Power consumption indicator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Miscellaneous electrical devices
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If your apartment does not have direct access to the network wiring, then you can assemble an indicator with a remote inductive sensor placed near the network wires at the place where they enter the apartment. True, the alternating voltage at the terminals of the sensor coil will be small in this case and an amplifier will be needed. It can be assembled according to the scheme shown in Fig. 7.14.
The alternating voltage induced in the sensor coil L1 by the alternating magnetic field of the mains wires is fed to the input of a linear amplifier made on the operational amplifier DA1 through the low-pass filter R2, C1 - it attenuates impulse noise.
(click to enlarge)
To expand the range of displayed powers, a logarithmic amplifier assembled on the DA2 operational amplifier was introduced into the device. From its output, the signal goes to the rectifier (on diodes VD3 and VD4) with a doubling of the voltage and then to a voltmeter composed of a dial indicator RA1 and resistor R9. Pointer indicator - with a full deflection current of the pointer 50 ... 100 μA. As a sensor, a coil with a magnetic circuit from a PCM relay or other small-sized relays (RES6, RES9, RES22) containing 1000 ... 1500 turns is suitable. Adjust the indicator in the following sequence. By connecting the power sources (two 3336 batteries), by moving the slider of the resistor R7, zero voltage is set at the output of the DA2 chip (pin 6) relative to the common wire.
Then, an AC voltmeter is connected to the output of the operational amplifier DA1 and a load of at least 100 W is connected to the network. By moving the sensor along the wall at the place of the proposed input of network wires, the maximum readings of the dial indicator are achieved. In this place, the sensor is fixed on the wall. Next, they turn on the load (say, several electrical appliances) of the maximum possible power consumption, and with a trimming resistor R3 they achieve an alternating voltage at the DA1 output of 0,1 ... 0,5 V, and then by selecting the resistor R9 set the microammeter needle to the final scale division.
It should be borne in mind that the batteries are discharged unevenly and after a while an imbalance of the operational amplifier may appear, which will lead to a violation of the graduation of the indicator scale. Therefore, periodically check the battery voltage, and if it differs from the original by more than 10%, replace the battery.
Author: Semyan A.P.
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