On 6/27/2013 11:51 AM, Steve Stallings wrote: > <snip> > >> I respectfully disagree. As long as the integral term is >> normalized to the >> run rate, there is nearly no effect to running the loop >> faster than then >> the time constant. Analog PID works at a (near) infinite >> rate. >> > OK, point taken. My caution comes from the fact that > many digital implementations do not handle very small > integral gains properly. > > Steve Stallings > >
It is best to keep the PID as simple as possible. A running average filter on the PV can work. If it is a relatively slow PID loop you can watch the various values update and see the response, watch the various PID components interact, windup, become limited etc and find errors in your software routine without graphing anything. Running the PID every ms makes doing that pretty much impossible as everything is a blur. Slow it down, get the PID working properly and then speed it up as needed. If needed, add mass to the system to increase the time constant so you can slow down the loop. Then once you get things working. Reduce the mass, and increase the PID calculation speed as required. Simple is good as long as it doesn't hinder performance. >>Analog PID works at a (near) infinite rate. Yeah... when was the last time anyone worked on one of those... Have you ever seen a Pneumatic PID controller? Those were common when I started working with controls way back when. They were not all that reliable especially in cold weather and they had to be constantly recalibrated. I'm glad those "good old days" are behind us. Dave ------------------------------------------------------------------------------ This SF.net email is sponsored by Windows: Build for Windows Store. http://p.sf.net/sfu/windows-dev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
