Hello Jackson,
Hope you are feeling better.
Here is a new article concerning the two-step PWM drive. It would be interesting to see if this PWM drive adds additional noise to your measurement circuit. The Arduino based PWM is only 1 kHz. I have slowed the system down using a 1 k gate resistor. However, the switching wavefronts are still steep. Perhaps it would be better to use 10 k or even 100 k to “round” out the waveform there by reducing the change for interference.
The leakage in the SSRs seems reasonable especially with the 10 kHz signal and anticipated capacitance in the SSR. I could be wrong, but I wonder if you are seeing an internal SSR snubber circuit.
The coil leakage is surprising. With a reed relay and a large glass enclosure, I would not have expected this problem. My first suspicion is capacitive leakage through the PCB trace.
I look forward to your analysis of the high voltage Sensata reed relays.
Sincerely,
Aaron