Temperature Variation Tollerance

[BuyLowSellHigh]

Put this in the "for what it's worth" (probably not much) box.

Did the seasoning thing today on my new 6-rack and decided to get some temp profiles as I did.  Set-up was simple, here goes.  Rack numbers are from bottom (1) to top (6).  Rack 1 and 6 contained a foil wrapped brick, 1 each.  Temp profile was 150 °F for 150 min (2.5 hrs) then 225 ° for another 150 min's.  Smoke generator was on for first 60 min's, then off until 160 min's total, then on again until 220 min's.  Oven temp was controlled via Auber dual probe PID controller with temp probe hanging between racks 3 & 4, the Tc position (midpoint of oven zone).  Additional Polder probes were on rack 2 (one up from bottom) and 5 (one below the top).  Temps were recorded periodically at intervals that depended upon the onset of a change in setting as well as stability.  Temps vs. time are graphed as shown below, the legend is as follows:
T Set = control setting
Tc = Auber actual reading at control point midway between racks 3 & 4
T2 = temp on rack 2 center
T5 = temp on rack 5 center
TB = temp shown by Bradley oven thermistor

Here's the graph, no real surprises base upon what I have read from the many experienced members here, but it helps me visualize what is going on inside.

[squirtthecat]

How did you create that graph??

[BuyLowSellHigh]

Excel

[squirtthecat]

Touché.   :D

By hand?  I mean, where did you get the times/temp logging points?  Also by hand?

[BuyLowSellHigh]

Logged the data by hand - only a few points well spaced.  In a former life it was different - 1000 x-y pairs or x-y-z triples every 0.5 sec's.  That WAS NOT by hand!!

[squirtthecat]

Ahh, Ok.   Very cool..

I thought you had a nifty logging thermometer that could upload to your PC.   8)

[BuyLowSellHigh]

I used to do that kind of thing - about 30 years ago.   It's not hard with the right interface and you can do it at a very high data rate.  But that's not needed here.  If I had the time and felt like wasting the money, about 30 points in the cabinet would allow me to develop a complete 3D thermal profile vs time and set point. If I used what I did 30 years ago, 30 measurements would take 15 milliseconds.

The real issue is if you put anything in the cabinet the profile will change - so it's not very useful.  The only way to overcome that is forced convection, which has it's own drawbacks.

From what I got here are my basic takeaways:

1. low temp control via Auber PID with the generator on is limited to about ambient + 60-70 °F in the normal configuration (no cold smoke attachment)
2.  Auber does an excellent job of control to that boundary
3. vertical thermal gradient in the absence of any interfering stuff (i,.e, no meats, just air) is about 4 °F per shelf at 225 °F.
4. vertical gradient increases with set temp (higher temp => greater gradient).
5. Bradley thermistor has a comparatively long time lag - probably the reason for the wide swings when it is the basis for control (likely a result of position and mounting)