PID Autotune not keeping temp?

[DrunkenMick]

I got my PID all hooked up and did a test run today.  I loaded up with a few bricks wrapped in foil (Shhh stole the bricks from my neighbors yard). 

Got the temp up to about 220 and ran the auto tune (SV was at 205).  Auto tune took like an hour or so (wasn't watching) and when i checked again the temp reading on the PID was 218.  I thought this was odd so i ran auto tune again.  Same results.  I didn't check my values but why isn't the auto tune keeping the temp stable?

Any ideas of what to try? 

[Mr Walleye]

Mick

I'm assuming you have one of the Auber Plug n Play units.

Does it stay at 218 or is it overshooting that much and then cooling down to your set temp?

Did you try using it right out of the box and what were the results? A number of people have no problem runing them this way.

Usually the manual will give you all the default settings and you can manually set them back if you choose. I usually put an average size load such as a pork butt in the smoker to set mine. I wait until I'm within about 7 degrees of the set temp before I engage the autotune.

Mike

[DrunkenMick]

Mike

No i bought basically followed the instructions here http://www.susanminor.org/forums/showthread.php?t=315 to the letter and built my own.

During the autotune i did see it overshoot and undershoot when i sat and watched it a bit.  Just after the autotune and letting it sit i saw it swing 8-9 degrees in either direction.  Just seemed to not want to hold the temp i had set.

[Mr Walleye]

Mick

When running autotune it basically will intentionally over shoot and under shoot 3 times. That is how it calculates how much heat to apply to maintain the set point. I wonder if it has more to do with the type of load (bricks). I wonder if the bricks finally got up to that temp during the process. Some people have used a good sized bowl with sand in it and water poured into the sand. It creates a heat sink similar to a good sized piece of meat.

Another thing I would do is everytime you run the autotune write the numbers down. That way you can manually go back to them if you choose to. There's no question you will get it dialled in tighter than that.

When I have done mine I load the smoker, typically have the setpoint at 200, allow the temp to rise to about 193 degrees, then turn on the auto tune. It will over shoot and under shoot approximately 3 times before it gets itself dialed in.

Mike

[love the smoke]

Mr Eye

What sequence of buttons do you push on the PID controller to put it into auto tune mode

Randy

[Mr Walleye]

LTS

To start you want to have your load in the tower and have the temp within 10 degrees of your set point.
I usually use the setting of At=2. To get there you push and hold the set buttom (bottom left) until it goes into it's programing mode. Then you keep pushing the set button to step through the menu until you get to "At=3". Once you are there you just use the down arrow button to change the 3 to a 2, then just leave it alone. It will automatically come out of it's programing mode on it's own, then 10 seconds later the Autotune feature will also start on it's own. Once the auto tune is complete it automatically switches the the autotune feature back to At=3.

Here is a quote from the Auber Manual...

6.3 Fuzzy Logic enhanced PID control and auto tuning
For the first time user, it is a good idea to use the auto tuning feature to let the controller automatically determine the PID constants. The auto-tune can be started in two ways. 1) set the At=2. It will start automatically after 10 seconds. 2) Set At=1. Then you can start the auto-tune any time during the normal operation by pressing the A/M key. During auto tuning, the instrument executes on-off control. After 2-3 times on-off action, the microprocessor in the instrument will analyze the period, amplitude, waveform of the oscillation generated by the on-off control, and calculate the optimal control parameter value. The instrument begins to perform accurate artificial intelligence control after auto tuning is finished. If you want to exit from auto tuning mode, press and hold the (A/M) key for about 2 seconds until the blinking of "At" symbol is stopped in the lower display window. Generally it will meet you need to perform auto tuning one time only. After the auto tuning is finished. The instrument will set parameter "At" to 3, which will disable triggering of auto-tuning with the (A/M) key. This will prevent an accidental repeat of the auto-tuning process.

Mike