Randusoleis

Set, Reset issue

4 posts in this topic

Good morning good people of the blog.

I have a situation where I have a set, reset for, lets say, a fan.  We press manual and it sets the coil, we press Auto and it resets the coil.  Here is my problem...when we set the fan to auto, it will stay there for about 20sec or so then the coil will set itself again and go back to manual.  While watching this occur in the logic I cannot see the contact actually engage the set command.

I have gone thru the logic and cannot see what could possibly change the bool back to a 1.  Any takers on this one?

-James

Share this post


Link to post
Share on other sites

Hard to offer any suggestions without seeing the code or knowing what hardware you're dealing with. Don't overlook the possibility of an HMI panel writing to the bit. Are the Auto and Manual signals coming from an HMI or are they hard wired inputs? If they are coming from the HMI, what action is programmed for the HMI objects that control the signals?

Share this post


Link to post
Share on other sites

Thanks for the reply. 

There is a local HMI and a remote SCADA.  99.9% of the comands come from the SCADA. A simple screen button for Auto and one for Manual change an internal bit (%Mxxxxx).

Could a worn HMI screen be activated because of latent pressure on the screen?

Share this post


Link to post
Share on other sites

A worn screen could cause a false signal to the PLC. I have seen it happen.

The more likely mode of failure is that the screen fails to send the signal in response to the touch. When that happens, the operator tends to hit the screen harder which accelerates the progression to the point of ultimate failure.

It is also possible that the local HMI and the remote SCADA are sending conflicting signals to the PLC.

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