RSLogix 5000 PIDE tunig

Hi,
This is my first post and I am relatively new to programming so please excuse my lack of knowledge. I am trying to tune a PIDE in RSLogix using Expertune software. I am having problems telling the software how to determine if the loop is in Auto or Manual. It asks for a Mode and I can browse to the PIDE parameters to tell it the path. I am not sure which parameter to choose and the ones that I have tried have not worked. The problem is that the PIDE has both an Auto and Manual parameter and choosing just one doesn't work. I am hoping that someone here has done this setup before and can help get me through it. Thank you in advance for any assistance you can give me.

first question: why are you using Expertune – rather than the PIDE's own built-in autotune feature? ...

see this link for a demo:

http://www.plctalk.net/qanda/showthread.php?p=492660&postcount=1

maybe you didn't purchase the autotune option with your RSLogix5000 package? ...

see this link to tell for sure:

http://www.plctalk.net/qanda/showthread.php?p=491581&postcount=2

next question:

why are you using the PIDE instruction (in Function Block Diagram format) – rather than the much simpler PID instruction (in Ladder Logic)? ...

many people think that the "Enhanced" name of the PIDE instruction means that it will give "enhanced" control over a particular process ... it won't ... see the picture at the bottom of this link for a demo:

http://www.plctalk.net/qanda/showthread.php?p=504603&postcount=1

in short, you'll get a LOT more "bells and whistles" settings with the PIDE (some people say "too many more") – but the actual control over the process isn't going to be any better than what a regular old PID instruction provides ...

moving right along ...

frankly I've never tried using Expertune with the PIDE instruction ... but I'll give it a shot later when I get to the lab ...

as for using Expertune with a PIDE – I'd be willing to bet (pocket change only) that the very same "which manual setting should I use?" question that you've brought up would make it difficult – if not impossible ... specifically, I doubt that Expertune has been "updated" to handle the mechanics of the new-fangled PIDE instruction ... (that's just a guess – I might be wrong) ...

so ...

I if personally absolutely HAD to use Expertune with a PIDE – I'd "cheat" ... first I'd drop in a temporary PID instruction (in ladder logic) and use Expertune on that one ... then I'd plug the resulting tuning values into the PIDE - and delete the PID ...

going further ...

if you are (as you've said) rather "new" to this, then I strongly suggest that you post your complete existing ACD project file ... (you'll have to zip it first – forum rule) ... in MOST cases, when PID or PIDE controls don't work right, it's because of the setup ... scaling issues – timing issues – etc. ... we can help with that – but we need to see the ENTIRE project file in order to give you any detailed information ...

and welcome to the forum ...

I tried the Autotune feature and it really didn't improve things any. This is a pond level control for a hydro-electric generating facility. The pond is big enough so that making as much as a 60% change in the gates takes too long to see any variation in the PV. I had hoped that the Expertune software would give me the ability to monitor the process over a longer period of time for better tuning. I can put in a basic PID temporarily or even permanently if that is a better way to go. Thank you for the advice.

This is a pond level control

Click to expand...

well, that changes things ...

the fact is that PID (or even PIDE control) isn't usually suitable for controlling the level in large tanks – or ponds ...

instructors and books have been using "level control" as classroom examples for PID control for years – but the fact is that the examples usually don't work well at all once the student gets out in the real world ...

you've already seen the reason ...

if you're trying to control the LEVEL – then you need to have the "amount coming IN" to match the "amount going OUT" ... the problem is that if the tank – or pond – is very large, then by the time the PID sees the level get out of range, then you've got a LOT of liquid involved ... (in simple terms, a difference of an inch (or a foot) of level amounts to a VERY LARGE amount (gallons) of liquid ...

so ...

when the PID sees the level get out of range, it obediently begins to regulate its output (valve, pump, gate, etc.) trying to bring the level back to the desired setpoint ... sounds good so far - but by the time that the level actually responds, the valve, pump, or gate has already reached its full range of control (either wide open or fully closed) ...

so ...

when all is said and done, you might as well just ditch the PID – and have the controller look at the level in the tank (or pond) and compare the actual level to the desired setpoint (target) ... if the level gets too low – or too high – just FULLY open or close the valve - turn the pump ON or OFF – move the gate FULLY open or FULLY closed ...

now you certainly might need to add some "deadband" to cut down on "chatter" when the system gets very close to the setpoint – but that's a lot easier to do than trying to tune a PID or PIDE controlled system ...

a highly intelligent gentleman named Peter will no doubt be along soon to explain all of this in mathematical terms such as "capacitance" and so on – but the basic idea is that when you have:

(1) a LARGE capacity container ... and

(2) a LIMITED degree of control over what comes IN and what goes OUT ... then

(3) PID/PIDE control (bless its little heart) is usually going to move its output either FULLY on/off – or FULLY open/closed – or FULLY from one extreme of its range to the other extreme ... ("slam–bam" control is a term that old timers once used) ...

summing up ...

if you've ever seen a PID controller successfully do a "level control" experiment in a classroom environment, think back to how large was the tank? (usually just a foot or so in diameter) ... and how much control was allowed over the input or output flow? (usually enough "capability" to easily overcome the amount of in-flow or out-flow without "hitting the limits" of the valve, pump, gate, etc. ...

in other words, if you carefully choose your equipment, then you CAN get a PID to successfully control a "level" operation by properly "modulating" its output ... but in the real world the size of the containers – and the limited degree of control that we have over the "in-flow" and the "out-flow" conspire against us ...

in other words, PID isn't usually the right choice for "level" control – even if you "enhance" it – and no matter how you "tune" it ...

party on ...

Thank you again for your great information. I am going to continue to play around with it as a learning experience. If you do get a chance to try Expertune with the PIDE and figure out the Auto/Manual I would be grateful for any assistance with that. I have the latest version of Expertune and it is supposed to support the PIDE but that part of it has caused me problems. Thank you

PIDE AUTOTUNE rslogix5000

Hi, i have come a across a problem and i am hoping someone is able to answer this question. My application is for a small level control system. There are two control variables, a VFD and a control valve operated by a i/p converter. The intention was to control the process using function block and possibly cascade control and autotune. I am having a problem with the autotune function using a control block. All the manuals I have read say the process must be in manual mode. However, I am not sure how this is done. When I try to operate the process from the ladder logic it wont allow me to download to the function block in manual. I am not sure what I am doing wrong and any feedback would be greatly appreciated. I am attaching a copy of my program in order for anyone to browse and look at.

Thank you in advance.