THC for Hypertherm 45XP based on DT-115 / LM393 comparator

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16 Oct 2020 14:08 #186286 by radek_marko
Hi,
I'm trying to add THC to my newly build plasma table. I have managed to do a few test cuts without THC, but I can see that the torch is hitting the metal and that THC would be very helpful.

I have a simple THC build around LM393 comparator, but I have some difficulties in making it work. I'm planning to give it few more hours of my time over this weekend, but I would like to know if there is anyone here having any luck with this kind of THC or should I not waste my time on DIY THC and buy ready-made THC.

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16 Oct 2020 14:39 #186288 by tommylight
I would not bother with it, just get a THCAD.
I have built my own THC and pretty damn good ones, but the cost came over the price of the THCAD, and still it is not fully integrated, so now i just buy THCAD, already have 5 in use and ordered another 4 of them.
At around 70$ when paired with LinuxCNC and PlasmaC config made by PhillC, there is nothing that comes even close until you get to 6 figure prices.

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16 Oct 2020 15:26 #186291 by radek_marko
Is it better to go for THCAD-10 and connect to Hypertherm divider or for THCAD-300 and install it the way it will directly probe the voltage of torch connectors?

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16 Oct 2020 15:32 #186292 by tommylight

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16 Oct 2020 19:19 - 16 Oct 2020 19:23 #186303 by AgentWD40
I'm using a THCAD-10 with my 45xp. I took the cover off the machine to find the onboard voltage divider and set the DIP switches to 20:1 to maximize the reading resolution.

*Note that the THCAD's aren't THC. They simply allow linuxcnc (plasmac) to sense the torch voltage and linuxcnc itself is the THC.
Last edit: 16 Oct 2020 19:23 by AgentWD40.

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16 Oct 2020 20:26 #186304 by radek_marko
Hmmmmm.... another lame question - my system is based on 2x LPT ports controling the system.

Is it possible to use THCAD-10 in non-MESA board applications?

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16 Oct 2020 20:32 #186305 by PCW

radek_marko wrote: Hi,
I'm trying to add THC to my newly build plasma table. I have managed to do a few test cuts without THC, but I can see that the torch is hitting the metal and that THC would be very helpful.

I have a simple THC build around LM393 comparator, but I have some difficulties in making it work. I'm planning to give it few more hours of my time over this weekend, but I would like to know if there is anyone here having any luck with this kind of THC or should I not waste my time on DIY THC and buy ready-made THC.


A home made comparator based up/down THC should work but probably needs close attention to:

1. Isolation. the low side of the torch voltage divider is at the work/table potential.This is nominally ground
but may have considerable HF noise relative to earth ground so the comparator and its power supply should
float at divider low end potential, not frame ground
2. There is considerable HF noise in the torch voltage so an 1 ms or so input filter is needed
3. You need some hysteresis in the threshold (ideally this should be adjustable)

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16 Oct 2020 20:43 #186306 by tommylight

radek_marko wrote: Is it possible to use THCAD-10 in non-MESA board applications?

Yes it is, i have one such machine using parallel port with THCAD, 9 months of work with no issues.

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21 Oct 2020 21:20 #186843 by radek_marko
Is this the correct product?
eusurplus.com/index.php?route=product/pr...ort=rating&order=ASC

Any links for wiring it to LPT? All I can find is the link to MESA board.

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21 Oct 2020 21:28 #186845 by tommylight
Yes.
From THCAD FO+ to parallel port input, set that input as the encoder A input in hal.

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