Sign in to follow this  
Followers 0
Guest Edgar Goodman

Troubles with the source in a SLC

5 posts in this topic

Hi, I want to know if somebody can help me, the English is not my natural lenguage but i'm going to try to explain as better as I can. Fisrt I have a SLC504 to control an oven, when i start to work here (in the plant), the people told me that in mornings when turn up the oven rhey had to turn on, turn off and tunr on the mail enclosure so many times until the led of source of PLC was in on. It was very funny for me becouse is like pumping something, but it dos't work in another way. One day I want to fix this situatión and I went with another source to change the "damage" source, but my surprise was that the new one makes the same and it wasn't the only one after a time the new one source dind't turn on anymore, I take it out and wanted to turn it ono in another alimentation and dind't work anymore. I make this test with two sources and i get the same result. I had to put the old one agian and work like always. Today The oven didn't run because the PLC didn't work, I went to see the fail and the PLC turning on and turning off cicling, because of the source, I cuold see i little flash in the led of the source each time the PLC turning of and after inmediattly the PLC again turning on. I checked the 110 voltaje to the source and always was in 112v. but the 24v fall down cicling. I change the CPU but it responsed in the same way. I have to put all the card and souce out of the rack and i started to put first another source that we check that turn on. We checje if the source didn't turn off, but it was turning on o..k. all time, after we put the CPU and the card one by one until finish and the oven work. The general manager ask why?. I really don´t know, and I really want to never going to happen agian. bUt I have to wait to morrow when turn on the oven again. I have to know why is happen this. Can somebody HELP ME?. THANKS.

Share this post


Link to post
Share on other sites
It's not the CPU, it happens probably because one or more of your relay outputs are shorting 24VDC. It is likely that one of the loads is shorted out so when your PLC energize output, there is no load to limit the current and relay shorts the power and you see the flicker.

Share this post


Link to post
Share on other sites
Then, do I have a 24v Output Card Damage?. Do you think with tour off all the outputs with the first step bit it coulve solved?

Share this post


Link to post
Share on other sites
Probably not yet... Why don't you stop program and then force outputs one by one till you find where is the problem. One common mistake is to have swapped wires on inductive loads like relay coils or solenoid valves. Many of them come with built in diode so wrong polarity will create problem just like you describe.

Share this post


Link to post
Share on other sites
Good thoughts panic. Here's another possibility: You could have a problem with your rack. Isn't there another 24V power supply in the enclosure for sensors and/or outputs? I'm guessing that the CPU supply is not being used for anything but rack power, so it shouldn't be affected by shorts in your device level bus. If you have 120V at the rack, there is a problem in the power supply, rack, or CPU. You have checked or replaced the power supply, but are you using the correct size? How big is the rack and what cards do you have installed? If you are using a 1746-P1 supply with a full 10 slot rack, you are probably in an overload condition at startup. If you calculate the rack load, and the supply is sized right, I would look more closely at the rack itself. The fact that the operator has to "pump" the disconnect points to a short or open - the vibrations may be making or breaking an intermittent connection somewhere. Good luck!

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0