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Ebay Rogowski current probe

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This is the latest schematic which involves 2 stages of integration, the LF is handled by the U1A as a classic integrator. The second higher frequency part is handled by the inductance of the Rogowski coil and R2/VR1 are meant to handle the crossover frequency, but at present that is not perfect due to some last minute mods to deal with common mode noise, hence the spike at each transition. The caps C10/C11 are not fitted, they provide some LF phase compensation but also introduce a LF peak that about doubles the noise waveform, so the square waves have more distortion than desired. The yellow traces are the output of the amplifier, the blue trace is the voltage across the 50R resistor passing through the Rogowski coil. There are some noise traces with the coil fitted but no signal and a 50R resistor fitted in its place as a dummy noise measurement.

Just a final note, I think I have gotten close to the best noise performance without heroic efforts like multiple opamps paralleled. The gain at 10Hz is around 180,000 so the 15mV p-p output noise is equivalent to about 83nv p-p noise on the input which is very respectable. Output sensitivity is around 1.2mV/mA or 1.2V/A from around 50Hz to around 300kHz, limited more by the phase response. The circuit would need fixing for the uncompensated part of the 2 stage integrator, because of a last minute change to pseudo differential input, due to minute levels of 50Hz and its harmonics. I hope you enjoyed the journey and might have even learned something, as I surely did during the process. :)


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