Try to look at self-tuning pid loops. It's fairly simple, one applies a unit pulse on the control input and observes the feedback over time. From this the necessary corrections can be computed or iterated to. However, if your pid loop controls something with *any* kind of deadband you will face difficult times. And there are *no* mechanical controls without a deadband. Peter -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body