SU894580A1 - Method of automatic balancing of digital extremum ac bridges - Google Patents

Description

(54) METHOD FOR AUTOMATIC EQUALIZATION OF DIGITAL EXTREME AC BRANCHES

I

The invention relates to electrical measuring equipment and can be used in the construction of automatic balancing systems for high-speed digital AC extremal bridges.

There is a known method of balancing digital extreme AC bridges, which consists in the fact that the magnitude of the regulating action is equal to several steps of balancing at once, and a greater regulatory effect corresponds to a greater imbalance.

The known method of balancing is based on modeling the amplitude of the signal of the disequilibrium of the AC bridge by some simplified approximating dependence on the subsequent prediction (extrapolation) of the imbalance according to the balanced parameter. To generate regulatory actions, not only the sign, but also the magnitude of the modulation increment of the imbalance signal, as well as the amplitude of the imbalance signal itself, are used. Due to the increase in regulatory influences during their formation in an extrapolative manner, the number of balancing cycles is reduced, hence, the speed of bridges increases.

The accuracy of regulating actions in the extrapolating method of balancing depends on the degree of approximation of the approximation to the real function. In a known method of balancing

15 this approximation is such that the methodological error in estimating the degree of disequilibrium can reach 2–3 equilibration steps with an initial imbalance of 10 steps (one decade).

20 Therefore, in order to rebalance the bridge in this decade, an additional balance step is required. Thus, limited accuracy

the formation of regulatory actions is consistent with the extruding extrapolative sposs ;; .- / balancing fundamentally limits the speed of ac bridges.

The closest in technical essence to the present invention is an extrapolation method of automatically balancing digital quasi-extremums, full AC bridges, in which the controlled parameter is modulated, a bridge imbalance signal is detected before and after modulation, the direction of regulation p is determined by the modulation increment sign.

The purpose of the invention is to increase the speed of automatic balancing of a digital extreme AC bridge with orthogonal balancing lines due to the elimination of the methodological error in the formation of control actions.

The goal is achieved by the fact that in the method of automatic balancing digital extreme AC bridges with orthogonal balancing lines, in which the controlled parameter is modulated, the imbalance signal of the bridge is detected before and after modulation, the direction of regulation obtained after detection is determined by the modulation sign squared, the modulation increment of the square of the detected signal is measured, and the adjustable parameter is changed by the amount prop rational to this increment

FIG. Figure 1 shows a vector diagram of the stresses of a measuring circuit of a digital modulation extremal bridge with orthogonal balance lines; in fig. 2 is a block diagram of a digital extremum AC bridge.

The method is as follows.

Since the balancing lines of the bridge are orthogonal, it follows from the right triangle dcd (Fig. 1)

 (one)

those.

I 01 I Up i 1 0, 1% (9РДР) () Ш

After modulation, for example, of the parameter q, the non-equilibrium voltage modulus satisfies the equality

5 | Ur - (5puP) ((o) l (3)

Up and and

- non-equipotential voltage, arising at an imbalance only in the p parameter or only in the q parameter, respectively;

SP and 5 „are the sensitivity of the bridge circuit; dr id - values of violation

balance in the parameters p and q;

L | and | p is the increment of the bridge imbalance signal modulus, due to the modulation of L Up along the perimeter of the RIs of equations (2) and (3), it immediately follows that the desired value of the imbalance in the q parameter is determined by

 . CUa) 1

(four)

whereD (V () / U / - / U / is the modulation increment of the square of the amplitude of the equilibrium signal.

Dividing both sides of equality (4) by the magnitude of the single step of balancing M, ..., we express the disequilibrium by the number of discrete steps Nn

N -

l {i) h) (5) 2KA% D,

sh

A similar expression can be obtained to determine the degree of disequilibrium using the second orthogonal 45 parameter Np:

jl 2

AND

d (i) (6) LR.

Ui

where L (i) {Jp) (modulation increment of the square of the amplitude of the signal imbalance when the bridge is modulated by the parameter p.

It follows from formulas (5) and (b) that the imbalance of the bridge with orthogonal and equilibration for each of the controlled parameters is prorated to the increment of the square of the amplitude of the imbalance signal, which is caused by the modulation of this parameter. It should be emphasized that formulas (5) and (b), which are used to calculate bridge imbalance, are absolutely accurate. Thus, in the proposed method of balancing, in contrast to the known methodological error in determining the amount of disequilibrium, it is fundamentally absent. This makes it possible to use the balancing method when building fast AC bridges with orthogonal balancing lines. Using the proposed method, the accuracy of determining the imbalance is limited only by the instrumental errors of the bridge elements, and these errors can be minimized. Calculations show that for a given: error T of measurement and instrumental error of determining the amount of imbalance, the number of counterbalancing steps and the proposed method are determined by equality, te ((f} For example, if the error O of determining the state of equilibrium, the characteristic quality extrapolation device of the bridge, is 1% (1 (Gt, and the measurement error should not exceed 0.01% (1 (V) that such measurement accuracy is achieved in 2 balancing cycles, for a ratio of 121.1.0 2 for comparison note that n When balancing a bridge using a known method, the minimum number of balancing cycles is eight, since the measurement accuracy T 0.01% is provided by balancing for 4 decades, and each balancing stage requires two balancing cycles. Thus, the proposed balancing method provides 4 times more speed than The known extrinsic bridge of alternating current, equalizing by the proposed method, contains 04 a sinusoidal voltage generator 1, a bridge measuring circuit 2, an internal structure travel which satisfies the requirement of orthogonality equilibration lines amplitude detector 3, Quad 4, the analyzer 5 increments, the voltage converter 6 in the number of pulses, a reversible counter 7, a trigger 8 reverse, the modulator 9 and the control unit 10. The bridge works as follows. The imbalance signal of the bridge measurement circuit 2 is subjected to amplitude detection, and then squared. These functions are performed by detector 3 and quad bridge 4. Its equilibration is synchronized by the control unit 10. If a signal appears at one output of this block, the increment analyzer 5 memorizes the current value of the square of the bridge imbalance signal, for example, DC voltage. When applying a permission signal from another output of control unit 10 to the input of modulator 9, the latter performs a trial change of the controlled parameter of the bridge circuit, its output signal receives a certain modulation increment containing information about the state of the bridge circuit. The new imbalance signal value is also subjected to amplitude detection, squared, and then stored in a 5-increment analyzer. At the same time, the magnitude and sign of the modulation increment of the square of the amplitude of the disequilibrium signal is determined in this block. If the sign of this increment is positive, then from analyzer 5 a pulse is applied to the trigger 8 of the reverse, changing the counting direction of the reversible counter 7. Then the increment of the square amplitude is converted in the voltage converter 6 to the number of pulses. / The sequence of pulses coming from the output of the converter 6 to the input of the reversible counter 7, changes the state of both this counter and the switched elements of the bridge metering circuit 2, bringing it closer to the equilibrium state. The degree of approximation depends on the tool. mental error is determined by the equilibrium state of the bridge. When

lack of accuracy of the procedure described, it can be repeated. When the bridge is balanced, the digital value of the output code of the reversible counter 7 is equal to the measured impedance parameter.

The use of the method of automatic balancing of digital extreme bridges of alternating current makes it possible to increase the speed of these devices by about 4 times in comparison with the devices with the most high-speed devices, while maintaining their accuracy.

Claims (1)

Invention Formula A method of automatically balancing digital extreme AC bridges with orthogonal balancing lines, in which a controlled parameter is modulated, detects a signal of bridge imbalance before and after modulation, according to the sign of the modulation increment is determined by the direction of adjustment, characterized in that, in order to improve speed, the signal obtained after detection is squared, the modulation increment of the square of the pro-detected signal is measured and the controlled parameter is changed by an amount proportional to this increment . Sources of information taken into account in the examination .one. USSR Author's Certificate No. 756301, cl. G 01 R 17/10, 1978. 2, USSR Author's Certificate No. 313163, cl. G 01 R J7 / 10, 1970 (psotiotype)