DBS Temp Swing Test

[Mr Walleye]

I had nothing to do this morning so I sat down with a pot of coffee for a few hours and did some testing on the DBS temp swing issue.

Here's my test criteria:
-   DBS with circulation fan running. (no PID running)
-   Tower had the water bowl (full of hot water) in it and all 12 racks that I have.
-   Suspended the ET73 at the same height as the factory TC but horizontally in the centre of the tower.
-   Vent half open.
-   Target temp 200 F.
-   Running both the main tower heater and the smoke generator (SG).

Here's my test data:
-   When I turned everything on the temp was at 64 degrees.
-   During warm up the ET73 read constantly 20 degrees higher than the SG display.
-   ET73 hit 200 degrees in 21 minutes and SG display was at 180.
-   SG display hit 200 degrees and ET73 was at 220.
-   SG hit 200 degrees I could hear the tower element cut out.
-   SG continued to climb to 207 degrees before ET73 began to drop. ET73 was at 225 degrees.
-   As the temps dropped they were the same at 203 degrees.
-   ET73 hit 200 degrees coming down and the SG display was at 203 degrees.
-   SG display hit 200 degrees coming down and the ET73 was at 192 degrees.
-   As soon as the SG display changed from 190 to 189 degrees you could hear the tower element cut in. The ET 73 was at 176 degrees.
-   SG display dropped to 187 degrees before beginning to rise.
-   ET73 dropped to 176 degrees before beginning to rise.
-   Both ET73 and SG display were equal at 191 degrees while the temp was rising.
-   ET 73 hit 200 degrees and SG display shows 196.
-   SG display at 200 degrees I could hear the tower element cut out.
-   1 hour point of testing.
-   SG display continued to rise to 205 degrees and ET73 showed 218 before it started to drop.
-   As the temps dropped they were the same at 203 degrees.
-   ET73 hit 200 degrees coming down and the SG display was at 203 degrees.
-   SG display hit 200 degrees coming down and the ET73 was at 192 degrees.
-   As soon as the SG display changed from 190 to 189 degrees you could hear the tower element cut in. The ET 73 was at 176 degrees.
-   SG display dropped to 187 degrees before beginning to rise.
-   ET73 dropped to 176 degrees before beginning to rise.
-   Both ET73 and SG display were equal at 191 degrees while the temp was rising.
-   ET 73 hit 200 degrees and SG display shows 196.
-   SG display hit 200 degrees I could hear the tower element cut out.
-   SG display continued to rise to 205 degrees and ET73 showed 217 before it started to drop.
-   As the temps dropped they were the same at 203 degrees.
-   ET73 hit 200 degrees coming down and the SG display was at 203 degrees.
-   SG display hit 200 degrees coming down and the ET73 was at 192 degrees.
-   As soon as the SG display changed from 190 to 189 degrees you could hear the tower element cut in. The ET 73 was at 176 degrees.

Thinking Through The Data
During the test the temp swing of the SG display was 187 degrees to 205 degrees. The temp swing displayed by the ET73 was 176 degrees to 218 degrees. Also during the test it came to mind that the temp I was measuring on the ET73 was the air temp at the same level as the factory TC mounted in the back of the cabinet and the temp that the factory TC was measuring was the temp of the metal in the back of the cabinet. Clearly the DBS was designed to shut off the heating element in the tower once it reaches the target temp. Also, it allowed the temp to drop exactly 10 degrees during the test before it cuts back in. Something I think this clearly demonstrates is the factory TC is mounted in the rear of the cabinet and either shouldn't be in the cabinet or it should have some type of insulator between it and the cabinet. If this was the case the temp swing would be less and the unit would be much more responsive. If you study the data you can clearly see that the air temp rises and falls more rapidly than the metal in the back of the cabinet. That's why the SG display temp appears to trail the ET73 temp regardless of rising or falling. The surrounding metal around the factory TC in the back of the cabinet is acting as a heat sink. The only difference in the data was during the warm up. The differential during warm up could be explained because the metal of the cabinet took longer to warm up than the air temp did.

A few things I learned from this.
-   The DBS is really quite constant and fairly accurate.
-   The DBS should really be monitoring the internal air temp as opposed to the temp of the metal in the back of the cabinet.
-   When I install my TC for my PID I will make sure it is not mounted to the cabinet unless through an insulated thimble. This way it won't be influenced by the heat sink effect of the metal cabinet.

Although I did this test with the DBS more of less empty I feel the data was fairly consistent. If you had a load of meat in it I think it would be fairly similar with the exception of taking longer for temps to change. This longer time frame may effect the over run and under run temps slightly.

Mike

[Consiglieri]

Thanks for running this test.  Over the last 18 hours or so I've been wondering how accurate the temp readings were.  I've had some butt in there since 6pm last night (cooking at 210 dbs setting) and neither piece is over yet.  Was getting concerned that the cabinet temp reading was incorrectly high due to insufficient sampling.  Instead simply sounds like I'm getting hungry (and impatient).  Time to start getting ready for the game. 

Cheers and thanks for posting your work, both on the PID and the temp sampling. 

[West Coast Kansan]

Mr. Walleye, That sounded like a 6 beer test and report. :D :D Your conclusion is the same as mine. :o  A while ago I messed around with a wood thimble and Silicone to create the space between the walls and probe mounted across the thimble.  I like your test criteria - it is repeatable. 

The world changes somewhat with an 8 pound butt however - the mind twisting I think has the same causes but blurs over time.  The butt initially is going to be cool and help keep the tower air temp cool. However, as it cooks and IT increases it 'sinks more toward the other direction and helps dampen the fluctuations.  :o ::) ??? - Or so it seems.  My kid tells me after 4 hours your at the cook point on an 8 pound butt and the temp swings become irrelevant for the balance of the cook.  That seems to be true. --- thankfully...

[Mr Walleye]

I think the biggest thing I learned is that the DBS could be much more accurate if it simply had the TC located in such a fashion as not to be influenced by the metal cabinet.

Mike

[West Coast Kansan]

Would probably not be a first choice to locate it in direct contact with the back or immediately above the heat element with the reflector focused in combination with the V pan on the back wall.

Hard to beat the idea of driving temperature based on cook area of the meat.  You will have this solved in a short time though...

Your point and test is a good one on the consistency factor as well.

Take care,

[Oldman]

wow interesting reading for sure....for whatever it is worth in my std bradly with the fan with no PID controller I'm 2 degrees up and down top to bottom empty box. It take me about one hour to balance the box  on average so that I can just walk away from it. Do go out every 3 - 4 hours to look at it. I would do that even if I had a PID controller.

[Mr Walleye]

I would do that even if I had a PID controller.

I think it's mandatory isn't it Olds?

::)  ::)  ::)

Mike

[Arcs_n_Sparks]

Even though I have a PID, I tell my wife I have to check it all the time. No coincidence I pass the adult beverage refrigerator in the garage each trip.

Arcs_n_Sparks

[MWS]

wow interesting reading for sure....for whatever it is worth in my std bradly with the fan with no PID controller I'm 2 degrees up and down top to bottom empty box. It take me about one hour to balance the box  on average so that I can just walk away from it. Do go out every 3 - 4 hours to look at it. I would do that even if I had a PID controller.

I have to say....I'm not sure about all the PID fuss. Like Olds, I spend an hour balancing the box and then walk away with a constant temp betwen 5 degrees either way. Did a 12 hour pork butt today and the temp stayed at 215 constant through the afternoon with the OBS.

[Mr Walleye]

Hi Mike.... Nice name by the way!  ;D

I can't speak for anybody else but I personally can never leave good enough alone. You know what they say... good enough never is.  ;D Seriously though I agree with you, you can produce some really good eats with both the OBS and the DBS without any modifications.

It's probably some deep rooted issue I have.  ;D  ;D  ;D

Mike

[nodak]

For me the PID is a must convenience with my air temp variance and cold weather temp and wind it's a must for me on unattended smokes and overnights.

my 2 cents.

nodak

[MWS]

Where are my manners.....what I should of said is....Thanks Mr. Walleye (Mike) for the test you did (on a Sunday morning yet). The great thing about this forum is the sharing of information and expertise. The PID has always intrigued me but so far I have yet to find the need. Maybe it's the milder west coast climate that keeps the temps constant  ;) Again... your contibutions are very much appreciated.

Cheers and Rauch those Beers....

[nodak]

yes that MIKE name is a great one indeed! ;)

[Mr Walleye]

Don't tell me we flopped a set!

A little poker humour

Mike

[West Coast Kansan]

Not to be confused with necessity - all this PID temp - fan stuff.  What else is there to do with a bradly.  Dont have any bottom corners rusting out and hardware to reweld, dont even have broken hinges or steel that is warped and don't seal anymore with the bradley.

So what ya gonna do  ??? Gotta play with something and if it gets better thats good and if it don't that's entertainment.  ;) 8) :D