THCAD-10 configuration, QtPlasmaC

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17 Apr 2021 18:23 - 17 Apr 2021 18:58 #206203 by sm2wmv
Hi,

First off I have enjoyed the last few days spending time getting my plasma CNC project working somewhat with linuxcnc.

I have been spending a few hours now trying to figure out how to configure the THCAD properly and been reading on the forum. I seem to have it functioning but it does not seem to matter what values I put in the configuration tool. I am using a 7i76e and THCAD-10 with 1 Meg resistors on IN+ and IN-. I try with a DC-voltage to test of 0-60V. The max voltage of 60V produce about 2.8V into the THCAD-10 which gives values on the arc voltage around 110000.

Where do I find the divider ratio and voltage offset in the files? I can't seem to find it anywhere.

I have calculated,
Scale: 0.00789993
Offset: 3718.7500

Here is the first cuts on the 1250x2500mm plasma build


This is from before I went with QtPlasmaC instead,
Last edit: 17 Apr 2021 18:58 by sm2wmv.

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17 Apr 2021 19:40 #206212 by tommylight
QTPlasmaC has that on the "parameters" tab, the "ARC" section.

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17 Apr 2021 20:09 #206220 by sm2wmv
Wow, how did I miss that? I was looking everywhere except in the GUI itself.

Thanks, will try tomorrow.

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18 Apr 2021 07:29 #206273 by sm2wmv
Put in the new values and it seem to work perfectly!

What are reasonable PID values to start with on the THC?

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18 Apr 2021 07:44 #206274 by phillc54
The default of P:10, I:0, D:0 is quite common.

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18 Apr 2021 09:22 #206278 by sm2wmv
I seem to be missing something fundamental when it comes to the THC. It measures the voltage all OK. I have set it to 110V just to see if it regulates but it does not show THC Enabled LED lit up, so I must be missing something. I tried to add M65 P2 in the G-code but without luck.

I also noticed that having any of the cables from the computer near the plasma torch is a bad idea, luckily it survived fine :side:


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18 Apr 2021 09:27 #206280 by phillc54
You have IGNORE ARC OK set, that disables THC.

linuxcnc.org/docs/devel/html/plasma/qtplasmac.html#qt_ignore-ok

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18 Apr 2021 09:35 #206281 by sm2wmv
Yes, that solved that issue. However the reason I disabled it is because I don't have any ARC OK signal and use Mode 0 for that reason. But when I have IGNORE ARC off it just triggers for a split second and alarms that ARC is not OK.

Probably something more I have overlooked :) I guess I should probably try to get a reed relay and fix an ARC OK signal as well, but eager to get it working :)

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18 Apr 2021 09:40 #206282 by phillc54

I guess I should probably try to get a reed relay and fix an ARC OK signal as well, but eager to get it working :)

Some plasma cutters just don't work with the soft arc ok, the reed is very reliable.

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18 Apr 2021 09:51 #206286 by sm2wmv
I've ordered some reed relays and I will try it again.

Thanks for all the help, I must say I am really impressed with LinuxCNC. I managed to get most of it up and running without asking for help.

I have an Morbidelli Author 400 CNC that I have used to mill all parts for this plasma table and I have intentions to convert that one later to use LinuxCNC as well.
The following user(s) said Thank You: phillc54

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