RU2140072C1 - Method testing and stabilizing sensitivity of capacitive converter - Google Patents

Abstract

FIELD: acoustic measurements based on contact-free methods of excitation and reception of ultrasonic vibrations. SUBSTANCE: vibrations of counter electrode put on sample are excited by means of generator. Vibrations of counterelectrode converted by capacitive converter to electric signal are fed to device isolating vibrations. Test of sensitivity is conducted by characteristic parameters of this signal, for instance, by magnitude of signal amplitude in specified point. With deviation of characteristic parameter from preset magnitude feedback signal is generated and fed to source of polarizing voltage. Voltage across output is so regulated that given signal goes to zero. Thus stabilization of sensitivity of capacitive converter is conducted in process of its operation and measurement precision is enhanced by way of exclusion of random and systematic components of errors. EFFECT: enhanced measurement precision and conducting of stabilization of sensitivity of converter in process of its operation. 2 dwg

Description

 The invention relates to the field of acoustic measurements based on non-contact methods of excitation and reception of ultrasonic vibrations.

 Currently, capacitive converters are widely used in installations for the precision measurement of acoustic parameters of materials. This is due to their broadband both in the radiation mode and in the reception mode. The main characteristic that determines the accuracy of measurements using capacitive transducers is the stability of their sensitivity. In auth. St. N 1518777, N 1404925, methods and devices are described that provide absolute measurements of the sensitivity of transducers in the radiation and reception modes, namely, that the certified transducer is located on an optically transparent prism, and the ultrasonic vibrations emitted or received by the transducer are measured using a laser interferometer. The described devices can accurately determine the parameters of the converters, however, they do not provide control and stabilization of their sensitivity during operation.

The closest analogue is the solution described in the article by A.N. Bondarenko, V.A. Lugovoi, A.I. Kondratyev "Thin-film self-aligning capacitive transducer of ultrasonic signals", journal "Instruments and experimental equipment", 1988, pp. 197-199. The essence of the solution is as follows:
- the sample is installed in the housing of the capacitive transducer, and then, with the help of a screw, a counter electrode with a solid dielectric is pressed until it contacts the surface of the sample;
- create acoustic vibrations in the sample;
- measure the parameters of acoustic vibrations by the absolute method, for example, a laser interferometer;
- measure the parameters of acoustic vibrations certified transducer;
- by comparing the measurement results with the absolute method and the capacitive transducer determine its sensitivity;
- changing the distance between the sample and the counter electrode, set the required sensitivity.

 The disadvantage of the described solution is that according to this method it is impossible to control and adjust the sensitivity directly in the process of operation of a capacitive converter.

 The aim of the proposed invention is to improve the accuracy of measurements by monitoring and stabilizing the sensitivity of capacitive converters directly in the process.

 The goal is achieved by the fact that in the method of monitoring and stabilizing the sensitivity, which consists in creating oscillations of the counter electrode of the converter, the oscillations of the counter electrode are isolated and the polarizing voltage is regulated depending on their characteristic parameters.

 The significance of the differences of the method lies in the fact that despite the popularity of creating oscillations of the counter electrode (see, for example, the article by Drobot Yu.B., Kondratiev A.I., Lugovoi V.A. “Excitation of short elastic pulses by the capacitive method.” Defectoscopy, 1985 ., N 3), as well as the dependence of the sensitivity of the capacitive converter on the polarizing voltage (see ibid.), For the first time use counter-electrode oscillations to control the polarizing voltage).

 In FIG. 1 shows a device that implements the proposed method.

 The capacitive converter of figure 1 contains a counter electrode 1 with a dielectric film P, a second electrode 2, which is used as a sample. Both electrodes are connected to a polarizing voltage source 3, an electric signal generator 4, and a counter electrode oscillation isolation device 5. The oscillation isolation device is connected in feedback to the polarizing voltage source. As a source of polarizing voltage 3, any standard rectifier with external control (for example, B5-50) with a sufficient output voltage can be used.

As a generator 4, in a radiation mode, a generator is used which is designed to excite ultrasonic vibrations in a sample 2. In a receiving mode, for example, a generator of the G5-63 type can be used as a generator. A possible implementation diagram of the vibration isolation device 5 is shown in FIG. 2. The device consists of an input circuit organized by elements C, R, D ₁ , D ₂ , which serves to prevent overloads, storage retrieval device 6 (UVX), made, for example, on the basis of microcircuit 1100SK2, differential amplifier 7, made, for example, based on the 0544UD1 chip. In the process of monitoring and adjusting sensitivity, an oscilloscope 8 of type C1-99 is connected to the device.

 The method of monitoring and stabilizing the sensitivity of a capacitive transducer (Fig. 1) is implemented as follows.

 Using a generator 4, the oscillations of the counter electrode 1 mounted on the sample 2 are excited. The oscillations of the counter electrode converted by the capacitive transducer into an electric signal are supplied to the oscillation isolation device 5. Sensitivity is controlled by the characteristic parameter of this signal (for example, by the value of the signal amplitude at a given point). When the characteristic parameter deviates from the set value, a feedback signal is generated, which is fed to the source of polarizing voltage 3, the voltage at the output of which is automatically adjusted so that this signal vanishes. Thus, the sensitivity of the capacitive converter is stabilized during operation.

 The proposed method allows to increase the accuracy of acoustic measurements by eliminating random and systematic components of errors due to the instability of the sensitivity of capacitive transducers.

Claims (1)

 The method of monitoring and stabilizing the sensitivity of a capacitive transducer, which consists in creating oscillations of the counter electrode of the converter, characterized in that during operation the oscillations of the counter electrode are isolated and the polarizing voltage is regulated depending on their characteristic parameters.

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