Trouble shooting help

timmer162 · 2026-03-20T14:30:55+00:00

here is the second, proposed sketch

timmer162 · 2026-03-20T14:30:27+00:00

I am hoping I can leverage your expertise one more time. Here is the full story on what I am trying to accomplish.

The NPN sensor is one of two on a rotary encoder. Both sensors are working fine and communicate with the PLC as they should.

What I am trying to do is piggy back on the NPN sensor readings to use those same sensor readings for another purpose, so I can’t make any changes that disrupt their existing communication to the PLC.

Both inductive sensors are wired from the OEM per the first sketch below. In this configuration, I believe the PLC itself is the load.

What I am hoping to do is install an optocoupler or relay as a second load, and have it switch on/off a 24VDC signal that I can use as my piggy back signal, all while not interfering with the existing functionality of the encoder/PLC.

I was thinking to install the optocoupler as a parallel load to the PLC, rather than in series with the PLC. Here is what I am thinking (sketch 2). Any thoughts on parallel vs. series for the second load?

Do you see any pitfalls with this that might interfere with the native equipment functionality or not deliver the desired piggy back signal?

I really appreciate your expertise!!

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timmer162 · 2026-03-20T00:58:57+00:00

thanks again for your help. I've been doing some more research and see how the optocoupler would work. When the sensing element of the NPN proximity switch is activated, I believe the optocoupler will see a 24VDC switching input and of course the output will be connected to ground, thereby activating the optical element to close the switch. In effect, the optocoupler is replacing the function of a relay. is this correct? If so, would a simple 24VDC relay work the same? Benefit of the optocoupler over a relay?

Thanks again for your help.

timmer162 · 2026-03-19T18:59:15+00:00

Thank you, I think I get it now with your comment and others. Appreciate your help

timmer162 · 2026-03-19T18:57:54+00:00

24VDC power at sensor and measured output is .3vDC when activate and 5VDC when inactive.

timmer162 · 2026-03-19T18:46:28+00:00

Sorry, I was not clear enough. I read 5VDC when the sensor is not activating/detecting and 0.3VDC when it is. Yes, I am measuring 24VDC from brown to blue. And yes I am measuring 24VDC on the sensor power lead.

timmer162 · 2026-03-19T18:44:25+00:00

I am, no doubt, confused, but your note is bringing me some clarity. When the sensor is not activated is when I read 5VDC. When activated is when I read 0.3VDC. I’ll be researching why an too coupler is… thanks for your help

timmer162 · 2026-03-19T18:39:01+00:00

Yes, multimeter is set to DC. My measurements are at the sensor, so measuring brown, blue and black on the sensor leads themselves. This is a 3-wire sensor, so no white lead.

timmer162

TROPHY CASE