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  1. #1
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    limit switches in parallel

    Hi; I want to use 2 limit switches , on the same axis side on my machine , I want one switch to be mechanical , and the other optical ,
    I want to mount the mechanical in the machine table while the optical mounted in the motor shaft, to attain a better stop resolution,
    I want both switches to switch a voltage of about +22v , and use only one + terminal in the Kanalog , and the switches must be set up in parallel .
    I have read somewhere that it could be done.can someone please help?
    regards
    Rasta

  2. #2
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    Re: limit switches in parallel

    Hi Rasta,

    To help we'd need more info on the mechanical switch (normally closed or open) and the optical sensor (PNP or NPN). I think the idea would be to wire the switch and sensor in a way that a current goes to the Kanalog input when both the switch and opto sensor are triggered. The problem with an optical sensor on the motor shaft is that it triggers every motor revolution. So it needs to be inhibited until the limit switch is enabled. The logical AND of both sensors.

    Note also a Kanalog opto input has 2 terminals. a + and -. Both terminals must be driven to activate it.
    TK
    http://dynomotion.com

  3. #3
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    Re: limit switches in parallel

    Hi Tom, thank you for your prompt reply
    The mechanical switch is wired as N.C.
    The optical sensor is a NPN , but if needed otherwise I can buy the PNP ones
    The ground side of the switches power supply is permanently attached to the - terminals on the Kanalog optho inputs jp15
    And the output of the switch is wired to the + side of the optho terminal on the jp15
    Of course the common of that switch goes to the + 22v in the power supply
    Because I want both switches wired in parallel , and to switch the plus side , the rotary signal won’t do anything until the mechanical switch is pressed ( turn off) then the opto will read the next transition , and both switches outputs will be low
    And the kanalog will sense home...

    So in the kmotion screen it shows that the terminal is being energised when the mechanical switch is not pressed
    And it clears the check mark when the mechanical switch is pressed

    Thank you mate for your help
    Rasta

  4. #4
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    Re: limit switches in parallel

    Hi Rasta,

    NPN switches to GND so it would switch the negatives side of the opto. Why not do that instead of switching the plus side?

    But the other question is how does the opto work? Does it conduct normally? Or only when at the desired trigger point?

    KFLOP can home to either polarity. But the input must only change when both devices are triggered. If you trigger the switch only and the input changes then it is wrong.
    TK
    http://dynomotion.com

  5. #5
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    Re: limit switches in parallel

    Hi Tom, thanks for the reply
    The reason why I like to switch the positive side , of the optho is that the machine generates
    A lot of electrical noise , and in my limited knowledge I figured that that way the signal will be
    More resistance to noise ,
    The optho switch can be made to be N.C. And N.O. By fitting a disk with a hole , or just a flagging arm.
    But like I say if I need to buy the optho it’s ok .
    Do you think that it’s too much hassle to switch the plus side?
    Thank you for the reply
    Rasta

  6. #6
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    Re: limit switches in parallel

    Hi Rasta,

    Its not clear to me why switching the positive side will be any less susceptible to noise.

    I think you will need a PNP opto to be able to switch the + side.
    TK
    http://dynomotion.com

  7. #7
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    Re: limit switches in parallel

    Hi Tom ,
    Thank you for your reply
    Would please advise the method of connection , with a PNP and NPN?
    Would it very hard to implement the PNP solution?
    Thank you
    Mariano

  8. #8
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    Re: limit switches in parallel

    Hi Mariano,

    Here would be a PNP method:

    Click image for larger version. 

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    TK
    http://dynomotion.com

  9. #9
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    Re: limit switches in parallel

    Quote Originally Posted by TomKerekes View Post
    Hi Mariano,

    Here would be a PNP method:

    Click image for larger version. 

Name:	Parallel.png 
Views:	0 
Size:	12.4 KB 
ID:	452340
    thank you Tom , as always you can't have better service than the one at Dynomotion.
    regards
    Rasta

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