We went to Auber to speak with the owner about our PID's and I needed to have a better understanding before I went. After much research and reading I acquired a nominal understanding of the workings of a PID. The following is from Wikipedia and is one of the easiest breakdowns that I've seen in regards to an explanation of the P the I and the D.
"These values can be interpreted in terms of time: P depends on the present error, I on the accumulation of past errors, and D is a prediction of future errors, based on current rate of change. The weighted sum of these three actions is used to adjust the process via a control element such as the power supplied to a heating element. By tuning the three parameters in the PID controller algorithm, the controller can provide control action designed for specific process requirements. The response of the controller can be described in terms of the responsiveness of the controller to an error, the degree to which the controller overshoots the setpoint, and the degree of system oscillation."
Hope that helps,
Ben
