SU1449915A1 - Instrument current converter - Google Patents

Abstract

The invention can be used in measurement technology and automation. The purpose of the invention is to increase the dynamic accuracy, stability and reduction of power consumption. The introduction of an additional transformer 5 with a core of the same material as that of the main transformer 1 allows the feedback circuit to be carried out by an error signal. It includes serially connected identical windings 4 and 6 and amplifier 9. 1 sludge.

Description

The invention relates to measuring equipment devices, is intended for converting an alternating Fock into a current with galvanic separation of the controlled and measuring circuits, and can be used in measuring equipment and automation.

The purpose of the invention is to increase dynamic accuracy, increase stability and reduce power consumption.

The drawing shows a diagram of a current converter.

The converter comprises a first transformer 1 with three windings 2-4 wound on its Core, a second transformer 5 with two windings 6 and 7, a load resistor 8 and an operational amplifier 9.

The converted current I _RX enters the primary winding 2 of the transformer 1. The end of winding 4 of transformer 1 is connected to the beginning of winding 6 of transformer 5, the other output of which is connected to a common bus, the beginning of winding 4 is connected to the inverting input of operational amplifier 9, the output of which is connected to the beginning of winding 7 of transformer 5, and the non-inverting input is connected to a common bus . The end of the winding 7 of the transformer 5 is connected to the load resistor 8, where the beginning of the winding 3 of the transformer 1 is connected, while the other terminals of the winding 3 and the load resistor 8 are connected to. common bus.

The converter operates as follows.

To simplify, we consider the characteristics of operational amplifier 9 close to ideal, which corresponds to the parameters of pre-industrial amplifiers.

operating room (I ₄ = 0), to • · (2)

Since the input current of amplifier 9 is very small, it follows from (1) that t N <1 <

Due to the fact that the voltage between the differential inputs of the amplifier 9 is close to zero, the voltage induced in the winding 4 of the transformer 1 and in us.

winding 6 of transformer 5, thus ^W 4 ^S '5F = ^W b ^S ^

W ₆ - the number of turns of the windings 4 and 6, respectively ^

S ₅ - cross sections of the magnetic circuits of transformers 1 and 5, respectively}

In _? - induction in the cores of transformers 1 and 5, respectively.

Assuming that the materials of the cores of transformers 1 and 5 are the same, and also that equality is observed:

where w ₄

So

Bo

W ₄ S, = W ₆ Sy, we obtain:

dB, _ dB _? dt dt or (4) (5) (6)

B, (t) ^ B _s (t).

Consequently,

H, (t) = H _y (t).

Determine the current 1 _? coming to the resistor 8 load. According to the law of the total current for the core of the transformer 5 we get

I ₆ W ₆ - I ₇ W ₇ + H _{5 1} °, (7) where

It follows from the law of the total current for the core of transformer 1 that i _Bx w ₄ ^e A ^w * ^{+ + н} | 1 </ 1) where W ₂ , W ₃ , •

n

- the number of turns of the windings 2-4, respectively ·,

- the magnetic field strength in the core of the transformer 1;

- the average length of the magnetic power line of the core of the transformer 1.

- the number of turns of the windings 6 and 7, respectively;

- the magnetic field strength in the core of the transformer 5;

- the average length of the magnetic power line of the core of the transformer 5.

previously made guess ^w 7

When

1 ₆ = 1 _Ф = о,

18)

The output current of the converter is determined by the sum of the currents 1 ₇ and

1 _in s = C ⁺ <9)

Substituting into the expression (9) the values of the corresponding currents from (2) and (8) we obtain m = _ H <1, ₊ H. d

W _e W, w _z ^A

From the expression (10) with the identity of the magnetic characteristics of the magnetic cores and the fulfillment of (6), as well as the conditions

-2 <- = b_

W, W ₇ (11) there is no current conversion error and

I

I =. (12) ^X o

As follows from expression (12), the output current of the converter is proportional to the input current I _βχ and does not depend on the characteristics of the magnetic core of transformers 1 and 5, which allows the use of transformers with a magnetic core from cheap and technological ferrite, and the core of the transformer 5 / expression (4) , (11)] can be significantly smaller than the core of the transformer 1, if W ₇ ^ W ₃ , and w _{6 7} w ₄ .

Claims (1)

SUMMARY OF THE INVENTION A current measuring transducer comprising a transformer On the core of which the primary and two secondary windings are wound, a load resistor and an operational amplifier, to the input of which is connected the first secondary winding, which means that, in order to increase dynamic accuracy, stability and reduce power consumption, a second transformer is introduced with two windings, the core of which is made of the same material as the core of the first transformer, the first terminal of the first winding of the second transformer connected to the second terminal of the first secondary winding of the first trans a rmitter, the second output of which is connected to the first input of the operational amplifier, the second output of the first winding of the second transformer is connected to a common bus and to the other input of the operational amplifier, and the second winding of the second transformer is connected to the output of the operational amplifier with one output, and to the common terminals of the resistor with the other load and the second secondary winding of the first transformer, the second terminals of which are connected to a common bus.