Hi Raghu,
Thank you very much for your valuable suggestions & comments.

When you said "Offset also will also be integrated .." were you referring to the op-amp offset or that produced by your input circuitry ? With a chopper stab op-amp you need only worry about the later ?

I was referring to the op-Amp offset. The first thing to be tackled with at this stage [ Op-Amp selection stage ] is ofcourse op-Amp offset. The circuitary offset can't be predicted at this stage, It will be seen only when I do some trials with the circuit. i.e. Rogowski coil + integrator + ADC + MCU.

- What happens to the EMF, when the di/dt term becomes zero or near zero like when the welding current is constant - at least theoritically ?

My welding machines use AC current [ chopped with thyristor ]. thus di/dt will be positive while the wave is rising will be zero at the peak of wave and will be neagative when wave is falling. thus di/dt will be at a phase difference of 90 degrees with the current being measured. If you wanted to indicate some other point please calrify I couldn't understand what you meant by di/dt becoming zero

- Scaling down a parameter of 25000 to a few Volts, your overall noise margin of the whole system can get very tricky ?

Right, due to scalling down 25000 to a few volts the overall noise margin will certainly be very tricky. Since ±10% error is OK in measurements, I am a bit on the safer side.

- How about calibration?

For caliberation I am planning to use a Miyachi make weld current measuring instrument. Earlier I was thinking of using a pre-caliberated CT but after STEVES post indication the non-linearity with Rogowski I have changed my mind.

Thanks & Regards,
Prahlad Purohit