Limit Switch Triggered! IS NOT!!

[Mr.Chips]

I’m still working on my first project, a Chinese symbol meaning Happiness for a friends wedding. So far it has not been bringing any happiness into my life. But like I said this is my first project and just going through a period working out the bugs.

Using Mach3
Windows XP
The code is attached below

When I start the cut it will run for a while and all of the sudden I get a “Limit Switch Triggered” error message.
When it gives this error message I am not near any limit switches. And if I run it with the Diagnostic screen displayed, the Limit Switch Leds never flicker and I will still get a “Limit Switch Triggered” error message.
It doesn’t happen at the same place but in random places on the cut.

I then do a “Reset”.
Then press Start, and it doesn’t start cutting where it stopped. It skips several lines of code and starts cutting again.

Any suggestions?

Thanks
Hager

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[ger21]

Most likely, you're getting noise. On the general config page, put 5000 in the debounce box in the top right corner and see if that helps.

[Mr.Chips]

Most likely, you're getting noise. On the general config page, put 5000 in the debounce box in the top right corner and see if that helps.

Help?

It helped so much that it didn't get a false trigger even after nine cycles.

Looks like that is another lesson learned.

Now what will be next?

It is so good to have people on line that are ready and able to help.

Thanks :rainfro:
Hager

[spoiledbrat]

I had the same problem before, and even tried setting the debounce up a bit. Now, although the limit switches are installed, and used as homing switches, I have limit switches turned off in Mach. That gremlin will pester me no more...

[Mr.Chips]

I had the same problem before, and even tried setting the debounce up a bit. Now, although the limit switches are installed, and used as homing switches, I have limit switches turned off in Mach. That gremlin will pester me no more...

When I installed my switches I used coax and grounded them, as I had read about problems like this. I even set debounce to 5000 and still get a false trigger once in a while. And every time I reset Mach3 it would skip a few steps, which is not a good thing.

I'm thinking of turning off the switches as limits and using it as Homing Switchs as you have.

When you use them as homing SW's does the interference give you any false signals?

Thanks

[spoiledbrat]

Never...

My cables have a grounded shield as well, but with 20 foot servo power wires in the near vicinity, I have always been plagued by this.

I have watched the diagnostics screen in Mach when it trips, and the light does not blink for any of my limit switch inputs, so it is happening very fast. (hence, the debounce method)

I simply became tired of my machine quiting on me, since it runs about 4 hours a day. Plus, I work well within my machine boundaries and use caution when jogging near my limit switches, so this is the right answer for me (until I buy a $200,000 router, that is.)

Good luck,

Rob

[ger21]

When I installed my switches I used coax and grounded them, as I had read about problems like this. I even set debounce to 5000 and still get a false trigger once in a while. And every time I reset Mach3 it would skip a few steps, which is not a good thing.

I'm thinking of turning off the switches as limits and using it as Homing Switchs as you have.

Increase it to 7000-10,000 if you still get occasional triggers. This will give a slight delay in switch activiation, but is better than no limits at all.

[multiplex]

i'm having the same problem here too.

where are you grounding your wires out to? maybe i need to improve this area on my machine.

5000 didn't seem to help much for me

[BobF]

I had the same problem. I put a .01 mf capacitor across the ground and signal pins for the limit switches. (found this in another thread here) No more problem. I tried several debounce settings never found one to completely eliminate the problem for me until the cap was added.

[Mr.Chips]

I had the same problem. I put a .01 mf capacitor across the ground and signal pins for the limit switches. (found this in another thread here) No more problem. .

Do you mean one cap between each stepper wire and ground?

Or one cap connected to all wires and ground?

Yep I'm electrically challanged.
But I'm having the same problem.
Thanks

[Greolt]

Not stepper wires. Limit switches.

Use one cap per input. So if all limit switches are in series to one input then use one at the input.

If each switch has it's own input then one per switch.

Greg

[Mr.Chips]

Not stepper wires. Limit switches.

Use one cap per input. So if all limit switches are in series to one input then use one at the input.

If each switch has it's own input then one per switch.

Greg

OK I understand now.

What exactly does the Cap. do when used in this manner?

[Greolt]

There will be more qualified people to answer this but here is my take.

A capacitor will pass AC but not DC. Noise tends to be AC in nature so gets passed to ground or filtered. So the input does not see it.

However the DC signal is not affected except for a very short delay.

The cap needs to appropriately sized for the situation to have this effect.

That is probably over simplified but is my way of understanding it.

Greg

[turmite]

OK I understand now.

What exactly does the Cap. do when used in this manner?

The cap stores a small amount of electricity, and when the switch is made, it discharges causing a slight surge in voltage. Most of the limit switches used on hobby machines, and even my old Digital Tool machine are 5 volts. The 5 volts are not enough to keep the contacts clean, which according to Mariss from Gecko, helps contribute to the noise problem within the switch. It worked for me as far as the false triggers, but I now have a problem with repeatability. I am in the process of designing and building optical switches to correct both problems.

Mike

[Mr.Chips]

I am in the process of designing and building optical switches to correct both problems.
Mike

That sounds like a good fix, if you can post your solution here.

[multiplex]

optical would be a great solution. i was hesitant to do that because of cost, but i'm sure if you are crafty there is a low cost solution.

for now i've added caps, and that has helped alot.

[BobF]

The caps help with the noise as Greg explained.
The optical switches would probably be more accurate if you are using some of the swithces as home switches and require more accuracy. For limits you don't need that much accuracy. I don't think the optical switches will make much difference with noise.

[turmite]

The caps help with the noise as Greg explained.
The optical switches would probably be more accurate if you are using some of the swithces as home switches and require more accuracy. For limits you don't need that much accuracy. I don't think the optical switches will make much difference with noise.

Well according to the electrical guy helping me with these, they are immune to noise. Now whether or not that is correct is yet to be seen but I can tell in in a week!

My noise problems were corrected with the caps. The optical's are for accuracy. I am using some military surplus switches that the electrical guy tracked down and found the manufacturer, and they told him the switches are accurate to within .0001". They were used in aircraft applications!

Mike

[keebler303]

The optical part is obviously immune to noise, but you can still get noise in the wires. Industrial proximity switches and the like are normally powered by 24V DC which is much more resilient than 5 V as far as noise is concerned. If you use shielded cable and 24V signals, you should have much less trouble with noise.

Matt

[Greolt]

Broadly speaking there is two contributors to noise problems in the typical homebuilt regarding limit switches running 5v.

The first is oxidation build up on the NC contacts. This is caused by typically using switches that are rated for 10 or more amps then running a few milliamps through them.

This can be helped by placing a 0.01uf cap across the switch which helps to keep them clean. Optical switches will of course help here, no mechanical contacts.

Better still run 24v through them. 24v is fairly typical on big dollar machines.

The second source is wiring acting sort of like an aerial. Shielding can help here. As will a filter cap on the input. Also a debounce setting in software.

Greg