 1 can be determined from the ratio 35

fPK - f

po

D ° Tk

where fpo is the resonant frequency of an exemplary piezo sensor 3:

That is the oscillation period of the response signal from the standard piezoelectric transducer 3;

TC period of oscillation of the response signal from the controlled piezoelectric sensor 1.

Comparing the polarity (shape) of the response signals from the sample 3 and the controlled 1 piezoelectric transducers (Fig. 2, U2 (t), oscillograms I and II or I and III) allows you to simultaneously determine the polarity of the inclusion of the controlled piezoelectric transducer 1.

Claims (1)

Invention Formula A device for calibrating piezoelectric sensors, comprising an electric pulse generator and a sensor signal indication unit, characterized in that, in order to increase the reliability of monitoring sensitivity, resonance frequency and polarity of sensor activation, an exemplary piezoelectric sensor with an adjustable compensating parallel connected to it is added to it a capacitor and a switch with six inputs and two outputs, with the first and second outputs of the switch connected to the inputs of the display unit, its first and second inputs are connected to an exemplary piezoelectric sensor, the third and fourth to the calibrated piezoelectric sensor, and the fifth and sixth to the terminals of the electric pulse generator, and the potential output of the electric pulse generator is connected to the terminals of the same polarity of the turned and exemplary piezoelectric sensors. ( about l FM lt Umo 7