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limit switch help
« on: July 17, 2007, 06:38:28 PM »
Limit switch ???


I have a limit switch that persistently trips during a program and requires me to stop the program, re-reference etc. I need some help in trouble shooting this thing. Following info might help:

Mach for the controller

Micro switches for the limits and home combined. A total of three dual purpose switches.

Mach does not indicate which switch is tripping.

Switch wires are shielded and grounded with the only bare area just before the screw terminals.

X and Y switchs are mounted upside down with the plunger hanging down.

Z switch is mounted with the plunger horziontal.

Wired for nc.

Due to Mach allowing it, Z and Y are using the same pins but when referencing the axis reference at different times.

Limit are set so any switch will Estop the machine.

Any help would be appreciated. I am at a loss and this is costing me precious time.


Switch is a Omron with a .016 pre-travel

General Purpose Snap Action Switch, Actuator Roller Plunger, Panel Mount, Maximum Operating Force 8.8 to 12.3 Ounces, Maximum Pre Travel 0.016 Inch
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Offline jimpinder

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Re: limit switch help
« Reply #1 on: July 18, 2007, 08:49:54 AM »
I take it then, all the switches are wired in series.

The thing to do is to short out two of the switches at a time, and see if the third one behaves, then try one of the other two, until you arrive at the one that is going open circuit. If they all behave (or conversly all mis-behave) then it must be a wiring fault.

I personally would wire the three switches seperately so that the led display will indicate which one is the trouble.

The alternative - and I don't know whether I am right or not - have you any of the soft limits set inadvertantly - and your program is tripping them - just a thought, and I don't know whether they would cause the same reaction
Not me driving the engine - I'm better looking.
Re: limit switch help
« Reply #2 on: July 18, 2007, 06:24:20 PM »
Hi Jim,

Thanks for the post. I don't use soft limits at all, so that wasn't an issue. I did install a .1uf capacitor across the switch today and that seems to have solved the problem. I will know more after I run the machine more.


Offline Chip

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Re: limit switch help
« Reply #3 on: July 21, 2007, 12:14:49 PM »
Hi, Mike

In Config, General Config, Set your De-bounce Interval to between  500 to 2000, Top Right of Screen.

If it's 0 now, This should help.

Thanks, Chip
Re: limit switch help
« Reply #4 on: July 21, 2007, 12:20:08 PM »
Hi Chip,

Thanks for the help.....but I already had the debounce at 2000. I had also posted this over on the yahoo group and had a suggestion of puttin a .1uf capicator across the switch contacts. So far this seems to have helped in the interruptions. It has yet to be seen it if helps with my homing accuracy.