[Disar]

Ken, Kiet,

Thanks for the replies!
Yes, I am a senior at the University at Buffalo - SUNY. Nice to see a fellow Wstrn NY'er. Ken, I am actually working for Greatbatch Inc. you may or may not of heard of them.

I am sorry if I was vague before. As I stated, I inherited this problem and trying to sort all of this new information out. I will relay everything I know of the problem while still maintaining confidentiality.

A spike for me is defined as something > than 340 mA and very sharp (think the Dirac Delta/Impulse function). (We typically run around 100 mA - 240 mA).

We use the PID algorithm to control current while voltage is steadily (linearly) increased. This is done for prescribed period of time. Then performed several more times. We use LABVIEW to retrieve data periodically (period depends on number of boards that need data collected from them). On the LABVIEW plots of the values collected, spikes DO NOT occur periodically. In looking at some graphs the spike is occurring at the end of a "ramp up". This causes noise on the next ramp up that occurs.

Let me rephrase that, the spike from the current (controlled by the PID) in the previous "cycle" will cause the voltage in the next cycle to "ramp up" in a sporadic linear manner (think of an irregular saw tooth waveform moving up linearly).

The spike is causing a problem. The boards are used in the manufacturing of certain medical components which have very little room for error. So this is not a problem we can overlook.

We use an ATOM chip (programmed in MBASIC) to control the whole process. We have other hardware on board for the analog to digital conversion and a switching power supply. I had to jury rig a communication circuit to allow for "in circuit" programming/debugging. During this process I found that one (or more) of the grounds on the board is faulty.

This leads me to certain to my ideas as to why the spike occurs:

1. It could possible be the faulty ground on the board causing values to be read incorrectly by the ATOM chip.

2. The PID is either tuned incorrectly or not implemented correctly (as I can tell it looks implemented correctly but I am in the early stages of troubleshooting)

3. As Kiet had stated, the math may have been done incorrectly and caused an overflow or mathematical error.

4. There could be a problem with the switching power supply (I have not begun to investigate this).

As you can see, I am in the infancy of my troubleshooting. I just want to hear peoples reasons for abnormalities in a PID Algorithm and see if it corresponds with anything I am doing. Furthermore, I would like to know if anyone has had any problems with hardware itself causing spikes.

I think I have been as specific as I could be given the information I have. If you would like me to define the problem further could you let me know which parts.