AC voltage current

The multi-range AC voltmeter circuit composed of an operational amplifier , a diode rectifier bridge and a DC milliammeter is shown in Figure 5-17.
In the figure, the measured AC voltage is added to the non
-inverting terminal of the operational amplifier. Therefore, the measurement circuit presents a high input impedance to the signal source.
The meters of the diode bridge circuit are placed in the feedback loop of the operational amplifier to reduce their influence on the parameters.
The negative feedback effect forces the voltage across Ri to be equal to the measured AC voltage, flowing through the ruler. The current will
flow through the bridge, and the meter indicates the average value of the full-wave rectified current . Let Vi(AV) be the full-pass rectified average value of the measured
AC voltage VI,