RU1770790C - Pressure pickup - Google Patents

Abstract

Usage: in measuring technique, in sensors for measuring static and dynamic pressures of liquid and gaseous media. The goal is to increase accuracy by reducing temperature error. SUMMARY OF THE INVENTION: the sensor comprises a capacitive transducer 1, including a membrane 3 with a rigid center 4 and a thickened peripheral section 7 16 VJuJ com 5, made integrally with the supporting base 6, a plate 7, which is attached to the peripheral section 5 with a predetermined gap, the value of which is set due to the angles 8. On the membrane 3 and the plate 7 are made in a mirror-symmetric image the central round electrodes 9, forming a measuring capacitor, and the annular peripheral sections 10, forming a reference capacitor. In addition, two additional voltage dividers are installed on the membrane 3, each of which consists of thermistors 11, 12, 13, 14 having the shape of half rings. One of the thermistors of each divider is covered with an additional dielectric layer 15. The topologies are protected from external factors by pressure enclosure 16, Positive effect: the accuracy is doubled. 1 ill. 9 f J P P YP L Y. XI XI o XJ che o

Description

The invention relates to measuring technique and can be used in sensors for measuring the static and dynamic pressures of liquid and gaseous media.

A capacitive pressure sensor is known comprising a deflection membrane and a flat reference plate. Two ring-shaped electrodes are mounted on the membrane: the first is a sensitive element, the second is a reference element. The reference plate, facing the deflection surface of the membrane, also contains a sensing element in the form of an annular electrode, which together with the membrane electrode forms a capacitive sensor. A mechanical spacer installed in the central part of the space between the membrane and the reference plate maintains a constant distance between them, without preventing the deflection of the membrane. The reference plate is closed by a lid that connects to the membrane along the perimeter. A reference ring-shaped electrode is mounted on the lid, the position of which corresponds to a reference ring-shaped electrode on the membrane. These two ring-shaped electrodes form a reference capacitive sensor (US patent No. 4562742, CL G01 L9 / 12, 1975).

A disadvantage of the known device is the high temperature error caused by the fact that the mechanical spacer has an excellent temperature coefficient of linear expansion compared to a membrane and a flat reference plate. Consequently, when the temperature changes, a false movement of the electrodes occurs, which means that a temperature error appears.

In addition, the output characteristic of the sensor has a large non-linearity due to the fact that when the membrane is deformed along with the movement of the measuring electrode, at a certain pressure, the reference electrode also moves in the same direction. As a result of these reasons, the measurement accuracy is reduced.

The closest in technical essence to the proposed design is a pressure sensor in which the strain transducers are made in the form of measuring and reference capacitors, the electrodes of the first placed opposite each other on the central, and the second on the peripheral parts of opposite elastic walls, and the internal cavity is sealed the chamber is evacuated. Plates

The measuring capacitor is round and centrally located on opposite inner planes of the elastic walls. With this arrangement, the pressure applied to the sensor housing from the outside causes a relative movement of the capacitor plates and provides a signal corresponding to the applied pressure, while the plates of the reference capacitor are essentially stationary (USSR patent N; 593674, class G 01 L9 / 12, 1974).

A disadvantage of the known construction is the presence of a temperature error due to different temperature deformations of the central electrodes, in comparison with peripheral ones located on a more massive element. In addition, in the known design there are no elements of thermal compensation, which is not

0 allows to achieve measurement accuracy at the modern level.

The aim of the invention is to increase accuracy by reducing the temperature error.

5 The goal is achieved by the fact that in the pressure sensor containing the evacuated casing, a strain transducer made in the form of two capacitors, the electrodes of which are placed one against the other on the central and peripheral elastic elements, two additional voltage dividers are provided on the membrane, each of which consists of two thermistors,

5 and in each divider, one thermistor is covered with an additional dielectric layer.

The introduction of two additional dividers, each of which consists of two thermistors, provides temperature compensation of the initial level and sensitivity of the output signal by changing the ratios of the resistance values of the dividers depending

5 from the temperature change of the half rings, as well as their placement between the rigid center and the thickened peripheral section - provides the necessary resistance value of each thermistor, and

They also perceive the average integral temperature on the membrane under the rapidly varying thermal effects of the measured medium.

The introduction of additional coverage

5 dielectric layer on the surface of two thermistors, one of each divider, provides the possibility of obtaining in each divider thermistors with different signs of the temperature coefficient of resistance, which, in its

in turn, it increases the efficiency of temperature error compensation.

Setting the thickness of the dielectric layer to not more than the maximum stroke of the rigid center ensures that there is no mechanical damage to the dielectric coating.

Comparative analysis with the prototype allows us to conclude that the claimed pressure sensor is characterized in that, in order to increase accuracy by reducing the temperature error, the second electrodes of the capacitors are placed on a plate inserted into the sensor installed inside the housing, and two additional dividers are applied to the membrane voltages, each of which consists of two thermistors with a positive and negative coefficient of resistance having the form of half rings and located between the rigid center of the membrane and its peripheral section, moreover, one of the thermistors of each divider is covered with an additional dielectric layer with a thickness not exceeding the maximum stroke of the rigid center of the membrane. Thus, the claimed technical solution meets the criterion of novelty.

An analysis of the known technical solutions (analogues) in the studied area allows us to conclude that there are no signs in them that are similar to the existing distinguishing features of the claimed pressure transducer and to recognize significant differences as the corresponding solution.

The drawing shows the construction of a capacitive pressure transducer and topologies on the surface of the membrane.

The pressure sensor includes a capacitive transducer (PE) 1 and a capacitance to voltage (PEN) 2 transducer (not shown in the description). PE 1 includes a strain transducer - a clamped membrane 3 with a rigid center 4 and a thickened peripheral section 5, made in one piece with the supporting base 6, a plate 7, which is attached to the peripheral section 5 with a predetermined gap, the value of which is set by the corners 8. the membrane 3 and the plate 7 are made in a mirror-symmetric image of the Central circular electrodes 9, forming a measuring capacitor, and the annular peripheral sections 10, forming a reference capacitor. In addition, two additional voltage dividers are installed on the membrane 3, the thermistors of which 11, 12, 13, 14 have.

the shape of half rings, and one of the thermistors of each divider 12 and 13 is covered with an additional dielectric layer 15. Topologies from the influence of external

factors protected by pressure enclosure 16.

The pressure sensor operates as follows;

When the measured pressure Px is applied to the membrane 3, it deflects and the relative movement of the hard center 4 by x increases, as a result, the distance between the electrodes 9 located on the hard center 4 and in the center of the plate 7 changes (decreases). is

(increases) the capacity of the central capacitor by the value of Cx and becomes equal to

twenty

SC Cx + ACx

(D

where SC is the capacitance of the central capacitor;

Cx is the initial capacitance of the central capacitor, consisting of electrodes 9; ACx is the value of the increment of the capacitance from the change in the gap.

Due to the fact that, without pressure, the initial capacitance Cx is equal to C0, expression (1) takes the form

 ACx (2)

Taking into account that when the pressure is applied, the peripheral electrodes 10 do not move, therefore, the capacitance of the peripheral capacitor is

Cn Co

where Cn is the capacitance of a peripheral capacitor consisting of electrodes 10.

Thus, from the pressure Px, the capacitance of the central capacitor, consisting of electrodes 9, increases by

ACx, and the capacitance of a peripheral capacitor consisting of electrodes 10. does not change. In PEN, the output signal is proportional to the magnitude of the emC bone relationship. . The magnitude of this ratio is

the lowest level of the measured pressure (Po), corresponds to the value

 .3

since the capacitances of the central and peripheral capacitors are set equal at the lowest level measured

pressure. The value of the ratio at the limit value of the measured pressure (Px) corresponds to the value

Sz, r Sz H-DSH / l)

u (Px) (4)

as the capacitance of the central capacitor increases and the peripheral capacitor remains unchanged.

In PEN, the output signal changes

SC

in proportion to the ratio p

vn

consequently, a change in pressure.

The conversion functions of the capacitive sensor can be represented as follows: i.e. the pressure change is transformed in the membrane into relative deformation, which causes the relative movement of the electrodes, resulting in a change in capacitance, which leads to a change in voltage in the PEN.

The output signal is generally expressed as

Uc

Kmp2

(Kmp1

With

SHU

where Uvykh - sensor output signal;

Uo - zero signal of the sensor;

КМп1., КМп2 - conversion coefficients of zero and sensitivity, respectively.

A change in temperature at the sensor causes uneven temperature deformations on the central and peripheral parts of the membrane. Consequently, the capacitances of the capacitors Cc and Cn do not vary equally with the temperature, which means that the initial output signal from the temperature in the PE also changes. The elastic properties (elastic modulus) of the membrane also change with temperature. Consequently, the increments of the capacitance Cx vary from the same pressure value, which means that the sensitivity of the output signal in the PE changes. In general, the output signal when the temperature changes on the sensor is expressed as

Total ((t)) {6)

where t is the temperature value at the sensor.

When the temperature in the temperature-dependent voltage dividers placed on the membrane 3 changes, the resistances of the thermistors 11, 12, 13, 14 change. Moreover, in the thermistors 11 14, the temperature increment causes an increase

the value of resistance, and in thermistors 12 and 13, an increase in temperature causes a decrease in the value of resistances.

5 The direct dependence of the resistance values in thermistors 11 and 14 is due to their positive temperature coefficient of resistance (TCR), as thin-film metal, for example,

10 nickels. The inverse dependence of the resistances in thermistors 12 and 13 is caused by negative TCRs, such as thin-film and metal, for example, nickel and coated with an additional dielectric layer 15. for example, silicon monoxide. The negative value of TCS of nickel thermistors coated with silicon monoxide is due to the incorporation of silicon elements into the intergranular spaces, along with depreciation compounds of the NISI2 type. NiaSI NiSi and oxides SiO and Si02 with low electrical conductivity. The temperature regime of formation provides a high diffusion (migration) rate of Si along grain boundaries several orders of magnitude higher than into the main body of the film and provides an equilibrium structure over the entire thickness of the strain gauge.

30 Thus, the connection of thermistors 11 and 12 to the PEN divider, which forms the initial level of the sensor, ensures the functional dependence of Kmp1 on temperature and thereby compensates for the initial level Ukhikh. The connection of thermistors 13 and 14 to the PEN divider, which forms the sensitivity of the sensor, ensures the functional dependence of KMp2 on temperature and thereby compensation for the steepness of the Uvykh characteristic.

Therefore, in the proposed technical solution, almost complete temperature compensation of the zero level and sensitivity is realized due to the functional dependence of the conversion coefficients on temperature KMn1 - f {t}, Km, - f (t)

In relation (6) due to changes

With 50 coefficients Kmp1 and Kmp2 versus temperature, a correction of zero level and sensitivity is achieved. In general, the output signal is expressed as

55

Ue (K-1 (-§) (7)

which means Uvykh; independent of temperature change.

The proposed pressure sensor compares favorably with the previously known improved measurement accuracy due to the almost completely eliminated error from the temperature of both the initial output signal and sensitivity.

Thus, the technical and economic advantage of the proposed design in comparison with the prototype is an increase of 2-3 times the measurement accuracy due to the exclusion of temperature error.

Claims (1)

SUMMARY OF THE INVENTION A pressure sensor comprising a vacuum housing and a strain transducer made in the form of two capacitors, the electrodes of which are placed one against the other, the first 0 5 0 capacitor electrodes are located on the central and peripheral sections of the pressure sensing membrane, characterized in that, in order to increase accuracy by reducing the temperature error, the second capacitor electrodes are placed on a plate inserted into the sensor installed inside the housing, and two additional voltage dividers are applied to the membrane, each of which consists of two thermistors with a positive and negative coefficient of resistance, having the shape of half rings and located between the rigid c ntrom membrane and its peripheral portion, wherein each one of the thermistors divider covered additional dielectric layer, not thicker than the maximum stroke of the rigid center of the membrane.