My Auber controller didn't like my RIMS loop until i put I=1000.... The auto-tune thought it should be about I=50, and it oscillated constantly. Moderate P control, soft I control and no D control should tune all of these loops to a good level of satisfaction. Unfortunately i can't tell you what constitutes moderate, tight or soft without a load of details about your system.
Manual PID tuning oddities.
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PlexVector
Mellow Goose Brewing
I found the link below helpful. Although it includes equations the descriptions for each of the PID parameters are decent.
http://www.thorlabs.com/tutorials.cfm?tabID=33653
http://www.thorlabs.com/tutorials.cfm?tabID=33653
TungstenBeer
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I will try that - and I just may take you up on that (when it warms up of course)! First I am going to try I=1 though, because I won't be able to upgrade until late summer 2016, and I certainly want to brew by then :cross:
The wikipedia article is a really good resource. Even looks like they might have been copying each other since their diagrams and tables are practically identical.
http://en.wikipedia.org/wiki/PID_controller
http://en.wikipedia.org/wiki/PID_controller
augiedoggy
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I set it to one which slows the response down and avoids overshooting. 0 would be off... I suppose I could experiment but the setting I have seems to work very well over the factory settings which did overshoot.
PlexVector
Mellow Goose Brewing
You're right. I like the wikipedia version better. especially the graphs.
I'm running a mypin (4 or 7, but its too cold to go to the garage to check) in a DIY RIMS at 120V. I ran the AT with water before brew day and during the actual mash it tracked quite well. Since I'm running 120v I use propane to get the HLT to temp and the RIMS to keep it at temp during mashing. Part of the system is also the flow rate. I estimated what that would be during AT with water. Also during AT with water the water volume was based on the total mass I expected to have in the MT on brew day. So, not only do you have P,I,&D, but also flow rate and mass to consider for the PID to work properly for a specific set of control constants. I hope I said all that right.
In other words: It depends.
ipe:BitterSipper
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The mypins do by shutting all three off.
Yea, your attitude is deplorable at best. You cannot be the least bit confident in that and it's just more petty crap.
You're claiming "incorrect information" but you just restated several things I already stated, but in more ambiguous ways. You shouldn't be using "aggressive" to describe P, most people would think you mean "more" when in fact you are trying to describe "less". NO P = off which is the most aggressive you can be. That's why "more" and "less" are better descriptors, and in this case happen to coincide with "higher" and "lower" for the values of most controllers as well.
English language is hard, I know.
augiedoggy
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It hard enough that the guys at Myin couldnt master it
instead our directions sheet comes in engrish... :cross: likely the cause of this thread...Sorry I saw this and thats the first "on topic " thing that popped into my head..
PlexVector
Mellow Goose Brewing
BitterSipper
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It hard enough that the guys at Myin couldnt master it
I threw those out. You see my post about looking at your output? Curious since you said you had little overshoot and good control if you have any output while above set point with your normal settings, and with I off.
augiedoggy
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I will play with it the next time I run pbw through the system since I usually heat the water prior to doing this. And I will report back.
BitterSipper
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Thanks, I have a feeling you do but the heat capacity of your system vs element wattage and transfer rate absorb it.
augiedoggy
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well I know the output fires a few times after the desired temp is met but at that point the temps are still fluctuating a bit and all in all I would say after about 30 seconds of it firing on and off while the temp is reaches it stops completely... and the output temp never goes more than a degree or two max over the setpoint for any period longer than a second or two... basically after about a minute its holding at the proper temp.
same with my rims... it will climb maybe a degree and flicker on and off 2 degrees higher than setpoint and within 30 seconds or so its settles to the correct temp.
My understanding it the pid operates close to thermostat mode yet still with minimal pid logic buffering things a bit this way... I will admit since its worked fine I havent researched this aspect of my build much.
This thread has gotten very contentious...
I have tuned HUNDREDS of PID loops in my career, many of them temperature loops. I know what I am talking about, and your response indicates you don't understand the nuance. In fact your terms are only valid for PID controllers expressed in a particular form, which although common, is not universal.
BitterSipper
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Really, so if I said "aggressive resistance" You would think less resistance? Of course you wouldn't. Proportional gain is a reduction in output, if you call for it to be used aggressively you're calling for more reduction, not less, that is the locution of the term.
If you want to use the word aggressive you need to attach it to temperature delta, not the control.
The only one making this thread contentious is you with conceited comments and claims of "certain user error" without providing anything constructive.
Also, I find it amusing that you are upset at being contradicted when you did the same thing to someone else earlier in the thread when they were using the less ambiguous terms.
Again "more" and "less" are not the same thing as "higher" and "lower" English is hard, I know.
You are spreading false information and I am trying to correct it. This statement is completely dependent upon the controller you have and the form of the PID controller that is used internally.
BitterSipper
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You still think I'm talking about values, I am not. I am sorry you are missing this. What proportional control does, does not change, though the values required for a certain outcome might.
I am not sure how you are misinterpreting my previous comments but you clearly are.
Did you get your controller working yet?
BitterSipper
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I said "proportional gain is a reduction in output" You said "This statement is completely dependent upon the controller"
There is no "misinterpretation" there.
I would like to hear you explain how, when no proportional gain means output is 100% like a thermostat, how applying proportional gain can be anything other than a reduction in output.
BitterSipper
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No I understood what you said, you kept talking about set values. You didn't understand that I was not talking about values despite my explicitly and repeatedly saying otherwise.
I challenge you again, to explain your claim knowing that I am not talking about specific values. This elusive "proof" I don't understand you when it can only be understood in one way.
muhteeus
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I hope something good comes out of this thread
For those of you who are not sure how the PID settins are expressed in the Mypin let me explain. Maybe this will help out anyone that has a mypin and are trying to get their process dialed in.
With the Mypins the proportional gain is expressed in degrees, not percent like some other controllers. This means that if integral and derivative are both turned off (zero) and proportional gain is set to 5 °F on a cold start your system will fire at 100% output until the process variable (PV) reaches within 5 °F of the setpoint value (SV). Once the temperature (PV) reaches within 5 °F of the SV the output will begin to taper off. For example, once the PV is within 2.5 °F of the setpoint the output will be at 50% and once the PV reaches setpoint the output should be 0%. I think this is where people with mypins are getting hung up. The controller is still outputing after the setpoitn has been reached/exceeded. This simply should not be happening. But I digress.
The problem with only using proportional gain to control at setpoint is that once the setpoint is reached the output is reduced to 0%. On really fast systems with constantly changing PVs that may be OK but on homebrew systems, we need some integral to maintain the setpoint.
Integral is typically expressed in seconds per reset (S/R) or resets per minute (R/M). Mypins express integral in seconds per reset. So if you set your integral to 60 on a mypin you will be capable of achieving 1 reset per 60 seconds. If you set it to 30 you will achieve 1 reset in 30 seconds, or 2 resets per minute. The more resets per minute, the faster your system will be able to react.
Don't worry about Derivative. It likely won't benefit your homebrew system enough to bother dialing in the proper setting. The proper P and I settings will get you where you need to be.
With the Mypins the proportional gain is expressed in degrees, not percent like some other controllers. This means that if integral and derivative are both turned off (zero) and proportional gain is set to 5 °F on a cold start your system will fire at 100% output until the process variable (PV) reaches within 5 °F of the setpoint value (SV). Once the temperature (PV) reaches within 5 °F of the SV the output will begin to taper off. For example, once the PV is within 2.5 °F of the setpoint the output will be at 50% and once the PV reaches setpoint the output should be 0%. I think this is where people with mypins are getting hung up. The controller is still outputing after the setpoitn has been reached/exceeded. This simply should not be happening. But I digress.
The problem with only using proportional gain to control at setpoint is that once the setpoint is reached the output is reduced to 0%. On really fast systems with constantly changing PVs that may be OK but on homebrew systems, we need some integral to maintain the setpoint.
Integral is typically expressed in seconds per reset (S/R) or resets per minute (R/M). Mypins express integral in seconds per reset. So if you set your integral to 60 on a mypin you will be capable of achieving 1 reset per 60 seconds. If you set it to 30 you will achieve 1 reset in 30 seconds, or 2 resets per minute. The more resets per minute, the faster your system will be able to react.
Don't worry about Derivative. It likely won't benefit your homebrew system enough to bother dialing in the proper setting. The proper P and I settings will get you where you need to be.
TungstenBeer
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This is the most helpful thing I've read so far. Thanks!
BitterSipper
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With mine at least, this is not the case. The default of 3 begins ramping far earlier than 3 degrees.
I agree, but mine still outputs over 20% if my memory serves me, after peaking the SV
Agreed, I only turned I off in order to tune P, to no or minimal overshoot. before applying I.
muhteeus
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By the way. I think the assumptions on P control are wrong. Hear me out.
Some applications are what is know as "integrating" such as filling a tank with water or level control. Most are not. Temperature control should be non-integrating, in that there is a residual output required to maintain temperature. I.E. the steady state is >0% output. This is what integral is for. To bring back down that proportional overshoot.
From the horses mouth. Proportional band is in % not degrees.
Some applications are what is know as "integrating" such as filling a tank with water or level control. Most are not. Temperature control should be non-integrating, in that there is a residual output required to maintain temperature. I.E. the steady state is >0% output. This is what integral is for. To bring back down that proportional overshoot.
From the horses mouth. Proportional band is in % not degrees.
[
From the horses mouth. Proportional band is in % not degrees.[/QUOTE]
I stand corrected on how the Mypins express proportional gain. It is not in degrees as I had mistakenly remembered. It is in %. Looking at the manual linked to above the input range for a PT100 on Mypins is -199 to 600 °C (-328 to 1112 °F). So the input range is 1,440 °F. That means that a proportional band setting of 1% is equal to 11.4 °F. The same rules would apply as I stated earlier. The controller will output 100% until it reaches within 11.4 °F of the setpoint and then will taper off. Sorry for the misinformation. I should have fact checked before posting.
From the horses mouth. Proportional band is in % not degrees.[/QUOTE]
I stand corrected on how the Mypins express proportional gain. It is not in degrees as I had mistakenly remembered. It is in %. Looking at the manual linked to above the input range for a PT100 on Mypins is -199 to 600 °C (-328 to 1112 °F). So the input range is 1,440 °F. That means that a proportional band setting of 1% is equal to 11.4 °F. The same rules would apply as I stated earlier. The controller will output 100% until it reaches within 11.4 °F of the setpoint and then will taper off. Sorry for the misinformation. I should have fact checked before posting.
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rudylyon57
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I stand corrected on how the Mypins express proportional gain. It is not in degrees as I had mistakenly remembered. It is in %. Looking at the manual linked to above the input range for a PT100 on Mypins is -199 to 600 °C (-328 to 1112 °F). So the input range is 1,440 °F. That means that a proportional band setting of 1% is equal to 11.4 °F. The same rules would apply as I stated earlier. The controller will output 100% until it reaches within 11.4 °F of the setpoint and then will taper off. Sorry for the misinformation. I should have fact checked before posting.[/QUOTE]
In the interest of developing some harmony on this post...I think you are both correct about proportional parameters. After all a % of a degree is still a degree!
muhteeus
Well-Known Member
In the interest of developing some harmony on this post...I think you are both correct about proportional parameters. After all a % of a degree is still a degree![/QUOTE]
PID runs off the ERROR. P only: Out % = Kp * (SP-PV). So yes, sortakinda, Kp is unitless gain, and the error is in degrees.
Convention is that error is defined as e = SP - PV. Otherwise you'd have negative output unless your gain was also negative.
muhteeus
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I apologize. This is correct for heating.
It is correct for error in general. I will give you that if you error is positive that you may want to do cooling, but now we're getting into a much more complex situation of double acting PID loops.
A heater can't actively cool. You need another device - e.g. a fan or coolant loop to do the cooling if you overshoot. That system has a different response than the heater does so you need another loop. Gets even more fun when you're tryign to cool something that is above the boiling point of your coolant. Been there done that.
augiedoggy
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like a fermetation chamber
Yep... but most of those at a home brew level are handled with thermostat style control - simple on/off with hysteresis and dead band - Not PID.
BitterSipper
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There are applications of PID control for cooling, so you can't say it's correct in general, but it's definitely the context of this thread. He also said;
When if anything (in heating), I is responsible for the overshoot in the first place, but if you translate it as speaking from a cooling perspective to heating, he's saying the job of I is to bring back up the droop [and keep it steady], which is fairly accurate.
So I'm going with either confused or uses PID for a cooling something.
augiedoggy
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Yes true, I am aware of this... I have just flashed my first stc 1000+ to replace my stc 1000s and knockoffs...
I cant believe we are on day two of debating and no one has yet bothered to try my suggestion to change the I to 1 and see how it performs... It seems its more fun to argue about the process than to attempt to correct the problem ... Now you have me concerned and I have had no problems (that I know of)
BitterSipper
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Wait, what problem are you talking about. The problem that created this thread was that my controller was choosing to heat past the SV even with I and D off, which is contrary to proper function.
I mean I can tell you setting I to 1 effects better control than the default 240, and in fact having I at 2 is even better (for me). But that's not the problem, the problem is this controller is making it impossible to go through the steps to manually tune it. I posted an example of that process in the first post (though I disagree a little with the suggestion on how to come to an initial proportional setting).
I can get the controller to hold around a degree by tuning both at once, but I know I can do better and improve the rise and settling time if it wasn't acting so retarded.
I don't think that by now anyone disagrees that under P only control, there should be no output past SV, yet I have two ta4s that both do it.
muhteeus
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I will disagree. We use reverse acting to control bubble diameter. This is an exhaust. So the delta output is inversely proportional to the delta error.
http://www.control.com/thread/1254819878 (maybe this is my rslogix5000 notation steering me wrong)
TungstenBeer
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Oh, I'll be trying it! I just brew outdoors so the temps we've had make chilling very difficult through my frozen hoses, so it'll be at least a couple weeks until I can try it. And plus I'm a big wuss with the cold, haha.
