SU1629861A1 - Device for dc voltage measurement - Google Patents

Abstract

The invention relates to a measurement technique and can be used to measure a DC voltage with galvanic isolation between a current and a measuring circuit. The aim of the invention is to simplify the device. Under the control of the control unit 18 containing a pulse generator 19 and electronic switches 20 and 21, the electromagnetic relays 5 and 8 are alternately turned on, the contact pairs 4.11, 7 and 12 of which are connected capacitor b alternately to the input terminals 1 and 2 or to the terminals 10 and 13 for connecting a measuring device, which uses a peak voltage meter 14. The constant charging and discharging times are determined by the resistance values of resistors 3 and 9. The introduction of a peak voltage meter, a control unit and two electromagnetic relays made it possible to exclude a precision transformer from the circuit and, therefore, to simplify the device. 1 Cpfla, 2 Il. sl С о ю о со ON

Description

figure 1

The invention relates to electrical measuring technology and can be used to measure DC voltage with galvanic isolation between the current and measuring circuit, for example, to monitor the voltage of a DC electric machine.

The aim of the invention is to simplify the device.

Fig, 1 shows a block diagram of the device; in fig. 2 - stress diagrams for his work.

The device contains the first 1 and second 2 input terminals, the first of which is connected through a series-connected resistor 3 and the first contact pair A of the first electromagnetic relay 5 is connected to the first output of the capacitor 6, as well as through the first contact pair 7 of the second electromagnetic relay 8 to the first output of the resistor 9 and the first terminal 10 for connecting the meter. A second input terminal 2 is connected via a second contact pair 11 of a first electromagnetic relay 5 to a second terminal of a capacitor 6, which is connected via a second contact 12 of a second electromagnetic relay 8 to a second terminal of a resistor 9 and a second terminal 13 for connecting a measuring device. The inputs of the peak voltage meter 14 are connected to terminals 10.13 for connecting the meter. The windings of the first 5 and second 8 electromagnetic relays are connected between the power supply bus 15 and the first 16 and second 17 outputs of the control unit 18, respectively, containing a pulse generator 19, the output of which is connected to the input of the electronic switch 20, the output of which is connected to the input of the electronic switch 21 and The first output 16 of the control unit 18, the second output 17 of which is the output of the second electronic key 21.

The device works as follows.

The pulse signals produced by the pulse generator 19 of the control unit 18 are transmitted to the first electronic key 20, from the output of which the inverted pulse signal is fed to the second electronic key 21. Since the first 20 and second 21 electronic keys of the control unit 18 receive the non-inverted and inverted pulse signals, respectively, The control windings of the first and second electromagnetic relays 5 and 8, respectively, are turned on and off in antiphase. In accordance with the operation of the control windings of the first and second electromagnetic relays 5 and 8, the first 4 and the second 11 contact pairs of the second electromagnetic relay 8 are closed and open.

The measured DC voltage is supplied to the first 1 and second 2 input terminals of the device. When closing

The first 4 and second 11 contact pairs of the first electromagnetic relay 5 and the opening of the first 7 and second 12 contact pairs of the second electromagnetic relay 8 charge the capacitor b with a constant charge time T3 RI C. When the first 4 and second 11 contact pairs of the first electromagnetic field 5 are opened and the first 7 and second 12 contact pairs of the second electromagnetic relay 8 are closed, the capacitor 6 begins to discharge through resistor 9 with a constant discharge time mp R2 C.

Since R2 RI, then Gr T3, then by the time of closing the first and second contacts of the first electromagnetic relay

the capacitor is completely discharged and ready for a new charge. The process then repeats.

Fig. 2 shows plots of charge-discharge voltage of a capacitor at

measuring voltage EI (curve a) and voltage E2 (curve b).

The capacitor discharge voltage, formed on the resistor, goes to the first and second outputs of the galvanic isolation unit and then to the first 10 and second 13 terminals. The peak voltage value at terminals 10 and 13 is measured using a peak voltage meter.

0 The first 5 and second 8 electromagnetic

the relays are chosen so that their trip times Tsrab and release to ™ follow the inequality

45

tcpa6 torn

0)

50

which ensures that the condition of galvanic isolation between the input and the measuring circuit is met.

Let, for example, contact pairs 4.11 be closed and contact pairs 7.12 open. When the first 20 and second 21 keys are triggered and, accordingly, the first 5 and second 8 electromagnetic relays, contact pairs 7.12 will start to close, and contact pairs 4.11 to open, but since inequality (1) holds, the contact pairs 4.11 is open before the contact pairs 7.12 are closed, for the time

A t tcpa6 toiHi

the capacitor 6 will be disconnected from the input and measuring circuits, and then (after closing the contact pairs 7.12) connected to the input circuit. Similarly, it will be obtained when closing the contact pairs 4.11 and opening the contact pairs 7.12. Thus, during the entire operation time of the device, the input and measuring circuits are galvanically opened.

Claims (2)

Claim 1. A device for measuring a DC voltage, comprising two input terminals, a capacitor, two resistors and two terminals for connecting a measuring device to which the first resistor is connected and the inputs of the measuring device, in order to simplify devices, a control unit and two electromagnetic relays with two normally open contact pairs in each are inserted, moreover, their switch-on time is longer than the release time, and as a measuring device A peak voltage meter is used, the first input terminal is connected via the second resistor and the first contact pair of the first electromagnetic relay to the first capacitor output, and also through the first contact pair of the second electromagnetic relay to the first terminal to connect the measuring device, the second input terminal through the second pair of the first an electromagnetic relay is connected to the second terminal of a capacitor, which is connected via a second contact pair of the second electromagnetic relay to a second terminal for connecting Cheney measuring device, winding the first and second electromagnetic relays are connected between the power supply bus and the first and second outputs of the control unit. 2. The device according to claim 1, wherein the control unit comprises a pulse generator and two electronic keys, the output of the first of which is connected to the input of the second and is the first output of the control unit, the second the output of which is the output of the second electronic key, the input of the first electronic key is connected to the output of the pulse generator. FIG. 2