Center Spot Sheetcam Post

Phill, did you allow for machines that have an ArcOK signal?
It seems to me that is the problem Stefan and the Doctor had because we were trying to turn the arc off before the ArcOK was issued.

Rod,

The second and third points rely on the Arc OK signal.

It was my opinion (and still is) that time based marking will not work as every plasma cutter has a different response time. This is mainly due to use of RC (resistor / capacitor) time delays in them so the reaction time is not consistent.
On an old Hypertherm MAX 45 or similar, the time from signal to fire the torch to when it actually fires the torch is from 3 to 5 seconds, and it varies a lot especially when there is a short period between fires.
Maybe the new ones use proper timers, but i have not seen any of those yet.

tommylight wrote: It was my opinion (and still is) that time based marking will not work as every plasma cutter has a different response time. .

Yes, I think the results here are a confirmation of that.

Well from what I saw in its present format as coded, this feature is not usable if you have an arcOK signal as you can't go shorter than this time frame and on my machine thats a pretty big divot.

I'm sorry my cool idea wasted Phill's time.

I Agree there is a lot of unknown latency in the system once the spindle on signal is enabled. I think some halscope plots are in order.

I started to write a separate component today that commenced the timer when the arc was sensed by my hypersensing component. My torch on relay turns off in 2 usec so any latency will be in the machine.

I do know somebody who had great success using current to set an ArcOK signal and also for spotting. But he hacked his machine, added a current sensor and built and programmed his own external THC using a microprocessor.

There are cheap current sensors that can be used for this or diy versions of it with hal sensors, they do require a bit of work and opening the plasma if using the DC side, but even that can be measured at the cables.
Measuring AC side is easier but it does require rectifying and filtering and so does the DC cable side.
Reed relay on the DC cable might work fast enough.
Do any of you have a reed relay to test that ?
Or any satelite dish motor, they have 2 of those inside.
3 windings are enough.