SU1451567A1 - Pressure-measuring device - Google Patents

Description

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This invention relates to a measurement technique, in particular, pressure measuring devices with differential inductive stimuli.

Atchikov.

The purpose of the invention is to measure the accuracy.

Figure 1 shows the functional diagram of the proposed device; and figure 2 - the transfer characteristics of the device.

The device contains a controlled alternating voltage generator 1, operational amplifiers 2 and 3, which include: wrap differential-inductive sensor 4, differential amplifier where the phase-sensitive Demodulator 6, low frequency filter 7, adder 8, the turns of which are connected to the outputs of the low pass and the source 9 of the direct current voltage, and its output to the control input of the controlled oscillator, and a recorder (not shown).

The differential-inductive pressure sensor 4 contains a membrane and two P-cores with windings.

The principle of operation of the device is based on the formation of the transfer characteristic of the measuring transducer with such a nonlinearity, which by its nature is inverse to the nonlinearity of the transformation function of the differential-inductive sensor.

The device works as follows .40

The output signal of generator 1, whose amplitude Up varies in accordance with the control signal Ua, is fed to the inputs of two operational amplifiers 2 and 3 with the windings of the differential inductive sensor 4 in feedback. Under the action of the measured pressure P, the membrane of the sensor bends, as a result of which the air gap between the membrane and the cores changes and, as a result, the values of the impedances of the sensor windings change. Due to the small values of the membrane deflections, the change in the active components of the sensor windings is, to a first approximation, neglected. Thus, as a result of the influence of the measured pressure of the sensors on the E

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Where

ft

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-tS where

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The PIA inductance of one of the sensor windings increases its value by Db, and the inductance of the other decreases by the same value, i.e. the conversion function of the differential-inductive sensor is D L

- f (P).

In view of the above, for the case of 10 linear conversion of a direct circuit of the device, the dependence of the output voltage Ug, OT of the change in the value of the inductance has the following form:

2oi. & L-Ur

)

(ABOUT

Where

oi, is the transmission coefficient of the direct circuit.

As with the introduction of the feedback device (OS)

Up S (| 3- Uo + .Uab ,,),

where S is the steepness of the control characteristics of the generator 1; and is the value of the reference voltage of the direct current source 9;

ft and - coefficients, the transfer of the adder 8 for the voltage Uj,

five

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5 5

and and

out

respectively,

what

and

out

0

then from (1) it follows

 .b§y ° (2)

1 - 2otJ-uLS

Analysis of expression (2) shows that in the absence of feedback (K - 0) the transfer characteristic of the measuring transducer is linear, with the introduction of the operating system (J O) it is non-linear. At the same time, for cases of positive OS (y O), the plot of U f (u.L) is located above the linear X

Node transfer characteristic of the measuring converter, negative OS (J – с О) - below (fig. 2), Tte. The linearization of the transfer characteristic of the device can be accomplished by introducing negative (positive) feedback into the measuring transducer. It should be noted that the non-linearity of the conversion function of the sensor over the entire range of the converted pressure cannot be fully compensated. It is possible only at one point, at which, for example, the nonlinearity of the transformation function is maximum.

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Denoting К 2etS, that ЛЬ f (P), we can proceed to the characteristic of the transformations of the proposed device as a whole:

and

out

K / 5Uof (P) T-k7 (P)

Suppose that the conversion characteristic of the device proposed, expressed by expression (3), has a maximum nonlinearity at a point corresponding to the middle of the range of change of the transformed pressure R. To compensate for the nonlinearity at the specified point, i.e. To ensure that this point belongs to the linear characteristic of the transformation passing through the points corresponding to the zero and final values of the change in the converted pressure P, the condition

(PM) .. RD

(p) (o, 5 p ;.)

where P,

- nominal final value of the pressure to be converted

Of

R. expressions

(4) we define

1 T 2 1 1

S to f (Рц) f (ОТзрн) J

(five)

When designing, in accordance with the described method, a device for measuring pressure in the range from 0 to 4 atm., Operating with commercially available domestic differential-inductive industry.

Compiled by V.Ul Nov. Editor A. Revin Tehred A. Kravchuk

1А51567

A sensor whose conversion function has a linearity error of 0.8% and in the first approximation is described by the expression f (X) 7.6210 g. „-Z.

X-

(5) Rav,

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- 3 10 X in accordance with the coefficient 5-10 determined. The error of the device according to the non-linearity of its transfer characteristic is reduced to 0.1%.

Claims (1)

Invention Formula A device for measuring pressure, comprising an alternating voltage generator with a control input, two operational amplifiers, a differential inductive pressure sensor, a differential amplifier, a phase sensitive demodulator, and a low-pass filter with a recorder, the generator being connected to the control input of the demodulator and to the inputs of operational amplifiers, in the feedback circuit of which the windings of the differential pressure sensor are connected, and the outputs of the operational amplifiers through a differential amplifier and a phase demodulator are connected to the input of a low-pass filter, characterized in that, in order to improve accuracy, a reference voltage source and an adder are inputted, the inputs of which are connected to the outputs of the low-pass filter and the reference voltage source, and its output - with an amplitude control input of an alternating voltage generator. Cutt Proofreader N. King