SU1296871A1 - Piezocrystal pressure transducer - Google Patents

Abstract

The invention relates to instrumentation engineering and makes it possible to increase the sensitivity and accuracy of measurements. Inside the frame of the elastic element 3 is placed a piezoelectric element 4 in the form of a polygon, in the central region of which a point piezoresonator 7 is made. The thin-film electrodes 5 of the piezoelectric element 4, made in the form of segments, and the electrodes 8 of the piezoresonator 7 are included in the auto-oscillator circuit. The measured pressure acting on the membrane 2 leads to a comprehensive compression of the piezoelectric element 4. The autogenerator provides simultaneous generation of signals with frequencies equal to the eigenfrequencies of the peripheral and central regions of the piezoelectric element 4. The information difference frequency is not affected by the change in ambient temperature due to the performance of both piezoresonators in a single piezoplastin . 3 il. R (L

Description

one

The invention relates to an instrumentation engineering, in particular to piezoresonance pressure sensors.

The purpose of the invention is to demonstrate the sensitivity and accuracy of measurements.

FIG. 1 shows the piezoquartz sensor design; in fig. 2 the dependence of the coefficient of the crush sensitivity of the natural frequency of a point quartz piezoresonator on the angle about the applied force action relative to the crystallographic axes of the piezoquartz; in fig. 3 is a diagram of the autogenerator of the pressure sensor,

The piezoquartz pressure sensor will hold the housing 1 with a membrane 2 placed in it, and an elastic element 3 in the form of a frame is installed between the membrane and the body. Inside the frame is placed a po zoelement 4, made in the form of a polygon and fastened to the frame with its corners. Thin-film 3 lectrodes 5 of the piezoelectric element, made in the form of segments, are included in the circuit of the autogenerator 6, and in the central area of the piezoelectric element a piezo-resonator 7 is made, the thin-film electrodes 8 of which are also included in the circuit of the autogenerator 6, located symmetrically with respect to the symmetry of the piezoelement, passing through the bonding points of this piezoelectric element with an elastic element. The bridges 10 connecting the body of the point piezoresonator with the body of the piezoelectric element lie on the axis of symmetry of the piezoelectric element coinciding with the axis of maximum negative power sensitivity of the point piezoresonator. To fasten the piezoelectric element with the elastic element and the elastic element with the housing, the sensor has screws 11 and 12, which also allow you to adjust the degree of compression of this piezoelectric element, and therefore adjust the frequencies as the main piezoelectric resonator

element, and located in the center of the last additional point piezoresonator.

The proposed piezoquartz pressure sensor operates as follows.

To realize differential measurement capability, 0

five

0

five

0

five

0

five

0

five

It is necessary to ensure in the system a sensitive element - an autogenerator to simultaneously generate two frequency signals, the frequencies of which would have different frequency coefficients of power sensitivity, and in absolute value would be close. In the proposed device, this is achieved by selecting a special con.

The structure of the sensitive element and the use of a two-frequency auto-generator, which simultaneously generate two information frequencies, each of which depends in a certain way on the pressure acting on the pressure sensor P. The first C0 from the generated frequencies is the anharmonic mode of the fundamental oscillation used in the piezoelectric element of the known device. Moreover, anharmonic mode of the main oscillation of the type 1, 2, L is used, the deformation zones of which are located in the peripheral regions of the piezoelectric element 4 at the locations of the sector-. the moat of thin-film electrodes 5 and do not occupy the central zone of this piezoelectric element. To ensure high activity of this anharmonic mode of the main thickness-shear oscillations, each of the two electrodes 5 of the piezoresonator piezoelectric element 4 is made in the form of two sectors located in the zones of maximum deformations of the piezoelectric element 4 when its main piezo resonator operates on mode 1, 2, 1 s the frequency of CO ,. This provides a significant increase in the amplitude of the oscillations of the anharmonic mode being excited in comparison with other modes of thickness-shear oscillations, as well as in comparison with the main oscillation of the piezoresonator.

Due to the use of such a mode of operation of the primary piezoresonator of the element 4, the entire oscillation energy with a frequency co, about 1 is concentrated in the area of the electrodes 5, made in two segments, and the zones of the piezoelectric element 4 near the points of the piezoelectric element 3 with the elastic element 3 are free from deformations, which allows to significantly increase the quality factor of the main piezoresonator

and improve the frequency stability of the generated oscillations compared with the known device

When the measured pressure P influences the membrane 2, the membrane 2 deforms and deforms the elastic element 3. As a result, the piezoelectric element 4 is angularly stressed and subjected to full compression, which is why the natural frequency sensitivity to pressure P is integral. the power sensitivity of the piezoresonator's piezoelectric element 4. This sensitivity can be determined from the dependence Kp (ei) given in FIG. 16 by calculating the following integral:

Kp ao Kp (oi,) doi,

(one)

where a is the coefficient taking into account the elastic properties of the membrane 2 and the transfer coefficient of the mechanical force by the elastic element 3,

As a result, for the dependence of the Z-axis, tots, from, on the acting pressure P, we obtain the following dependence:

CO, (P) OO, + KR, (P-PO), (2) where cOj, is the initial frequency value

20 is the coefficient of sensitivity for pressure P of the frequency of CO, and Kp is the coefficient of force sensitivity of the point piezoresonator 7 when it is loaded along

As a result, for the difference frequency of the signal removed from the output of the oscillator 6, we obtain the following expression:

CO, with the initial value of the measured p (P) (o, (P) -and (P) (+ (Kp + Kp, j) "

pressure, t, e, at ..

and

Due to the fact that the basic piezoresonator of the piezoelectric element 4 operates on the anharmonic mode of the basic oscillation of type 1, 2, 1, free from thickness-shear vibrations is not only the peripheral part of the piezoelectric element 4, but also its central region. As a consequence, it is possible (R-RO). (four)

Selecting the area of the electrodes 5 of the main piezoresonator of the piezoelectric element 4, it is possible to ensure the equality of 35 pressure sensitivity factors Kp and Kp, t, e, Kp Kpj, Kp and you can write

Qp (P) (co, -Woa) + 2Kp (PP). (5) Since both piezot piezoresonators in this area perform additional element 4, they are made into a single piezotal piezoresonator 7, a quartz plate, the information natural frequency of which (j3 is close to frequency O), and differs from the latter by the value of the difference frequency cf ( P) practically does not depend

sieve from changing ambient temperature sensor.

45

the cp of G3, -C02, which, at frequencies of CO, and cOj in the order of 5-10 MHz, is 100-150 kHz,

The thin-film electrodes of the 8-point piezoresonator 7, as well as the electrodes 5 of the main piezoresonator 50. Piezoelectric element 4, are included in the basic circuit of the auto-oscillator 6, which provides simultaneous generation of signals in the multi-frequency mode

with frequencies of CO, and Og. To ensure 55, the element is designed as a multi-high stability of the mode of the generator, fastened at the corners with the elastic two-frequency oscillations in the circuit with a Roman element that differs with the multi-frequency auto-oscillator 6, in order to increase

Claims (1)

Invention Formula A piezoquartz pressure sensor containing a housing with a membrane and an elastic element of a closed form in contact with the membrane with a piezoelectric element attached to the circuit of the oscillator connected to the circuit of the oscillator, with a piezodenal load band HC filter connected to the difference circuit frequency (, -c02. Since the additional point piezoresonator 7 is circumferentially bounded by slots 9 (FIG. 1) and connected to the body of the piezoelectric element 4 by two bridges 10, lying on its axis Z, its maximum negative power sensitivity (FIG. 2), for the dependence of frequency with, determined by resonant the frequency of the piezoresonator 7, from acting on pressure sensor P. get C02 (P) 42-Kpi (P-Po). (3) where COgj, is the initial value of the frequency (0 at the initial value of the measured pressure;, 20 is the coefficient of sensitivity for pressure P of the frequency of CO, and Kp is the coefficient of force Ch, Z, value of the piezoresonator 7 when it is loaded along Z axis, As a result, for the difference frequency of the signal removed from the output of the oscillator 6, we obtain the following expression: p (P) (o, (P) -i (P) (+ (Cr + Kp, j) " p (P) (o, (P) -i (P) (+ (Cr + Kp, j) " (R-RO). (four) Selecting the area of the electrodes 5 of the main piezoresonator of the piezoelectric element 4, it is possible to ensure the equality of the coefficients of sensitivity for pressure Kp and Kp, t, e, Kp Kpj, Kp and you can write Qp (P) (co, -Woa) + 2Kp (PP). (5) Since both piezoresonators of the piezoelectric element 4 are made in a single piezo-quartz plate, the information The frequency of the COP (P) is practically independent sieve from changing ambient temperature sensor. the element is made in the form of a polygon, fastened in corners with an elastic element, characterized in that, in order to increase Invention Formula Piezoquartz pressure sensor, containing a housing with a membrane and placed in it an elastic element in contact with the membrane of a closed form with a piezoelectric element mounted inside the electrodes included in the oscillator circuit, with piezosensitivity and measurement accuracy, each of the two piezoelectric electrodes is made in the form two segments, and in the central region of the piezoelement there is a point piezoresonator with electrodes, bounded along the contour by two arc slots arranged symmetrically with respect to no symmetry axes of the piezoelectric element extending through the point of bonding piezoelectric element with an elastic member, wherein a point piezo resonator electrodes included in the oscillator circuit. Editor M. Nedoluzhenko fie.Z Compiled by N. Bogdanova Tehred I.Popovich Proofreader L. Pilipenko Order 767/43 Circulation 777 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, st. Project, 4