The method of calibration of a reversible piezoelectric transducer and a device for its implementation

 

(57) Abstract:

The invention relates to measurement techniques, in particular to a device for the calibration of hydrophones. The method is based on the linearity of forward and reverse piezoeffect for mutual converters. Reversible piezoelectric transducer excite the radio pulses with different frequencies filling, the end of impulses occurs when the amplitude value of the voltage. Measure the amplitude of the free oscillations, which take the receiving transducer. These values determine the relative sensitivity of the hydrophone to receive on different frequencies of excitation. The absolute sensitivity of the determined one of the absolute methods on one or more frequencies. The invention improves the accuracy and simplify the calibration of hydrophones in the region of low frequencies from a fraction of a Hertz to several kilohertz without the use of a small volume chambers. 2 S. p. f-crystals, 1 Il.

The invention relates to measurement techniques, in particular to methods and devices for the calibration of hydrophones.

The known device for the calibration of hydrophones in radiopulse mode [1], [2].

As a prototype for the statement in the electric pulses of known amplitude free vibrations and the selection of the response to the excitation after the termination of the electrical pulse at the moment the minimum short circuit current at the Converter output when its free vibrations [3].

The disadvantages of the method include the need to measure the short circuit current provided at the end of the radar pulse. The accuracy of this cast is affected by the moment of measurement: at the end of the radar pulse significant transients, as well as the damping of forced oscillations decreases the amplitude of the current.

Another disadvantage is the need to measure the flexibility of the transducer, which is also, generally speaking, depends on the frequency. To accurately determine the sensitivity of the Converter when using this method requires knowledge of the inaccuracy of the description of acoustic properties using electrical circuits.

As a prototype for the proposed device is selected known device for calibration of an acoustic receiver, containing the emitter in the form of shestipolosnoy acoustic output associated with the calibrated receiver connected to a recording device. The method of calibration of the device is carried out according to a formula based on measurements of EMF on the second electrical input of the emitter and other known process data calibration [4].

The disadvantages of the device should include the fact that gradeii of excitatory frequencies, that takes time and may lead to the influence of reflections on the result of the calibration. In addition, the double integration of the EMF of the receiving hydrophone assumes that the radiation is proportional to the square of the frequency, but this is the position for each particular hydrophone requires validation.

The disadvantages of the method include that in the formula for determining the sensitivity is constant radiation, the constancy of which operating frequency requires a separate check. Another disadvantage is that the parameter of reciprocity requires a separate definition for a specific measurement conditions.

The aim of the invention is to remedy these disadvantages and simplification of procedures for the calibration of hydrophones in the region of low frequencies (with the possible exception of the use of cameras) from fractions of a Hertz to several kilohertz, and improving calibration accuracy.

The proposed method of calibration is based on the linear dependence of the equations of the direct and inverse piezoelectric effect piezoelectric mutual converters, including transducers based on piezoelectric ceramics.

The idea of the method is that the calibrated hydrophone is subjected to the hydrophone (when the peak value of the exciting voltage) and the hydrophone passes in a mode of free vibrations. Its radiation takes hydrophone receiver and the magnitude of the received signal is measured.

The voltage at the output of the hydrophone receiver UCRproportional to the magnitude of the sound pressure at the frequency of free oscillations, which, in turn, is proportional to the amount of displacementcp. At low frequencies the hydrophone does almost elastic vibrations. In this case, the amount of displacement at the excitation frequencyequal to the amount of displacement at the frequency of free oscillations cf. In accordance with the equations of the piezo effect, the ratio of the displacement at the excitation frequency(which is proportional to UCRto the voltage applied to the hydrophone U[Izl]- M proportional to UCR/U[Izl]and with the constant value U[Izl]- M proportional to UCR.

Measuring at different frequencies of excitation of the magnitude of the signal emitted by the hydrophone at the frequency of free oscillations, get the relative sensitivity of the hydrophone on the frequency of excitation.

To move to the absolute sensitivity you can use any of the absolute calibration methods, for example, the hydrostatic method, one or more of the frequency range the response to the prototype of the method and the device allowed to establish their compliance with the criterion of "novelty".

Analysis of the known technical solutions in the area of study allows to draw a conclusion about the absence of these symptoms that are similar to the main features of the proposed method and device, and to recognize the claimed solution that meets the criterion of "significant differences",

The device according to the proposed method is shown in the drawing.

The device comprises a sinusoidal signal generator 4 generator trigger pulses 5, emitting 16 and receiving converters 17, the amplifier 13, the third octave analyzer 18, a digital oscilloscope 14, the keys of the first 1, second 2 and third 3, the control circuit 7 keys, the comparator 9 level control actuation of the comparator 8, the count of the number of periods of the sinusoidal signal 11, schema matching 12, an adjustable amplifier 6, the phase shifter 10 and summing amplifier 15.

The operation of the device is as follows. The signal generator 4 is supplied to the key 1, which is controlled by the control circuit 7, and the latter is controlled by the pulse generator 5 and the circuit 12 matches.

The output signal from the key 1 is fed to an adjustable amplifier 6, the amplifier 13 and the comparator 9. The output signal from the amplifier 13 is supplied to the key 2, and the output of the latter is Yu from schema matching 12. With generator 4 receives the strobe signal to the input of the counter 11, and permit operation of the counter 11 is supplied from the circuit 7. The actuation level of the comparator 9 is set by the controller 8, and the signal received at the hydrophone 16 is recorded on the first input of the oscilloscope 14, the synchronization of which is established ahead of the clock signal from the circuit 12 matches. The clock signal is generated after the count set in the counter 11, the number of periods of the excitation signal, since the comparator at each period of the signal when the amplitude value is triggered.

At this point, the key 2 is closed, and the switch 3 opens and short circuits the terminals of the hydrophone 16 on the body. Keys 1 and 2 turn off the signal generator 4 from the rest of the device and hydrophone 16, and the key 1 is opened with a delay equal to the propagation delay of the acoustic signal from the hydrophone 16 to the receiving hydrophone 17. The delay is implemented in the control circuit 7 keys. Until that time, when the signal generator 4 is not disconnected, the hydrophone 16 radiated acoustic signal, which is received hydrophone 17, and the electric signal is amplified 1/3 - octave analyzer 18 that is configured on the frequency closest to the frequency sabastopol the signal from the phase shifter 10, and to the input of the last signal from the controlled amplifier 6. To the input of the amplifier 6, the signal comes from the output of the key 1. By means of the amplifier 6 and the phase shifter 10 can achieve a compensation signal from the output of summing amplifier 15 to the second input of the oscilloscope 14, at those frequencies, which is noticeable through the analyzer 18 of the exciting signal frequency hydrophone 16.

At the moment of closing of the key 3 hydrophone 16 passes in a mode of free vibrations and the size of the emitted when this signal is measured using an oscilloscope 14.

The proposed method of measuring sensitivity of the hydrophones and the device for its implementation have advantages compared with the known methods and devices.

For how is fixing the exact value of the amplitude of the exciting voltage, since it is at a peak value stops the supply of the exciting voltage.

You do not need to measure the value of the short circuit current provided at the end of the radar pulse. You do not need to define the parameter flexibility of the Converter. Used acoustic properties of the transducer directly, not electric.

For us the, which is measured EMF to determine the sensitivity of the calibrated hydrophone. There is no operation double integration of this EMF. Calibrated hydrophone mode radiation only on the frequency of free vibrations.

All of the above allows you to extend the measurement range sensitivity to simplify the process of measuring sensitivity.

Application of the proposed invention makes it possible to measure the sensitivity of the hydrophones without the use of the measuring chamber and to improve the accuracy of the calibration. Economic efficiency can be very significant.

Measurements of the sensitivity of the hydrophones on the model proposed by the invention has shown that it is possible to measure the sensitivity in the frequency range from fractions of a Hertz up to 10...15 kHz, the resonant frequency calibrated hydrophone 40 kHz.

Sources of information

1. Kolesnikov A. E. "Acoustic measurements", Leningrad: Sudostroenie, 1983

2. Bobber R. "Acoustic measurements" - M.: Mir, 1974

3. A. S. N 1175036, CL H 04 R 29/00. The method of calibration of the piezoelectric transducer (prototype).

4. A. S. N 782186, CL H 04 R 29/00. The device for calibration of an acoustic receiver and method osushestvleniya the radio pulses of fixed amplitude with a frequency of filling, corresponding to the frequency of calibration, characterized in that will end the radar pulse with a peak voltage value with simultaneous short-circuiting the terminals of the transducer and acoustic communication with the transducer-receiver in the environment that produce calibration reversible piezoelectric transducer, the amplitude of the signal frequency of the free oscillations of which is measured by the transducer-receiver and in these dimensions determine the relative sensitivity of the calibrated transducer at the frequency of calibration, and the absolute sensitivity of the calibrated transducer determine the absolute method on one or more frequencies and count on other frequencies according to the values of the relative sensitivity of calibrated preobrazovala.

2. The device for calibration of a reversible piezoelectric transducer comprising a generator of sinusoidal signal generator trigger pulses, emitting and receiving transducers, amplifier, third octave analyzer and digital oscilloscope, characterized in that for the calibration it introduced the first, second and third keys, the control key is ham matches adjustable amplifier, phase shifter and a summing amplifier, the first input connected to the output of the phase shifter, the input of the latter is connected to the output of the controlled amplifier, an input connected to the output of the first key and the first key is connected to the generator output sinusoidal signal, the second input of the summing amplifier connected to the output of third octave analyzer, the input connected to the output of the transducer-receiver, and the output of the summing amplifier is connected to a second input of the digital oscilloscope, the input radiant (calibrated) Converter, the input of the third key and the first input of the digital oscilloscope connected to the output of the second key, an input connected to the output of the amplifier, the input of the latter is connected to the output of the first key and the first input of the comparator, the second input is connected to the level control operation of the comparator, and the output of the comparator connected to the first input schema matching, the second input of which is connected to the output count of the number of periods of the sinusoidal signal, and a counter input coupled to the output strobe signal generator sine wave signal, the output of the circuit matches is connected to the clock input digital oscillograph signal and the control input of the third key is connected to an inverted output of the circuit control keys, direct access to key management schemes connected with the control input of the second key, and the detainee direct access scheme key management is connected with the control input of the first key, the first input key management schemes connected to the generator trigger pulses.

 

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