RU1770794C - Piezoelectric pressure pickup and method of manufacturing the same - Google Patents

Abstract

Use: in the design and manufacture of miniature sensors of rapidly varying pressures and forces. The goal is to ensure stable transmission characteristics and simplify manufacturing. SUBSTANCE: device consisting of a piezoelectric element 1 with current collectors 2, enclosed inside a piezoceramic holder body 3, made in the form of a sheath, the inner wall of which is spaced from the outer surface of the piezoelectric element, since the material of the case and the piezoelectric element are the same, no residual stresses occur during heat treatment. 2 s.p. f-ly, 6 ill.

Description

The invention relates to the field of measurement technology and can be used in the design and manufacture of sensors for quick-change, acoustic and pulse pressures.

A pressure sensor is known, comprising a housing, a sensing element in the form of a set of piezoelectric disks covered by a temperature compensating washer and current collectors.

The disadvantages of this sensor are reduced sensitivity due to the need to provide tension to the holder body; limited measurement temperature range due to internal stresses arising in heterogeneous sensor materials - metal body, piezoelectric element, sealing materials and adhesives; drift of the transfer characteristics of the sensor due to relaxation processes occurring in the sealing and adhesive materials, which lead to unsteady deformation fields acting on the piezoelectric element.

A piezoelectric sensing element of a sensor of stereoplastic pressure is known, comprising a housing, a glass in which a disk piezoelectric ceramic element and a thermally insulating gasket are placed.

The disadvantage of this design is the complexity of the design, low measurement accuracy due to the presence of dissimilar materials and nodes with different thermal expansion coefficients, which, when exposed to temperature, will create deformation fields in the piezoelectric element and cause its destruction s | h o h

Yu

nor the occurrence of an uninformative signal.

A known method for manufacturing a piezoelectric sensor, comprising mixing a piezoelectric ceramic powder with a thermosetting or thermoelastic resin, pouring the mixture into a housing with electrodes placed therein, and curing the mixture.

A known method of manufacturing piezoelectric pressure sensors, including the manufacture of a piezoelectric element, applying to the side surfaces not sensitive to the pressure of the film, sublimating adhesive, pouring with sealant and heat treatment.

The disadvantages of the method include the low manufacturability due to the difficulty of applying the film and the uncontrollability of its thickness, which can lead to loss of sensitivity of the sensor when the measured value (pressure) reaches its maximum value due to the fact that the increment of the transverse size of the piezoelectric element under the action of deformation exceeds the gap obtained by evaporation of the film of sublimating glue.

The aim of the invention is to increase the accuracy of measurement and increase the manufacturability.

This goal is achieved in that in a piezoelectric pressure sensor comprising a housing and a piezoelectric sensing element with current collectors fixed therein at its ends, a gap D is made between the side surface of the housing and the housing, the housing is made in the form of a closed shell made of piezoelectric ceramic, and the gap size D satisfies the relation

Max

where D is the clearance;

Rmax - maximum force acting on the sensing element;

h; S; E; and c, respectively, the distance between the ends of the sensitive element, the value of its cross section, the elastic modulus of the material of the sensitive element.

This goal is achieved in that in a method for manufacturing a piezoelectric pressure sensor, comprising pouring a piezoelectric sensitive element with current collectors with sealing material, heat treatment and pblization of the sensitive element, before filling the sealing material, a sleeve is made of sublimating material, a piezoelectric sensor is installed in the sleeve current collectors, after filling with sealing material, it is crimped around the sleeve and of the element, and heat treatment is carried out by successively raising the temperature until the sleeve is evaporated, and then until the piezoelectric material is fired. moreover, the polarization of the sensing element is carried out by applying a high electrical voltage to the current collectors.

The implementation of the proposed devices and the method of its manufacture are shown schematically in FIG. 1 (device) and in FIG. 2 - FIG. 6 (method).

The list of items: 1 - piezoelectric sensitive element, 2 - current collectors. 3 - piezoceramic case - holder, 4 - gap; 5 - measurable value; 6 - technological sleeve, 7 - hole for current collectors, 8 - piezoelectric element, 9 - piezoceramic material, 10 - mold, 11 -seal, 12 - prepress force, 13 - pin, 14 piezoelectric pressure sensor before

polarization, 15 - heater. 16 - source of high voltage; 17 - electric power lines of the polarizing field.

The piezoelectric pressure sensor consists of a piezoelectric sensitive element (hereinafter referred to as the piezoelectric element) 1 with current collectors attached to it at the ends 2. The piezoelectric element is surrounded on all sides by a piezoelectric housing-holder 3, made in the form

shell, the inner wall of which is spaced from the outer surface of the piezoelectric element by the value of the gap D-4.

A piezoceramic pressure transducer operates as follows; at

when exposed to a rapidly varying or acoustic pressure, the piezoelectric element is deformed. As a result of the direct piezoelectric effect on the current collectors, an electric charge arises, which

fed to secondary equipment for measurement and recording. The gap D between the walls of the piezoelectric element and the shell allows the piezoelectric element to be freely deformed.

The manufacture of a piezoelectric pressure transducer is as follows; a technological floor is made of a sleeve (from a sublimating adhesive with a thickness equal to the gap D, in which

two through holes 7 for current collectors are formed. The piezoelectric element 8 is pressed from piezoelectric ceramics and placed in the technological sleeve 6. Current collectors 2 are applied from above through the holes on the piezoelectric element (in some cases, the piezoelectric element can also be equipped with current collectors). The assembly is placed in a releasable mold 10, which is filled with raw piezoceramics (slip) 9 with the necessary additives. The piezoceramics are pressed with a sealant 11, for example, a piston, with the necessary prepressing force of 12, the assembly is dried and subjected to stepwise heat treatment with a heater 15, as a result of which the material of the process sleeve is sublimated through the pores of the raw piezoceramics or special technological holes, and with a further increase temperature - firing piezoceramics. As a result of heat treatment, a non-polarized piezoelectric pressure sensor 14 is obtained, in which a gap D is formed between the piezoelectric element and the inner wall of the housing. The final operation of the method is a polarization operation in which a polarizing voltage is applied to current collectors 16 from current collectors 2 ; a strong electric field (conventionally indicated by force lines 17) arises in the volume of the piezoelectric pressure sensor, which orientes the electric domains of the piezoceramics in the direction of the force lines. Polarization of the material occurs both in the piezoelectric element and partially in the side walls of the shell, which leads to an increase in the overall sensitivity. After removing the polarizing voltage in the piezoelectric module, the polarization of the domains is maintained.

An example of the method. The starting material, KS-1 sublimating glue, is melted at a temperature of 65 ... 70 ° C and the melt is poured into a mold, as a result of which a technological hollow sleeve is obtained. For ease of installation of the piezoelectric element, a cut is made in it. A PZ type ceramic piezoelectric element is pressed and dried. A ready-made mass-produced piezoelectric element, for example, PM-8, PM-7, can also be used. The piezoelectric element is inserted into the process sleeve, and the assembly is placed in a releasable mold, which is filled with a piezoceramic slip material consisting of TsTS-19 piezoceramic mixed with oleic acid solvent and paraffin plasticizer. Piezokera is pressed.

Miku with a specific force F 0.3-0.5 kg / cm2 and dried in air at room temperature for 10-12 hours. Next, the assembly was placed in a vacuum microwave oven

and heat treatment was performed in stages - first, at a temperature of 110-125 ° C for 10-15 minutes to remove the adhesive sleeve, then the temperature rose to 700-100 ° C and the ceramics were fired in

for 4-5 hours. The vacuum was maintained at the same time as mmHg. The piezoceramic pressure sensor was placed in a special device and a voltage of 1200 V was applied to it for 10 minutes,

after which its electrophysical characteristics were checked: piezoelectric sensitivity, temperature and temporal stability, insulation resistance, etc.

twenty

Claims (2)

The claims 1. A piezoelectric pressure sensor comprising a housing and a piezoelectric sensing element fixed to it at its ends with current collectors between the side surface of which and the housing have a clearance A, characterized in that, in order to increase the accuracy of measurement and improve manufacturability, the housing is made in it a closed shell made of piezoelectric ceramics, and the gap size satisfies the ratio: Max . S E where Pmax is the maximum force acting on the sensing element when pressure is applied to the shell; h, S, E, / g are, respectively, the distance between the ends of the sensitive element, its cross section, the elastic modulus, and the Poinson's ratio of the material of the sensitive element. 2. A method of manufacturing a piezoelectric pressure sensor comprising pouring a piezoelectric sensitive element with current collectors with sealing material, heat treatment and polarization of the sensitive element, characterized in that, in order to improve manufacturability, they are made before filling with sealing material a sleeve of sublimating material, a piezoelectric sensitive element is installed in the sleeve, with current collectors, after filling with sealing material, it is crimped around the sleeve and the sensor, and heat treatment is carried out by successively raising the temperature until the sleeve is evaporated and then firing the piezoelectric material, and the sensor is polarized by applying a high electrical voltage to the current collectors. L x / F e / 7 6 R. 2 ъ.4  &