PLC circuit ?

[Ken9876]

I take care of several draw bridges and have a problem with our gates, when there is an electrical problem the operators have to crank these gates back up manually, the problem is they will crank to much or to little and not know it till later. Often the drum limit will roll back over and force the traffic signals red or not allow some other function to occur. So I want to add a pilot light in parallel with a plc input. At the gate I have two cams, one raised and one lowered indication circuits that go back to plc inputs is it possible to add a pilot light in parallel with the plc input or will this cause problems. I'm looking for a solution with the least amount of wiring to pull off so I wanted to see if this could be done. They PLC system is an PLC-5

 

[ptonsparky]

I have used lights in parallel with 120v plc inputs. AB 1000 and AB1500s. Also with PICOs. Found no problems. Small indicating lights. Limited by the size of your Input fusing of course. Interposing relays would work as well.

 

[Ken9876]

Thanks for the info.

 

[Jraef]

I would be very very careful messing around with the controls of a drawbridge PLC system, people can get killed.

I had a friend who lost her foot in this accident, it was related to electrical modifications (this article is old, it came out later that there were mods made).

 

[Ken9876]

Engineering is onboard with this. I think there is a lot more to the story you posted. Our bridges have quite a bit of interlocking built in.

 

[Controls]

Is there a spare output card already on the P.L.C rack?.IF so, proper way of doing this is to add a rung in the logic to trigger an output for the status light indicators.Either way, your wiring will be the same whether you go to the input card module or the output module card.

 

[justdavemamm]

The way you want to do is quite common. Most of the time it'll work just fine. Sometimes it won't.

What is the distance to the limit switch ? What voltage ?

A recent application I was a consultant to used AB 800 series (LED) lights that are rated 28V to 240v and due to the distance to the switch, there was inductive pickup between the light wire and other wires in the same conduit. Even when the switch was open, the light was on. They read about 5 volts on the line.

The light wasn't the only thing on the line, a relay coil was in parallel with the light, but it didn't pull in nor provide enough current draw to keep the light off.

Don't let that happen to you !