SU698171A2 - Method of testing resonant piezoelectric transducers fastened to an object - Google Patents

Description

I

This invention relates to technical acoustics and can be used to control resonant electroacoustic transducers.

Of. main auth. N 547977 a method is known for checking resonant piezoelectric transducers mounted on an object, based on electric pulse excitation of a transducer, selection of a response and its spectral analysis. The transducer is excited by a radio pulse. The filling frequency of which is equal to the resonant frequency of the converter, and the number of oscillation periods is equal to the value at which the boundaries of the main lobe of the pulse spectrum coincide with the limits of the resonant characteristics of the converter measured at 0.1 of maximum 1.

However, the pulse spectrum in this area is uneven, which requires frequency correction of the response before analyzing it, and leads to errors when checking the converter.

The purpose of the invention is to increase the reliability of control converters.

This goal is achieved by the fact that the frequency of filling the radio pulse varies linearly within the limits of the resonant characteristics of the converter at a rate determined by the expression

au Cfa-fH i i

Wgde D f

width of the resonant characteristics of the converter, measured at the level of 0.707 from the maximum, Hz. f in and fn are the upper and lower limits of the frequency range, respectively.

The drawing shows graphs of the resonance characteristics of the converter A (f) (curve 1) and the spectrum of the excitation pulse S (f) (curve 2). Dashed curve 3 represents the pulse spectrum, the filling frequency of which zap is equal to the resonant frequency fp of the controlled transducer and remains unchanged.

Claims (1)

When choosing the parameters of the excitation pulse, according to the rule described above, its spectral characteristic is close to rf GF, and in the frequency range of the resonant response of the converter, over 95% of the excitation energy is distributed. The piezotransducer fastened at the object is a dual armature, and the excitation and response signals (response) follow the rio to one channel, which excludes the possibility of simultaneously actuating the transducer and analyzing its response. If the rate of change of frequencies 1.g is backwired, then the action of such a pulse is equivalent to the action of a radio pulse with a frequency of filling equal to the maximum fg if the frequency increases, or minimum if the frequency decreases. The spectrum of such an impulse is not rectangular, but the response to the action of the first periods of the pulse, i.e. of its initial part, it has time to significantly decrease or end altogether, since the pulse duration is large. If the rate of change of the filling frequency increases, the number of oscillation periods in the pulse and its duration decrease. The peak of the spectral characteristic of an impulse is more and more rounded, and the duration of its front increases. A further increase in the rate of change of frequency leads to the degeneration of radio pulses into video pulses, which are not very suitable for testing resonant transducers. For this reason, the choice of the rate of change of the filling frequency must be made in strict accordance with the inertial properties of the controlled transducer. A measure of the inertial properties of a resonant converter, like any other resonant system, is its time constant, t, which is related to the Q-ratio. where fp is the resonant frequency of the HF generator, Hz. The time constant t characterizes the time it takes for the converter to oscillate when a voltage is connected to it with a frequency fp. In practice, it can be assumed that the oscillations are set at a time of 2.5-3 tons. This time determines the minimum possible duration of the radio pulse T, the frequency is constant and equal to resonant fp. In the proposed method, the filling frequency varies symmetrically with respect to the frequency f and within small limits, since resonant transducers have a high quality factor. For this reason, a pulse duration of 14 with a variable filling frequency is chosen equal to the pulse duration with a constant filling frequency, i.e. T 3 T. Even if the resonant frequency fp is not the middle frequency of the 3g range shifted to that wider side, the value of the pulse duration T can be saved. By the duration of the pulse and the range of change of the filling frequency, the rate of change of this frequency is found. Hiimful T-FH-3Q get the final expression for speed. 2ir () t, Excitation with a radio pulse with a variable filling frequency makes it possible to refuse the frequency correction of the response of the converter, since the spectrum of such a pulse has a plane verticality. This also increases the proportion of the pulse energy distributed in the effective frequency range of the resonant characteristics of the converter, which leads to an increase in the reliability of the control of the converters. The invention The method of checking an object mounted on the object resonant piezoelectric transducers auth. No. 547977, characterized in that, in order to increase the reliability of the control, the frequency of filling of the radio pulse is varied according to a linear law within the limits of the resonant characteristics of the converter with a speed defined by the expression. I3 where Д f is the width of the resonant characteristics of the converter, measured at the level of 0.707 from the maximum, Hz. f in and fn are the upper and lower limits of the frequency range, respectively. Sources of information taken into account during the examination 1. USSR Author's Certificate No. 547977, cl. H 04 R 17/00, 1977.