Dear Kai,
Thanks for your kind reply,

Did you see true inverse proportionality? If not, then there's somewhere an error.

Yes I could see inverse proportionality, by increasing 10k pot value the signal output from rogowski reduces. The swing obtained by using 10k resistor is exactly 18%. For example with 47k alone the RMS current output shown by my LCD is 21.4kA and with 47k+10k pot for same current the output on LCD is 17.6kA.

Try to properly display the spikes from Rogowski coil by a good storage scope. Choose R + Ra in such a way, that no more than about 1mA is flowing.

Kai, unfortunately I dont have access to a DSO. But on my analog scope the spike height is never more than 35V. Even when the thyristor is fired at 90 degrees of voltage waveform @ 50kA RMS current thats the maximum rate of change of current I target.

Actually I was planning to use R=100k but then this stuff [National opAmp AppNote] scared me...


In case of my integrator with C=47nF and R=47+10=57k Fc=59Hz

If I use 100k as R and say 20k as Ra then Fc=31Hz ]

and I am using this integrator for F=50Hz and ofcourse a lot of harmonics.


[ Please correct me if above is Incorrect. I am not at all good when it comes to analogue ].


Yes, even very thin alu foil is sufficient.

Thanks for confirming the use of Al foil.

Please be very careful with this asbestos shield!!! Do not produce asbestos dust, do not inhale it!!! Could you use an alternative?

You are right Kai, I am aware of carcinogenic nature of Asbestos, and I also know that due to this its use is prohibited in a lot of coutries.

Here in India use of Asbestos is not prohibited thats why I was thinking of using it but there hasn't been any final decision on using Asbestos. I will certainly use some alternative if it can protect my coils from welding sparks and heat.

Thanks & Regards,
Prahlad Purohit