Say a mains AC (120v, 60hz) 10 amp load with a 0.003 ohm current sense resistor in series with it. The voltage across the resistor is roughly 30mv. How do you rectify such a small voltage (I read precision rectifier, but haven't been able to make the circuit work in Circuit Simulator Applet), or amplify it? Basically, how do you get a usable signal out of that tiny voltage?
30mV (peak-peak?) is in the same order as the output from a microphone so a 100x voltage amplifier could easily take this up to 3V. A precision rectifier (active diode) simply uses the op amp (open loop) gain to overcome the turn on voltage of a diode.