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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.

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.

Current
                        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.

(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.

Data sheets and info useful to study and build this circuit.