TI-505 trouble shooting help needed

[Dan747]

Before diving into my problem I should explain, my employer has several TI-505 PLC's that control some of our operations. We did have a technician who programmed and maintained them but he is no longer here and has not been replaced. I normally install and maintain the mechanical parts of the system but it has fallen on me to keep the PLC's going as best as I can until a new PLC technician is hired, so forgive me if I ask some really basic questions.

Before he left, the technician did give me a one day crash course on keeping the 505's running, and up till now I've managed to solve every problem that has come up but I've run into a problem that I just can't figure out.


The Problem:

In one of our 505's we have a 505-4816 110v output board. One of the outputs goes to a relay. When the output is turned on and the relay is energized the relay occasionally momentarily de-energizes. There is no real pattern I can discern, it may be anywhere from 15 seconds to 3 minutes between the relay "clicks." The whole time the signal is on the relay just randomly clicks off then back on.

What I've tried:

My first thought was that it was probably a bad relay, so I replaced it, but that didn't solve the problem.

Next I thought maybe it was a problem with the 110v going to the 505-4816 board, so I rewired it and even tested it using a separate relay, and that didn't solve the problem.

So I thought it had to be the 505-4816 board. I had a spare board on hand so I swapped it out but that didn't solve the problem.

I read the ladder program in the 505, and as best as I can tell there isn't anything that would be momentarily turning off the output signal then turning it back on. It should be staying on until the operator manually opens a valve.




So I'm at a loss to figure out what is causing the relay to click off and on. Can anyone familiar with TI-505's offer advise on how to solve the problem?

 

[jrwb4gbm]

It has been too long for me to give a precise exact answer. It sounds like
either low voltage going to the relay or possibly an intermittent loose connection with the common or neutral for the relay or card. Even the relay socket could be defective.

 

[sigmadelta]

If you can, stop the machine, try forcing that output on and listen for chatters. If it doesn't at all, then something in the program might be causing it. May be a problem with an input device "chattering".

 

[Steve Bailey]

You said you replaced the relay. If it is a socketed relay, did you also replace the socket? Did you check for loose wire connections between the output module and the relay? If the output module has a removable terminal strip, did you replace that?

 

[Dan747]

Thanks for the input. I should have said more clearly that when I replaced the relay I also replaced the socket, and when I rewired the 110v supply I replaced both the supply and the common wires.

In fact I even wired the 110v directly to the relay, bypassing the 4816 board just as a test and the relay never "blinked" for over an hour. It only happens when the 4816 is in the circuit.

But, now that sigmadelta mentioned it, the culprit may very well be the signal that turns on the 110v output is chattering. I feel dumb now for not thinking about that, I guess I was just convinced it was something in the PLC and didn't literally "think outside the box."

The signal comes from an electrically actuated valve, I'll bet the problem is in the relay in the valve, because of course it is really difficult to get to.

 

[GaryS]

try replacing the output card first it sounds to me like you have as component in the card overheating and dropping the output. it will only get worse. and it could go on like that for a very long time

 

[sigmadelta]

Did you get it resolved, Dan?

 

[Dan747]

Did you get it resolved, Dan?

I haven't had a chance to check the valve, as I said it's pretty difficult to get to, especially without stopping operations.

The relay clicking problem at this point is mostly just an annoyance, it isn't causing any real problems. I just want to nail it down before it grows to be a serious thing.

It will probably be a few days before I get the chance to check the valve.

Thanks for your input.

 

[robertmee]

I haven't had a chance to check the valve, as I said it's pretty difficult to get to, especially without stopping operations.

The relay clicking problem at this point is mostly just an annoyance, it isn't causing any real problems. I just want to nail it down before it grows to be a serious thing.

It will probably be a few days before I get the chance to check the valve.

Thanks for your input.

I programmed TI-505's for 25 years, but this isn't really a TI specific issue. However, a simple and easy test is to simply force on the Y address to the coil when it is chattering, assuming it is safe to do so. If it stops chattering, then it is the logic causing it. Could be duplicate instances of the Yxxx in an OTE/OTL or some condition of the rung that turns Yxxx ON that is chattering. Will be difficult to see because the update time of SoftShop with Diagnostics turned on you won't likely catch it in the rung. But build a data chart with all the C's, X's, Y's in that rung and watch them closely to see if you see any unwarranted flickering.