SU873138A1 - Current-to-voltage transducer - Google Patents

Description

one

The invention relates to electrical measuring technique and can be used in various measuring devices where low levels of secondary current are needed, in tea, to carry measurement transducers and automation devices as input current devices.

A device for converting current B is proportional to a voltage containing a current transformer, the secondary winding of which is connected to the active resistance.

one.

The device closest to the proposed one is a current transformer and an operational amplifier, the input of which is connected to the input winding of the current transformer CC2.

The disadvantage of these devices is the large size of the current transformer and the significant leakage inductance, which increases the phase and current errors of the transformer.

The purpose of the invention is the accuracy of conversion.

This goal is achieved by introducing a second current transformer into the measuring current-voltage converter containing the first current transformer and operational amplifier, the primary winding of which is connected according to the primary winding of the first current transformer, the first terminals of the secondary winding of each transformer are connected to the common bus , and the second pins are with the inverting input of the operational amplifier through an adjustable resistor and a current limiting resistor, respectively, and the secondary windings of the transformer Ator current according included.

15

FIG. 1 shows the principle-. to the circuit of the current-to-current measuring transducer; in fig. 2 vector diagrams.

The measuring converter co20 holds the first current transformer 1, the second current transformer 2, the operational amplifier 3, the current limiting resistor 4, the adjustable resistor 5, the resistor 6.

25

The measuring transducer operates as follows.

On the inverting input of the operating y (line 3, the difference of the secondary currents of 12.2 is supplied. Ov of the first

30 current transformer 1 and second

a current transformer 2, and a voltage proportional to this t) a3HOCTH is generated at the output of the operational amplifier 3. Since the difference current tJoj is determined by the difference in the transformation ratios of current transformers, they are performed with a small transformation ratio, which makes it possible to use transformers with a small number of turns.

Improving Conversion Accuracy Achieved by eliminating the initial phase shift by incorporating active resistance currents in the secondary windings of the transformers, one of which is adjustable, and is illustrated by vector diagrams (Fig. 2 a and b). The differential current 3ov 2.-3g is phase-shifted with respect to the primary current 3 by an angle C) and (FIG. 2a). Increasing the resistance value of the adjustable resistor 5 increases the maximum induction in the core and reduces the phase shift of the secondary current 3-2; By adjusting the resistance value further, one can achieve such a position of the vector 3, at which the difference current,; coincides in phase with the primary current 3-1 (Fig. 26), and a current without an initial phase shift relative to the primary is supplied to the input of the operational amplifier 3.

The absence of an initial phase shift eliminates the need for additional phase correction circuits.

which greatly expands the frequency range in which the device can be used, and improves the accuracy of the conversion of TOfca to voltage.

Claims (2)

1.Vestnik Kharkov Polytechnic Institute. Electric power engineering and power plants stacking. 0 1979, no. 7, s. 3-7, fig. one. 2.Japan ElectronTc Engineering, June 74, 91, p. 37-41, ftg 1 (prototype). -; phage.1 S i g tpui.Z