SU1182413A1 - Transformer measuring bridge - Google Patents

Abstract

one . TRANSFORMER MEASUREMENT, ELASTIC BRIDGE, containing a power source, current clamps for connecting a series-connected measured object and a sample measure, a two-step transformer, on two cores of which two windings are located, and on one of the cores one third winding is located, a separation transformer with three windings an equilibrium detector connected to the first winding of an isolation transformer, the first winding of a two-stage transformer connected in series with the second one coil separator transformer connected in parallel to the terminals for connecting the measured object, the second winding of a two-stage transformer connected in series with the third winding of the separating transformer is connected in parallel with potential terminals for connecting an exemplary measure, the first of the third winding of a two-stage transformer connected to the first potential terminal of a potential transformer connected to the first potential transformer exemplary measure, about tl and whiteness by the fact that, in order to increase accuracy and extend the limits of measurement s, the bridge comprises an additional transformer having three windings and us1shitelem, the primary winding of the transformer dopolnitelBnogo podkpyuchena to power source terminals, one of which is connected to the OBO) conductive bus, two additional secondary windings of the transformer compounds; us in series and connected to. current terminals for connecting a series-connected measured object and an exemplary measure, the first input of the amplifier is connected to the output of the second winding of a two-stage transformer connected to the output of the third section of the winding, the second input of the amplifier is connected to the common bus, the output of the amplifier is connected to the first secondary winding of an additional transformer connected with the second secondary secondary winding of the additional transformer, the second output of the third winding of the two-transformer nchatogo transformer is connected to the common bus. 2. The bridge according to claim 1, characterized in that the first secondary I winding of the additional transformer is made adjustable

Description

one

The invention relates to electrical measuring equipment and can be used to measure parameters of complex resistances by means of bridge and compensating alternating current circuits, in particular, when measuring low resistances.

The purpose of the invention is to increase the accuracy by forming a compensating voltage, which eliminates the influence of the residual parameters of the windings and connecting wires, and extends the limits of measurement,

The drawing shows a block diagram of the device, 5

The device contains a power source 1, clamps for connecting the measured object 2, a sample measure of 3 J two-step transformer with cores 4 and 5. and windings 6-8, 20 separation transformer 9 with windings 10-12, equilibrium detector 13, additional transformer 1A windings 15-17, amplifier 18, potential clamps 19-22, current clamps 23 and 24 for connecting the measured object 2,

The windings b and 10 are connected in series and connected to potential terminals 19 and 20 of the measured object. The windings 7 and 11 are connected in series and connected to potential terminals 21 and 22 of exemplary measure 3 (resistor), Source 1 is connected to the terminals of the winding 15 of the additional 35 transformer 14, Winding 16 and 17 of the additional transformer 14 are connected in series and connected to the current terminals 23 and 24 The first input of the amplifier 18 is connected to the terminal of the connection of windings 7 and 11, and the output of the amplifier is connected to the common terminal fy of the windings 16 and 17. The second input of the amplifier 18 and the first terminal of the winding. 8 is connected with the total thickness, and the second 45 winding clamp 8 - with the current clamp 24.

The number of turns in the winding 16 is equal, the number of turns in the winding 6, The number of turns in the windings 7, 8 and 17 are the same. 50

The state of equilibrium of the circuit is monitored by a detector 13 connected to the terminals of the winding 12.

The ratio of the voltages on the windings 6 and 7 of the bottom of the einia stupas of that transformer -ii must be installed with high accuracy, the additional transformer 14 and the amplifier 18 serve for a higher 11824

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NIN of the accuracy of the transfer coefficient of a two-stage transformer and protection of the device against the influence of leakage currents through unwanted capacitive conductances relative to the grounded node of the bridge “The switching accuracy of the winding 16 may be lower than the switching accuracy of the winding 6,

The use of an isolation transformer 9 makes it possible to eliminate the influence of the resistance of the connecting wire between the object to be measured and the exemplary measure.

The device works as follows.

When the supply voltage is applied to the winding 15, an EMF is induced in the windings 16 and 17 connected to the terminals of the resistances compared. The voltage drops across these resistances are compared to the voltages on windings 6 and 7. When the voltage is unequal, a current of imbalance arises in the winding 12. Switching the coils in windings 6 and 16 ensures equal current turns in windings 10 and 11, as evidenced by zero readings detector 13.

Excluding measurement errors, the chain equilibrium condition is described by the equation:

7 - (about m

resistance measure

Where

i V

an object;

exemplary resistance

Z. measures;

the number of turns in the windings

m and .m, 6

6 and 7 respectively. The number of turns in the winding 6 is proportional to the measured resistance

As a result of the flow of residual currents through the working windings 6 and 7 at the time of equilibrium of the circuit, measurement errors occur due to the influence of the residual resistances of the windings 6 and 7 and connecting wires to them;

In the absence of compensation, if the effects of second order smallness are not taken into account, these advantages can be determined from the expression:

u zc +

Zj

Q 7 7 .6 1

where Zg, Zj - residual parameters

(active resistances and inductive scattering. windings 6 and 10 connecting wires to terminals 19 and 20 of the object being measured; Zg, Zj - residual parameters of windings 7 and 11 and connecting wires to clutches 21 and 22 are exemplary; ZgH b- the input resistances of the coil 6 and 7. The reduction of the error y is achieved by reducing the currents flowing through the windings 6 and 7 at the moment of circuit equilibrium, which is ensured by the combined use of an additional transformer 14 and amplifier 18 with a two-step transformer, as a result of supplying windings 8 to the terminals exactly equal to the voltage drop on the reference measure 3, the magnetization of the core 5 through the winding 8 and negligible currents through the windings 6 and 7 is ensured, which leads to an increase in the input resistances of the windings 6 and 7 and a reduction in the influence of the residual resistances of these windings and connecting wires to them on the accuracy of the measuring circuit. To ensure high accuracy of the compensation of these errors, it is necessary that the voltage at the terminals of the standard measure 3, windings 7, 17 and 8 be equal to each other with high accuracy. In fact, since the switching of the turns in the winding 16 is done with less discretion than in the winding 6, and also due to the influence of the residual parameters of the windings 7 and 17 and the connecting wires to them, the voltage on the windings 7 and 17 differ from the voltage exemplary measure on the value of l i corresponding to the specified error. This voltage difference also exists between the voltages on the windings 7 and 8. This error is compensated by the amplifier 18, the voltage difference 41 at the terminals of the windings 7 and 8 is fed to the input of the amplifier 18, the output voltage of the amplifier is summed with the voltage the winding 17 and the winding terminals 8 are not supplied and thus the indicated error is compensated. In addition, measurement errors caused by the influence of leakage currents through unwanted capacitive conductances between the bridge elements and a grounded node are automatically reduced. By the joint operation of an additional transformer 14 and amplifier 18, the potential of the junction point of windings 7 and 11 leads to ground potential, which prevents leakage currents from flowing between the instrument case (grounded) and the primary circuits of the equilibrium detector and automatically reduces measurement errors due to leakage currents. As a result of the joint switching of the windings 6 and 16, the operating current in the branches of the bridge is constant when it is balanced, independent of the measured resistance, which reduces the dependence of the circuit sensitivity on the measured resistance in the measurement range and improves the accuracy measurements. When a compensating voltage is formed, shunting of the model resistance is excluded, which allows one to expand the limits of measurements to greater resistances without visible limitations.

Claims (2)

1 . TRANSFORMER MEASURING BRIDGE, containing a power source, current clamps for connecting a series-connected measured object and. Exemplary! measures, a two-stage transformer, on two cores of which there are two windings, and on one of the cores there is one third winding, an isolation transformer with three windings and an equilibrium detector connected to the first winding of the isolation transformer, the first winding of a two-stage transformer connected in series with the second winding of the isolation transformer, connected in parallel to the clamps for connecting the measured object, the second winding of a two-stage transformer connected in series with the third winding of the isolation transformer, connected in parallel with potential clamps for connecting an exemplary measure, the first output of the third winding of a two-stage transformer is connected to the first potential clamp for connecting an exemplary measure, which means that, in order to increase accuracy and expand the limits of measurement, the bridge equipped with an additional transformer with three windings and an amplifier, the primary winding of the additional transformer is connected to the terminals of the power source, n of which is connected to the common bus, two secondary windings of the additional transformer are connected _: they are connected in series and connected to | current clamps for connecting the measured object and exemplary measures in series, the first input of the amplifier is connected to the output of the second winding of the two-stage transformer connected to the output of the third winding of the separation transformer, the second input of the amplifier is connected to a common bus, the output of the amplifier is connected to the output of the first secondary winding of the additional transformer connected to the output of the second secondary winding of the additional transformer, the second output of the third winding of the two-stage transform ora is connected to the common bus. 2. The bridge according to claim 1, characterized in that the first secondary winding of the additional transformer is made adjustable. 1 1182413