PID Controller Changes Mode by Itself

More than likely you are having issues with your power supply... low power surges, a nearby drive affecting your frequencies. Not knowing the area, and surrounding equipment, in which this functions; you may want to look at the quality of your power first.

Good point! Monitor, with a strip chart, your keypower lines.

I don't have any experience with the actual controller that you are talking about but I have had problems similar to this caused by RF spikes getting on to the motherboard or backplane depending on the design.

The usual culprit is some sort of unbalanced load, usually inductive in my experience, but it could be anything. Take a step back and see if there is anything that you can associate with the problem. Keep an open mind though as the offending item may be a fair way away and may not even be connected to the unit in question in any way at all. You may also get spikes when loads are switched at the peak of the AC wave that don't cause problems when they switch at lower instantaneous voltages of the wave and hence look fairly random and disassociated.

I once had a spike of extremely high frequency spike (up in the GHz range) getting into a unit via fire proof cable. The spike was using the copper sheathing as a wave guide jumping onto the backplane and causing the microprocessor to reset, the result was a real mess to the process that it was controlling.

I would be interested in what you finally find is the problem so please post your results.

You state that this issue appeared recently. I would look for things in the facility environment that recently changed, especially about the time this problem initially occurred.

I am not familiar with your particular product, but things that are normally stable don't just start to misbehave without a source cause.

Power line issues (espcially low voltages) can be a serious problem, as can spurious RF coupling in along the shielding or power cables.

Good luck, Mr Phelps.

- Yankee Bruce
If life was't so difficult it would be easy!

check for proper grounding (noise)