Thanks for your reply… This is about machines and drives… The current transformer is to measure the motor current (0 to 9 Amps max), so the C.T transforms it to 0 to some milliamps since it has a 1000:5 current ratio… So I have to put a shunt resistor and measure the voltage drop across it, of course I have to put up a low pass filter to filter noise and a rectifier to convert that a.c voltage signal to D.C somewhere… and the op-amp to amplify…

The reason I asked is, in the textbooks they simply say, current reference is given by us, and the current feedback from current transformer is compared with the reference current, and the error is give to PI controller which produces a control voltage which is what we want in the end… so i was wondering how, is it currents or just voltages proportional to currents…