We earlier found that the intended LPF isn't working so we thought of this external LPF idea. So I checked today the PZT input with LCR meter to see if it is in good condition or not. It gave C = 406.4nF, L=60.6 mH and R = 31kOhm 17MOhm. From the spec sheet, the C value looks 20% below the rated value but the spec value has uncertainity of +- 15%, so maybe our PZT is still good.
With the measured values, I calculated again (fitted using LISO) what good value of output resistor would make it closest to 10Hz pole. The value came out to be 37.1k Ohm. I have replaced this output resistor with 39k Ohm now. I'm attaching updated schematic for future reference.
keywords for search: PMC North Driver Board Schematic
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should probably put back the 30k resistor. It makes a low pass filter with the PZT capacitance (not the cable capacitance). This is to prevent shorting of the HV drive.
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