SU1553858A1 - Piezoresonance pressure pickup - Google Patents

Abstract

The invention relates to piezoresonance pressure sensors and can be used to measure absolute and differential pressures with increased accuracy. Sensor (D) is characterized by increased thermal stability and vibro-impact resistance and low hysteresis. Case 1 D is made at the same time the whole with a cantilever beam 2, equipped with piezoelectric elements 7, 8, and with a power-transmitting and balancing systems. Two rocker arms 14, 15 of the force-balancing system have elastic supports 16, 17 in the form of two-sidedly cut rods, made entirely with the body 1 in its opposite walls. The rocker arms 14, 15 are made entirely with supports 16, 17, have one end balancing weights 20, 21 at one end. The other ends of the rocker arms are made integral with the force-transmitting rods 10, 13 located above and below the frame konstruktrukie piezoelectric elements 7, 8, and each rod has double-sided cuts to improve flexibility. The action of the measured pressure through the membrane 9 and the force-transmitting rods is transmitted to the cantilever beam 2, causing strain elongation - compression of the piezoelectric elements 7, 8. The deformation of the piezoelectric elements is transformed into a frequency and the output signal in the form of a difference of two frequencies proportional to pressure is obtained at the sensor output. 2 Il.

Description

its opposite walls. The rocker arms 1, 15, made in one piece with the supports 16, 17, have at one end movable balancing weights 20, 21. The other ends of the rocker arms are made in one piece with the force-guiding rods 10, 13 located above and below the frame of the piezoelectric elements 7 , 8, and each stem has double-sided cutouts for

their compliance. The action of the measured pressure through the membrane 9 and the force-sending rods is transmitted to the cantilever beam 2, causing strain elongation - compression of the piezoelectric elements 7, 8. The deformation of the piezoelectric elements is transformed into a frequency and the output signal in the form of a difference of two frequencies proportional to pressure is obtained at the sensor output. 2 Il.

The invention relates to a control technology and, in particular, to sensors for measuring absolute pressure.

The aim of the invention is to reduce the measurement error by improving thermal stability and vibro-impact resistance.

Figure 1 shows a piezoresonance sensor; Fig. 42 is a block diagram of the measurement.

The sensor includes a housing 1 in which piezo elements 7 and 8 are fixed to a cantilever beam 2, which is made in one piece with it, a cantilever beam 2 through quartz bars 3 6. The lead ends of the piezoelectric elements are connected to the leads of a hermetic lead (not shown) attached to the housing 1. The housing 1 has a membrane 9 with a rigid center connected through the rod 10 to the end of the beam 2. The stem 10 has bilaterally cut-outs 11, 12 that increase his malleability. To the opposite side of the beam 2 is attached an additional rod 13, also having cutouts. The force balancing system is made in the form of two arms And and 15, which are supported on the projections 18, 19, resiliently supported by supports 16, 17, which are entirely made in the housing 1. The balance arms on the ends have balancing weights 20 and 21, the location of which is established experimentally. The pressure through the nozzle 22 is transferred to the membrane 9 with a rigid center. Fig. 1 shows the technological holes required for manufacturing in the milling process, Alignment rods 10, 13, cantilever beam 2, rocker arms 1, 15, elastic supports 16, 17 are made in one piece with the body 1 of a single blank.

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The piezoelectric elements 7 and 8 are included in the circuit of the autogenerators 23, 2k (Fig.2). To increase the sensitivity, frequency multipliers 25 and 26 are included, the output signals of which with frequencies f; and f are fed to mixer 27. At the output of the mixer, the signal has a frequency f / | -f2.

The sensor works as follows. 5 The pressure P is transmitted through the rigid center membrane 9 as a force through the rods 10 and 13 to the end of beam 2. If, due to beam deformation, piezoelectric element 7 expands and increases its frequency by + DЈ, then piezoelectric element 8 compresses, reducing its frequency by magnitude - & f.

After multipliers 25 and 26, the frequency of the autogenerators becomes n (f0 + Af) and n (f0- & O (the frequency of the autogenerators is taken to be Јо), where n is the multiplication factor. After the mixer 27, the output signal frequency will be + n2uf. The possibilities of measuring both the pressure and the rarefaction of the initial frequencies of autogenerators should differ somewhat from one another.

To increase thermal stability, the front and rear walls of the sensor are covered with lids and welded around the perimeter with the housing. After that, a vacuum of 0 - mm Hg is created in the closed volume of the piezoresonance sensor.

In Fig. 1, the dotted line shows a second, similar membrane with a rigid center, attached to the body and closed with a lid containing a fitting. 5 This design is already a differential pressure sensor.

In the proposed sensor is much higher thermal stability. This is obus0

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This is due to the fact that force-balancing systems in the form of rocker arms with balancing weights have a symmetrical arrangement above and below the beam, connecting each rocker arm through the supports to the opposite walls of the body. If, due to the temperature change, the structural dimensions of the elements located above and below the piezoelectric elements change, the deformations will be the same and this will not lead to the appearance of spurious output signals.

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Full of force-transmitting symmetry,

A force-balancing system with respect to the piezo-element frame design allows a stable vibro-shock state to be obtained without the appearance of false output signals.

Performing the mechanical part of the sensor from one piece of metal makes it possible to exclude mutually shifting structural elements, i.e. the created monolithic structure allows to significantly reduce the possible hysteresis. Since the frame structure with attached piezoelectric elements allows to obtain a sufficiently high sensitivity, the need for deformation of the membrane with a rigid center is insignificant and does not exceed ten microns, the resulting hysteresis is small and practically can be neglected. If necessary, a membrane made of an amorphous quartz plate can be used instead of a corrugated membrane. In the proposed design, the absence of shifts has double-sided cuts.

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This allows us to significantly reduce the possible corresponding errors.

The proposed construction is made by milling.

Claims (1)

Invention Formula A piezoresonance pressure sensor, comprising a housing in which a membrane is fixed, connected through a main force-transmitting rod with an elastic element in the form of a cantilever beam with two notches on opposite faces, on which piezoelectric elements are fixed, in order to reduce the measurement error by increasing thermal stability and vibro-impact resistance, it is equipped with two rocker arms — the first and second with movable balancing weights at one of the ends and elastic supports connected to the body, and up to An additional force-sending rod, wherein the first rocker is connected to the main force-sending rod, and the second to an additional force-sending rod, which is connected to the end of the cantilever beam from the side opposite to the main force-transmitting rod connected to it, and the body, cantilever beam, is force-transmitting stocks, yokes and elastic-. These supports are made in one piece, and the main and additional force-transmitting rods at the points of their connection with the cantilever beam and the rocker arms5 0 five FIG. 2 .