I have a voltage multiplier circuit (basically a villard cascade design) using several stages of diodes and caps. My output should be in the 500V - 600V range (DC of course) and I believe is working as it is powering the sensor I am using it for.

With that said, I am having no luck measuring it with my 10MOhm input resistance DVM. I suspect such a circuit is easily loaded down, but I'd think 10MOhms would be enough to prevent such a thing. I'd also have to assume that the DVM manufacturer probably made the input resistance as high as possible without limiting the current below that which their A to D could handle.

So what does one do in such a situation?

 

Determine that the dmm works in the first place.
10Mohm load would load down a 20Kv multiplier significantly, not a 500 volt system.

 

What is the base oscillator? The drive must be low impedance (very). A square wave also works best.

A schematic would let folks help better.

 

So what does one do in such a situation?

Increase the input resistance of the DVM.

Place as much as twenty 10MΩ or 22MΩ resistor in series with the DVM. Measure and record the unknown voltage reading, using a suitable range.

Using the same arrangement and DVM voltage range to measure a known DC voltage, preferably one that is more than 50% of the unknown voltage and work out the actual voltage from the readings.