RU1829014C - Method for measuring parameters of rc- and rl- circuits - Google Patents

Abstract

Usage: in measuring technique and is intended for automatic measurement of parameters of RC and RL circuits. SUMMARY OF THE INVENTION In order to increase accuracy, a signal of a rectangular or ramp shape is applied to the measuring circuit, the signal at the output of the measuring circuit is compared with a reference signal, the polarity of the input signal and the polarity of the reference signal are changed at the moment of equal output and reference signals, the initial period of oscillations, change the value of the input or reference signal, measure the period of current oscillations, compare it with a given value of the period, repeat the changes in the value of the input or supports signal until the current period equals the specified period value, determine the value of the variable input or reference signal and determine the desired parameters of the RL and RC circuits according to the formula Пх (Кн, Кз, Тз, Тн), where Пх - determined parameter of the circuit under study (Lx, Cx, Rx); a const is the initial value of the input signal; b const is the initial value of the reference signal; f (KH, K3, Tn, T3) is a linear function of the known form a, ± 1}. Zil. Cha Pa

Description

The invention relates to the field of measurement technology and is intended to automate the measurement of parameters of two-element RC and RL circuits.

The aim of the invention is to increase accuracy.

In FIG. 1 is a block diagram of one embodiment of a device that implements the proposed method (in the measurement mode of RL circuit parameters); in FIG. 2 is an example of constructing a measuring RC circuit; in FIG. 3 - time diagrams explaining the operation of the device.

The device comprises an input impact driver 1, the output of which through the measuring circuit 2 is connected to the first input of the comparison unit 3, the output of which is connected to the input of the input driver 1, with the first input of the scaling unit 4 and the input of the computer 5, the first input of which is connected to the indicator 6, and the second output is connected to the second input of the scaling unit 4, the output of which is connected to the second input of the comparison unit 3.

The device operates as follows (Fig. 3). When the voltage is switched on

voltage at the output of the comparison unit 3, which can be used as a differential amplifier-limiter, the voltage Us occurs abruptly,

for example, positive polarity. It is fed to the input of the former 1, from the output of which - to the input of the measuring circuit 2 a linearly varying voltage Ut

Ui (t) -U3t / n,

where TI is a time constant determining the rate of change of exposure.

At the output of the measuring circuit 2, which can be constructed, for example, on the basis of an operational amplifier containing a Ro resistor in the input circuit, and for the purpose of feedback the RL circuit under study, a voltage (informative signal) of the form

VD

Uz

VoP

(Lx + Rxt),

where Ro is the resistance of the reference resistor;

Lx, Rx - the desired parameters of the RL-circuit.

This voltage is applied to the inverting input of the comparison unit 3, at the non-inverting input of which there is a reference signal - the scaled output voltage of the comparison unit 3

,

where KN is the initial value of the scaling factor of block 4,

At the time when the value of the voltage difference at the inputs of block 3 comparison

AU U4-U2 (t)

changes sign, the voltage at the output of the comparison unit 3 jumps, changes the sign to the opposite, and the described process is repeated taking into account the sign change,

In the circuit, undamped relaxation oscillations arise, the period of which T is determined from the equality

KHU31 s „, r Tn .. .Rx-y).

T

2 (KnGpYar Lx /

Rx

Then, one of the reference parameters determining the period of self-oscillations (mn, Kn, Ro) is forcedly changed (decreases, increases), which leads to a decrease

(increase) the period of self-oscillations until the specified value of the period Tz is reached.

In FIG. 1 a change in period is made by changing the level of comparison

block 3 by changing the scaling factor K of the scaling block 4.

The latter is controlled by a microcomputer 5, which measures the current value

period of self-oscillations and compares with a given value of the period Tg.

If, a command is issued to further change the scaling factor K of the scaling unit 4, in

which can be used as a code-controlled voltage divider.

At a certain value, TKhz equality is achieved and the process of changing the period is stopped.

The microcomputer captures the value of the code corresponding to KZ.

As a result, the following system of equations is formed instrumentally:

thirty

T

2 (CntNo -) Rx

t- 2 (KZgKr - Lx) 3Rx

Solving the system of equations for the desired parameters Lx, Rx, we obtain

40

U-rRo

TnKz - T3K „

Tn - Tz

Rx 2 rR0

Kn-Cz Tn-Tz

Similar formulas are obtained by changing the period by changing g, RO.

In order to measure the parameters of the RC circuit, the measuring circuit 2 is constructed according to FIG. 2.

The computer 5, using the previously entered values of Kc, Tz and fixed during the measurement of the values of Kz, Tn, calculates the desired values of Lx, Rx, Cx. In general terms, the formula for determining the parameters of RC and RL chains is represented by the following expression

, Tn, Cz, Tz),

where Px is the desired parameter of the circuit under study (Lx, RX. Cx);

a const is the initial value of the input impact parameter;

b const is the initial value of the reference signal parameter;

m (Kn, Tn, K3, T3). is a linear function of the known form a, / 3 {0 ± 1}. The values of a, ($ depend on the specific implementation of the method. Thus, in the proposed method, in comparison with the prototype, an increase in accuracy is achieved by introducing a predetermined period of the current oscillations T3, the operations of determining the ratio of the current and initial values of the period, determining the ratio of the current value of the variable input or reference signal to the value of their initial value with the associated errors.

Claims (1)

SUMMARY OF THE INVENTION A method for measuring the parameters of RC and RL circuits, which consists in supplying a signal of a rectangular or linearly varying shape to the measuring circuit, comparing the signal at the output of the measuring circuit with a reference signal, changing it at the moment of equal output and reference signals, the polarity of the input action and the polarity of the reference signal, measure the initial period of oscillations, which, in order to improve accuracy, change the value of the input or reference signal, measure the period of current oscillations, compare they add it with a given value of the period T3, repeat the changes in the value of the input or reference signal until the current period of the given value T of the period T3 is equal. determine the value of the variable input or reference signal and determine the desired parameters of the RL and RC circuit according to the formula Ph aVffKH, KZ, TN, TZ), where Px is the determined parameter of the circuit under study (Lx, Rx, Cx); a const is the initial value of the input signal: b const -: initial value of the reference signal; f (KH, K3, Tn, T3) is a linear function of a known form: a, ft (0 ± 1). 6 Figure 1 Cx fe.Z FIG. 3 Ko Q i i