SU651271A1 - Device for measuring quartz resonator active resistance - Google Patents

Description

hanging O-T its active resistance to 2.

The real disadvantage of this device is that the imimeric bridge contains reactive elements; capacitors and a semiconductor diode used as a controlled fMKOcTK. So, fy when the active co-direction of the quartz resonator is varied, the amplitude of the generated oscillations, and with it the feedback voltage, displacing the p p junction of the semiconductor diode in the opposite direction. As a result, the capacitance of this transition is displaced, which leads to a change in the total conpt of the compensation chain connected in series with a quartz radiator.

It is known that in case of automatic generation, the ratio should be

k-f.i,

Where

K - coefficient of gain amplifier p - coefficient of transmission of the measuring bridge.

The feedback in a known device ensures the operation of the amplifier on the first part of its characteristics. Therefore, in this case K will be a constant value. From relation (l) it follows that the transmission coefficient of the measuring bridge p must also be constant. This condition is equivalent to the constant sticking and reactive (.) Components of the resistance of the measuring bridge arm, which includes a quartz resonator and a control compensatory chain, since the parameters of the elements of its other arms depend on the feedback voltage. The condition must be met

Xy con% -t,

C2)

m-h

where X c is the reactive component of the complete matching of the quartz resonator;

Hz is the reactive component of the impedance of the compensation chain.

With a change in the feedback loop, the equivalent capacity of the controlled compensation chain changes, and with it the Hz. From expression (2) it follows that the reactive component must also change

quartz rezolatorp X hollow co-coupling | . This means that the quartz resonator will work with a detuning with respect to the frequency of the series resonance, where its resistance is purely active and R ",.

Thus, in the well-known device, the device is measured not by Rj, but by magnitude.

-L equals

. r that in rezulE / tate

leads to significant errors in the measurements that are further increased due to the fact that X, o, j

is invariable.

The use of a nonlinear element of a semiconductor diode in the known device, as well as a change in the detuning of a quartz resonator with a change in its resistance R, leads to a non-linear relationship between R c and the output M voltage. As a result, the scale of the measuring device is uneven, i.e. compressed in some areas and stretched in others. This circumstance additionally increases the measurement errors.

The purpose of the present invention is to improve the measurement accuracy of the active resistance of quartz resonators.

It is achieved by the fact that, in a device containing a measuring bridge with a quartz resonator included in it, an amplifier that, together with the measuring bridge, forms an autogenerator, a detector and a recording device, opposite to where the crystal resonator is located, is a field-effect transistor, the gate of which is connected to the detector output.

FIG. 1 shows the basic electronic scheme of the proposed device; in fig. 2 given curves, noc-Droennye according to the results of experimental measurements.

The proposed device contains a measuring bridge consisting of resistors 1 and 2, a quartz resonator 3, and a field-effect transistor 4; amplifier transistors 5 and 6, having a resonant transformer 7; the detector diodes 8 and 9 and the recording device 1O. The secondary winding of the transformer 7 is connected to the diagonal of the measuring bridge.

When the measuring bridge is unbalanced, self-oscillations arise in the device, the stationary amplitude of which is set automatically by applying the detected output voltage to the gate circuit of transistor 4. When the active resistance of the quartz resonator changes, for example, a change in air humidity, the transmission coefficient of the measuring bridge changes. the output of the detector, which is supplied to the gate of the transistor 4, the resistance of the latter varies in such a way that a previous value of the unbalance of the measuring bridge. Thus, the output voltage of the detector, measured by the recording device 10, is dependent on the active resistance of the quartz resonator. The recording device can be a pointer or digital pointer, calibrated in units of resistance, humidity or pressure.

The resistance of the field-effect transistor channel is active. Therefore, the use of a field-effect transistor as a controlled resistance favorably distinguishes the proposed device from the known one, since, unlike the latter, in it the measuring bridge does not contain reactive elements. As a result, the detuning of the quartz resonator is minimized, which improves the measurement accuracy of the active resistance of the quartz resonators.

The inclusion of a field-effect transistor in the measuring bridge arm, opposite the arm in which the quartz resonator is connected, provides a linear connection between the active resistance of the resonator and the output voltage. This eliminates another source of measurement error inherent in the known device.

Curve 1 (Fig. 2) reflects the dependence of the active resistance of the resonator and the output voltage of the device. Minor deviations of curve 1 from linear dependence occur only near the limits of the operating range of the device. Tao 2 corresponds to the measured values of the output voltage. The discrepancy between the theoretical curve and the experimental data does not exceed 2-3% and is apparently due to experimental errors.

Thus, the use of a field-effect transistor in the device allows for reaching the minimum {detuning of the resonator relative to the frequency of its series resonance and, thus, increasing the accuracy of measurements. The inclusion of the field-effect transistor in the measuring-measurement arm, opposite to where the quartz resonator is located, allows one to obtain a linear connection between the active resistance of the resonator and the output voltage of the device. This further increases the accuracy of the measurements.

The linear dependence of the output voltage of the proposed device on the active resistance of the cavity, regulates the measurement results, so in this case it will be possible to use recording devices with a linear scale without introducing corrections for discontinuities.

Claims (2)

1. USSR author's certificate number 2O2320, cl. G O1 R 27 / O2, 1972. 2. USSR author's certificate number 256854, cl. G 01TR 17 / GS, 1972.