Voltage Drop Measurement

Hi folks,

I have a inductive sensor that is connected in series with a pull up resistor. Now when I pass a metal object near the coil the Vcoil drop by a certain magnitude. My objective is to measure the magnitude of the voltage drop between the ORIGINAL Vcoil and the final voltage and hence amplify the reading and supply it to a peak detector Any suggestions??

Is the coil being supplied with AC or DC? How big a voltage drop (approx)?

Hi, The coil is powered by an AC signal. The contact with the metal object reduces Vcoil and I would like to measure the difference of the voltage drop. The voltage drop is about 1.5Vpp

Hi, The coil is powered by an AC signal. The contact with the metal object reduces Vcoil and I would like to measure the difference of the voltage drop.

I think my approach would be to build a precision rectifier around an opamp, apply Vcoil to the rectifier and feed the rectifier output to either a peak detector or a storage capacitor via a resistor so that the cap stores the long term average Vcoil voltage. Then use a differencing opamp to measure the difference between the peak/stored voltage and the instantaneous rectified Vcoil.

You can connect the inductor to two different types of oscillators. One will produce a change in frequency and the other will produce a change in voltage.
You can find both these types of circuits in metal detectors.