The CTN PMC has a troublingly low range on its PZT; it can't even cover a single FSR when driven from 0 to 300 V. So I wanted to see if the HV supply is really delivering what it says it is.

I unplugged the HV BNC from the PMC and plugged it into a voltmeter. I got good agreement between the nominal voltage as reported by C3:PSL-PMC_PZT and the actual voltage as read out on the voltmeter. 0 V is 0V, 50 V is 50V, 300 V is 300 V, etc.

Then I put the voltmeter in parallel with the PMC PZT. The relationship between nominal voltage and actual voltage is shown below. Evidently the PZT is not being held at nominal voltage. The presence/absence of the voltmeter does not affect the location of the PMC's modes (with respect to the nominal voltage), so this tells me that the voltmeter isn't skewing the measurement.

According to the ohmmeter, the resistance of the PZT (with the HV unplugged) is 800 kΩ, so there's no obvious short.