RSLogix 5000 PIDE function block. Scaleing the PIDs

Okay here is the deal; I am using a compact logix to do multi loop temperature control in an industrial furnace. It seems that you can input any real number into the PIDs inside of the PIDE function block, and this just doesn't make sense to me. When working with a Honeywell or Eurotherm the proportional gain is just that proportional, based off of the percentage of change of the PV in a given time (0-100). In logix I can put in 1 billion for my proportional gain; what gives! does anyone have any good experience using PIDs in Logix.

I think the gain is effected by the input range i.e. if you change the range the gain knows about it.
It's hard some times to figure out what the different terms mean, the different venders take all sorts of poetic licence with PID terminology.
Whenever I strike a new controller I set the integral to zero, gain at 1 or 100% PB then change the setpoint by 10% to see how much the output changes. a 10% SP change should give a 10% output change. After that I change the integral to see how fast the output changes that way I can figure out if it's minutes/repeat or repeats/minute. Sometimes you strike seconds per repeat or repeats per second. Sometimes reset is effected by gain, other times not. Sometimes you toggle a bit for reverse acting other times use negative gain.

The PIDE uses PVEUMin and PVEUMax and the reset units is i/min which I figured out to be Repeats/minute Once you get it working it behaves quite well.

Roy

Hey Roy,

Sorry about the delayed response. Thanks for the post. I have used your method for tuning PIDs and it normally does work well except this 5000 processor. I don't get it I thinks that PIDs are really some genius's way to make us normal folks bang our head against the wall

Yes, I agree. I learned PID back in the dark ages when it was done pneumaticly, you could sort of visualize what was happening. Now days we get mathmatical explanations that go way over my head, but it still works the same. Temperature is one of the harder processes to control.
Post me direct if you like, I am using the PIDE on my project I can give you my parameter settings, that may help.
roy undescore matson at yahoo dot ca
Regards
Roy