RU1793286C - Capacitive pressure transducer - Google Patents

Abstract

A pressure transducer is a measurement technique and can be used in various fields of science and technology to measure the pressure of a liquid or a different medium. The goals are to increase the gas sensitivity, noise immunity and precision measurements. SUMMARY OF THE INVENTION: This pressure sensor comprises a cushion capacitively 1, an elastic element 1 in the form of a membrane 2, which is integral with the support base 3, a movable electrode 4 of the measuring capacitor located on the surface of the membrane, an annular stationary electrode 5 of a reference capacitor, placed on the supporting base 3, the stationary electrodes 6 and 7 of the measuring and reference capacitors located on the plate 8. A distinctive feature of the sensor is that in it the membrane 2 is made without a rigid center and the surface of the plate 8, on which the fixed electrode 6 of the measuring capacitor is located, satisfies the surface equation of an elastic flat membrane deformed by a pressure 1.2 to 1.5 times the nominal pressure of the sensor. Mathematical expressions are given for the shape of the measuring capacitor electrodes 4, 6, the satisfaction of which minimizes the non-linearity of the sensor conversion function. Positive effect: increase in sensitivity by 4 times, decrease in the influence of stray capacitances on measurement accuracy by 30%. 1 ill. (L C

Description

The invention relates to measuring equipment, in particular to capacitive sensors, intended for use in various fields of science and technology related to the measurement of static-dynamic pressures of liquid and gaseous media.

A capacitive pressure sensor is known which comprises an elastic element in the form of a circular membrane with a circular annular electrode at the periphery, in the center of which a circular disk is attached with an electrode at the periphery mirror-symmetrical to the electrode of the elastic element.

A disadvantage of the known construction is the large dynamic error in the measurement of rapidly varying pressures, associated with the low natural frequency of the elastic element due to the considerable mass of the plate attached to the center of the membrane.

Known capacitive pressure sensor containing a housing, an elastic element in the form of a membrane with a rigid center, made in one piece with the supporting base, a circular movable electrode of a measuring capacitor located on the surface of the membrane in the region of the rigid center, an annular fixed electrode of a reference capacitor located on the supporting base , mirror-symmetric fixed electrodes of the measuring and reference capacitors located on a plate connected by spacers with an elastic element around se ries at three points, and the gap between the electrodes is formed with the excess of the maximum displacement of the movable electrode by 10-20%.

A disadvantage of the known capacitive sensor is its low sensitivity to pressure due to the large cylindrical stiffness of the membrane having a rigid center. Other disadvantages of the known capacitive sensor are the low noise immunity and the large influence of stray capacitances on the measurement accuracy due to the small working capacitances.

The invention is aimed at increasing pressure sensitivity, noise immunity and accuracy. According to the invention, in a capacitive pressure sensor comprising a housing, an elastic element in the form of a membrane made integrally with the support base, a movable electrode of the measuring capacitor located on. membrane surfaces, an annular fixed electrode of a reference capacitor located on a support base, mirror-symmetric fixed electrodes of a measuring and reference capacitors located on a plate

not connected to the elastic element, the membrane is made without a rigid center, the surface of the plate on which the fixed electrode of the measuring capacitor is located satisfies the equation of the surface of an elastic flat membrane deformed by a pressure Рmax 1.2-1.5 times higher than the nominal pressure of the sensor:

9

ft) ah (1 - -2) 2,

R

where a) the deflection of the membrane under the action of pressure at a point remote by a distance of g from the center of the membrane, 1

R is the radius of the membrane;

WQ - deflection in the center of the membrane (g 0),

(Wo - TsgRmax

s

L v).

where c is the Poisson's ratio of the membrane material;

E is the elastic modulus of the membrane material;

h is the thickness of the membrane,

and the electrodes of the measuring capacitor are shaped so that their area is determined from the expression

(y4g6

2RZ 6R4 The drawing shows a sensor in section. The relationship between the dimensions of the interelectrode gap and the thickness of the dielectric film and electrodes for

Inaccurate changes. The capacitive pressure sensor contains an elastic element 1 in the form of a membrane 2, made in one piece with the support base 3. A movable electrode 4 of the measuring capacitor is located on the surface of the membrane. The fixed electrode 5 of the reference capacitor is placed on the supporting base. Mirror-symmetric electrodes 6 and 7 of the measuring and reference capacitors, respectively

located on the plate 8. Lead conductors 9 are connected to the contact pads of the electrodes and contacts 10 located in the holes of the housing 11. The elastic element and the plate are made of

70NHBMYu alloy. AteCb-SiOa-SiO films 12 of 3 microns thick are used to electrically insulate the electrodes. The electrodes and pads are made of Mo-Ni film with a thickness of 1.5 microns. Output

conductors are made of tape 0.05-1- 79NM. The case and contacts are made of 29NK alloy. The contacts are soldered into the casing with SK-7 glaze. The gap between the electrodes is 50 μm. The diameter of the membrane is 8 mm.

The capacitive pressure sensor operates as follows.

 The measured pressure acts on the membrane from the outside. Under the influence of the measured pressure, the movable electrode of the measuring capacitor located on the membrane moves / toward the fixed electrode of the measuring capacitor, as a result of which the capacitance of the measuring capacitor increases. The capacitance of the reference capacitor is independent of the measured pressure. The capacitance values of the measuring and reference capacitors are transferred to the output conductors and then to a normalizing device (not shown in the drawing), which pde generates an output signal depending on the ratio of the capacitance of the reference capacitor to the capacitance of the measuring capacitor. Thus, the output signal depends on the measured pressure.

In the proposed capacitive pressure transducer, there is no rigid center on the membrane. This makes it possible to increase the sensitivity to the measured pressure by increasing the deflection of the membrane. The displacement of the center of the membrane without a rigid center is 4 times greater than the displacement of the center of the membrane with a rigid center.

In the proposed capacitive pressure sensor, the size of the moving electrode of the measuring capacitor is limited only by the size of the membrane, while with known sensors the size of the moving electrode of the measuring capacitor is limited by the rigid center. This makes it possible to increase the area of the electrodes and, therefore, the value of the initial capacitance of the measuring capacitor by no less than 30%. Increasing the initial capacitance of the measuring capacitor makes it possible to increase the noise immunity and reduce the influence of stray capacitances on the measurement accuracy. ;

Thus, the advantages of the design of the capacitive pressure sensor are a 4-fold increase in pressure sensitivity, an increase in noise immunity by 30%, and a decrease in the influence of stray capacitances on measurement accuracy by 30%.

Formula and Capacitive pressure transducer, containing; th casing, elastic element in the form of a membrane | made in one piece with the support base, a movable electrode of the measuring capacitor located on the membrane surface, an annular fixed electrode of a reference capacitor located on a support base, mirror-symmetric fixed electrodes of the measuring and reference capacitors located on a plate connected to an elastic element, characterized in that, in order to increase the In order to achieve a high level of immunity, noise immunity and measurement accuracy, the membrane was made without a rigid center, the surface of the plate on which the fixed electrode of the measuring capacitor is located satisfies the equation of the surface of an elastic flat membrane deo-normalized by a pressure Рmax, which is 1.2-1.5 times higher nominal pressure of the sensor:

(1-4) 3,

R

where o) is the deflection of the membrane under the influence of pressure at a point remote from the center of the membrane by a distance g;

R is the radius of the membrane; (Oo-deflection in the center of the membrane (g 0).

° b - PMax R4E 1 h 3 - (1 -} 2-);

p is the Poisson's ratio of the membrane material;

E is the elastic modulus of the membrane material;

h is the thickness of the membrane,

and the electrodes of the measuring capacitor have a shape that satisfies the dependence of their area S, enclosed in a circle of radius r, on this radius, according

expression

2R2

1 6R4

)