Sensor circuit. Inputs are HV+ and HV-, Output signal of sensor is on M, which is fed to op-amps

I'm trying to view the phase difference between a high voltage AC signal (230V rms) (measured on HV+ and HV-), and the final output of the signal processing circuit on an op-amp (between pin 6 and ground of the op-amp +/-15V supply) on the same DSO (using different probes).

The high voltage signal is sensed using a Hall effect sensor, and further processed using inverting op-amp circuits. As a phase-shift is introduced, I need to check if the final op-amp stage output and actual voltage waveform are in-phase, which is fed to an ADC for control purpose.

When I view one signal at a time, nothing happens. When I measure both at the same time on the same DSO, the last stage op-amp draws large current and burns out.

I think there must be a ground problem, but I need to view both together to check for the phase-shift. How to do it?

Please note: The DSO is powered using a 1:1 isolation transformer from the same high voltage power supply, which I sense in the above case.

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  • 2
    \$\begingroup\$ Please add a circuit diagram showing where you are attaching the probes and their respective grounds. I suspect you are connecting two grounds together via the probe earths and this is causing your problem, but without a diagram no one can be sure. \$\endgroup\$ Sep 20 at 12:39
  • \$\begingroup\$ @PeterJennings Shall add it \$\endgroup\$
    – SMS
    Sep 20 at 12:50
  • \$\begingroup\$ @PeterJennings Hope the diagram of sensor helps to understand. \$\endgroup\$
    – SMS
    Sep 20 at 12:54
  • \$\begingroup\$ Need a full diagram to make this answerable. I'm going to close this, ask to get it reopened once the diagram is posted (you can do that with the comments.) \$\endgroup\$
    – Voltage Spike
    Sep 20 at 16:12