UDC 621.316.722.1.078

PRECISION GENERATOR-CALIBRATOR OF AC VOLTAGES GK-8A

Yu. A. BULATOV

(Submitted by the scientific seminar of the Department of Radio Engineering)

For the verification of AC-voltage meters or converters of AC voltage into DC, sources of AC voltage with a calibrated and also sufficiently stable output-voltage level are used. Such sources of AC voltage are generator-calibrators. The GK-8A generator-calibrator described here has a system of two measuring transducers (MT), one of which provides high time stability of the output voltage, while the other provides a calibrated value of this voltage.

The structural diagram of the GK-8A and its technical characteristics are presented.

Illustrations 1, bibliography 1.

The principal distinguishing feature of the GK-8A generator-calibrator, compared with other multi-valued measures of AC voltages developed at the Department of Radio Engineering of TPI, is the very high short-term stability of its output voltages.

To achieve the required stability and accuracy of the output voltages, the GK-8A generator-calibrator uses a system of two measuring transducers (MT).

The structural diagram of the GK-8A is shown in Fig. 1. MT\(_1\) is intended to stabilize the output voltage \(U_{\text{out}}\), and, consequently, it must above all have high time stability; the second—MT\(_2\)—serves to guarantee the value of \(U_{\text{out}}\) [1].

The investigations carried out showed that two-half-period diode rectifiers with thermal compensation by an auxiliary diode possess good short-term stability over a wide frequency range. Such a rectifier is used as MT\(_1\). MT\(_2\) is a differential comparator of the effective value on photoelectric transducers and compares \(U_{\text{out}}\) with the constant voltage of the reference source.

The master oscillator (MO), the controlled divider (CD), the power amplifier (PA), and the system of two inductive dividers (ID), one of which operates in the frequency range 20 Hz–20 kHz and the other in the frequency range 20–200 kHz, are the same as in the GK-12 calibrator.

The remaining designations of the structural diagram are:

I — integrator with switchable time constant;
RS — reference source of DC voltage;
NI — null indicator;
MC — measuring circuit.

The remaining technical characteristics of the GK-8A are given below:

1. The frequency range from 20 Hz to 200 kHz is covered by means of 4 subranges, within which the frequency varies smoothly.

2. Range of adjustable output voltages:
   0.1 mV—10 V—adjusted in steps of 0.1 mV.

3. Error in setting the output voltage:
   a) at the 10 V level in the frequency range 65 Hz—200 kHz—\(\pm 0.01\%\);
   in the frequency range 20—65 Hz—\(\pm 0.03\%\);

Fig. 1

b) at levels below 10 V for \(R_{\mathrm{L}} \ge 50\ \mathrm{k}\Omega,\ C_{\mathrm{L}} \le 500\ \mathrm{pF}\);

in the frequency range up to 50 Hz,

\[ \pm 0.01\% \pm \frac{10\ \mu\mathrm{V}}{U_{\mathrm{out}}}\cdot 100\%, \]

in the frequency range 50—200 kHz,

\[ \pm 0.1\% \pm \frac{50\ \mu\mathrm{V}}{U_{\mathrm{out}}}\cdot 100\%. \]

1. Time instability of the output voltage over 10 min:
   a) in the frequency range 20 Hz—2 kHz—less than \(\pm 0.003\%\);
   b) in the frequency range 2—200 kHz—\(\pm 0.001\%\).

2. Coefficient of nonlinear distortion:
   in the frequency range 2—50 kHz—0.06%;
   b) in the frequency range 20 Hz—200 kHz—0.4%.

3. Coefficient of nonlinear distortion for odd harmonics:
   a) in the frequency range 2—50 kHz—0.02%;
   b) in the frequency range 20 Hz—200 kHz—0.3%.

REFERENCES

1. M. S. Roitman. Multivalued Measures of Alternating Voltages, Proceedings of TPI, vol. 270, Tomsk, TSU Publishing House, 1973.