Why do I have 120VAC from ground to a Triac output that is not on ???

I trying to use the an output signal to stop a machine upstream ???

Triac outputs leak. Try putting a pilot light on the output for a check to see if the output is actually on.

Are you trying to provide an E-Stop signal to the down stream machine? Best to keep those in a "hard wired" (i.e. relays and pushbuttons) circuit and not rely on the PLC for that.

If it is a simple control signal it still may be easier to use an interface relay to avoid problems if the PLC's are powered at different potentials.

nOrM

yeah, but

Also, it may not matter if the output is on or not as there will be leakage through the triac. Should also point out that in failure mode a triac will almost always fail in a shorted condition, so there would be voltage present all the time. I would completely remove power from all terminals and check resistance across the output side against a known good one, if available and compare results. A zero ohms reading should indicate a failed triac.

Bob

You can parallel a 10k ohm resistor with the output eliminate the false reading caused by the leakage of the triac.









If you have a 'wiggins' or other solenoid type voltage checking device they will read 0 if the triac is not gated.

you need a wiggy or a voltprobe with a low resistance button

any solid state device leaks. if you are using a multimeter, forget it, as it will show 110V across a digital 110V output card, with the output off without a load. I always use a Voltprobe, which has a button you can push to put a load in the circuit, which will show you the true value which is probably 0V. You would not be the first person to chase their tail due to leakage. I would be included in my early years.
Bob

Put a load on it. geeeeeez

Not every one is an expert, big fella

I'm not sure if this is your problem, but you can also get a false reading if you lose a common neutral. A few years ago we had an output card showing one side of a solenoid valve was on, but the valve stayed in the center position. There was 120V on the terminal, the coil's resistance read good, the fuse was good, but when I checked the voltage on the other coil, it also read 120V. I changed the output card and got the same reading. After several hours, I finally clipped a jumper from the common neutral of the two coils to ground and the valve moved and the mysterious voltage on the other coil went away. Turns out the neutral wire in a flexible conduit some how got pinched in half.

Not every one is an expert, big fella

Click to expand...

Thats for sure.

Tboatman,

Did not mean to come across that way. Some time the guys that are new to this career have to learn to exhaust their efforts trying to read/research everything available.

This "effort" will be a very important part of any job you encounter.

Any device you want to learn, grab a test bench and some modules and go for it! (Damn,thats 2 smiles today.)