Auto Tuning a PID

[Frymn1969]

Hey All-

Please help!!

I'm looking to auto tune a PID without fuzz logic. I'm running a 120v 15amp 1800watt RIMS system that I'm using to maintain mash temp (raise maybe 5 degrees then hold) and then mash out (15-20 degree rise). I'm using a 10 gallon igloo cooler and have a few questions about how to proceed with the auto tuning.

1. Process - which should I simulate for the auto tune? Mash hold, or, mash out? (I'm leaning towards mash out since it has the biggest swing).

2. Environment - should I just use an approximate volume of water for my average mash? Or should I simulate having grain (if so any ideas what to use short of milled grain) so the flow represent what the recirculating mash will be like?

3. PID starting point - should I start with the default settings? Or should I crank up the P until I get the gain response (oscillation) I'm looking for, zero out the I and D, then run the auto tune?

Moderate speed in gain with accurate hold of mash temp is what I'm looking for.

Thanks
Todd


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[mkirkland]

I am almost done with my RIMS build as well so im curious as to this autotune procedure

 

[Minbari]

not sure this will be alto of help, but this is a great little tool for getting an idea of what a PID does. might get you close enough that you dont need to autotune

PID assist

 

[Frymn1969]

Thanks, I'll try opening this later. Won't open on my iPhone


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[Frymn1969]

not sure this will be alto of help, but this is a great little tool for getting an idea of what a PID does. might get you close enough that you dont need to autotune

PID assist

Sorry but the exe file contains a program that has no directions and looks very complicated. No offense, but its as if you answered an Algebra question, with a quantum physics question.

 

[ajdelange]

1. Process - which should I simulate for the auto tune? Mash hold, or, mash out? (I'm leaning towards mash out since it has the biggest swing).

You should simulate the one you want to control. Each situation (temperature, grain mass, grain to water ratio) has its own tune set. Fancy controllers store several so that you can pick the one for dough-in, the one for ramp up, the one for mash-out etc.

2. Environment - should I just use an approximate volume of water for my average mash? Or should I simulate having grain (if so any ideas what to use short of milled grain) so the flow represent what the recirculating mash will be like?

Same answer as for 1. To get an applicable tune set you must duplicate the load conditions for which the tune set it sought.

3. PID starting point - should I start with the default settings? Or should I crank up the P until I get the gain response (oscillation) I'm looking for, zero out the I and D, then run the auto tune?

That I don't know. I would depend on the controllers algorithm. Most will start from the SP, apply heat until a temperature is above that by a certain amount and then shut the heat off watching as the load cools to a certain amount below the SP. The controller determines P, I and D from that data.

Moderate speed in gain with accurate hold of mash temp is what I'm looking for.

That's what we are all looking for - boxcar response - but that's not what you are going to get. You can set things up for slow response which results in it taking forever to reach SP but there will be no overshoot or for rapid response with lots of overshoot and then you can try to deal with the overshoot by tweaking D. Settin these things up is an art!

 

[ajdelange]

Duplicate post. Used to be able to delete but can't seem to find that button any more.

 

[Minbari]

Sorry but the exe file contains a program that has no directions and looks very complicated. No offense, but its as if you answered an Algebra question, with a quantum physics question.

its not as complicated as you might think. only thing you really want to worry about is diff and int anyway. unless you know exactly what those settings are going to do in your PID, having a visual of how changing D from 4 to 5 will effect it is helpful.

set the output to "1" for digital

here is tutorial if you want to see how to set it up. otherwise just use auto-tune and hope it does what you want.

http://www.splatco.com/skb/2637.htm