Controller build for Plasma

snowgoer540 wrote:

xnaron wrote: Do you know what my THCAD divider setting should be?

F/32 is what is recommended, unless you are using a parallel port (which I dont think you are).

F/32 can be used with parallel port, but requires RTAI kernel and a lot of fiddling, i have a system running like that for 7 months without any issues.

Making progress.

The step/dir signals pass directly under a THCAD connector. They cross the input at 90 deg so they should be ok. I am planning to use that one for 50:1 plasma voltage. I can raise the THCADS up with some higher standoffs if I need to.

What the heck I had the taller standoffs so I raised it up.

I think I can retire now! Snowgoer has got it nailed. Just keep plenty of air around that 25k resistor as it could get hot!

So with 50:1 divider and a THCAD-5, you don't need any scaling resistor. That gives you a full scale reading of 250 volts and remember the THCAD can handle 500 volts indefinitely. But at 250V it will be really rare for it to hit full scale and it will be at times we don't care about.

On hypersensing, the 390 k resistor is a standard value and gives a full scale of 24.5 volts. This is a bit above our 24V power supply if you adjust it to that value. The THCAD can always see a little bit more than its full scale so if it sees > 24.5 volts, it will turn on the arc-on pin. Its not used for anything but who knows what the future holds?

xnaron wrote: What the heck I had the taller standoffs so I raised it up.

Looks good. I always wondered if it would not pay to mount the 7i96 to a L shaped mounting plate and stand it up on its edge when mounting it to the DIN rail to save space. If I did that, I'd put the THCAD's side by side on a plate mounted the same way.

rodw wrote: I think I can retire now! Snowgoer has got it nailed.

Not so quick, we didn't get your Gold Watch retirement gift in the mail yet! Plus, there's plenty I haven't got nailed... modifying the ohmic comp if it needs it in the future...Hal Scope... The list goes on and on I'm sure.

On that note, ohmic3 seems to work well. I was seeing these false start issues, and weird probe errors that have all seemed to go away. I'll be cutting tomorrow (and testing Phill's Cut Recovery upgrades), so I'll let you know, but so far, so good.

I did get a compare plugin for notepad++, was interesting to see the line you change from ohmic2 to ohmic3.

At any rate didnt mean to hijack the thread. Box looks great!

snowgoer540 wrote:

rodw wrote: .

At any rate didnt mean to hijack the thread. Box looks great!

Thanks and I appreciate all the interactivity in the thread,

snowgoer540 wrote: ............ Box looks great!

I have to agree.

What is the thinking behind the optional ac relay to switch the power on and off for the ohmic probe?

xnaron wrote: What is the thinking behind the optional ac relay to switch the power on and off for the ohmic probe?

Someone suggested that with a wet torch and the voltage present by power supply, galvanic corrosion could be sped up and the consumables could wear faster/be eaten by the corrosion process. It seems more likely for a table that is idle and on all the time. Nonetheless, I installed one. Cheap insurance I guess.