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Reference all home
« on: February 26, 2013, 08:26:40 PM »
I am having trouble with my system referencing all home. There are no LEDs lit on the diagnostic screen for the home switches. When you test the switches all the lights on the diagnostic screen work correctly. When you reference all home the motors move and inconsistent amount and then the DRO is set to 0. The x,y,z  never reach the home switches. When I turn the power supply for the stepper motors off the DRO's count until the limit switches are manually tripped and then the DRO's are zeroed.

Thank you for your help.

Offline Hood

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Re: Reference all home
« Reply #1 on: February 27, 2013, 04:03:40 AM »
You have electrical noise on your wiring. Properly shielded and grounded wiring is best for low voltage signalling so that would be your ideal solution but setting a value in General config for Debounce Interval will likely help, try with 2000 , if it helps then lower as much as you can.
Hood
Re: Reference all home
« Reply #2 on: February 27, 2013, 07:49:11 AM »
I am using 18 gauge shielded cable on all the stepper motors. All of the cables from the controller to the stepper motors are approximately the same length about 25 feet. The cables have an overall shield the cable is a 3 pair plus a drain. I am using a 22 gauge 4 conductor shielded cable on all the home switches. The shield is not currently grounded on either set of cables I will try grounding it before I change the values.

Thank you very much for your help. 

Question should the pairs be individually shielded or is an overall foil shield acceptable?

Parnell

Offline Bodini

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Re: Reference all home
« Reply #3 on: February 27, 2013, 07:52:59 AM »
FWIW,  I had terrible noise on my encoder lines (twisted pair, foil shielded) only when I DID ground the drain wire.  Go figure!

Offline Hood

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Re: Reference all home
« Reply #4 on: February 27, 2013, 07:59:56 AM »
Shielding without grounding will probably be worse than not having a shield at all. Grounding is needed to let the noise drain to earth and not providing that path just traps it where you least want it.
Hood
Re: Reference all home
« Reply #5 on: February 27, 2013, 08:03:10 AM »
Question should the pairs be individually shielded or is an overall foil shield acceptable?

Offline Hood

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Re: Reference all home
« Reply #6 on: February 27, 2013, 08:09:49 AM »
overall should be fine.
Hood
Re: Reference all home
« Reply #7 on: February 27, 2013, 09:45:12 AM »
Grounding the cables did not solve the problem the Debounce Interval did solve the problem is their a negative to having the Debounce Interval at 1500?

Offline Hood

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Re: Reference all home
« Reply #8 on: February 27, 2013, 10:45:18 AM »
Did you connect the shield wires only at one end, to a single point and that point be earthed?

Regarding debounce Interval, basically what it is telling Mach to do is ignore any signals it sees unless the are longer than the specified time. 1500 should be fine but personally I prefer to have zero there.
Hood

Offline Chaoticone

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Re: Reference all home
« Reply #9 on: February 27, 2013, 10:49:26 AM »
FWIW,  I had terrible noise on my encoder lines (twisted pair, foil shielded) only when I DID ground the drain wire.  Go figure!

The best way I have heard shielding explained is this.  The shield is like an antenna.  It can transmitt and it can receive.  The common practice is to always ground at the controller end.  This is where I suggest everyone start but if you need to unhook it at the controller end and ground at the device end, as long as it works, that's good and I have no problem with it.  Your problem may well have been the motors are emitting the noise and grounding the shield at the controller end gave it a good easy path to follow back to the controller.  In short, where you divert the noise to has a lot to do with where it is coming from.  Its best to start following good practices and adjust as necessary if you need to.  We would like to think we have all the answers but when it comes to EMF, say what you will but there is a bit of black magic and luck involved.  With persistence it can usually be dealt with effectively but the best experts in the world will admit they cant explain all of it.

Brett
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