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Author Topic: Wiring Limit & Home Switch  (Read 15651 times)

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Offline kolias

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Wiring Limit & Home Switch
« on: January 18, 2011, 10:43:27 AM »

I started wiring my limit switches. The Y axis is driven by two motors and I will have 2 limit switches which will be used to home this axis. On the X axis I will also have 2 limit switches and on the Z axis the same.

I plan to use one cable with two wires (black and red) per axis and wire the 2 limit switches of each axis to the BOB in series. I have attached a picture of the BOB for reference

Is this a good wiring method?


Nicolas

Online Tweakie.CNC

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Re: Wiring Limit & Home Switch
« Reply #1 on: January 18, 2011, 11:22:50 AM »
Just a suggestion,
You should really be using screened / shielded cable (grounded at the BoB end only) for connecting these switches in order to avoid any future problems with possible noise pickup and false triggering.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Wiring Limit & Home Switch
« Reply #2 on: January 18, 2011, 01:18:15 PM »
I think you want separate switches for the home operation of Y and A.  Depends on how rigid your system is, and how little noise you get, but generally, you home A separately from Y.

You can, if you want to, wire all the limit switches for X, Y and Z into one input, and even include the opposite (from home) A in that loop, and have one input for A, a total of 2 inputs on your BoB.  A more conventional setup is 4 inputs, one each for X, Y, Z and A. 

You really, really want to use shielded cable as Tweakie says.  It used to be that the recommendation for shield grounding was one end only.  Today, the recommendation is earth all metal really well and ground both ends of the shield.

Your basic wiring  idea is sound.  If you want to use 2 inputs, you can use a single conductor shielded cable running all the way around the machine, or you can use the 2 conductor shielded running per axis, and series them close to the BoB.  If you use 4 inputs, then your basic idea works. 

To put them in series, on the "near" switch, you cut one of the wires and put the switch on the two ends of, say, black, leaving the other intact and not connected.  On the "far" switch you connect the two wires to the switch.   

Offline kolias

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Re: Wiring Limit & Home Switch
« Reply #3 on: January 18, 2011, 02:09:47 PM »
Thank you both, I should have been more specific but my cable is shielded.

brtech now you mentioned it I agree that the Y and A should have separate switches and I will follow this since my BOB has 4 input connections.

Regarding grounding both ends of the shield I agree that there is a controversy about this and therefore I will start by grounding the end at the BOB and see how she works.

Your last paragraph explanation is perfect
Nicolas

Offline kolias

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Re: Wiring Limit & Home Switch
« Reply #4 on: January 18, 2011, 06:15:55 PM »
I made the attached simple schematic

Can someone let me know if it looks ok?

Thanks
Nicolas
Re: Wiring Limit & Home Switch
« Reply #5 on: January 18, 2011, 06:35:19 PM »
Sure.  Looks fine.  Why wouldn't you put 2 switches on Y?  It's probably overkill for A, but if you are taking the trouble, put one on the "far" (opposite of home) on Y.

Offline kolias

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Re: Wiring Limit & Home Switch
« Reply #6 on: January 18, 2011, 08:10:09 PM »
Sounds like an excellent idea brtech, thanks for pointing out to me

I also revised my schematic
Nicolas

Online Tweakie.CNC

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Re: Wiring Limit & Home Switch
« Reply #7 on: January 19, 2011, 02:53:00 AM »
Quote
Today, the recommendation is earth all metal really well and ground both ends of the shield.

Brtec,

I would be grateful if you could tell me your source for the recommendation to ground both ends of the shield.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Hood

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Re: Wiring Limit & Home Switch
« Reply #8 on: January 19, 2011, 02:58:26 AM »
Often one switch is all that is needed on an axis as it can be triggered at either end of the travel, just depends on your setup.
Hood

Offline kolias

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Re: Wiring Limit & Home Switch
« Reply #9 on: January 19, 2011, 07:47:49 AM »
Often one switch is all that is needed on an axis as it can be triggered at either end of the travel, just depends on your setup.
Hood

Good point Hood and I will follow it
Nicolas