SU1700491A1 - Device for measuring direct current - Google Patents

Abstract

The invention relates to electrical measuring equipment and can be used for contactless measurement of direct current. The purpose of the invention is to improve the accuracy and the expansion of the measurement range. The device contains magnetic conductors 1, 2, covering conductor 3 with measured current, compensation windings 4, 5 and excitation windings 6, 7 placed on the magnetic core, measuring resistors 10, 14, 15, 16, integrating capacitors 8, 12, amplifier 11 current and a registering device 17. Achieving the goal is also ensured by the presence of a generator of 20 unipolar periodic current pulses, keys 21, 22, a control unit 23 and two valves 9, 13. The principle of operation of the device is based on the dependence of the inductive resistance of windings spinning the magnitude and direction of the magnetomotive forces generated by the ampere turns in the chains of the measured current, the compensating winding and the excitation winding 1 yl. (Ls

Description

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The invention relates to the field of electrical measuring technology, namely to the contactless measurement of direct current. The purpose of the invention is to improve the accuracy and expansion of the measurement range,

The drawing shows the functional diagram of the device for measuring the DC current.

A device for measuring direct current contains magnetic cores 1 and 2, which cover successively conductor 3 with measured current (conventionally depicted as two series-connected windings).

The magnetic lines 1 and 2 respectively have the compensation windings 4 and 5 which are identical in their flow data. The beginning of the compensation winding 4 is connected to the end of the compensation winding 5, and its beginning is connected to the common power supply bus.

By the action of the magnetomotive forces, the compensation windings 4 and 5 are connected in opposite direction with the conductor 3 of the measured current.

The first 6 and second 7 excitation windings are also placed on the magnetic core 1, the End of the winding 6 and the beginning of the excitation winding 7 are interconnected with each other and with a common power supply bus. The first integrating capacitor 8 is connected by its first output through the first valve 9 to the start of the excitation winding 6 and through the first limiting resistor 10 to the inverting input of the current amplifier 11.. The second integrating capacitor 12 is connected to the end of the excitation winding 7 through the second valve 13 and to the non-inverting input of the current amplifier 11 via the second limiting resistor 14

In parallel with the first and second integrating capacitors 8 and 12, the first 15 and second 16 measuring resistors are connected respectively. The second terminals of the integrating capacitors 8 and 12 are connected to the offending bus, the recording device 17 is connected to the output of current amplifier 11 by one input terminal, and the other is connected to the end of the compensation winding 4,

Similarly, the placement of the excitation windings on the magnetic core 1 on the magnetic core 2 is placed on the first 18 and second 19 excitation windings / on parameters identical to the windings 6 and 7 of the excitation of the magnetic core 1. The excitation generator 20, which is a generator of monopolar periodic sawtooth current pulses current), its input is connected to the power supply terminal, and the output is connected to the input of the first switch 21, the second switch 22 and the input of the control unit 23. The first and second outputs of the control unit are connected respectively to the control inputs of the first 21 and second 22 keys. The beginning of the excitation winding 18 of the magnetic circuit 2 is connected to the output of the key 21, and its end is united

0 with the end of the excitation winding 7 of the magnetic circuit 1. The end of the excitation winding 19 of the magnetic conductor 2 is connected to the output of the key 22, and its beginning is united with the start of the excitation winding of the magnetic conductor 1

5 The device operates as follows.

Single-pole periodic servo current pulses generated by excitation generator 20

0 (excitation pulses) through switches 21 and 22, which are open-ended and closed by control unit 23, according to signals from excitation generator 20, flow alternately with frequency of excitation pulses5 not through windings 18, 7 and 19, 6 of excitation and power supply (1 Upit). In the absence of a measurable current in the conductor 3 and the compensation windings 4 and 5, the magnetic induction of a constant magnetic field in

0 magnetic cores 1 and 2 is zero. Flowing along the windings 18, 7 and 19, 6 of the excitation, the excitation pulses of the same shape and maximum value periodically peremagnetized magnetic cores 1

5 and 2 through identical, unsaturated, symmetrical hysteresis loops.

Inductive resistances of the windings 6 and 7 of the excitation, which are nonlinear functions of the intensity of the external

0 magnetic field will be in this case symmetrical to each other. Under these conditions, the excitation pulses flowing through the windings 6 and 7 induce them, in relation to their common point, unipolar, EMF-self-induction pulses of the same magnitude and shape. At the same time, voltage pulses of opposite polarity are induced on the windings b and 7 of the excitation, which are not streamlined at the moment of the excitation current. The selection of constant or slowly varying component pulses of EMF self-induction arising on the windings b and 7 of the excitation is carried out in two symmetric chains, the first from

5 which includes a valve 9, an integrating capacitor 8, a measuring resistor 15, and the second - a valve 13, an integrating capacitor 12 and a measuring resistor 16.

Formed on the integrating capacitor 8 (with respect to the common bus), the constant component of the EMF-self-induction pulses of the excitation winding 6 is supplied through the limiting resistor 10 to the inverting input of the current amplifier 11. Similarly, the noninverting input of current amplifier 11 through the limiting resistor 14 receives a constant component of the EMF-self-induction pulses of the excitation winding 7, which is formed on the integrating capacitor 12. h

In the absence of a measurable current in the conductor 3, the difference of the constant component voltages (differential signal) arriving at the inverting and non-inverting inputs of the current amplifier 11 is zero. The output current of the current amplifier 1 1 is equal to zero, and therefore the current flowing through the recording device 17 and through the compensation windings 4 and 5 is also zero.

When the measured current flows through the conductor 3 in the magnetic conductors 1 and 2, a constant magnetic flux is created that violates the symmetry of the inductive resistances of the excitation windings 6 and 7. When the excitation pulses are constant in amplitude and shape, this leads to a violation of the symmetry of the EMF-self-induction pulses on the windings 6 and 7 of the excitation, and therefore the constant components of the voltages on the integrating capacitors 8 and 12 change, becoming unequal in size. At the same time, the inverting and non-inverting inputs of current amplifier 11 receive an input signal equal to the difference between the constant component voltages generated on the integrating capacitors 8 and 12, which causes the appearance of a corresponding output current of current amplifier 11 and its flow through the recording device and along the compensation windings 4 and 5. The magnetic flux generated by the current flowing through the compensation windings 4 and 5 is directed oppositely to the magnetic flux created by the measured current in the magnetic flux 1 and 2. Due to the large gain value of the current amplifier 11, the magnetic flux generated in the magnetic cores 1 and 2 by the measured current is compensated.

At the same time, 1X IK WK, where lx is the current to be measured; IK and WK are the ampere-turns of the compensation winding 4 or the compensation winding 5 (due to the equality of their turns and the series connection), i.e. the current flowing through the compensation windings 4 and 5 is proportional to the measured

The meter is counted directly using a recording instrument.

Remagnetization of magnetic cores 1 and 2 during the operation of the device with excitation pulses leads to induction (induction) on the sections of conductor 3 magnetically coupled to the magnetic cores 1 and

2, and on the compensation windings 4 and 5 of the voltage pulses with the frequency of the excitation generator 20.

With the same type of magnetic cores 1 and 2, their identical hitch data and successively flowing (and, therefore, equal) excitation pulses along counter-connected windings 18, 7 and 19, 6 excitation, the voltage pulses induced in the conductor section

3, magnetically coupled with magnetic core 1, are equal in shape and amplitude to pulses

0 the voltage induced on the section of the conductor 3, which is magnetically coupled with the magnetic core 2, but opposite in sign. As a result, the total voltage induced in the conductor 3 by the excitation pulses, which is the interference introduced by the device into the circuit of the measured current, is close to zero. Therefore, the power transmitted from the excitation circuits of the magnetic cores 1 is also close to zero.

0 and 2 in the circuit of the measured current.

Everything considered in relation to conductor 3 is also true for the circuit, which includes compensation windings 4 and 5). In the process of magnetization reversal

5 excitation of magnetic cores 1 and 2 on the compensation windings 4 and 5 induce voltage pulses of slightly different shape and amplitude, but opposite in sign. Total voltage induced

0 in the compensation windings 4 and 5, and the power transmitted from the field windings to the compensation circuit is also close to zero. Low, close to zero power level transmitted from excitation circuits.

5 into the circuit of the measured current and the circuit of compensation, makes the device less sensitive in sensitivity to the magnitude of the measured current from the change in resistance in the circuits of the measured current and compensation current), which leads to an increase in measurement accuracy.

The use of a current pulse generator (current generator) as the generator 20, the parameters of which do not depend on the external load of the generator, allows the excitation windings 6 and 7 to be supplied with the same form and amplitude current pulses regardless of the degree of saturation of the magnetic cores 1 and 2.

As the saturation of the magnetic conductors 1 and 2 increases, the inductive resistances of the windings 6 and 7 of the excitation are reduced due to the measured current flowing through Conductor 3 (within the measuring range), and EMF self-induction pulses on these windings decrease at constant excitation pulses which leads to a decrease in the voltages on the integrating capacitors 8 and 12. In this case, as the useful (differential-g) signal decreases at the inputs of the current amplifier 11, the level of the common-mode signals decreases steadily,

The technical solution of the problem of alternately dual-channel powering of the windings 18, 7 and 19, 6 of excitation based on a generator of 20 unipolar periodic pulses and alternately opened and closed keys 21 and 22 ensures that the device’s indications are not dependent on de-factors (ambient temperature, eg power supply, etc.) affecting the operation of the excitation generator and keys. Possible variations in the destabilizing factors of such parameters of the current pulses of the excitation generator 20, such as the rate of increase, amplitude, linearity, frequency, etc., do not have a significant effect on the measurement error, so that each subsequent current pulse of the generator 20 its parameters are fully consistent with each previous one, as a result of which the symmetry of the current pulses of Che is not violated; the excitation windings 6 and 7 and the balance of the constant component voltages on the integrating condensers 8 and 12 (in 1 steady state).

The resistance of the switches 21 and 22 and their instability is possible (for example, when the ambient temperature changes) also do not have a noticeable effect on the error of the device, since the parameters of the excitation pulses of the current generator do not depend on the resistance of the external load.

Claims (1)

DETAILED DESCRIPTION OF THE INVENTION A device for measuring direct current, comprising a first magnetic core, covering a conductor with a measured current, a compensation winding, and two excitation windings placed on the first magnetic core, a current amplifier, the inverting input of which is connected to the first output of the first integrating capacitor through the first limiting resistor, the non-inverting input of the current amplifier through the second restricting resistor is connected to the first output of the second integrating capacitor, two trimming resistors, each of which is connected in parallel to the corresponding integrating capacitors, the second terminals of which are connected with a common bus, characterized in that, in order to increase accuracy and expand the measurement range, registers are entered into it a stripping device, the first input of which is connected to the output of the current amplifier, the second is connected to the second output of the compensation winding of the first magnetic conductor, the second magnetic conductor, made like the first magnetic conductor and enclosing the conductor with the measured current, the second compensation winding, the third and fourth excitation windings placed on the second magnetic conductor, two valves, the excitation generator, two keys, the control unit, the first output of the first compensation winding connected to the second output of the second compensation winding, the first output of which is connected to the common bus, the first valve is connected between the first output of the first excitation winding and the first output of the first integrating end ensatora, the second valve is connected between the second output of the first excitation winding and the first output of the second integrating capacitor; the first output of the third excitation winding is connected to the output the first key and the second output of the third excitation winding are connected to the second output of the second excitation winding, the first output of the fourth excitation winding is connected to the first output of the first excitation winding, the second output of the fourth excitation winding is connected to the output of the second switch, the second output of the first and first output of the second excitation windings connected to a common bus the input of the excitation generator is connected to the power supply terminal, the output of the excitation generator is connected to the inputs of the first and second keys and the input of the control unit, the first and second outputs of which are connected respectively to the control inputs of the first and second keys.