PID Autotuning doesn't seem to work?

Recently just build a RIMs tube using the "RIMs for Dummies" thread as a guide. 1.5" stainless plumbing from Murray Equipment (10" nipple), 1500w 120v element from Plumbing Supply and the Auberins 2362 w/ 2" RTD probe. All I plan to use the tube for is maintaining my mash temps, and since I didn't want to rewire the garage with 220v and only had a 15A circuit readily available I went with the smaller system.

Brewed with it for the first time this last weekend and it didn't work as expected. After getting my mash to 152, I set the PID to 154 and tried auto-tuning. Over the course of the next 5-10 minutes my mash temp dropped down to 148. I decided to switch over to manual mode to get the mash back up to 154 and ended up going manual mode @ 55% power or so the rest of the time and w/ some tweaking every 5-10 minutes on the power was able to maintain my mash temp manually alright.

I reset the PID to default settings, tried the same method again for the 2nd beer and the auto-tune feature failed again so had to resort to running the PID manually again. What am I doing wrong? Is my nipple too long and I'm getting some stagnant water perhaps? I notice since I ordered the 2" probe it doesn't really make it all the way down to the outlet "T". I know the element is strong enough to get my mash temps up since I was able to do it in manual mode, so not sure why the PID auto-tune function doesn't work for me.

For clarities sake, auto-tune mode, or automatic mode? I don't know your particular controller, but when I think of autotuning controllers, I'm thinking of an controller which can determine its best tuning parameters through a series of steps where it measures the response of your system. You would not want to use the auto-tuning feature to hold a mash constant, as it would intentionally be moving the otuput to the element in order to determine the best tuning parameters to use in the future.

Again, I don't know your controller, I'm just going from my overall control experience and what "auto-tune" would mean to me.

BrewKnurd said:

For clarities sake, auto-tune mode, or automatic mode? I don't know your particular controller, but when I think of autotuning controllers, I'm thinking of an controller which can determine its best tuning parameters through a series of steps where it measures the response of your system. You would not want to use the auto-tuning feature to hold a mash constant, as it would intentionally be moving the otuput to the element in order to determine the best tuning parameters to use in the future.

Again, I don't know your controller, I'm just going from my overall control experience and what "auto-tune" would mean to me.

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There is a setting on the 2362 PID to determine the best parameters to use. I tried running the PID with the out of box settings and it didn't seem to work so I tried "auto-tuning" so that the PID can figure out what the best parameters to use were for my system. From my understanding the PID would go through 3 cycles of "over shooting" the set temp. value and then letting it cool back down to learn the PID paramters. But instead of overshooting the temp, the temp kept on dropping.

I guess long story short, I was trying to use auto-tune to let the PID learn my system so that I can use automatic mode and have it work correctly. I hope that makes sense?

DTV said:

There is a setting on the 2362 PID to determine the best parameters to use. I tried running the PID with the out of box settings and it didn't seem to work so I tried "auto-tuning" so that the PID can figure out what the best parameters to use were for my system. From my understanding the PID would go through 3 cycles of "over shooting" the set temp. value and then letting it cool back down to learn the PID paramters. But instead of overshooting the temp, the temp kept on dropping.

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From looking at the manual for the 4342, which is what was referenced in teh RIMS for dummies thread, all i see is that it executes 2-3 cycles of on-off control for the auto-tune feture. This, to me, doesn't necessarily say it starts in ON and overshoots. The first step in its algorithm could be to turn (or leave) the element off and see what happens. You may have more detailed information.

DTV said:

I guess long story short, I was trying to use auto-tune to let the PID learn my system so that I can use automatic mode and have it work correctly. I hope that makes sense?

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Yes, it makes sense, I guess I'm just not sure that isn't exactly what it was trying to do. That said, trying to accomplish an autotune and a successful mash at the same time could provide some challenges, since you will guaratneedly have temp fluctuations. Maybe next time, once you're done mashing, fill it back up with water and let it autotune on spent grain.

BrewKnurd said:

From looking at the manual for the 4342, which is what was referenced in teh RIMS for dummies thread, all i see is that it executes 2-3 cycles of on-off control for the auto-tune feture. This, to me, doesn't necessarily say it starts in ON and overshoots. The first step in its algorithm could be to turn (or leave) the element off and see what happens. You may have more detailed information.



Yes, it makes sense, I guess I'm just not sure that isn't exactly what it was trying to do. That said, trying to accomplish an autotune and a successful mash at the same time could provide some challenges, since you will guaratneedly have temp fluctuations. Maybe next time, once you're done mashing, fill it back up with water and let it autotune on spent grain.

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Thanks for the reply. Yea, I knew trying to autotune during a mash wasn't the best idea, but I figured it wasn't any worse than my direct-fired RIMs system which was always all over the place on temps. This is what it says on the manual for 2362:

6. Auto-Tuning
The Auto-tuning function (also called self tuning) can automatically optimize
the PID parameters for the system. The auto-tuning function will use the On/
off mode to heat up the system until it passes the set point. Then let it cool
down. It will repeat this about three times. Based on the response time of thesystem, the built-in artificial intelligence program will calculate and set the PID parameters for the controller. If your system has a very slow response, the auto-tuning could take a long time.

Maybe I just need to do what you recommend, do the auto-tune on spent grains. Just odd since the 2 times it went through the auto-tune it never overshot the set point, and always dropped in temps.

DTV said:

Thanks for the reply. Yea, I knew trying to autotune during a mash wasn't the best idea, but I figured it wasn't any worse than my direct-fired RIMs system which was always all over the place on temps. This is what it says on the manual for 2362:

6. Auto-Tuning
The Auto-tuning function (also called self tuning) can automatically optimize
the PID parameters for the system. The auto-tuning function will use the On/
off mode to heat up the system until it passes the set point. Then let it cool
down. It will repeat this about three times. Based on the response time of thesystem, the built-in artificial intelligence program will calculate and set the PID parameters for the controller. If your system has a very slow response, the auto-tuning could take a long time.

Maybe I just need to do what you recommend, do the auto-tune on spent grains. Just odd since the 2 times it went through the auto-tune it never overshot the set point, and always dropped in temps.

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HA! I just noticed that you mentioned the model number in your second post. Oops.

One section i noticed in your manual:

Note 4. The autotune offset will shift the SV value down by the Atdu value
during the autotune process. That will prevent the system from damage due
to overheating during the autotune.

Dunno what your Atdu value is set to, but sounds like the controller might atuomatically drop the setpoint when it goes into auto-tune.

Oh, just found that Atdu defaults to 10. So its going to drop your setpoint by 10 at the start of auto-tune. I'm guessing that's your problem.

BrewKnurd said:

HA! I just noticed that you mentioned the model number in your second post. Oops.

One section i noticed in your manual:

Note 4. The autotune offset will shift the SV value down by the Atdu value
during the autotune process. That will prevent the system from damage due
to overheating during the autotune.

Dunno what your Atdu value is set to, but sounds like the controller might atuomatically drop the setpoint when it goes into auto-tune.

Click to expand...

Damn, maybe that was it then! Wish a) I knew what all these values were for and how they work so that b) I could understand the manual better when I read it. That must/may be it then. Guess I'll have to try auto-tuning again and not freak out when I see the temperature drop a lot. Thanks so much for your help.

Probably a stupid question but if I auto-tuned with just water instead of wort, would that be a huge difference in parameter settings? I just ideally want to have the PID tuned before my next batch of beer. I guess worst case I could auto-tune w/ water first, brew a batch, and then auto-tune again w/ the spent grain?

DTV said:

Probably a stupid question but if I auto-tuned with just water instead of wort, would that be a huge difference in parameter settings? I just ideally want to have the PID tuned before my next batch of beer. I guess worst case I could auto-tune w/ water first, brew a batch, and then auto-tune again w/ the spent grain?

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I think you'd be fine using water for an initial auto tune.

Auto-tune with water only. Start the process with your initial water temperature about 10° lower than your target temperature. This will allow the PID enough differential to accomplish a proper Auto-tune. If the initial temp is very close to the target temp, it is possible that it will not complete properly. Next thing is to give it the time it needs to complete the Auto-tune.

Hope this helps you.

P-J said:

Auto-tune with water only. Start the process with your initial water temperature about 10° lower than your target temperature. This will allow the PID enough differential to accomplish a proper Auto-tune. If the initial temp is very close to the target temp, it is possible that it will not complete properly. Next thing is to give it the time it needs to complete the Auto-tune.

Hope this helps you.

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Thanks for the help!

One thing worth mentioning is the flow of wort/water through your system while autotuning. The flow out of your pump should be very similar to that of what you'll have on brew day. Keeping that variable under control while autotuning will result in the PID knowing how much heat your system can put into a given volume over time on a real brew day.