SU960640A1 - Ac bridge for measuring large resistance - Google Patents

Description

(5) AC BRIDGE FOR MEASURING GREAT RESISTANCE

one

The invention relates to electrical measuring technology, more precisely, to the field, which is associated with the measurement of parameters of complex resistance using bridge and compensating alternating current circuits.

A method is known in which high-resistance resistances are measured in a four-arm bridge circuit at a constant current. Simulators of high-resistance, built on the basis of an integrator with a capacitor at the outlet, are used as an exemplary measure. This ensures a high accuracy of the IJll measurement.

The disadvantage of this method is that only the main parameter of the resistor, ohmic resistance, is measured.

When using resistors in AC circuits, it is very important to know its time constant, as

torus DC is not measured. . ; ,

The closest technical solution to the invention is a transformer bridge, containing a power source, a measured object, two exemplary measures, a voltage transformer with a primary winding to which a power source is connected, and two secondary windings connected (first to the terminals of the an object and an exemplary measure, respectively, and an equilibrium detector-fop, connected between the junction point of the object being measured and the exemplary measure and the grounded bus of the bridge 2.

The disadvantages of this device is the need to use

20 high-resistance reference resistor when measuring high-resistance.

High impedance resistors (more than 10 ohms) that can be used as a measure are either not stable enough (nonwire resistors) or have a long time constant (microwire resistors). Their use reduces the accuracy of measurements. If exact average resistors are used as a model, and the required transfer coefficient is provided by a large ratio of turns of the shoulder windings, then the sensitivity of the bridge circuit decreases, which also reflects on the measurement accuracy. The aim of the invention is to improve the accuracy and sensitivity of measurements. This goal is achieved by the fact that an ac bridge for measuring high resistances, containing a power source, a measured object, exemplary measures, a shoulder voltage transformer with a primary winding connected to the power supply terminals and secondary windings, the first terminals of which are connected respectively to the first terminals of the object to be measured and exemplary measures second (the secondary terminals of the windings are connected to the grounded bus of the bridge, and an equilibrium detector connected between the junction point of the second terminals of object and model measures and a grounded bridge bus, equipped with a non-inverting voltage amplifier with a reference element in the feedback circuit and with a voltage divider connected to the output of the non-inverting voltage amplifier, the first input of the non-inverting voltage amplifier is connected to the input of the equilibrium sensor , the second input of the non-inverting voltage amplifier is connected to the midpoint of the voltage divider, and the second output of the voltage divider is connected to the grounded busbar of the bridge, and as one of the exemplary p used an integrator with a condenser, rom included at the output of the integrator. FIG. 1 is a schematic diagram of the device; in fig. 2 shows a variant of the device diagram with an integrator as an exemplary measure. The device (Fig. 1) contains a power supply 1, a shoulder voltage transformer 2 with windings 3-5 of the measured object 6, an exemplary resistor 7, an equilibrium detector 8, a non-inverting voltage amplifier 9, a voltage splitter 10 and 11 model resistor 12 ,. The nur.av) bridge is updated by the commutation of the turns in the winding 5 When the bridge is balanced, the number of turns in the adjustable winding 5 is proportional to the resistance of the measured object 6, the equilibrium is monitored by the equilibrium detector 8. The increase in ch1; the viscosity of the bridge is carried out as follows. . The signal from the equilibrium detector 8 is fed to an amplifier 9, in the feedback circuit of which resis - - - is turned on. torus 12, the resistance of which is equal to the resistance of the reference resistor: 7. The current through the resistor 12 is supplied to the diagonal of the equilibrium detector 8. If we denote the resistance of the reference resistor 7 by R0 and, accordingly, the resistance of the resistor 12, which is equal to it, also by Rp, then the connection of the amplifier 9 with the resistor 12 (Fig. 1) is equivalent to the connection -. resistance (-RQ parallel to detector 8. Let us show how the sensitivity was increased in the proposed device. In the absence of amplifier 9 in the known bridge circuit, the voltage U at the terminals of detector 8, determined by simple circuit calculation, is O - O Ro-UsRx - ° ( RX Яо) where 0л is the voltage at the winding terminals L, the voltage at the winding terminals 5, the resistance of the object to be measured 6, the resistance of the reference resistor 7. The relative sensitivity of the measurements is -C04 0g) Ro. - iHo. o CrfRx g R, is the relative increment of resistance IV. Since when measuring large resistances P, the sensitivity of the bridge is small.

In the proposed device, by means of an amplifier 9, a resistor (-K) is connected in parallel with the detector. In this case, when calculating the circuit by a known method (for example, by the method of loop currents, we obtain the voltage at the detector terminals

(i - L o-Obalyh / J. k5

where the designations coincide with the designations accepted for the known bridge; : .fl0. - resistance of the resistor 7 and 12.

Relative sensitivity of measurements in this case

ei

- (“X

C4)

9 ((fR)

As can be seen from a comparison of the expressions i (2) and (4), in the invention, the relative sensitivity of measurements increased by a number of times equal to the ratio of the considered sensitivities.

 , „.4 -et),

 If we take the value of iV 10 R, i and, therefore, U s 4 °, the sensitivity of this device is 100 times greater.

FIG. Figure 2 shows a variant of the circuitry of this device, which makes it possible to measure super high impedance resistors. The device contains a power supply 13, a shoulder voltage transformer with windings 15-18, a measured object 19, an exemplary capacitor 20, an equilibrium detector 21, an integrator 22 with a resistor 23 at the input and a capacitor 2C in the feedback circuit, a capacitor 25, a non-inverting amplifier 26 voltage with voltage divider 27 and 28 and capacitor 29 in the feedback circuit. The bridge is balanced by the commutation of the turns in the windings 17 and 18. The number of wit. The coil in the coil 17 is proportional to the relative component of the measured object, which characterizes its time constant. The number of turns in the winding 18 is proportional to the measured cfpro. object 19.

Increasing the sensitivity of the bridge is accomplished by the voltage amplifier 26 in a manner similar to that described by.

In this case, the capacitance of the capacitor 29 is chosen equal to the capacitance of the capacitor 25.

The techno-econonic effect of reteni consists in a significant increase in the sensitivity and accuracy of measurements of high-resistance resistors, achieved by a relatively simple method. At the same time, the sensitivity depends linearly on the value of the measured resistance, which greatly simplifies the process of balancing the multi-range bridge circuit.

Further improvement in measurement accuracy can be achieved.

5 by replacing the reference resistor with an integrator with a capacitor at the output. The integrator is easy to perform with the exact transfer ratio. The capacitor at the output of the integrator has a small capacity and its accuracy is also high.

The application of the proposed device allows superhigh impedance resistors to be measured with high accuracy to hundreds of Gbms.

Claims (2)

1. AC bridge for measuring high resistances, containing a power source, measuring an object, exemplary measures, a shoulder voltage transformer with a primary winding connected to the power supply terminals and secondary windings, the first terminals of which are connected respectively to the first terminals of the measured object and exemplary measures 0 the second clips of the secondary windings are connected to a grounded busbar by an equilibrium detector connected between the connection point of the second terminals of the object being measured and the model five . a grounded busbar bridge, characterized in that, in order to increase the sensitivity and accuracy of measurements, the bridge. equipped with a non-inverting voltage amplifier with a reference element in the feedback circuit and a voltage divider connected to the output of the non-inverting voltage amplifier, the first input of the non-inverting voltage amplifier is connected to the input of the equilibrium detector, the second input of the non-inverting voltage amplifier is connected to the midpoint of the divider the voltage of the second output of the voltage divider is connected to the grounded bus of bridge 2. The bridge is pop.1, which is also distinguished by the fact that one of the exemplary methods (1 includes an integrator with a capacitor m at the integrator output. 0 Sources of information taken into account during the examination 1.Ilukovych AM Methods of imitation of high resistance Measuring equipment, 1978, No. 12, pp. 50. 2. Transformer measuring bridges. Ed. K. B. Karandeeva. Energy, M., 1970, p. 169.