mschneider
Member
So we currently have a CPU 374+ running a sort of feed bin process. We've had the PLC installed since 2008, with really no problems. I am currently running into a problem with our alarming function. Basically we have about 100 normally open one-shots paralleled to a set coil (4092m) and a normally open reset coil (4092m) with one normally open tied to an acknowledge button on an HMI. So, what usually happens is something goes into an alarm, on-shot goes true and sets our set coil (4092m). operator goes to HMI and pushes acknowledge button which then resets (4092m). But now recently it's happening that set coil (4092m) goes true because something is in alarm. Operator pushes acknowledge (4092m) is reset until acknowledge button isn't pressed anymore, then goes back to true. I can watch this happen online and none of my 100 normally opens in parallel are going true again to set the set coil (4092m)again? What is going on? Like I say it has worked great this way for 5 years and now something funny is happening. Any ideas?