SU1471068A1 - Movement transducer - Google Patents

Abstract

The invention relates to a measurement technique and can be used to accurately measure displacements. The proposed displacement transducer contains a piezoelectric element 1, the first two-section electrode 2 of which is made of variable thickness and is included in the circuits of dual-frequency oscillators 3 and 4. The second electrode 5 of the piezoelectric element 1 is mounted for movement along the surface of this piezoelectric element 1 and is also made two-section, with the first section 6 of the movable electrode 5 is connected to the circuit of the first dual-frequency oscillator 3, and the second section 7 of the movable electrode 5 is connected to the circuit of the second dual-frequency oscillator 4. The output of the first two-hour oscillator The hundredth autogenerator 3 is connected via a series-connected bandpass filter 8 and the first high-frequency amplifier 9 to the first output of the sensor (temperature data), and through the series-connected first low-pass filter 10 and the second high-frequency amplifier 11 to the first input of the mixer 12, connected by its output through the second low-pass filter 13 with the second output of the sensor (data on the movement). The output of the second dual-frequency oscillator 4 through a series-connected third low-pass filter 14 and the third high-frequency amplifier 15 is connected to the second input of the mixer 13. 3 Il.

Description

05 00

The invention relates to a measurement technique and can be used to accurately measure displacements and temperatures.

The aim of the invention is to improve the accuracy of movement measurement.

FIG. 1 shows the functional diagram of the displacement sensor {2 and 3 - the oscillation spectra obtained at the outputs of the first and second dual-frequency oscillators, respectively.

The displacement sensor contains a piezoelectric element 1, the first two-piece stationary electrode 2 of which is made of variable thickness and is included in the circuits of dual-frequency oscillators 3 and 4. The second electrode 5 of the piezoelectric element I is installed with the possibility of displacement along the surface of this piezoelement 1 and is also performed. two sections, the first section 6 of the moving electrode 5 being connected to the first dual-frequency oscillator circuit 3, and the second section 7 of the moving electrode 5 to the second dual-frequency oscillator circuit 4. The output of the first dual frequency oscillator 3 through a series-connected band-pass filter. 8 and the first high-frequency amplifier 9 is connected to the first output of the sensor, and through serially connected the first low-pass filter 10 and the second high-frequency amplifier 11 to the first input of the mixer 12 connected by the output through the second low-pass filter 13 to the second output of the sensor. The output of the second two-frequency auto-oscillator 4 through the third low-pass filter 14 and the third high-frequency amplifier 15 connected in series to the second input of the mixer 1 2. The displacement sensor works as follows.

In the initial state, with zero displacements of the moving electrode 5 of the piezoelectric element 1, this electrode is set so that its plane of symmetry passes along the interface between the fixed electrode 2 into two different thickness two-stage sections of the same area, but of different volume. Moreover, each of the two-step, multi-thickness; sections of the fixed electrode 2 is different

0

five

0

from the other thickness of their steps, and in area all four steps of electrode 2 are the same. In the initial state, sections 6 and 7 of the moving electrode 5 are installed symmetrically with respect to the center of symmetry of each of the two-stage halves of the fixed electrode 2. Due to the multi-stage design of the fixed electrode 2 of the piezoelectric element, 1 in the proposed oscillatory system, when it is included in the multiple-frequency auto-generator circuit, possible simultaneous excitation of several sufficiently intense anharmonic oscillations, the number of which in this case is equal to the number of steps of the thin-film electr genus 2.

five

0

As a result, at frequencies depending on the thickness of the core of the piezoelectric element 1 and proportional values of 1 / 0.25a, where a is the size of an electric 5 and 2, four anharmonic oscillations with frequencies Wj — co occur in piezoelement 1. Due to the effect of energy capture, the energy of the first bond of them with. frequency And, mainly concentrated between the first section 6 of the movable electrode 5 and the overlapping part of the electrodes 2 of the smallest thickness. The energy of the second oscillation with a frequency (0, concentrated on between section 6 of the moving electrode 5 and the second half of the left section of the electrode 2 of variable thickness, Energy; oscillations with a frequency

0 zoelement

the moving electrode 5 and the thickest part of the electrode 2 of variable thickness. The energy of the fourth gauge is concentrated in the area of pie-1 between the right section 7

The frequency baths are concentrated in the body of the piezoelectric element 1 mainly between section 7 of the moving electrode 5 and the right-half of the second section of the electrode 2 of variable thickness. The spacing between the frequencies (O, - CO of four anharmonic oscillations is determined by the mass difference between the different thickness parts of electrode 2, overlapping at each instant of time by the surfaces of the right and left sections 6 and 7 of the moving electrode 5. This is due to the fact that the piezoelectric element 1, located between the mutually overlapping areas of the electrodes 6,7 and 2, create favorable conditions

to localize the energies of the corresponding anharmonic oscillations.

The excitation of all four anharmonic oscillations in piezoelement 1 is also possible when using one oscillator, which should work in this case in the multi-frequency mode. However, this mode of operation is associated with the emergence of a large number of combination frequencies at the output of the autogenerator, which makes it difficult to select the information components of the output signal spectrum, and also significantly worsens the short stability of these frequencies. As a result, the level of 1pum at the output of the selection elements of the displacement transducer increases, and, consequently, the error of zero increases in measurements of the latter. To reduce the level of instability of the information components of the sensor output signals, as well as to provide the necessary low

the level of the side components of the spectrum in the proposed displacement sensor introduced the second two-frequency oscillator 4, the circuit of which is connected to the electrode 2 variable

thickness and right section 7 of the moving electrode 5.

Thus, the two-frequency auto-oscillator 3 provides continuous excitation of anharmonic oscillations with frequencies co, and do (Fig. 2 and the two-frequency auto-oscillator 4 - generation of anharmonic oscillations with frequencies co and a (Fig. 3). Because each of the two-frequency auto-generators 3 and 4 contains a nonlinear transistor element, the spectra of their output signals contain components with frequencies n (o, g, and mWj ± TC04, respectively, where type is integer numbers. The maximum amplitudes in the spectra of the output signals of autogenerators 3 and b FLS have components with aggregate (G,., and with (3 .2 also raznostny- E SDR and Mp frequencies prdaem

 Wi -,

Qp, CO, - COj-,

"C w, + c04-,

G) pj. c04-c0j.

The component of the output signal of the autogenerator 3 with the total frequency is derived from the discrete spectrum of the

(FIG. 2) and through the first high frequency drive 9 is fed to the first output of the sensor. The difference component of the spectrum of the same signal with a frequency to p is selected by the first lowpass filter 1 O and through the second high-frequency amplifier P enters one of the outputs of the mixer 12, the second input of which receives the signal with the difference frequency Op, j, the output HZ output the signal of the second two-frequency oscillator 4 using the third low-pass filter 1 4 and amplified by the third high-frequency amplifier 1 5.

A signal from the output of the mixer 12, containing components with combination frequencies PEP, is fed to the input of the second low-pass filter 13, which separates the component with the differential frequency. This signal is then fed to the second output of the sensor.

When the electrode 5 is moved, the mass of the electrode in the active zone of the most high-frequency oscillation with frequency W decreases, and in the active zone oscillations with frequency W increases. As a result, changes in the frequencies QJ and SL will be different in sign and approximately equal in magnitude, with CO increasing, CO decreasing, and the difference frequency tOp, "s, - (ja. Increasing (Fig. 2). In contrast, the shift to the right of the moving electrode 5 leads to a decrease in the mass of the electrode electrode 2 in the zone of active oscillations of the lowest frequency 65 and to a corresponding increase in the mass of electrode 2 in the active zone of oscillations with a frequency of CO. In accordance with this, the frequency 63J grows, the frequency 63 falls, and the difference frequency 02 604 - with J Decreases (Fig. 3). The formation frequencies C04 60p and cp are functions of both physical quantities measured by the sensor — temperature T and displacement / il. For the indicated frequencies, we obtain

c, (,) 4о34- 5t + LO),) -,

С0р, (с ,, +) - {и1- «а + с.и2т); : Wpl (4o-Ш4 + Ш4т; (iQ + ьco, + co),

where so, oh, slts ,,

Ie initial frequencies, -U at

p, lso

& U

g

rm

LM, & CO

middle position of the moving electrode 5;

- increments of the frequencies W, ω of the displacements of the electrode 5 with respect to the symmetry of the piezoelectric element 1;

Lt

, MAT temperature increments of CO, gbE,}. with changes in ambient temperature T. The total frequency of the OE practically depends on the magnitude of the displacements and is, with great approximation accuracy, a function of temperature T

, (,) - 2 & se,

where tw °

 (o ,, +) - the average increment of the total frequency QP, under the influence of temperature. Result difference frequency

(ABOUT

R

about . J -co p, - (about zod + COoel - (to, o - (- (o, 0 jj

- “- with

B (t) mi

(ABOUT,

.),

35

thirty

“2

& 4 (& Yes) M,

of different thickness parts of the left and right sect of the non-movable electrode 2 {- masses of four different thickness parts of the fixed electrode 2J

L, (4t),,

af (& t) - increments of mass difference of different thicknesses

 - m (

- f) L, (LSh1)

30, the inputs of the bandpass filter and the first lowpass filter are connected to the output of the first two-frequency generator, one of the piezoelectric electrodes is of varying thickness and closed on its surface, and the other is mounted for movement along the opposite surface of the piezoelectric element, which differs from By the fact that, in order to improve the accuracy of the measurement of displacements, it is equipped with series-connected mixer and a second low-pass filter connected in series by a second two-frequency autogen Ator, third low-pass filter and the third high-frequency amplifier, the outputs of the second and third high frequency amplifiers are connected to inputs smrsitel movable and stationary electrodes formed dvuhsektsi oinmi piezoelectric element, and the second section podvizhnog electrode and the stationary electrode

parts of the electrode 2. in the active vibration zones with g are connected to the second two-frequency

frequencies S, - j auto generator.

,

five

The output from the output signal of the mixer 12 through the second low-pass filter 13 is practically independent of temperature and is determined only by the value of the measured displacement.

Thus, the change in the functional scheme of the known sensor

Q displacements and. An improvement in the design of the sensing element of this sensor provides an increase in almost two times the slope of the displacement-frequency conversion characteristic. In turn, this leads to a corresponding increase in measurement accuracy and a decrease in the sensitivity threshold of the sensor.

Ula Invention Form

0

A displacement sensor containing the first two-frequency auto-generator piezo element with two electrodes connected to the first two-frequency

5 a generator, a serially connected bandpass filter and a first high-frequency amplifier, a series of first low-pass filter and a second amplifier

0 high frequency, the inputs of the bandpass filter and the first low pass filter are connected to the output of the first two-frequency generator, one of the electrodes of the piezoelectric element is made of varying thickness and is marked on its surface, and the other is mounted for movement along the opposite surface of the piezoelectric element, so that that, in order to increase the accuracy of the measurement of displacements, it is equipped with a series-connected mixer and a second low-pass filter connected in series by a second two-frequency auto generator, the third low pass filter and the third high-frequency amplifier, high frequency amplifiers of the second and third outputs are connected to inputs smrsitel, the movable and stationary electrodes formed dvuhsektsi- oinmi piezoelectric element, and the second section of the movable electrode and the stationary electrode

0

five

0

, -u / 2

l: -L

(iJl

CDuz.l

and).

C1

tt}

 ,

to,

 sg

(t)

Fig.z

Claims (1)

The claims 20 A displacement sensor comprising a first · two-frequency oscillator; a piezoelectric element with two electrodes connected to the first two-frequency 25 generator, a bandpass filter and a first high-frequency amplifier connected in series, a first low-pass filter and a second high-frequency amplifier 30 connected in series, the inputs of the band-pass filter and the first low-pass filter are connected to .. the output of the first of a two-frequency generator, one of the electrodes of the piezoelectric element is made of variable thickness and mounted on its surface, and the other is mounted with the possibility of movement. ^ along the opposite surface of the piezoelectric element, distinguishing ₄₀ s in that, in order to increase the accuracy of measuring displacements, it is equipped with a series-connected mixer and a second low-pass filter, 4g in series connected by a second two-frequency oscillator, a third low-pass filter and a third high-frequency amplifier, outputs the second and third high-frequency amplifiers are connected to the inputs of the mixer, the movable and fixed electrodes of the piezoelectric element are made in two sections, and the second section of the movable electrode and fixed electrode 25 are connected to a second two-frequency oscillator. Fig. G