SU146209A1 - Analog converter of electrical resistance to frequency of alternating current - Google Patents

Description

The present invention relates to analog electrical impedance converters to an alternating current frequency proportional to it using a Wien bridge and a / C generator. (for example, thermistor).

Such an embodiment of the converter allows to obtain a linear relationship between the measured resistance and the period of the alternating current / C-generator.

The drawing shows a diagram of the Converter.

The converter is an A-C generator with a T-shaped A / C-bridge (Wien bridge), the thermistor is connected to the bridge arm parallel to capacitance C, and the measured resistance i is in series with capacitance Cc. The capacitance of the bridge Ci and C2 is constant, as well as the resistance of the bridge and the electric generator with a frequency-dependent bridge, the voltage at the input of the amplifier is negligible, and the bridge is in a state close to equilibrium, which is established and maintained automatically. and equality of the modules and equality of the phases of the stresses in the arms of the bridge. These conditions are:

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No. 146209-2-B existing at C-generators, when the measured resistance changes, the resistance of the thermistor included in the Jaz arm changes. resistances in tg7

with constant resistances R and R and constant capacitances Ci and Ci

must be kept constant, i.e. -5 const. As a result

during the measurement, the resistance of the thermistor Rz will automatically be kept constant, proportional to the measured

resistance R. Hence -i-: or according to (1) we have: 11

and. With

2r-.R,}

Thus, the oscillation period of the generated voltage T is proportional to the measured resistance Ri. The layout of the jRC generator, whose circuit is shown in the drawing, has been experimentally investigated with the generator data: 000 ohm: R 650 ohm; Ci 2.1 mf; Cz 2.1 mf. A thermistor type TP 2 / 0.5 is used as the resistance Rz in the generator. The dependence of the oscillation period T on the resistance RI is obtained linearly proportional. A impedance-to-frequency converter can find wide applications for telemetry of a number of non-electrical quantities. On the receiving side, data can be entered into digital. Tele-measured non-electric quantities include: temperature, velocity, density, gas composition and flow rate, and a number of other non-electrical quantities converted to electrical resistance. It should be noted that the output frequency of the generator does not depend on the stability of nonlinear elements. With a sufficiently large gain of the amplifier, the bridge will be close to equilibrium and therefore according to (2) the resistance of the thermistor depends only on the parameters of the bridge, at the same time it does not depend on high conditions and stability of nonlinear elements. When the ambient temperature changes by + 10 °, the generation frequency changes less than 0.2%.

The converter can also be used to convert sensor resistance (tens meters) with negligible resistance deviation to frequency. If a strain gauge is placed in the shoulder of the bridge RZ and the parameters of the bridge are selected in such a way as to satisfy,

to call inequality C 1, then a small change in resistance C;

This will cause a sharp change in the resistance of the thermistor and, therefore, a significant change in the generated frequency. In practice, if the resistance is changed ./ by 1%, the maximum frequency deviation will be 18%.

Subject invention

1- Analog converter of electrical resistance to the frequency of alternating current containing an A-C generator and a Wien bridge, characterized in that, in order to provide a linear relationship

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const

R

between the measured resistance and the period of the alternating current / regenerator, the measured resistance is connected in series with the Wien bridge capacitance, and a nonlinear resistance (for example, a thermimeter) is connected in parallel with another capacitor.

2. The device of 1, distinguished by the fact that, in order to increase the sensitivity of the conversion, the measured resistance and non-linear resistance, shunted by the capacitor, are included in the opposite shoulders of the Wien bridge