Voltage Drop Measurement

[Jeswin]

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??

 

[alec_t]

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

 

[Jeswin]

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

 

[Jeswin]

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.

 

[alec_t]

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.

 

[colin55]

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.