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Thread: How do I electrically disconnect my Z axis limit switches

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    Default Re: How do I electrically disconnect my Z axis limit switches

    Thanks for the Ferrite core info Michael. I'm assuming the core needs to be suited to relatively low frequency noise.

    Phil



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    Default Re: How do I electrically disconnect my Z axis limit switches

    Quote Originally Posted by john-100 View Post
    Hi Phil

    I'd stick with normally closed switches
    I expect its more likely for a cable to go open circuit than go short circuit

    using an opto-isolator as in post 16 you don't need to change the mach3 config

    have a look at any extra earth wires you have added and check they don't add parallel earth paths to the original wiring
    its possible they have caused ground loops that could of added to your problems

    John
    Thanks John, yes I had concluded from my read-up that normally closed was the safest option, I assume then that the opto-isolator doesn't care which option (NC or NO) is selected.

    The VFD to HSS cable screening is earthed at the VFD and at HSS casing and the HSS casing is earthed to the mill body. In turn both the mill body and the VFD are earthed through the mains supply cable to each. Would this constitute a ground loop?

    Phil



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    Default Re: How do I electrically disconnect my Z axis limit switches

    Philbur,

    Yes, as many others have shared it is best to keep the LIMIT switches in the NC configuration. You can easily mod the wiring very basic. In the normal mode the 12 or 24V relay should be activated. Optos work great as well but figured if you are only doing this on the limit/estop circuit one relay might be easier to install unless you buy a small board that has an OPTO configured with screw terminals.

    Russ



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    Default Re: How do I electrically disconnect my Z axis limit switches

    Hi Phil

    If I have read your post correctly you have a ground loop between the VFD and HSS that may cause additional radiation from them
    what machine do you have ?

    as I have not worked on Tormach machines I don't have any details of the breakout board / control board tormach use in conjunction with a PC

    its not easy to tell how sensitive the limit switch inputs will be to interferance radiated from the VFD
    a photo of the BOB / control board would help and if possible the voltage across an open limit switch - is it 5V or more ?

    John



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    Default Re: How do I electrically disconnect my Z axis limit switches

    Quote Originally Posted by CNCMAN172 View Post
    Philbur,

    Yes, as many others have shared it is best to keep the LIMIT switches in the NC configuration. You can easily mod the wiring very basic. In the normal mode the 12 or 24V relay should be activated. Optos work great as well but figured if you are only doing this on the limit/estop circuit one relay might be easier to install unless you buy a small board that has an OPTO configured with screw terminals.

    Russ
    Thank's for the input. However the limit switches are also utilised for homing/reference so I assume they need to be able to provide individual signals to the controller.

    Phil



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    Default Re: How do I electrically disconnect my Z axis limit switches

    Philbur,

    Since you have combined Limit/Homing switches you will need to have one relay per axis.

    You might want to get a relay bank with either 4 or 8 relays all ready to wire up. I think I would get the 8-bank so you can do all three axis and the e-stop circuit and have a few spares you can use later. They make these in 5V, 12V, 24V. I would go with the 12V or 24V as the 5V will not solve your problem.

    Russ




    https://www.amazon.com/SainSmart-Mod...mart+relay+24V

    https://www.amazon.com/SainSmart-OMR...ay+module+8-CH



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    Default Re: How do I electrically disconnect my Z axis limit switches

    Quote Originally Posted by john-100 View Post
    Hi Phil

    If I have read your post correctly you have a ground loop between the VFD and HSS that may cause additional radiation from them
    what machine do you have ?

    as I have not worked on Tormach machines I don't have any details of the breakout board / control board tormach use in conjunction with a PC

    its not easy to tell how sensitive the limit switch inputs will be to interferance radiated from the VFD
    a photo of the BOB / control board would help and if possible the voltage across an open limit switch - is it 5V or more ?

    John
    I have tried a number of different earthing scenarios but maybe I need to revisit regarding the loop issue. I have a Tormach PCNC 1100 series 1 with a number of upgrades so I believe the controller is the same as a PCNC series 3.

    The open voltage on the limit switches is 12 volts DC not 2v as I previously stated. The limit switches are connected to the controller via the J2 terminal block. Complete manual is here https://www.tormach.com/product_pcnc_main.html#docs - manuals - Mach 3 version. Complete electrical info is at the back end.

    See attachment for electronic details:
    How do I electrically disconnect my Z axis limit switches-complete-panel-lowres-jpg
    How do I electrically disconnect my Z axis limit switches-controller-lowres-jpg
    How do I electrically disconnect my Z axis limit switches-electrical-skematic-jpg



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    Default Re: How do I electrically disconnect my Z axis limit switches

    Philbur,

    I just looked over the documentation quickly on the links you provided and noticed they actually have a noise suppression kit, which contains several Capacitors with lead terminals. Check and see if this got installed in your machine, they make this kit for a reason, someone else complained about noise issues.

    Russ


    File name: TD10160_Supression_Kit_Installation



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    Default Re: How do I electrically disconnect my Z axis limit switches

    Quote Originally Posted by CNCMAN172 View Post
    Philbur,

    I just looked over the documentation quickly on the links you provided and noticed they actually have a noise suppression kit, which contains several Capacitors with lead terminals. Check and see if this got installed in your machine, they make this kit for a reason, someone else complained about noise issues.

    Russ


    File name: TD10160_Supression_Kit_Installation
    Thanks for the info RUSS. I don't have this kit fitted. The link you give says

    "The Suppression Kit is a set of 3 RC (resistor/capacitor) filters
    that will effectively suppress electrical noise generated by the
    on/off operation of machine contactors and any external
    equipment connected to the switched convenience outlet
    (coolant outlet)."

    This suppressor kit is intended for specific components within the control cabinet. As I have changed nothing other than add the HSS and VFD, which is in no way electrically connected to the machine contactors or the switched convenience outlet
    I can't see how these suppressors would have any impact on my current issue.

    Phil



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    Default Re: How do I electrically disconnect my Z axis limit switches

    Quote Originally Posted by philbur View Post
    Thanks for the input Lens42, but as I said I think I have already done all I can with the spindle and dedicated VFD. This includes a shielded cable from the VFD to the motor, as short as possible and grounded at both ends.

    Phil
    Standard practice is to ground the shield at one end only.

    Also, the RC filters mentioned in your last post will filter any noise, not just what comes from within the cabinet. I'm not sure what voltage the limits on the Tormach operate at, but I have found that higher voltage is better for noise issues. I run 24V to my limits, and use a relay at the BOB to switch the pins. The relay is as close to the BOB as practical. This is much like was shown by someone else previously. This has pretty much eliminated noise problems I had running a router as a high speed spindle. Previously I used 5V to the switches and the limits would trip as soon as the router was turned on.



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    Default Re: How do I electrically disconnect my Z axis limit switches

    Quote Originally Posted by 109jb View Post
    Also, the RC filters mentioned in your last post will filter any noise, not just what comes from within the cabinet.
    Can you be more specific. If the suppressor is connected across a particular contactor or an unused convenience power socket, how can it influence noise entering through say the limit switch wiring. What am I missing.

    Phil



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    Default Re: How do I electrically disconnect my Z axis limit switches

    Philbur,

    You are probably correct, sometimes you often see suggestions to put .1uF caps from the Limit switch inputs on the BOB to ground. This basically traps low high speed signals that can cause a system to think it is seeing a limit fire. The relay or opto approach if run at 12V to 24V isolates this from the BOB. The relay would typically be operated at 24VDC and that runs through your limit switch providing power to the RELAY. The contacts of the relay are completely isolated from the coil in the relay so you put the relay very close to the BOB so there is very little opportunity for noise to impact these LIMIT/HOME sensor inputs to the BOB. The coil side of the relay which is at 24VDC will not be impacted by the EMI noise as it is a much higher level. I actually tried capacitors on my system and it did get better but I still would get false ESTOP/LIMIT failures when the spindle went above 10,000 RPM. Every spindle and VFD combo is different but this approach is used in all commercial machines, as it is a common issue. It was hard to tell on your BOB if the limit inputs are just ground level inputs from the switches.

    Russ



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How do I electrically disconnect my Z axis limit switches
How do I electrically disconnect my Z axis limit switches