limit switches in parallel

[rasta]

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

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[TomKerekes]

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.

[rasta]

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

[TomKerekes]

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.

[rasta]

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

[TomKerekes]

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.

[rasta]

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

[TomKerekes]

Hi Mariano,

Here would be a PNP method:

[rasta]

Hi Mariano,

Here would be a PNP method:

thank you Tom , as always you can't have better service than the one at Dynomotion.
regards
Rasta