CS259355B1 - Electric alternating current's real component's measuring connection - Google Patents

Abstract

The connection solves the measurement of the real component AC power for automation needs technological processes. In engagement is behind the current measuring transformer, a capacitor which is circuit switched from switching diodes, capacitors and resistors charges for proportional real tension component of the measured current.

Description

The invention solves the measurement of the real component of the alternating current by simple passive circuit elements.

Until now, the real component of the current has been measured by deflection meters or complex electronic devices working on the principle of high frequency sampling or switched resistance bridges. Deflection meters cannot be used in automatic control because they do not produce an electrical signal. Electronic devices are complex, bulky and expensive. Measurement of dirty resistive bridges is obstructed by a non-linear inductive load error.

The above-mentioned drawbacks are eliminated by the circuit according to the invention, which is based on the fact that a current measuring transformer is connected to the measured current circuit. This transformer is loaded with a load resistor. The first measuring terminal or transformer is connected to the first output terminal of the wiring via a capacitor. The second terminal of the measuring transformer is directly connected to the second output terminal of the wiring and at the same time to the middle terminal of the voltage transformer. The first output terminal of the wiring is connected to the first terminal of the voltage transformer via a first switching diode and a parallel connected second resistor to the second capacitor. At the same time, the first output terminal of the wiring through the second switching diode and the parallel connected third resistor to the third capacitor are connected to the second terminal of the voltage transformer.

The advantages of the wiring according to the invention are that the wiring is simple and easy to use. Construction costs are low. By sampling the current at a time when the current reactant is zero, the measurement does not affect its non-linearity. The simplicity of the wiring and the good quality of the output signal make it possible to apply wiring in the automation and control of technological processes.

The attached drawing shows the wiring diagram.

The first secondary terminal 11 of the measuring transformer 1 is connected to the output terminal 16 via the capacitor C3. The second secondary terminal 12 of the transformer 1 is directly connected to the second wiring output terminal 17 and at the same time to the middle terminal 16 of the voltage transformer 10. The first wiring output terminal 16 is connected via a first switching diode 4 and parallel resistor R6 to the second capacitor C8 connected to the first terminal 14 of the voltage transformer 10.

At the same time, the first output terminal 16 via the second switching diode 5 and the parallel connected third resistor R7 to the third capacitor C9 are connected to the second terminal 15 of the voltage transformer 10.

The measured current transformed by the measuring transformer 1 creates a voltage drop proportional to the magnitude of the measured current on the load resistor R2 connected between the terminals 11, 12 of the measuring transformer 1. By sampling this voltage, capacitor C3 is charged at the time of the maximum reference voltage at the voltage transformer 10. The switching circuit for charging capacitor C3 consists of switching diodes 4, 5, which are briefly opened by reference voltage from terminals 13, 14 and 14, 15 of voltage transformer 10. Opening of switching diodes 4, 5 at the moment of maximum reference voltage provides counter-voltage C8, C9. These capacitors C8, C9 are slowly discharged by resistors R6, R7. The voltage sample to which capacitor C3 is charged is proportional to the instantaneous value of the measured current at the time of the maximum reference voltage. If the reference voltage is in phase with the real component of the measured current and the real component of the measured current is sinusoidal, then the unidirectional voltage on the capacitor C3 is proportional to the real component of the measured current. An analog-to-digital converter or control circuit with input resistors R1S is connected to the output terminals 18, 17. In order for the device to function reliably, the values of its circuit elements must switch as follows:

C3 C8 C8 = C9 R6 = R7

C3. R18> R6. C8> -> C3. R2 ω

where ω is the circular frequency of the measured current.

The connection is also suitable for measuring 1'arbitrary vector current components, if the reference voltage vector is rotated in the direction of the vector of the measured current.

Claims (1)

SUBJECT Circuit for measuring the real component of an alternating current, characterized in that a measuring transformer (1) having a load resistor (R2) connected in parallel to the secondary winding, is connected between the first secondary terminal (11) of the measuring transformer (1) ) and the first wiring output terminal (16) is a capacitor (C3), the second secondary terminal (12) of the measuring transformer (1) is connected to the middle terminal (14) of the voltage transformer of the invention (10) and the second wiring output terminal (17). wherein the first output terminal of the wiring (16) is connected both through the series-parallel connection of the first switching diode (4), the second capacitor (C8) and the second resistor (R6) to the first terminal (14) of the voltage transformer (10) and a diode (5), a third capacitor (C9) and a third resistor (R7) with a second terminal (16) of the voltage transformer (10).