Need everyones help on a PID problem

[Arcs_n_Sparks]

I am begining to think that as the meat temp rises, the autotune needs to be re-done.

I am beginning to think that you are at a point in the control looping tuning where a beverage needs to be re-done.   :D :D :D

Arcs_n_Sparks

[Wildcat]

 ;D ;D If it were not so late I would do so.  The autotune was holding within 2 degrees either side of set temp for a good while.  It is now 3 degrees either side.  If this will continue to hold then I think I will take a few naps during the night.  Got the Maverick alarms set.

If the temp swings remain stable, then my new numbers are:
P = 304
I = 88
D = 67

[Wildcat]

Temp swings went back to 2 degrees either side of set temp and stayed there.  Now if it will do likewise on the next smoke I should be good to go.

[Tiny Tim]

Just food for thought here, but when you did the first autotune on this particular project, was the meat just put in or was it in for a while to get some heat into the mass of meat?

I'm thinking that if the meat is cold (or room temp), and the PID learns to control the heat in that environment, that it's not going to be quite as accurate when the meat would get to the higher temps, and conversely, if the meat was almost done when autotuning, that it won't be quite as accurate when the meat is at the lower temps.

I could be way off on my thoughts though.

[Wildcat]

Makes sense Tiny.  I did the first autotune after the meat reached about 100 degrees.  I did the final autotune while the meat was in the plateau (160 - 170 range).  I do not think I will have to autotune anymore.  Still do not understand why the difference in the Maverick and PID cabinet temp kept changing.  I plan to put new batteries in the Maverick and do another boiling water test on it before the next smoke.  I may have to invest in a thermo set.

[Mr Walleye]

Wildcat

I agree with Tiny's thoughts on the cold meat theory. With regards to your temp variations between the Maverick and the PID I have noticed that when sitting and watching as the heat cutts in the temp display on my Maverick will climb quicker, then when the heater is off the Maverick will tend to drop quicker. It would appear as though the Maverick is more sensitive to the small changes. In my setup now my PID pretty much stays within 1 degree of it's set temp. My Maverick will vary a couple of degrees higher or lower depending on the cycle of the heater. Keep in mind I have my circulation fan blowing back to front no as well.

Mike

[Wildcat]

My PID is holding pretty steady at +/- 1 degree.  There is one thing that has me puzzled.  My Maverick is off by 1 degree on the boiling water test.  I replaced all batteries.  Started smoking today and adjusted the Pb on the PID to match the Maverick.  After 4 hours the Maverick started showing a box temp 6 degrees higher than the PID.  This happened on my last smoke also.  If it does like last time, by the time the meat hits its stall period it will be off another 4 or 5 degrees.  After that it will remain the same.  I am not referring to a fluctuation, but rather a constant difference.  Last time I simply adjusted the Pb setting to match and will probably do the same this time.  Is this indicative of something not right with the PID  (settings, probe, or unit) or the Maverick.

[Arcs_n_Sparks]

I am begining to think that as the meat temp rises, the autotune needs to be re-done.

I am beginning to think that you are at a point in the control looping tuning where a beverage needs to be re-done.   :D :D :D

Arcs_n_Sparks

I think my theory still applies.    :D

[Wildcat]

Then I guess that I can assume there is no answer.  I will search elsewhere.  Beverage cooler here I come.

[Arcs_n_Sparks]

Wildcat,

Your boiling water test is good at one point. Not clear how accurate it is over span. Are the probes right next to each other?

This reminds me of the "clock" problem; trying to get clocks to all read the same over time. Turns out a collection of clocks, averaged out, is more accurate than any single clock in the collection.

Given variables and not knowing how accurate each of the tempeature measuring systems are, getting them within a few degrees over span would be pretty good in my view.

Arcs_n_Sparks

[Wildcat]

Arcs,

Yes, the probes are right next to each other and not touching.

I understand what you said regarding the clocks.  Averaging from multiple sources does give one a relatively accurate picture.

The few degrees you mention in my case is simply too large of a spread.  The PID is working great at keeping the set temperature.  My problem at this point is not maintaining a constant temperature, but rather not knowing what that temperature really is.  The Maverick starts out reading a certain temp.  I set the PID to match.  By the end of the smoke, if I let the PID alone, the Maverick temp reading will be between 10 and 15 degrees higher than the PID.  This is not a fluctuating reading, but rather an averaged constant.

In other words and as an example, say I want to smoke/cook at around 200 (give or take a couple of degrees) for butts, but am unsure if I am at 185 or 215 or somewhere in between.

I am trying to figure out if my Maverick needs to be replaced or if the PID has a problem in dealing with being manually calibrated.  The PID seems to be functioning perfectly in all other aspects.  I suspect it is the Maverick.  I was hoping someone else would have some thoughts on the subject.  I apologize if folks are irritated or simply tired of this particular thread (or me for that matter).  If this is the case just say enough is enough and I will stop with no hard feelings and will simply find another source or wing it and start making some more purchases.

[Arcs_n_Sparks]

By the end of the smoke, if I let the PID alone, the Maverick temp reading will be between 10 and 15 degrees higher than the PID.

Was under the impression you were <5 degrees off between the two. 10-15 is more than one would expect. Perhaps the integration error in the PID is growing too large (not likely)? May want to experiment with the "I" term.

Regarding the Maverick, I have another wireless temperture system that I use to compare with my Maverick (yes, adding clocks!). Have not had a problem.

Arcs_n_Sparks

[West Coast Kansan]

I got this DBS unit and it has fluctuations once set point is reached the first time.  This is a strategic feature included in the DBS to facilitate a controlled breakdown of connective tissue. You want an intermittant break down because it allows the fibers of the meat to recover and reabsorb as the geletin begins to move.  It will then rest some and then move again.  This has been the temperture sequence employed by championship bbq winners for decades now.  Only the DBS has the controls that will accurately mimic the temperatures used by purist smokers everywhere for as long as anyone remembers. Why else would you also incorporate a design where the temperature fluctuations decrease as the meat approachs set point. It is ONLY with the DBS that you can get the cake and eat it too.

The application of a steady heat such as with a PID defeats the intermittant break down of the tissue described above and should not be pursued.

Actually I have no clue what I am saying but it sounded good to me.

However, then again it may have just been a real dumb ass mistake to call something digital and put a profoundly stupid control scheme into the unit....

Personally I would like to think it was a purposeful design and that someone at Bradley would have resisted the group brain flushing and said like == excuse me, but that aint digital ==

::)  ::)  ::) So there is my story and I am sticking with it.  ;D  ;D  ;D

Dont be frustrated Cat, we are all making some pretty good BBQ and it sure is a lot easier than burning our fingers on those hot iron, temp fluctuating, ash makers that traditionalists use.  Give me an ez bake oven any time.  ;)  ;)  ;)

[Arcs_n_Sparks]

I am, drinking, at a distance............   :D :D :D

[Gizmo]

Wildcat,
The only thing I could add to possible help is to check out the new Thermapen device that has been recently posted on a new thread.  If you don't mind spending some more cash, the Thermapen's have a calibrated temp probe and I would trust is explicitly and adjust all other devices to what it reads.  With the wired probed that was shown, you could probe the meat (or water, or what ever) and keep it in the whole time.  At least that is what I am guessing since I don't have one of the new ones.  I have the older model that is hand held with probe attached.