Series wiring

[Skidog]

Have you ever? Did it work? I'm going to try this in a few hours, will post how it went. Usually one ties the signal wire to a PLC and then uses an output from the same PLC to light the light. I'm not sure why I was asked to do it this way but I'll try anything once.

[TimWilborne]

It will probably work with an LED because the voltage range that it can switch on. If you were switching an actual load putting a LED in series would not be a good idea

[gravitar]

I don't think you would want to put the LED in series, as the voltage range in which a prox operates is too much for the LED. If you put a resistor in to drop the voltate for the LED, then you probably wouldn't have enough of a signal left to turn the PLC input on. I would think that you would want to put the LED/resistor (wired to the DC return) in parallel with the connection to the PLC input terminal. That should work.

[geniusintraining]

I just tried something similar to this yesterday, I had the switch leg from one prox supplying the + 24vdc to the other one, I have done this in the past and it works well. This time I was using two ifm efector's that not only have a indicating LED but also a red laser (for lack of better words) for alignment, they are very good prox switches. But the load on the second one was to much and drained the voltage to low. I ended up pulling the first one to din mounted Weidmuller optical relay, that supplied my dc to the second one, that worked, but the other way was better. This is were we would need to measure the cost of the of having the "better" prox switches….are they really better?

[Money4Nothing]

Determine the input impedance and on-current level of your PLC input. Then take the prox switch voltage output and subtract the LED drop. V=IR will let you know if you'll have enough voltage to power your LED and still detect the signal level. $

[gravitar]

We'll cascade prox switches together (where one feeds the next, that one feeds another one, etc) when we're short on inputs..It does work, but keep in mind that this is a PITA for the poor maintenance guy that comes along later on and has to figure out which prox and/or wirenut is to blame for the whole string of sensors not lighting up.. This would be all the more frustrating with photos because you have alignment issues added in the mix. Those ifm efector switches sure are slick though, with the visible red laser and alignment LED on the face!

[wborst]

I have also done this in a pinch. But as pointed out previously, it is truly a PITA to troubleshoot. I think I was using an Omron photosensor.