AB1400 Bit

[ptonsparky]

At least a couple of you are into PLCs.

I have a project that has been operational for six years. Yesterday, one of the bits, B3:1/1, decided to lock true. This is the Start bit via an HMI, so everything would start right back up after the Stop sequence had finished.

The operator suspected the screen but changing to the backup did not help. Cycling power did not help.

I 'toggled' the bit once I got back from the West Bank of the Missouri and everything is back to normal for now.

I have a fix in mind and will get that done this morning. Power off will now move 0 to B3:1.

Just one of those things that happen occasionally or is something getting ready to go toes up?

 

[cpickett]

how is the HMI connected? ethernet or serial? Typically 'stuck' bits are caused by communication loss from the HMI, assuming it is not used elsewhere in the program. If the bit is a start, you can add logic to unlatch it after it's true for a second or two, similar idea to your fix.

 

[ptonsparky]

how is the HMI connected? ethernet or serial? Typically 'stuck' bits are caused by communication loss from the HMI, assuming it is not used elsewhere in the program. If the bit is a start, you can add logic to unlatch it after it's true for a second or two, similar idea to your fix.

Ethernet connection. Less than three feet of cable.

I'm rethinking my fix as an operator would need to be present to cycle off the control power. Typically they can start the process, walk away and it shuts down automatically. Not sure if they do that on a regular basis or not. This time an operator was there.

 

[ptonsparky]

Used multiple times but only as xic or xio .

 

[Bluegrass Boy]

There may be something stuck “high” in the fixture, or maybe something is not going high that needs to be seen by the PLC for a “cycle complete “ . Also if you have pneumatic solenoid stuck on causing fixture to cycle. I have also seen proximity switches cause a fixture to cycle again. You may need to watch it cycle to see if it is doing something unusual. Like not seeing part present for a moment and then seeing it again. Just guessing some since I don’t know what the machine does.

 

[ptonsparky]

It makes corn flakes for cattle. The bit that stuck is the Start Button on an HMI. Really a slow, normally stable, operation.

Well slap me silly. There is a small second touch screen that could have an issue. Rarely used, maybe not at all.
I needed a reason to be up at this hour.