A fuse for a water valve would randomly blow. Weeks would often pass, then it would blow again. Everything checked out fine and after replacing it, it would be ok for a few more weeks.
The only trouble was, it often liked to blow in the middle of the night and I was dragged out of my bed to repair the fault.
So, I wired an input to the plc from the fuse and programmed a screen on the HMI to tell them which fuse had blown. I decided that this was sparse information - so I filled the screen with a full procedure of what to do. This included telling them where the spare fuses were kept. ie spare fuses can be found in the maintenance stores, shelf 6B.
I never heard another thing about it for a few years until one day........
I was altering the plc program and an operative came wandering in and was marveling at the technology, the laptop, the HMI the plc etc.
He said 'These things are brilliant, I am constantly amazed how far modern science has come'
I nodded in agreement
He continued ' Do you know, the other day the alarm went off and I came in here to see what it was and the screen said a fuse had blown for the water valve.
I continued to nod in agreement.
he said 'but listen to this, not only did it tell me which fuse had blown, it told me whereabouts exactly in the stores the spares were kept'
He wandered back out saying 'bloody marvelous things them'