SU1765734A1 - Capacitive pressure sensor - Google Patents

Description

where Cx is the capacitance of the measuring capacitor.

For sensors whose membrane has a hard center, this function is linear relative to the deflection, however these sensors have insufficient absolute sensitivity, small initial capacitance and, as a result, low noise immunity, since the size of the measuring capacitance C is limited by the area of the hard center center decreases membrane sensitivity.

Flat membrane sensors have satisfactory sensitivity and noise immunity, but their conversion function is nonlinear.

Closest to the present invention is a capacitive pressure sensor that contains a membrane fixed on the periphery and a flat plate attached to it in the center, forming a measuring capacitor. This sensor has high sensitivity and good noise immunity.

A significant disadvantage of this sensor is the non-linearity of the characteristic, due to the fact that the movable electrode is located above the deformable section of the membrane and has a flat surface.

thirty

(i-p2) 2

(2)

where y is the coordinate along the axis of symmetry; do - plate center deflection; , g is the distance from the axis of rotation, R is the radius of the membrane.

Figure 1 shows the design of a capacitive pressure transducer; Fig. 2 is a schematic diagram explaining the calculation of the capacitance of the measuring capacitor; FIG. 3 is a plot of the ratio of initial

the capacitances of the measuring capacitor of the proposed sensor CH and the prototype CH from the relative value of the smaller radius limiting the electrode, with

.

The sensor contains a flat membrane 1,

made in one piece with the housing 2, with the electrode 3 of the measuring capacitor located on it, the plate 4 connected to the membrane in the center,

for example, spot welding 5 and having a profile b profiled (2) surface on which the second electrode 7 of the measuring capacitor is located, an annular plate 8 bonded to the housing, for example, spot welding 9 at several points, with a reference capacitor 10 placed on it , the second electrode 11 of which is located on the non-deformed front part of the body.

The capacitive pressure sensor operates as follows. Under the action of pressure, the membrane 1 bends and moves the plate 4 bonded to it. In this case, the capacitance of the ring element of the measuring capacitor will be

d Cx

2 jrrdr Ј0

d0 (i + A) 1 - (1 V)

where O is the dielectric constant of air;

A - is the modulation depth of the gap;

do

(L, - deflection of the center of the membrane. Integra this expression in the range from n to G2, we get

Cx

-HN

1 +

where is cx

R2Ј °

2do P

- initial

capacitance value of the measuring capacitor.

With the conversion function (1)

(C0 / Cx) K (1-A)

linear with A.

The use of this invention allows to increase the measurement accuracy by reducing the nonlinearity error.

Claims (1)

Invention Formula A capacitive pressure sensor containing a membrane made in one piece with the housing and a plate bonded to it in the center, characterized in that, in order to reduce the nonlinearity error, it is equipped with a reference capacitor, one electrode of which is located on the nondeformable front part of the housing, and the other on the inserted board, bonded to the housing, while the plate is made concave and its surface facing the membrane is made in the form of a surface rotation is formed in accordance with the ratio (1-p2) 2, where y is the coordinate along the axis of symmetry; do - plate center deflection; thirty P - Rg is the distance from the axis of rotation; R is the radius of the membrane. one FIG. 2    i (lii-  - t, -, -V 1 V -. - i0,1 -irt- y, Ј f   . J% g n Sn 0.2 0.3 Fig.Z