Dear Kai,

Thanks a lot for your reply, I was waiting for it desperately.

I assumed that this inverting amplifier is identical to the last OPamp of this classic rectifier circuit

Not just identical its indeed the same rectifier circuit. I am using this recitifer for gain control and rectification both. Sorry for not mentioning this. I said amplifier to keep the things simple.

I assumed that you insert 14.67kOhm, 22kOhm or 44kOhm resistors where this 22kOhm resistor can be seen in the feedback loop of last OPamp in above circuit,

Your assumption is absolutely correct. I use the exactly same resistors in place of 22k resistor in the feedback loop of the recitifier.

So, the OPamp with the 13kOhm resistor in series to 4k7 trimmer is nothing but the last OPamp of your rectifier.

Oh.., Thanks a million for this clarification. I turned your schematic all upside down and went through all op-amp reference I had to figure out what exactly the first section was. Stupid me.

Why taking this series combination of 13kOhm resistor and 4k7 cermet trimmer instead of 14.67kOhm resistor?
It would allow you to trim certain gain error caused by the manufacturing tolerances of resistors in the integrator and rectifier. So, with the trimmer you can compensate for all these tolerances, which you still had to do elsewhere when using a fixed 14.67kOhm resistor instead.

Thanks for this It will help me a lot to keep the measurement accurate.

Thanks & Regards,
Prahlad Purohit