Category: Show Your Stuff
From what I have seen during the tests the torch voltage is below 200V. During start and piercing it easily goes up to 180V but not above that.
It cuts around 100V. Thin material in the 80s-90s, thick in the 110s.
The arc is also DCEN, DC electrode negative, I have been told. The work piece ground is not connected to mains ground.
200V isn't uncommon to have on a PCB, mains 230V AC is common here. My understanding is that with enough isolation distance it is fine. And the whole ADC side is isolated.
I think an ADS1115 can be used just as well, ebay aliX amazon are full of them at super low cost. To go with the 11-bit version meant that I get 3.3 kHz sample time. The ADS1115 is only 860 Hz max. That was the main factor. For the ADS1xxx ADCs one need to put them in continuous conversion mode or the time to get a value is terrible, several milliseconds. In continuous mode its 150 microseconds. I know now how to read the ADS1014 which is actually two channels A0 A1, and I think it would be possible to use the ADS1115 with 15-bit resolution in continuous mode reading one differential channel (between A0 and A1). How important is updating exactly every 1 ms with a new value? It can't be that important, there is a bit of noise in the voltage and to read the same value every 7th time can't be that bad, can it? Anyway, that was the decision point and I choose 11-bit resolution, one differential channel and 3.3 kHz updating rate. The footprint is the same for those ADS1xxx so one can easily solder in another one, and reprogram. It is actually only something like 10 lines of code for the ADC.
The BAT54S is there to protect the input of the op-amp. Don't know much about that, it is something I found. The lmv321 was also not actively chosen but was known to work. I do see non-linearity at the very bottom of the range, so it isn't fully rail-to-rail. They aren't as I understood it, and it isn't important, it isn't working close to the rail voltages. But it means the display says 2V when it is 0V, but it should be linear above say 5V (in the 0-200V range).
Do you have an ohmic sensing solution when the plasma nozzle is the same polarity as the work piece?
I can see no change in voltage when the torch touches the work piece. I was hoping for that, but no.
I am very interested to include that.
