Re: E. Stop signal error

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Peter Rosenholm
<treelaw45@...> wrote:

>
> Hey Glen, I had a machine shop once and a company moved in that did

welding and messed my computer up. My computerized machine must have
been well shielded because it wasn't effected once the program was loaded.

>

Peter Rosenholm

>
> roboticscnc <gsm42@...> wrote:
> Hi Group,
> I'm getting fake emergency stop signals from my router / plasma
> cutter. I have 3 Gecko 320s with their err/res wires joined together
> connected to the "optional external fault LED circuit",( as shown on
> the G320 PDF Manual ) and to the PC via a CNC4PC C10 breakout board.
> I noticed when connected in this way the Geckos' fault light has a
> constant dull glow, possibly due to pulldown resistors on the breakout
> board.
> I any case it doesn't seem to take much to E Stop Mach 3, sometimes
> without tripping the drives.
> This usually happens when the plasma starts or the router motor is
> switched off. The Gecko's power supply ground is common with the
> breakout board ground.
> Thanks,
> Glen.
>

If the breakout shares a ground with the power supply (LOTS of noise
from plasma and AC sources) and there is no isolation of inputs what
you are seeing is pretty typical. There is a misconception that all
you have to do is ground everything and all the problems go away. I
then real world your grounds have to be local and perfect or noise
leaks across like a bad basement!

The only real ground is a golden rod driven to the molten core of the
earth. Think in terms of "clean" and "dirty" grounds. Your PC and
logic level control needs to be on the clean side. The Gecko's have
opto isolation on the inputs so you can run them and their motor power
separated from the "clean" ground. If your wires to switches have one
side tied to dirty ground and it's common to PC (Clean) ground they
are no longer two separate systems.

Plasma has enough power (especially larger HF units) to reachout and
reset electronics even on isolated systems.

Tom Caudle
www.CandCNC.com