Is your Allen Bradley SLC-500 finally kaput now that you’ve reprogrammed channels on the I/O cards about 10 times? (Did you think we didn’t know you did this? Everyone does this.) Did your GE Fanuc PLC processor suddenly just “lose” its program? Has your ABB PLC faulted, the little red light is on and you can’t get your error codes to clear? Then you would definitely NOT be alone. We hear these tales of woe day in and day out from manufacturing plants and shops of all sizes.
In a nearly perfect world you would perform maintenance checks on your PLCs every month or two, but even if you do this, many of the most common PLC problems are not caused by lack of maintenance. Machine age and environmental conditions are often at the heart of the problem. Assuming you have ruled out ridiculously obvious problems such having the wrong cables or loose cable connections, a few of the evil PLC poltergeists include:
- Power fluctuations or surges
- Over heating
- Blown power supplies
- Blown I/O cards
- Bad I/O channels
- Bad cables/loose cable connection
However, another frequent PLC problem is absolutely a maintenance issue – bad batteries. If you’ve been neglecting to replace your back-up battery, bad things are sure to happen. If the red fault light indicates battery status you are in danger of losing your program. If you do not have a current program on hand to reload after you’ve replaced the dead battery, then you are in even more trouble. (Hint: If the red battery light comes on don’t down the power!) Get the program backed-up BEFORE you attempt to change the battery(s). Whether you are the boss or the operator, this is not the place you want to be. Let the finger pointing begin!
In almost all of the above mentioned cases, you will need to remove the unit and have it repaired. If the PLC unit is still under warranty, you will need to contact the OEM. If not, you will need the services of a reliable third-party industrial electronic repair shop.