Author Topic: Temperature of back wall on digital 6 rack and actual internal air temperature  (Read 131 times)

Offline solcany

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Hi, I am trying to correct the reading that is taken from the back wall temperature probe on my digital 6 rack and the actual measured ambient temperature.  I use a Meater probe that works exceptionally well.  Ambient air around the meat is about 75-90C on the Meater while trying to reach 107.2C/225F.  The back wall temp is is much higher and corresponds and responds to the setting on the Bradley digital controller.  I maxed out the temp on digital setting and it was the back wall temp being measured, which was reached what I set it to and was maintained, so therefore that does work.  When the back wall probe temperature reaches the digital controller set temperature, the heating elements cycle on and off to maintain the temperature based on the back wall probe temperature.  The actual measured air ambient can be 30C less, which was my case.  The 107C ambient temp was never reached, although the back wall temperature exceeded  that value.  Due to this type of measurement, increasing the ambient air temperature is seriously limited.  I have two elements for 900W installed, Is there any fix for this, such as measuring the cavity ambient air temperature with a Bradley probe on an extension cable using a small thermal mass for stability?  I will not be able to use a circulating fan and will not change to another controller.  It seems the best choice is to move the probe  out into the smoker cavity and eliminate the effect of the wall temperature falsely affecting the air ambient.  When using it today in Edmonton, it was sheltered from some of the wind and the outside temp 16C.  Thoughts and ideas are appreciated.

Offline Habanero Smoker

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It sounds like both probes are working accurately. Usually you will see swings in the digital as much as 20°F.

When the probe or sensor is very near the meat, which is the case of the Meater probe, the reading can be 20 to 30 degrees F lower than an ambient probe that is farther away. Moisture evaporating from the meat cools the air around it, thus lowering the temperature closest to the meat. The difference in the temperature of the Meater will be influenced by the amount of moisture escaping from the meat at any given time. That is why you Meater probe is reading much lower than the Bradley sensor Also the reading between the two sensors can be much greater at times. The Bradley sensor reading is also influenced by the placement of the meat, so if the meat was closer to the sensor in the Bradley, the evaporation from the meat would also cause the ambient temperature to read lower than the rest of the cabinet. In many of my posts I have recommended keeping the ambient probe away from the meat
 
So it is not falsely measuring the ambient temperature, but reporting the ambient temperature at the sensor. To me I would say this is normal, and happens at every cook. Although it is not practical in your case, a fan that can circulate the air would some what even out the temperatures, but if you are getting good results by going with the internal meat temperature I would say not correction is needed.

Again I'm amazed that the Bradley is keeping such accurate temperatures.





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Offline solcany

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Thanks, the issue is that the control was maxed out at its highest temp setting and the measured temp matched the setting, with the air around the roast at 90C.  This could not increase due to the controller being maxed out.  The back wall probe was measuring the same as the maxed out set temp setting, which meant that the temperature could not increase.  Target was 107C and was a longer cook for the roast @ the 90C actually measured above the roast.  I would like to extend the Bradley probe close to the surface of the meat, which will call for more heating as that temperature will be cooler than the setpoint on the controller.  Any ideas?

Offline Habanero Smoker

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No ideas how you can extend the Bradley probe closer to the meat. The only idea I have is purchasing a controller like the Auber PID and placing the Auber ambient probe near the meat.

I'm not sure if you would be able to get the ambient temperature near the meat above 100°C, and that would be at sea level. What is being measured near the meat is steam, and the highest temperature you will get is 100°C; while there is still moisture in the meat. It will only get above 100°C when there is no more or very little moisture for the meat to expel. If you wrap the meat in either foil or butcher paper that will contain the steam, you will be able to get the ambient temperature of the meat near the surface higher without drying out the meat.

For what it is worth, I feel that creating a situation in which the ambient temperature near the meat is 107°C you are cooking the meat at a higher temperature then recommended. Your meat may cook faster, but the end result may be drier, and a tougher texture.


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  ::)

Offline solcany

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Hi, in addition, are there any good designs for added insulation to be able use on the OBS digital 6 rack during the cold Edmonton Alberta Canada winters (-30C at times)