SU1631328A1 - Pressure measuring device - Google Patents

Abstract

The invention relates to a measurement technique and can be used to accurately measure pressures. The aim of the invention is to improve the accuracy. The goal is achieved by the fact that a grounded central 3 and peripheral ring 4 electrodes are made on the measuring membrane 2, and a central 6 and two ring 7 and 3 electrodes are on the compensating membrane 5, a constant amplitude and duration voltage pulse generator 16 and a converter are inserted into the measuring circuit 13 voltage to frequency with trigger 14 at the output. With increasing pressure, the capacitance between the electrodes 4 and 7 changes, which leads to an increase in voltage at the first input of the comparison circuit 10 and an increase in the frequency at the output of the voltage-to-frequency converter 13, respectively, the duty cycle increases and the effective compensating pressure generated by the electrodes 3 increases. and 6. 2 Il. (L

Description

This invention relates to a measurement technique and can be used to measure pressures.

The purpose of the invention is to improve the measurement accuracy.

Figure 1 shows the structural diagram of the device; figure 2 - timing charts of his work.

The device comprises a housing 1 in which a rigid input membrane 2 with central grounded 3 and an annular peripheral 4 electrodes and a thin membrane 5 with a central 6 and two annular 7 and 3 electrodes are installed. Electrode 4 is electrically connected to the inverse input of the operational amplifier 9, electrode 7 - with its output, which through resistance

R, s

and electrode 3 through a capacitor

R ,, is connected to an ini and resistance k. It is connected by an upstream input of an operational force, the comparator body 10 (SU), the output of which is connected to a phase sensitive demodulator 11 (PSD), the output voltage of which is added to the reference voltage S0 the source 15 and is fed to the input of the voltage converter - frequency 13 (FSP). The output of the FNC is connected to a trigger (TG) 14, and the output of the trigger is connected to the outer ring electrode 8 of the compensating membrane and to the control input of the pulse shaper 16 of stable duration and amplitude, the output of which is connected to the central electrode 6

with y

oo

J163

membrane membrane. The input of the imaging unit 16 is connected to the output of the source 15 of the sample voltage U0. Electrodes 3 and 4 form an electrostatic compensator, 7 and 4 a capacitive displacement transducer, 3 and 4 a reference capacitor CQ.

The proposed pressure gauge works as follows.

In the absence of a measured pressure (Г 0) at the output of the FNP 13 from U, ", the initial pulses are formed

op

frequencies

according to which

A swarm of shaper 16 control pulses of a constant duration t0 are created, which also, via trigger 14, supply power to symmetric pulses of frequency fd / 2 of the capacitive voltage divider. A capacitive voltage divider (hyperbolic circuit) is formed by a constant capacitor capacitor CQ between electrodes 4 and 3, as well as a measuring capacitor Su between electrodes 4 and 7. The first is connected to the input, the second is connected to the feedback circuit of the operational amplifier 9 to correct for direct current (not shown). The capacitor C0 is located close to the fitting of the movable part of the pressure gauge, therefore, as calculations show, its capacity is practically insensitive to changes in the input value.

Output Voltage Operationally

The amplifier Ux U0 С „/ СА is compared to the voltage U at the output of the separation capacitance Cp by means of scale resistances, referred to as R ,, / R2 CO / GXO where Sho is the capacitance value of the measuring capacitor with PЈ 0. At Px 0 the output compares device DP 0, while the output frequency is equal to f.

Lo

HO

and the compensating pressure

 -1 ° - 4- "

equalized, for example, by pre-deformation of the membrane 5, providing an initial gap ofl.

If there is a measured pressure, for example, P 0, the gap of the capacitor C decreases by x and the amplitude of the output voltage Ux of amplifier 9 decreases U x

U

Ј3

stress

IVCo, PC

 -р-75- (QO х) Amplitude Difference

transformed

H and them

Q

0

five ,.

by comparing device 10 and demodulator 11 to direct current voltage UU and further, summing up to iop, with the help of LPF 13 is converted into a pulse frequency f .. Kf - U, while compensating pressure

Wg

p tfi, Lo Pk2 $ g h

reduced by 60

(fv - f)

UP, to pk

Uo2

- R

To

-oX

V - Ј If- 4х Г2 со гх

° 0

compensating measured pressure with accuracy of the balancing system.

Then the measured pressure is proportional to the output frequency and is expressed as

Wg

oo

px

f G with

The sensitivity sensitivity of the proposed gauge

k feo + 2 + ft0-2R The first part of G + 2jJfUo + Y can be provided less than 0.01%, which means that the error of the pressure gauge will mainly be determined by the instability of the gap 04, which will not exceed a few hundredths of a percent.

The initial frequency ЈQ (in the absence of a measured pressure) corresponds to the initial deflection of the compensating membrane 5, caused by the attractive forces of the plates 3 and 6, compensated, as noted above, by preliminary deformation of the membrane 5.

Claims (1)

Calculations show that if the reference electrode of the capacitor Co occupies 20% of the membrane area, then the linearity error with the greatest deformation of the membrane will be no more than a few percent. In compensation mode, it decreases K by a factor of 10. Invention Formula A device for measuring pressure, comprising a pressure sensor consisting of a housing in which a measuring and compensating diaphragm and a measuring circuit, co-1, are installed This is made up of an amplifier and a demodulator, characterized in that, in order to improve the measurement accuracy, a comparison circuit, an adder, a voltage-to-frequency converter, a stabilized voltage source and a pulse shaper of stable duration and amplitude are introduced, and on the measuring membrane the first central electrode and the first ring electrode are placed, and on the compensating membrane - the second central electrode opposite the first central electrode, as well as the second and third ring electrodes, is installed opposite the first ring electrode, the first central electrode is grounded, the first ring electrode is connected to the input of the amplifier, the output terminal the second is connected to the second ring electrode and the first input of the comparison circuit connected by its output to the first input of the adder connected to the voltage-frequency converter, the output of which is connected in parallel to the trigger input, to the input of the pulse generator 10 and to the output of the pressure measuring device when This trigger output is connected to the third ring electrode, to the second input of the comparison circuit and to the control input 15 of the demodulator, and the output of the stabilized voltage source is connected to the trigger power supply circuit, to the second input of the adder and the power supply circuit of the pulse former, the output of which is 20 Go is connected to the second central electrode. 3 Р Si A U J / 1 Phie I fig 2 Compiled by A. Zosimov Editor I. Segl nik Tehred L. Serdyukova Order 536 Circulation 355 VNIIPI State Committee for Inventions and Discoveries at the State Committee on Science and Technology of the USSR 113035, Moscow, Zh-35, Raushsk nab. 4/5 Production and Publishing Combine Patent, Uzhgorod, st. Gagarin, 101 Proofreader M.Maksimishinets Subscription