RU1778577C - Capacitive pressure pickup - Google Patents

Abstract

Usage: the invention relates to measuring technique and can be used in the measurement of static-dynamic pressures at fixed temperatures. Purpose: reducing the temperature multiplicative error. SUMMARY OF THE INVENTION: in a capacitive pressure sensor containing a membrane 1, a support base 2, a circular electrode 3, an annular electrode 4, a plate 5 with response electrodes 6, 7 fixed with a gap on the support base, the lead wires 8, the lead wires are made of material with determined temperature coefficient of linear expansion. The invention allows to reduce the multiplicative temperature error by 2 times without introducing new structural elements. 2 ill.

Description

those.

(9)

(10)

10

Co cot

Cx cxt

To ensure a zero value of the multiplicative temperature error, it is necessary:

Wed Cot

Cxxpt

where Cpr, Cxpt is the capacitance of the measuring capacitor under the influence of the measured pressure and temperature t.

Capacitors capacitance Cxp, Cxpt equal

Mr. S. Go. (L

 Јo and, -, ... (1 ")

RO, Rt — membrane radius at temperatures to, t, respectively;

he, ht-thickness of the membrane of the pre-temperature is 1 s. TOUR TO. t respectively;

ЕО, Et is the elastic modulus of the membrane material at temperatures to, t, respectively.

Ro

Q

R

J C

(17)

 - radius of the hard center;

Tso, Poisson's ratio of the membrane material at temperatures to, t, respectively.

Cxpt Јо

do -

.. ° YDM v. / -, (12) 25. as the value of C is the ratio

0 t the radii of the membrane and the hard center, then

where Wo, Wot are the deflections of the rigid central thermal expansion of the membrane and the hemp under the influence of the measured pressure of the centra are mutually compensated for

at temperatures to and t, respectively. due to their ratio / a, the value is kozffitsien | Poisson's PoE and squared is small in comparison with (Ponomarev S: D „And- |

NL F ParUAT OnOhJICiLJTrkD l d d / - d

reeva L.E; Calculation of the elastic elements of machines and devices, M., Mechanical Engineering 1980, p.242) the values of the deflection of the membrane are

Then

jr (ri -rf) (do - aro

R4 Co.

R

n, 3 to Po

  Ar -

PRo

Echo (13)

10

n

RO, Rt — membrane radius at temperatures to, t, respectively;

he, ht-thickness of the membrane of the pre-temperature is 1 s. TOUR TO. t respectively;

ЕО, Et is the elastic modulus of the membrane material at temperatures to, t, respectively.

Ro

Q

R

J C

(17)

 - radius of the hard center;

Tso, Poisson's ratio of the membrane material at temperatures to, t, respectively.

Then

.

to

jr (ri -rf) (do - aro

R4 Co.

R

n, 3 to Po

do Јo l go

(nineteen)

ot

Cxpt

e07r () (1 + aMAt) (1 + abAt) -Apo 1 Ep (1 + PM At) hp

do (1 +) Ј0 L: ri (1 + Ohm At) 2

Equated in the last two expressions, we learn sex:

(-) (d0-Apo -) (rS-) do (l + a.At) -Apo R; 0 + g Jl

E0h

do GP

about Po

Eo (1 + j3MAt) hg

do Go (1 + 0v At)

do - aro

p -RQ

EO ho

Having carried out the necessary transformations, we obtain:

-,4

(1 + aBAt) - d0-Apo-ido (1 + aBAt) -Apo- lI-- LAJL} (23-l

 -3 / -E0 (1 + / 3MAt) ho- l

E0h

1 + av At) -do + A

 PO

P-ro

Eo h

about Po

, 3

(twenty)

) do (l + a.At) -Apo R; 0 + g Jl

Eo (1 + j3MAt) hg

do Go (1 + 0v At)

n, n .PftoQ + gMAt)

d (i + aBAt) -Ap0- Eo (l + 0MAt) hg

ho

1 + CteAt

(21)

(22)

PRo (i + DMdt),

,. , 4, d A L.z1

E0 (1) ho.J

(24)

i I tf

A ApoP Ho (l) lEoho, - 4

  - - P)

Fo (1 f / JM At) ho ApoPRo

1 + “M L t

LT

(26)

Figure 1 shows the proposed capacitive pressure sensor; in Fig.2 - place I in Fig.1.

The relationship between the dimensions of the interelectrode gap, the thickness of the electrodes and the dimensions of other structural elements for pressure has been changed. The capacitive pressure sensor contains a membrane 1 made integral with the supporting base 2, a circular electrode 3 located in the center of the membrane, and a ring electrode 4. located on a support base, a plate 5 fixed with a gap on the support base with response electrodes 6 and 7, lead conductors 8 partially located between the support base and the plate. The characteristics of structural elements are related by the claimed ratio. When performing the membrane and the support base of the alloy 70NHBMYu (am

13-K) -300-10 ° C 1) and At 600 ° C, t 0,. To ensure such a low TEC value, they are made of 40 micron thick quartz strips coated on both surfaces with a 0.5 micron nickel film. The conclusions are soldered to the contacts of the germanium adapter with a special solder. The ratio of the thicknesses of quartz and nickel films, if necessary, is ensured by the required TECL of the leads.

The inventive sensor operates as follows. The measured pressure acts on the membrane. Under the influence of the measured pressure, the circular electrode located in the center of the membrane moves to the return electrode 6 of the plate. As a result, the capacitance of the measuring capacitor formed by these (3 and 6) electrodes increases. The capacitance of the reference capacitor formed by the electrode 4 located on the supporting base and the response electrode 7 of the plate does not depend on the magnitude of the measured pressure due to the significantly greater rigidity of the support base compared to the rigidity of the membrane. Measuring and reference values

capacitances are supplied through the pressure-contacting device to a normalizing device (not shown in Fig. 1), which forms an output signal depending on the ratio of the reference capacitance to the measuring capacitance

When the pressure sensor is operated at a stationary temperature that is different from the temperature of normal climatic conditions, for example, at elevated temperature, due to a change in the elastic modulus of the membrane material from the temperature, the capacitance of the measuring capacitor under the influence of the measuring pressure can differ from the capacity of the measuring capacitor when the measured pressure is temperature of normal climatic conditions. But due to the selection of the characteristics of structural elements, the output signal of the normalizing device, formed according to the same algorithm as for normal climatic conditions, does not depend on the acting temperature.

Thus, an advantage of the invention is the reduction of the multiplicative temperature error by compensating for the change in the modulus of elasticity of the membrane material from the temperature by thermally changing the dimensions of the structural elements, as well as the fact that the reduction in the error is achieved without introducing new structural elements.

Claims (1)

The claims A capacitive pressure sensor comprising a membrane integrally formed with a support base, a circular electrode located in the center of the membrane, and an annular electrode located on the support base, a plate with mating electrodes fixed with a gap on the support base, lead wires partially located between the support a base and a plate, characterized in that, in order to reduce the multiplicative temperature error, in it the output conductors are made of material, the temperature coefficient of linear the expansion of A is determined from the relation 1 + «m A t "B  1 + ym At kg - 1 where g / m is the temperature coefficient of linear expansion of the membrane material, the temperature coefficient of the elastic modulus of the membrane material A t is the range of operating temperatures rig.2