CNC Interface and Torch Voltage Capture

[EmptyNester]

I ended up with a voltage divider of 100k and 2.53k. This gave me a divided voltage reading of 1.2V while the full output voltage was at 50V.

The voltage reading I used was a meter on the output. The difference between the meter and the scope is the scope is about 0.4 volts higher. I trust the meter more than the scope (scope is a DSO201 and I used two different meters). The graph below shows the full voltage with my divider and using a 100 mf filter capacitor.



I still don't understand why I'm not seeing a negative voltage on the output of the CNC port since the cutting voltage is negative.

I did connect both my scope and my meter between the CNC port outputs and the ground on an Arduino board (running on A/C). I check both the positive and negative torch voltage outputs (one, then the other) against the Arduino ground.

When powering up the Arduino, the meter reading jumped on very quickly (too fast to read), but then settled at around 84 milivolts. The scope traces for both are the similar.



I'm not sure what's going on. I'll talk to my consulting electric engineer tomorrow to see if he can shed any light on what I'm seeing. Any thoughts anyone else has would be appreciated.

[Rambozo]

I was under the impression that the torch outputs were basically isolated from ground, so that all measurements must be taken between them and not referenced to ground as far as cutting arc voltage is concerned?

[EmptyNester]

I was under the impression that the torch outputs were basically isolated from ground, so that all measurements must be taken between them and not referenced to ground as far as cutting arc voltage is concerned?

If that's the case, it might make the A/D circuit simpler. I'm under the impression that if the voltage is isolated from ground and its negative, you can just swap positive and negative and read it as a positive voltage.

Can anyone from Everlast weigh in on isolated grounds?

I wonder if the fact that I've only dealt with the pilot arc voltages so far figures in in any way too.