Will a PID help narrow the differences in temp at different areas in my Bradley

[canyonman]

Hey everybody!  I spent allot of time with my BDS today getting the average temp at different areas.  First I have a BDS 4 rack.  I have added an additional 500 wat heating element - the same as the original and right next to it like the mod described elsewhere on this forum.  I pre heated my BDS until it got to 230* prior to the test ~ 30 minutes.  I also have a 13 by 9" cake pan in the bottom.  I have covered ~ 2/3rds of the back half of the heat shield with HD foil.  I found that this foil helps keep the meat that is at the back of the smoker from getting to crispy/burnt/dried out.   For this test I had both the oven and the smoke generator on.  The oven temp was set at 220 (still waiting for my PID - Dual probe).  The cake pan was filled with boiling water and the vent was at half open.  I also put two foil wrapped bricks (simulated load) on the middle shelf (3rd from the top).  I tested my Maverick with boiling water to ensure it was accurate just prior to the test.  During each test I had both Maverick probes working at the same time and ran each temp check for ~ 1 hr.  The probes where hung 1/2" below each shelf for all tests.  The first hour I had a probe just below the top shelf and the 2nd probe just below the bottom shelf.  The second hour I had the 1st probe just below the second shelf from the top and the third probe just below the third shelf from the top.  When I started the second hour of testing on the middle shelves it occurred to me that I might of been getting a big difference in temps because one probe was directly below the two foil covered bricks and the other was over the top of them.  I thought some heat might of been radiating back at the probe below the bricks so I moved one brick directly above the probe that was on the second shelf from the top and that seemed to narrow the gap between the two.  For the front and back temps I just hung both probes using the shelves to hang them from and I positioned one probe 1" form the back wall and the other probe 1" from the front wall at about the mid line from top to bottom.  So here is what I got.  Remember oven was set at 220* for all tests.
               Top shelf  -  213* average over 1hr
Second shelf from top - 223* average over 1hr
   Third shelf from top - 228* average over 1hr
            Bottom shelf - 232* average over 1 hr
Looking at what I got for numbers I figure the bottom shelf is ~ 20* hotter on average then the top shelf.

The average temp at the back of the smoker was 248* average over 1 hr
The average temp at the front of the smoker was 226* average over 1 hr
Looking at these numbers I figure the back of the smoker is ~20* hotter then the front on average.

Now I was smoking a cigar and drinking a beer when this all took place so I did get into some deep thoughts.  One of which some of you guys with PIDs might be able to answer.  If a PID keeps the temp at a more constant level wouldn't this help to narrow the difference in temps at different places in the smoker?  As I was watching the temps the gap would increase when the heat was on but it would narrow or even equal out when the heat was off and that is what got me thinking about it.  I know even with a PID there will be different temps in different places but I was just curious if it helped narrow the gaps.  2nd question should I get the wall mount temp probe with the PID or should I get the free hanging one.  I'm kinda hedging toward the free hanging one because I can put it directly below what ever I am cooking.  This would ensure the heat the meat would be getting was pretty close to what the PID is set at?  Then I thought, if I did mount it on the back wall I could just do the temperature test I did above and adjust accordingly.  What do you all think?  3rd and final question for now, When I auto tune the PID do I do that with the SG on or off.  Dose it matter?  Do I have to auto-tune every time since my loads will likely be different?  Ok, I slipped one more question in but I had to ask.  Thanks in advance for all your replies.

[classicrockgriller]

The PID won't even out your temps in the Cabinet, it will help keep the temp constant at the place the probe is set.

What will help "even" out your temps is a fan kit.

I personaly kinda like having the probe in hand, not fixed. Not saying it is gospel, just saying what I like.

The Auber is set for the Bradley, But if you need to run auto-tune, you don't have to run it everytime.

When I did auto on mine it was during a long smoke after the SG was off, but don't know for sure it matters.

I just read back that you have duel elements, I would run an auto tune on the next smoke.

[canyonman]

Thanks CRG.  I just saw  :o your new and might I add beautiful smoker.  I am truly jealous!  Green with envy!  I want it, I want it, I want it!  The fan kit is my next project.  I just have to space things out other wise the war department gets angry.  Looking forward to you future posts.

[FLBentRider]

I move my PID probe around.

[Toker]

Me i would run auto-tune at every time i judge it necessary but it is just me. I say so because every loads are different and have different weight. Example, once you smoke with only one rack of food, your pid will be calibrate for it but the next time, if you smoke with an heavier load the pid (i think) won't give you the same result. Like i said it is just a thought, if you feel it is OK enough for you then just don't do it again.

[pensrock]

IMHO If tuned properly you should not have to retune unless there is a major change, such as adding another heating element, maybe adding a fan. I have not touched my PID setting since I put it together. And there are times when I only have a couple pounds in there and other times when I have 25-30 pounds in. It works the same.

A temperature controller will not even out hot/cold spots in the tower, it will keep a closer range where the probe is placed. I keep mine in the middle of the tower. And if doing a smoke with several racks being used, I rotate top to bottom and front to back every hour to hour and a half. I like my thermocouple just under the food. So if I only have one rack of food, it goes in the middle. I know it will be a little warmer lower and cooler as you go up. That is why I rotate.

[OU812]

I have not re-tuned my PID sense I got it years ago. The fan or as in my case fan's do help with the hot spots. Mine are with in 9 deg top to bottom but still have a hot spot in the back left bottom corner. Good enough for me.

[Mr Walleye]

I agree with Pens and OU... once you get the PID dialled in it should work fine for varying loads and not require re-tuning.

As far as... will a PID help narrow the temp differences? I say yes to a certain extent. Your DBS controller is an on/off type. When it arrives at the set temp it shuts down power to the element. Then when it cools down below the set point it fires it back up. Because it is either full on or full off and takes time for cool down/heat up of the element, it magnifies your temp differences in various parts of the smoker, especially the hot spots.

The PID will mathematically calculate how to hold the set point that has been set. It will apply varying degrees of power in order to maintain the set point. By doing it this way it doesn't have the temp swings of an on/off type controller. This will help smooth out your temp spikes in the hot spots of the cabinet, it won't eliminate them but the temps will be consistent.

Mike

[canyonman]

Thanks Mike.  That's what i was thinking.  Since I would not have such big temp swings the temp in the entire cabinet would be more consistent.  I realize I will still have hot or cold spots but just to a lesser extent.  It sounds like most of the reply's have stated they like the temp probe that you can move around over the stationary one.  What are your thoughts on this? 

[Mr Walleye]

I have 3 different PIDs on smokers and all of them are probes that I can move around. Having said that, once you get an idea of where you want the probe on a regular basis I have built brackets to mount them, although they are really just a stainless clip so they are easy enough to re-position.

Mike

[Rich_91360]

Do you have a picture of the clip you are using / installed

[Mr Walleye]

Do you have a picture of the clip you are using / installed

Sorry Rich, I've been away for a few days.


Here is a picture of one that I built that mounts to the back of the cabinet. The TC just clips into it.




Here is one that clips to the bottom of a rack.



Mike

[Rich_91360]

Mr. Walleye,

Thanks for the pics. Can you advise where I can get the clip hat attaches to bottom of rack..  Seems this would work on several levels by testing front/back of rack to get difference , same for side to side.

Thanks again
Rich_91360

[classicrockgriller]

They send you one with your Auber and Suyi (from Auber) may sell you some more.

[Mr Walleye]

Mr. Walleye,

Thanks for the pics. Can you advise where I can get the clip hat attaches to bottom of rack..  Seems this would work on several levels by testing front/back of rack to get difference , same for side to side.

Thanks again
Rich_91360

Rich

I made this out of a piece of stainless trim for a GM truck. Really simple to cut out with a pare of snips. The Maverick ET73 comes with one that is very similar.

Mike