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Current Shunt Amplifier with digital control - del20014

R6 is the Shunt thru which the current to be measured passes. F1 fuse is to protect shunt. D1-D4 ensures that the current flow is not broken if the shunt blows. The Ammeter is always used in series in a circuit.

Test Measurement and Test jigs

OP07 is used here as a digitally controlled amplifier as the voltage offset error is around 75uV. 4052's digital controls A-B set the  range by selecting R1, R2, R3, R5 for the digital code at A-B. The inverting amplifier changes the gain and four current ranges are got. The output of this circuit has to go to a buffer and cannot be loaded directly. R8 is offset trim at very high gains, it has to be adjusted for a zero output of opamp for zero current measured.

                        Shunt Amplifier with digital control
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Current Shunt Amplifier with digital control - del20014

Rf and Ri are 0.1% MFR, if costly, use bourns 10T trimpot or a difficult way - use series parallel combination and scratch 10% part of resistor network to increase value.

Mains Current Indicator with a LED

(first remove paint on resistor with a blade then with ohmmeter connected scrape black film to increment value till done)

Let voltage current and resistance sockets be separate and of different color or use a high voltage electrical rotary switch. or relays if you want the same sockets switched. for greater currents use external shunts or current transformer CT