SU386345A1 - PHASE METHOD FOR SEPARATE EQUALIZATION OF AC VOLTAGE BRIDGE - Google Patents

Description

The invention relates to a measurement technique and can be used in the measurement of complex resistances.

The known phase method of separate balancing of an AC bridge, in which, first, based on a comparison of the phase angles between the voltage vectors of the bridge supply and the voltage on the shoulder adjacent to the shoulder of the measured object, and between the voltage vectors on the measuring diagonal and voltage on the shoulder, opposite the shoulder with the object being measured, bring the bridge into a quasi-equilibrium state over the reactive component, and then balance it over the active component, reducing the unbalance voltage to zero, require rex sequential operations. The first of them is auxiliary and only increases the measurement time.

The proposed method makes it possible to eliminate the auxiliary operation, i.e., reduce the equilibration time due to the fact that when it is used to establish a quasi-equilibrium on the reactive component, the phase angles are simultaneously compared between the voltage drop on the shoulder adjacent to the arm of the object being measured and the voltage the power supply of the bridge and between the on-voltage voltage and the voltage drop on the arm opposite the shoulder of the object being measured.

algebraically summed with a half period of the bridge supply voltage, for example, by inverting the phases of one of the voltage pairs — the bridge supply voltage and

The voltage drop across the shoulder opposite the shoulder of the object being measured, or the voltage drop across the shoulder adjacent to the shoulder of the object being measured, and the unbalance voltage. FIG. 1 is a schematic diagram of a bridge measuring circuit; in fig. 2 is its circular diagram explaining the method; in fig. 3 - a digital bridge that implements the method; in fig. 4 - time diagrams that show the operation of the bridge.

The measuring pavement circuit consists of the measured complex resistance with the active component Ri and the reactive component Ci, the resistors Rz, Kz, which serve to balance the reactive component, the resistor Ri, which serve for spelling on the active component, and the sample capacitor d ,. The diagonal of the bridge circuit is ab, the measuring diagonal is cd.

From the pie chart, in which R, var, and Rvar are the equilibration circles, respectively, along the reactive active components, Co; di, ..., dn are the positions of the potential points of the vertices end of the measuring circuit; it can be seen that the relation between the phase angles between the voltage Il and the inverted voltage Vdc, and between the voltage Uab and the inverted voltage Uc, b changes only during the transition through the state of the bridge quasi-equilibrium with respect to the reactive component of the measured impedance (point d passes the position dn, i.e., unambiguously determines the necessary direction of change of the parameter that balances the circuit along the reactive component.

Thus, in the area not covered by the circle R, var corresponding to the bridge quasi-equilibrium with respect to the reactive component of the measured complex resistance, the phase angle between the voltage Udb and the inverted voltage Uac is greater than the phase angle between the voltage Uab and the inverted voltage of the area covered the indicated circle, the phase angle between the voltage Uab and the inverted voltage Uac, is smaller than the phase angle between the voltage Uab and the inverted voltage

.

The digital bridge contains a bridge measuring circuit 1, a sinusoidal voltage generator 2, a switch 3, phase change converters 4, 5 that convert the phase angle between two voltages at a time interval, integrator 6, balance blocks 7, 8, respectively, by the reactive and active components , digital indicators I 10, respectively, on the reactive and active components, extremum detector //.

Measurement at the bridge begins with the establishment of quasi-equilibrium over the reactive component by adjusting the resistance of the resistor Rs.

At the same time, through the switch 3 from the bridge circuit / "and the inputs of the phase-time converter 4, the voltages Oa and Uc are supplied. (Fig. 4, a), and the inputs of the phase-time-converter 5 are voltages Udc and (Fig. 4.6).

Each phase shifter has reference and signal inputs. The leading edges of the pulses at the output of each phase-change converter are formed at the moment of the start of the positive (negative) half-wave voltage applied to its reference input, and the back edges of the pulses - at the time of the end of the positive (negative) half-wave voltage applied to its signal input. For the case discussed in FIG. 4, the voltage inputs Lа and Udb are supplied to the reference inputs of phase-to-phase converters, and the signal inputs are supplied to the voltage Uc „1 and / l„ Phase-time converters 4 and 5 produce pulses of the same amplitude (Fig. 4, c, d), the duration of which is

 - G / 2 h DT,

where: t is the pulse duration at the output

phase converter; DG is the length of time corresponding to the phase shift angle between voltages supplied to the inputs of the phase-time converter;

T

- period of the frequency of these voltages.

Formation of pulses at the output of phase change converters 4 w. 5, respectively, elongated at T / 2 provides such conditions that the change in the sign of the signal at the output of the integrator 6 occurs only at the transition of the circuit through the state of quasi-equilibrium

reactive component of the measured impedance.

The pulses from the outputs of phase change converters 4 l 5 are fed to the inputs of the integrator 6, which compares them in duration.

So far, for example, at the first input of the integrator 6 only momentum acts from the output of the phase-time converter 4, the output of the integrator 6 is generated

linearly increasing voltage. As a result, the second input of the integrator is affected.

A 6 pulse from the output of the phase-time converter 5 at the output of the integrator 6 generates a linearly falling voltage.

Naturally, while simultaneously acting on the inputs of the integrator 6 by pulses of equal amplitude, coming from the outputs of the phase-time converters 4 and 5, the voltage at the output of the integrator 6 remains

constant (voltage generated at the output of integrator 6, shown in Fig. 4, d).

It is easy to see that the resulting voltage at the output of integrator 6, after acting on both of its inputs with single pulses from the outputs of phase-time converters 4 and 5, will only have a negative polarity when the phase angle between the voltage Udb and the inverted voltage Uac, more of the phase angle between the voltage Uab and the inverted voltage Uc, b.

Blocking, for example, all changes in the parameter, balancing the scheme with the reactive component (), leading to the resultant positive polarity signal at the output of the integrator 6 and, discarding all changes of the parameter, balancing the scheme with reactive component

(Rz), leading to the resultant negative polarity signal at the output of integrator 6, achieve the quasi-equilibrium state of the bridge with the reactive component of the complex resistance.

After the final switching of the balancing parameter by the reactive component of the measured impedance at each step, the balancing unit

7 closes the output of the integrator 6, thereby preparing it for a new comparison

on the next bar. After reaching equilibrium in the reactive component of the measured impedance, the unbalance voltage Ucd {in the presence of losses in the measured-complex impedance) through the switch 5 is fed to the input of the extremum detector 11, from the output of which the control signal goes to the balancing unit 8 through the component of the measured impedance proportional to the active loss m.

Subject invention

The phase method of separately balancing an ac bridge, in which quasi-equilibrium in the reactive component is first established, using a comparison of the phase angles between the bridge circuit voltages for this, and then balancing the bridge of the active component, reducing the unbalance voltage to zero, differing from By the fact that, in order to reduce the equilibration time, in order to establish quasi-equilibrium, the phase angles are simultaneously compared between the voltage drop across the shoulder adjacent to the shoulder of the object being measured and em power between the bridge and the unbalance voltage L voltage drop on

shoulder, opposite the shoulder of the measured object, algebraically summed with a half period of the bridge supply voltage, for example, by inverting the phases of one of the voltage pairs - the supply voltage

the bridge and the voltage drop across the shoulder, opposite the shoulder of the object to be measured, or the voltage drop across the shoulder adjacent to the shoulder of the object being measured, and the unbalance voltage.

Fig z