Regular Guest
I need some help manually tuning these loops. I have a forwarded email from a johnson rep detailing the steps for tuning out the loops. The problem is if I set my integral to anything less than 120 the PID goes unreliable from an input that is out of range. Is this some how linked to one of the other settings? etc Interval or process dead time? Does anybody have basic tactics for setting up there loops? Are you just messing with prob band and integral or are you going all out with process range, dead time and time constant as is suggested in the email I have received.
Regular Guest
Also for some reason the loop keeps going up a bit and then just goes right back down to zero and its no where near setpoint. It doesn't do that if the integral is at zero which strangely is the only thing you can set it below 120 with out it going unreliable...
Professional Member
Hello dhoyt,
Shoot me an email. My address is in my profile. I have a solution for you.
Professional Member
Ziegler-nicholls
120s is 0.5 repeats per minute...way way too fast ... You have what is called "integral windup". Double yr proportional band and Try something in the order of 600 for integral time.
What process are you trying to control?
What is yr proportional band or p-constant?
Professional Member
Just out of curiosity, what are you trying to control?Originally Posted by dhoyt
Professional Member
Just take a look at the AI input and the PID processor input and make sure they are setup for the same control function. For example, if one is setup for GPM and the the other setup for PSI, it will cause complications. Didn't really mean to quote noskilltech, just a general response.
Regular Guest
Im trying to control steam Hx's and steam coils on AHU's. The inputs for the pre processor and loop are good. Im going to try increasing my integral and prop as matrix suggested and see how that goes.
Professional Member
Have you tried just setting it to autotune and leaving it alone for a day? There have been some instances that I've had to manually tune my PID's in CCT or PCT (steam to dom hw hx's), but for the most part if you use system selection tool in CCT or PCT, the loops for preheat coils will usually tune themselves out pretty tight after about 6-8 hours. This may not be the case for everyone, but I've had fairly good luck with them in the past.
Regular Guest
They where set up for auto tuning and would work great in till you changed the setpoint then they would freak out and go out of control. This seems to be the common issue with auto tune from what I have read. I had the Hx's running at 140 deg F for weeks then they where having some issues and they wanted me to bump them up to 180 deg F. The loops never quite came under control and when I set them back down to 140 deg F at the end of the day that was it. They couldnt recover and the valves would open close open close... It ended up over heating and I had to have a guy cycle power to the control as I wasnt onsite anymore. I have been dealing with crazy logic to limit the outputs of the PID's and resetting there tuning based off of this and that and honestly its ridiculous... At this point I would just rather tune them out myself like every other control software I deal with and be done with it... Unfortunately these loops are not cooperating... I can get them close with my prop band but as soon as I try to add any integral at all they go out of wack. I had the temp almost right at setpoint so I figure perfect a little integral will get me right there. I put in 600 as preciously suggested in an above post and the valves go closed and still have opened 15 mins later and Im 15 deg F below setpoint... I dont understand its like the dont work anything like any other loop I have tuned in the 5 other software's im familiar in... What am I doing wrong here?????
Regular Guest
So Im tring to control steam Hx's for a building Hw Loop. I have a loop and a pre processor. Adaptive tuning is off in the PID and manual tuning is set true in the pre processor.
process range: 60
Time constant: 300
Process Dead Time: 300
Prop Band: 25
Integral Time: 600
Interval: 120
Professional Member
This may be in the thread but I didn't see it. Are you using a PID and PRAC or just a PID? Do you have a log in for the JCI website?
Regular Guest
I do not have a login for the jci website... I'm using a prac and a pid. I talked to one of the guys in the company and he said to hook up the prop band and the integral to the pid and not the prac which I did and it was still acting funny. What I ended up doing way blowing out the pid and prac I was messing with and started from scratch. The info I had said to try and set up the process range the dead time and the one other thing I can't think of right now... I abandoned all of that and just attached the prac to the pid just as it was, set it up for steam hex, tied the prop band and integral straight to the pid, set them to 30 and 300 and she was butter after that... it seems messing with anything causes some unwanted reactions. I'm sure it mostly because I'm not experienced enough with manually tuning these loops and this was the first time so there was a lot of frustrating trial and error.
Professional Member
I have an integration loop that I use with the PCG controllers that I made for steam heat exchanger control. Just set the integration rate and control action and let it go. Put an email in your profile and I will send it to you.
Professional Member
I took a class on PCT awhile back. The instructor was a ex JCI tech support guy for 20 years, and now works for our local distributor. When he started on PRAC tuning the first paragraph said PRAC doesn't work 60 to 70 % of the time, I have had nightmare's with the stupid control loops, and feel your pain. Wish I had a way of getting his manual tuning lesson to you it has worked for me. I have also let PRAC run for a day or two and then taken it off. The last one, that gave me problems, was a static pressure PID if it is something where the valve is too big, damper don't close right, these pid's will tune, tune, then do nothing. It was 100% all the time on that one. They suck, and manual tuning is the only way to go in your case. A PID should just adjust to correct for error until they melt the AO'S down. I hate to rant but CCT,PCT is a pure debacle in my opinion. I have programmed, with honeywell care, spyder tool, hvac pro, some GX9100, and I'm currently righting my own custom programs, just get away from the Q&A, state based, setpoint determination, output control CRAP. It's like what turn's this thing on??Let me look view logic, OH!! 500 layer's of JCI pre programmed modules, now it all makes sense. That view logic button makes me laugh when I press it. So logical!! It make sense, if you don't think about it!!
Professional Member
[QUOTE=dhoyt;14263051]They where set up for auto tuning and would work great in till you changed the setpoint then they would freak out and go out of control. This seems to be the common issue with auto tune from what I have read. I had the Hx's running at 140 deg F for weeks then they where having some issues and they wanted me to bump them up to 180 deg F. The loops never quite came under control and when I set them back down to 140 deg F at the end of the day that was it. They couldnt recover and the valves would open close open close... It ended up over heating and I had to have a guy cycle power to the control as I wasnt onsite anymore. I have been dealing with crazy logic to limit the outputs of the PID's and resetting there tuning based off of this and that and honestly its ridiculous... At this point I would just rather tune them out myself like every other control software I deal with and be done with it... Unfortunately these loops are not cooperating... I can get them close with my prop band but as soon as I try to add any integral at all they go out of wack. I had the temp almost right at setpoint so I figure perfect a little integral will get me right there. I put in 600 as preciously suggested in an above post and the valves go closed and still have opened 15 mins later and Im 15 deg F below setpoint... I dont understand its like the dont work anything like any other loop I have tuned in the 5 other software's im familiar in... What am I doing wrong here.
I've been using these controllers with great respect to the auto-tune feature. To be honest I'm always within the JCI realm, meaning DAT control or duct pressure control etc. etc. I'm really not a big fan of it but so far so good. I can see where it maybe suspect or fragile. What you are trying to control doesn't seem to out of the normal, maybe it just doesn't fit in the JCI box. I know eventually I'd would have to cross this bridge, you just beat me to it. I'd love to see your program file, please, please, please forward it my way. It's only a matter of time before I'm in same boat as you. Either way, please let me be included with your resolve.
Professional Member
http://cgproducts.johnsoncontrols.co...F/12011147.pdf
Interval: Sets the Eff Period. This value is the time period between normal PID algorithm executions -- 120 is TOO BIG
...do you want this thing controlled in near-real-time ... or only evaluated every 2 minutes?
1 + 1 = 3 ( *** for very large values of 1)
...everybody wants a box of chocolates and long stemmed rose
Be brave. You cannot get eaten by an imaginary tiger.
Regular Guest
I agree with pretty much everything you have said here. O&A is a joke I have never used it for anything but VAV programs. You have to write your own stuff or you will never know whats going on or will will never get everything you need for the sequence of operations. Johnson is definitely my least favorite of all the control systems I work on. I would rather do alerton or invensys any day... hell I would almost rather do reliable! hahaha Everything has good things and bad things about them, auto tune loops in johnson is for the birds. They made it so they could keep hiring new guys that dont know a lot about what there doing because they are a revolving door. People come and go like crazy. Sorry if you work for johnson but you know its true, at least in new england it is...
Anyway final resolve is hook up prop band and integral to your PID and not your pre processor, everything else hook up per usual and adjust prop and integral as you would with any other software. In other applications adjusting everything else that I was trying ie process dead times, time constants etc may be necessary but for me the defaults have worked just fine. Reaper has also sent me a loop he has made that Im going to play with and see how she goes. Thanks again.
Banned
Proper valve sizing is critical for steam. no matter what you do may not be good enough if sized incorrectly.
Regular Guest
I guess I don't seem to see the big issue with the PCT logic view. Just my opinion.
It's kind of similar to Workbench wire sheet.
All you see with HvacPro is inputs, outputs, and parameters. None of the underlying logic is shown. Are you saying you don't want to see all of the logic in the std app?
Note: I'm not familiar with care or spyder, so I don't know how their apps can be examined any better. Do they show their underlying logic?
Regular Guest
The logic view is an absolute necessity when you write the logic yourself. I think he was referring to when you do the Q&A (which is the worst thing you could possibly attempt) and then look in the logic of those modules... **** show... If you cant write the programs yourself you need more training or you should think of another career path.
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