PID or PIDE

[Ben 1]

Hi everybody, In one of my project I have to use couple of PID controllers on Logix5K. I don't have much exposure to PID instruction. Moreover, there is PID and PIDE (enhanced), I don't know which one to use. Also, there are lots of tags under base tag "PID", want to learn how to use many of those tags. I know the SP, PV, KP, Ki & KD etc. I am trying to control flow by one controller and the other is a level controller that will adjust flow setpoint (tweak it by say 10-20%). This is neither cascade nor ratio control, to the best of my knowledge. Two separate controllers with possibility of using the O/P of one to partially adjust the setpoint of second. If you gentlemen could point to documentation on PID instruction and few examples, would greatly appreciate it. I am sure there would be lots of discussion on this forum in past but searching for "PID" in forums doesn't give me any results! Am I missing anything?

[Armadillo852 25]

Ben, Check out this article from AB: 40236 - Basic Setup Help for Logix PID

[Michael Lloyd 85]

Personally I prefer the PIDE instruction over the PID. If I understood you correctly you need two loops and the output of one is the remote setpoint of the other. This is called cascade control and its pretty simple to implement.

[Ben 1]

Armadillo, Is this article "40236 - Basic Setup Help for Logix PID" on knowledge base or somewhere else? The A-B websites are huge, past few searches revealed nothing..Would appreciate if you can post link. Thanks.. Michael, I would like to know the reasons why you prefer PIDE, Enhanced sounds better then regular PID but what are the technical advantages. I used PIDs 12 years back on PLC5 so don't remember much. Need some insight here.. On second point, I don't think it is a cascade as the O/P of first is not the setpoint of second loop. Both loops has their own PV and setpoints. The flow loop has Final control element, level loop doesn't have any. The flow loop will run as an independent loop till level loop is engaged. Level loop is just to fine tune the flow setpoint (only say 20%), it does not give SP to flow loop. That is the reason I stayed away from primary/secondary or inner/outer or master/slave lingo.. Thanks for quick reply friends..

[Ben 1]

OK, found it on knowledge base after login (I have TechConnect access level). I am pasting the link below, it will ask for login info. Create an account if you don't already have one. http://rockwellautomation.custhelp.com/app/answers/detail/a_id/40236/kw/40236

[Armadillo852 25]

Here you go.http://rockwellautomation.custhelp.com/app/answers/detail/a_id/40236/kw/40236 Yes it is a knowledge base tech connect required listing.