I am also trying to add a thc in my new plasma machine, and for now I have made the voltage divider and putted it inside of the plasma unit machine.
Before connecting the output of the voltage divider to the pokeys, I have tested the voltage divider output during cutting to make sure that the output would not damage the pokeys. I have measure the output with a simple, low cost multimeter, where in DC mode I register during normal cutting from 0.80V to 2.10V, that seams ok. The problem is during the piercing and if, for example the plate "ends" during cutting (both are limit situations), where the multimeter does not show a consistent value, and goes up to 20V for a brief instance.
I think that it is not possible to reach such a value, because the voltage divider is about 40x; and the 20V output from it was meaning that I would have 800V at the output of the plasma. I really think that is the multimeter that gets confused from the high frequency variations of the DC voltage during the limit situations (piercing and end plate).
The voltage divider also have a high speed voltage suppressor, that should take care of peak voltages if present.
Neverless I would like to receive a comment, before I have connected it to the computer and so on, of anyone that made such a voltage divider.
Thanks, Filipe