PID AUTO TUNE HELP

[HJL]

I built a pid using Rob's instructions. Used a Auber PID, SSR and the recommended Omega TC recommended on this site. Used it for the first time yesterday to make summer sausage. I did the auto tune using 160 as the set value. When I smoke sausage I start at 120 degrees and gradually increase the temp to 160 until I get an internal temp of 155 degrees.
My question is do I need to auto tune everytime I set a different temp? I auto tuned  at 160 degrees. When I started out I set the temp at 120 and the Temp overshot to 128 to 135 degrees and bounced back and forth between 128 and 135. I had the same problem each time I increased the temp.
Can someone advise about the auto tune.

[Tiny Tim]

I guess I don't completely understand your problem, but, here are some questions to help me out.  The 128-135 readings that you are stating, are they taken by the PID or by a different thermometer at possibly a different level in the cabinet?  Did the temp ever go under the 120 set point?  Did you do the autotune with a load in the smoker, and wait for the autotune to be completed (sometimes an hour or more)?

One thing I can tell you...depending on your ambient temperature, the cabinet can get to 150 easily with only the bisquette burner on, unless you're using an offset box/dryer hose setup.

[Scotty-G]

My PID is using Auberman's T/C Probe (should probably upgrade to the Omega) but I've noticed that at temps below 160 I have to slide the temp contol knob at the bottom of the cabinet to the middle otherwise temp control at such a low temp is difficult.  160 - 180 I have to slide to about 3/4.  180 and above, all the way to the right.

[Gizmo]

HJL,
When you ran your auto tune, did you have a simulated load in the BS?  Was the puck burner on or off?  These factors and others can affect the accuracy of control.  The closer your auto tune simulation environment is to what you will actually be doing, the more stable and accurate your results and future uses will be.

[HJL]

I did the auto tune with 4 bricks in the smoker. The temperature never went below 120. I waited for the auto tune to finish. It took about 45 minutes. The temperature of 128-135 temp reading was from the pid. The outside temperature was around 30 degrees. we had a cold spell. I did the auto tune several days earlier when it was in the 50's.
I can see how the smoker generator would affect the pid at lower temperatures. This may have been my problem. I usually, do my smoking the first 4 hours at a lower temp. Maybe, I should turn the smoke generator off for the first 4 hours when I have lower temp settings and wait to apply smoke at the higher settings. However, I dont know how applying smoke at higher temps would affect the taste/flavor of the sausage.

[Mr Walleye]

HJL

I tuned mine several times. Each time I did it I got it a little closer. I did my final tune when I had a butt in the tower. I was about 2 hours into the 4 hour smoke portion with the temp set at 210 degrees I thought what the he11 and hit the autotune. It ran through its tuning cycle and it's been pretty much perfect ever since. Recently while doing sausage at lower temps it over shot by about 3 degrees initially but soon corrected itself. I have had no problem maintaining temps for jerky either. The other thing I did was after every auto tune I would look up the P, I & D numbers and write them down along with a brief description of how it worked at those settings. That way if I was going to tweak settings at any given point I would have these numbers to work with.

Mike

[Tiny Tim]

I would suggest instead of doing the low temp cook before smoking, to rig up an offset box to hold the smoke generator, and use a dryer vent hose to get the smoke into the tower and smoke from the beginning.  The box will contain a lot of the heat, allowing mostly just the smoke to go into the tower, keeping your temp lower.

The reason I wouldn't wait until later in the cook, is because it's mentioned on here that meats tend to quit absorbing the smoke around 140*...don't know if that's internal temp or external temp though.

[pensrock]

Mike,
  When using an autotune feature in a PID controller, what you did is the best way to get a good set of PID's. When I'm tuning one of our industrial furnaces and using the autotune, it is not uncommon for me to run an autotune 3,4 or even 5 times till it begins to control close to what I expect. Then I do some fine tuning on my own. Granted our equipment normally runs at temperatures up from 1400 to 2800 degrees F, but the principle is still the same. If you are controlling withen a couple degrees, great job! Do not be upset if you run a smaller load or a lower temp and see some overshoot and undershoot, the instrument will make the corrections and after a couple high/low osolations it should find the correct temperature.

[Arcs_n_Sparks]

The other thing I did was after every auto tune I would look up the P, I & D numbers and write them down along with a brief description of how it worked at those settings. That way if I was going to tweak settings at any given point I would have these numbers to work with.

I think you guys with the Auber should be sharing your P, I, & D parameters. The thermal variables on the BS are modest, and a good set of numbers should cover most smokes with confidence.

Arcs_n_Sparks

[Mr Walleye]

Here's my Auber numbers

P=400
I=225
D=225

Not sure if it makes a difference or not but I have the Omega TC, circulation fan and it's in a heated garage.

Mike

[Arcs_n_Sparks]

Great start...

The TC makes no difference. The fan should have a small influence.

The big factors will be vent control, food load in the BS (or bricks), and outside temperature (delta T: inside box to outside box).

Of course, peeking does not help the thermal management challenge, and can dump a lot of heat :D

For those that post their Auber settings, I will build a spreadsheet and post for the members here.

Sparkler

[Mr Walleye]

Arcs

That's a great idea! It will be interesting to see for sure.

Post them numbers guys!

Mike

[Tiny Tim]

I will as soon as I can retrieve it for my next use...possibly this weekend.

[Tiny Tim]

Well, here's my numbers:

P=400
I=1583
D=28

Thermocouple is an Omega 6" Stainless probe, 8' wires; No Circulation fan; was autotuned in the summer inside the storage shed I keep it in, while doing a butt.

I don't sit and watch it, but when I go check on things, the temp reading is usually right on the set point.

[Arcs_n_Sparks]

Tiny Tim,

Are you using the Auber?