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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > Getting False Limit Switch Triggers.
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  1. #1

    Join Date
    Nov 2020
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    Getting False Limit Switch Triggers.

    Hello,
    I am in the final process of finishing my first DIY CNC machine. I can jog all my axis but I constantly get interrupted by false triggers from my limit switches.
    I have currently re-wired everything with the exceptions of my power supplies with shielded wire and I am still getting false triggers. Although my E-stop appears to not be triggering anymore.

    From what I read this is not a way to solve the problem but a workaround. I got some 0.1uF capacitors to try and stop the noise and I could not get a signal into Mach 3 with them in the circuit. Diagnostics page had all the switches lit up. I used https://www.amazon.ca/gp/product/B00...OUHD0RRM&psc=1 and tried putting them into all the limit switch inputs (Input 10, 11,12,13) on the BOB. They have been removed.

    Tried debouncing in mach3 with no luck. Almost seemed to have no effect at all even at 3000.

    The whole wiring process is completely new to me and I think I must have ground some shielded cables to the wrong place or maybe the power supplies are too close to the BOB?

    My next course of action I am thinking is getting ferrite beads for power supple cables. Or trying a whole new BOB system.

    Sorry this is another post on an already common issue but I have tried doing the research in forums and trying to find any DIY build video with this breakout board and I still can not figure this out.
    This has been very new to me, a project way harder then expected. Any help would be very appreciated!

    I will attach images of my electrical plans I made and attach pictures of my wiring and cnc machine.

  2. #2

    Join Date
    Sep 2018
    Posts
    20

    Re: Getting False Limit Switch Triggers.

    I had a similar problem for a long time. I ended up making a custom Limit Switch Filter Board that has I connect between my switches and my electronics that cleans up the signals and stopped my false triggers. If you google search "Limit Switch Filter Board" you'll find the one I use.

  3. #3
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    515

    Re: Getting False Limit Switch Triggers.

    Can't really see where you'd have an issue.
    I haven't fully finished mine yet but I do have my switches connected up/active sitting near the machine.
    It hasn't false triggered at all so far.

    I have a similar board.
    I am wired up via:
    60v supplies to all staeppers.
    5v supply to board outputs into usb (via a supply not the PC).,
    24v to board inputs and spindle.

    Limits are 3 wire inductive switches: Are connected +/- direct to the 24v psu with only the signal wire going to the board.
    They are NPN type wired in series.

    All my cables are NOT sheilded.
    I'll see what happens when I get my servo system for the spindle.

  4. #4
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    Sep 2006
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    490

    Re: Getting False Limit Switch Triggers.

    What type of limit switch are you using? Actual switch? Proximity (if proximity is it NPN or PNP)? Key bits of info missing there, as well as how they are wired (voltage and normally closed or normally open).

  5. #5
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    Re: Getting False Limit Switch Triggers.

    Quote Originally Posted by Snazzy View Post
    Hello,
    I am in the final process of finishing my first DIY CNC machine. I can jog all my axis but I constantly get interrupted by false triggers from my limit switches.
    I have currently re-wired everything with the exceptions of my power supplies with shielded wire and I am still getting false triggers. Although my E-stop appears to not be triggering anymore.

    From what I read this is not a way to solve the problem but a workaround. I got some 0.1uF capacitors to try and stop the noise and I could not get a signal into Mach 3 with them in the circuit. Diagnostics page had all the switches lit up. I used https://www.amazon.ca/gp/product/B00...OUHD0RRM&psc=1 and tried putting them into all the limit switch inputs (Input 10, 11,12,13) on the BOB. They have been removed.

    Tried debouncing in mach3 with no luck. Almost seemed to have no effect at all even at 3000.

    The whole wiring process is completely new to me and I think I must have ground some shielded cables to the wrong place or maybe the power supplies are too close to the BOB?

    My next course of action I am thinking is getting ferrite beads for power supple cables. Or trying a whole new BOB system.

    Sorry this is another post on an already common issue but I have tried doing the research in forums and trying to find any DIY build video with this breakout board and I still can not figure this out.
    This has been very new to me, a project way harder then expected. Any help would be very appreciated!

    I will attach images of my electrical plans I made and attach pictures of my wiring and cnc machine.
    You have some major wiring problems, Your Shield Grounding is really badly done, you need to mount everything on a metal Ground Plane ( a Metal Plate either aluminum or steel thick enough to support mounting your parts on, ) this plate is then Connected to the input Power supply Ground, this can be with a Ground Buss or a single star point Grounding Stud, this is your starting point,

    You can not use wood to mount parts on like this

    You need to separate all your wiring no wires crossing over the Breakout board

    Adding caps to switches only slows down the reaction of the signal will not solve the problem, correct wiring solves these problems

    Shield have to be Grounded direct to the Ground plane with a 360 degree clamp
    Mactec54

  6. #6
    Community Moderator ger21's Avatar
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    35168

    Re: Getting False Limit Switch Triggers.

    Tried debouncing in mach3 with no luck. Almost seemed to have no effect at all even at 3000.
    Try 10,000 or 15,000, and see if that makes any difference.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  7. #7
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    Re: Getting False Limit Switch Triggers.

    Quote Originally Posted by ger21 View Post
    Try 10,000 or 15,000, and see if that makes any difference.
    If he fixes his wiring which he has to do, the debounce can be 0 ( Blank ) which is where it should be with a correctly wired system adding debounce only slows down the reaction time of the signal which is also the same reaction if someone adds caps

    None of this fixes the wiring problem he has
    Mactec54

  8. #8

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    Quote Originally Posted by mactec54 View Post
    You have some major wiring problems, Your Shield Grounding is really badly done, you need to mount everything on a metal Ground Plane ( a Metal Plate either aluminum or steel thick enough to support mounting your parts on, ) this plate is then Connected to the input Power supply Ground, this can be with a Ground Buss or a single star point Grounding Stud, this is your starting point,

    You can not use wood to mount parts on like this

    You need to separate all your wiring no wires crossing over the Breakout board

    Adding caps to switches only slows down the reaction of the signal will not solve the problem, correct wiring solves these problems

    Shield have to be Grounded direct to the Ground plane with a 360 degree clamp
    Thanks for the help.
    I had a steel piece of sheet metal. I placed over my old my current setup and started pinning the wires down so the shielding is hitting the steel. I am putting all the shielded wires to a terminal that will go to into the pcgnd on the BOB. My wires are touching going to the terminal. I hope this is okay.
    I wasn’t sure what you meant by 360 clamp. I found a ground clamp at Home Depot. I will attach that in the corner of the steel sheet metal and have a wire going to the shielding wire terminal from it.
    I ran out of time today. Will continue on the weekend.
    At the very least it is looking a lot nicer. Not as much of a mess.

  9. #9
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    Re: Getting False Limit Switch Triggers.

    Quote Originally Posted by Snazzy View Post
    Thanks for the help.
    I had a steel piece of sheet metal. I placed over my old my current setup and started pinning the wires down so the shielding is hitting the steel. I am putting all the shielded wires to a terminal that will go to into the pcgnd on the BOB. My wires are touching going to the terminal. I hope this is okay.
    I wasn’t sure what you meant by 360 clamp. I found a ground clamp at Home Depot. I will attach that in the corner of the steel sheet metal and have a wire going to the shielding wire terminal from it.
    I ran out of time today. Will continue on the weekend.
    At the very least it is looking a lot nicer. Not as much of a mess.
    You can not connect the shield to a terminal block just look at the attached this is how shields have to be Grounded, a 360 degree clamp is something you can make with a piece of copper this must be a tight clamp around the shield

    Twist all Power wire pairs Don't have wires crossing over terminal blocks

    Ground Wires ( Green / Green / Yellow ) all go to a Grounding Bus or a single Star Point Grounding Stud mounted on the Ground Plane

    Shields can only be terminated direct ( Clamped ) to the Grounded Plate ( Ground Plane ) you can not connect them to a terminal block like you have this will create EMI noise that will kill your low voltage electronics
    Mactec54

  10. #10

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    Nov 2020
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    Re: Getting False Limit Switch Triggers.

    I want to check in before I move forward.

    I removed the terminal with all the shield wire going to it. From what I gather this is not necessary since the wire will be grounded from the shield clamp on the ground plane. Those wires will be cut once I know that is correct.(Attached Image)

    I have made a grounding wire mount on the ground plane. It is going to my stepper motor power supply 3-line ground(earth). (Attached in Image)

    If I am doing things correctly. I will clamp all 3 power supply shielded cables to the ground plane. I could not find any metal shield clamps in town today. I will find some and replace what I am using later.

    I wasn’t sure what you meant when you said Ground Wires ( Green / Green / Yellow ) all go to a Grounding Bus or a single Star Point Grounding Stud mounted on the Ground Plane.

  11. #11
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    Re: Getting False Limit Switch Triggers.

    Quote Originally Posted by Snazzy View Post
    I want to check in before I move forward.

    I removed the terminal with all the shield wire going to it. From what I gather this is not necessary since the wire will be grounded from the shield clamp on the ground plane. Those wires will be cut once I know that is correct.(Attached Image)

    I have made a grounding wire mount on the ground plane. It is going to my stepper motor power supply 3-line ground(earth). (Attached in Image)

    If I am doing things correctly. I will clamp all 3 power supply shielded cables to the ground plane. I could not find any metal shield clamps in town today. I will find some and replace what I am using later.

    I wasn’t sure what you meant when you said Ground Wires ( Green / Green / Yellow ) all go to a Grounding Bus or a single Star Point Grounding Stud mounted on the Ground Plane.
    Yes you must cut those Shield tails off clean at the end of the cable, or they can be wrapped around the shield and clamped at that point this must be a clean connection they work like an antenna the way you where doing it

    Ground Wire / Cable can only be Green or Green Yellow

    Are you only using ( 1 ) 120v / 240v Ac supply to the panel ???
    Mactec54

  12. #12
    Community Moderator Al_The_Man's Avatar
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    Re: Getting False Limit Switch Triggers.

    I have suggested a cure here on many previous occasions that has worked, that is to earth GND any or all P.S. negative side of the supplies to the star point GND , your BOB input is commonly at GND anyway due to the PC P.S. being at GND potential.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  13. #13

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    Re: Getting False Limit Switch Triggers.

    "Are you only using ( 1 ) 120v / 240v Ac supply to the panel ???" This question has me worried.

    Currently I have stepper motor power supply in one 120V wall outlet. Limit switches and computer/computer monitor in another. Rarely turned spindle on except to see if I set it up in mach3 correctly. I am worried about overloading a circuit. I'm hoping if I did a breaker switch would go off.

    I plan to make a drawing of my house and the circuits. I'm not even 100% sure if I'm wired in for 15amps or 20amps in my house panel. Maybe I will need to get an electrician to add another circuit or two just for this machine.

    Still need to figure power usage from spindle, computer, computer monitor and limit switches.

    Nema 23
    3.0 Amps x 24V = 72W
    X4 Steppers
    12.0 Amps Total 288W Total

    BOB Power Supply
    ____? Amps x 24V =____W

    Computer (115/230V, 50/60hz, 5/3AMP)
    ____? Amps x 115V? =____W

    Computer Monitor (100-240V, 50/6-hz, 1.5A (1,5A))
    1.5Amps? x 100V? =____W

    Spindle (1-100V DC 500W-ER11) https://www.amazon.ca/gp/product/B07...0?ie=UTF8&th=1
    ____?Amps x 1-100V? =____W
    Attached Thumbnails Attached Thumbnails HousePanel.jpg   HousePanel2.jpg   HousePanel3.jpg  

  14. #14
    Community Moderator Al_The_Man's Avatar
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    Re: Getting False Limit Switch Triggers.

    That is not a good Idea to supply from different sources.
    In that situation it is very possible to have 240v across the two sources if they are are fed from both L1 & L2.
    Although in most situations this will not cause a problem, it can when using L.V. from different sources, also the two GND sources should be bonded in the panel.
    In any case, a single source can eliminate many of the noise problems.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  15. #15
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    Re: Getting False Limit Switch Triggers.

    Quote Originally Posted by Snazzy View Post
    "Are you only using ( 1 ) 120v / 240v Ac supply to the panel ???" This question has me worried.

    Currently I have stepper motor power supply in one 120V wall outlet. Limit switches and computer/computer monitor in another. Rarely turned spindle on except to see if I set it up in mach3 correctly. I am worried about overloading a circuit. I'm hoping if I did a breaker switch would go off.

    I plan to make a drawing of my house and the circuits. I'm not even 100% sure if I'm wired in for 15amps or 20amps in my house panel. Maybe I will need to get an electrician to add another circuit or two just for this machine.

    Still need to figure power usage from spindle, computer, computer monitor and limit switches.

    Nema 23
    3.0 Amps x 24V = 72W
    X4 Steppers
    12.0 Amps Total 288W Total

    BOB Power Supply
    ____? Amps x 24V =____W

    Computer (115/230V, 50/60hz, 5/3AMP)
    ____? Amps x 115V? =____W

    Computer Monitor (100-240V, 50/6-hz, 1.5A (1,5A))
    1.5Amps? x 100V? =____W

    Spindle (1-100V DC 500W-ER11) https://www.amazon.ca/gp/product/B07...0?ie=UTF8&th=1
    ____?Amps x 1-100V? =____W
    One 120v 15A circuit can run what you have, you don't want to use 2 circuits as you will have much more EMI noise to deal with

    If your computer is battery powered like a laptop then no problem

    The power usage of the spindle is a max of 500W = around 5.2 A @120v
    Mactec54

  16. #16
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    Re: Getting False Limit Switch Triggers.

    I had the same problem and was so fed up with nuisance trips I isolated all my limit switches with Allen Bradley slimline din rail mount relays. 24vdc out to limits, return to activate the slimline relay. Relay contacts go to the bob. Was worried about it for a little while but they're limits, not estops. Even use the slimlines for some other I/o on the plasma table.

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