Hi everyone!

I am trying to measure the skin conductance, for that I found this circuit online.

So from it what I have understood so far:

- There is a low pass active filter at first stage with cut off of 1.6 Hz and variable gain.
- The second stage is also a filter with unity gain and is biased at half the voltage supply and the first stage is biased at the output of second.

What I don't understand:

- Why is the gain variable at first stage as the Rskin chages the gain would change?
- Isn't the first stage enough?
- Can't understand the biasing of the op-amps as well.

 

Guys please help me out!!

 

I think the circuit is intended to be an oscillator comprising two integrator stages in a loop, with an oscillation frequency dependent on Rskin. Spice simulation says it doesn't oscillate.

 

This has got me more confused.