SU109915A1 - Device for measuring capacitances and inductances by the resonance method - Google Patents

Description

In laboratory and factory practice, there is often a need for fast and accurate measurement of inductances and capacitances with a variety of constructive implementation of the relevant details. Also, there is often a need to select parts of the required inductance or capacitance from a large batch.

Measuring instruments existing for this purpose, operating mainly on the principle of bridge circuits, cannot fully satisfy various demands.

It is more convenient to use for this purpose measuring devices based on the resonance method, in which the measured reactance (capacitance or inductance) is compared with the reference.

The purpose of the described invention is to improve the accuracy and speed up the measurement process with the resonance method. For this, it is proposed to include a measurable and a reference resistance of two

paralel branches, and comparing the reference capacitance or inductance with that measured by applying the voltages of the compared circuits to the two deflection systems of the plates of the cathode oscilloscope.

The drawing shows a schematic diagram of the proposed device.

The device uses two identical step-up transformers Tc to Tp with two primary windings having an equal number of turns (the inductance of the primary windings is very small and is about 0.05 mgn). The transformer Tc is summing, the transformer Tp is subtractive, which is ensured by the corresponding inclusion of their primary windings.

Two phase-shifting cells 1-С are included in the circuit of the secondary (boosting) windings of the transformers Tc and Tp; and RZ- € 2, providing, regardless of the frequency, a constant additional shift

phases of 90 ° between the output voltages of these cells.

The primary winding circuit of the transformers Tc and Tp includes an oscillator of increased frequency G, some constant inductance Bn or capacitance Cn, the measured reactance L ,. or capacitance C ,, and the reference inductance store L, or capacitance C,.

To compensate for the active resistance of the measured parts, as well as the active resistance of the stores of the reference inductance and capacitance, a potentiometer R is provided in the device circuit.

Thus, two resonant circuits are created in the device, created respectively: measurable and reference inductances (or capacitances) and total capacitance (or inductance) for both circuits. Both circuits are powered by an oscillator of increased frequency F, and the indicator is a cathode oscilloscope O, for two pairs of plates of which the voltages of both circuits are applied.

Measurement using the proposed device is carried out by comparing the phases of electrical oscillations in the above circuits near the resonance. Resonance is obtained by selecting the capacitance or inductance in stores C, or L, and the instant of coincidence of the resonances is determined by the equality of the oscillation phases in both circuits, which are determined from the Lissajous figures on the oscillo graph screen.

Subject invention

A device for measuring capacitances and inductances by a resonant method, by comparing the measured reactance (capacitance or inductance) with the reference one, containing two resonant circuits, one of which includes the measured resistance, and the other one and an indicator-electron-beam oscilloscope , characterized in that, in order to increase the accuracy and speed up the measurement process, the measured and reference resistances are included in parallel branches connected to different deflection systems of the oscilloscope, and in series with these resistances, a constant reactance is included, which for the measured and reference resistances forms the second element of both resonant circuits.