thc up or down signal active clear it first

[Bartmanoz]

Hi I’m new here and to the cnc world. I have built my cnc plasma table and have had some issues with HF interference but think I have that sorted now thanks to previous posts on this forum
I have built my cheap THC and have it hooked up and programmed into Mach3. My thc puts out a “torch up” signal whenever the torch is off. Because it does this I am getting an error message “thc up or down signal active clear it first” even before I try to do anything. The error starts as soon as Mach3 finishes opening and won’t let me do anything. I have to go in and turn the pin off in ports and pins so I can clear the error message.
Why is it so interested in the signal before the machine even has a program loaded and told to start? I have read everything I can find but have not found anything specifically on this subject. Thanks

[acourtjester]

Have you tied the "Arc Ok' signal in as a condition controlling the up signal, by that I mean if you do not have arc ok from the plasma unit it does not look at the up signal.

[tcaudle]

MACH reads inputs, period. If you send it a signal it performs the "Function" (in this case THC UP) when it sees that. it does not decide because the torch is not on it should ignore it. You need to rethink your THC design. It needs three states. THC UP is on (THC DOWN is not) THC DOWN is ON and Both are off. You should only have a THC UP when the torch is fired and the voltage is BELOW the Preset Volts. DOWN is the opposite. Neither should default ON.

[Bartmanoz]

Thanks tcaudle I was thinking that would have to be my next move.

[Bartmanoz]

Acourtjester, my ark ok signal is not active but it still looks at the thc up ??

[Bartmanoz]

Hi acourtjester, I understand what you are saying and yes that would be a nice work around but how do I do that? Any help with the setting I need would be great, thanks.

[acourtjester]

On your plasma unit does it have a signal out called Arc Ok, or one that says the plasma unit has plasma current flowing (Mach calls it THC ON). There are 3 signals that Mach looks at THC ON, up and down from the THC. If there is not THC ON signal it should not act on any up or down signals. This is the reason for the G4 p0.5 in the G-code for the plasma to have current flow (time of 0.5 seconds) before it starts the cutting motion. Also are you using a Post Processor that is set up to use a THC. And look at the diagnostic page in Mach at the THC on. up, and down when you start Mach none should be lit, they should only be lit when testing and actually under THC control when cutting.

arc.jpg (49.28 KiB) Viewed 1835 times

arc.jpg (49.28 KiB) Viewed 1835 times

arc 2.jpg (43.97 KiB) Viewed 1835 times

arc 2.jpg (43.97 KiB) Viewed 1835 times

[AdrianH]

I will stick a reply in here as Bart is trying to use the very simple sorta like $30 THC idea I had and have been using myself for some time. So have a few others from here and as a basic learning thing before going on to better/faster units it works well enough.

The down side is that in the initial set-up it provides a THC up signal when there is no arc, this can be changed if required, but as it is Mach3 can differentiate and ignore the signal only acting on it when Arc is OK. But!

There is a tick box that Bart has switched on that I believe is causing the issue and that is the tick box that is in:-

Config/Ports and Pins/Mill options/THC Options/Allow THC UP/DOWN Control even when not in THC mode.

A search of the Machsupport forum showed this:
'The tick box "Allow THC UP/DOWN Control Even When Not In THC Mode" is for when you
have manual switches wired to the THC UP/DOWN inputs and you want to manually
control the Z, even if THC is not switched on. This is typically done with oxy acetylene
cutting where you may not have a THC control and you just adjust the Z height manually. '

And if I switch on the tick box I get the same issue, untick and it works OK on mine. Bart is away for a few days and will report back when he can.

Adrian