Posted by Chef JimmyJ on “Temperature Probe Insertion Question – Timing” http://www.smokingmeatforums.com/t/126885/temperature-probe-insertion-question-timing/20#post_1016128
“Since you guys are HIJACKING THIS THREAD!...And I am a major contributor to answering the OP's question, I will add my observation...
What is the point of building a Thermal Probe that conducts Heat? Are the sensors not Heat Isolated from the rest of the probe and the probe non-conductive? If not then ALL metal Probes would conduct heat to the meat, especially that in contact with the senor AND the sensor itself! There would not be a single accurate thermometer with a Metal Probe...Not to mention in this senario, Corporate customer demand and therm manufacturer profit savings would have switched to sturdy non-conductive Plastic Probes with just Metal Tips, years ago. I can see, maybe, a cheap probe thermometer conducting heat and being off a few degrees but the metal is very thin and there is just not enough Thermal Mass to make a significant difference. Additionally, I highly doubt general statements about conduction are valid. During my Electronics Controls and Measurement days, I was not always a Chef, all the Industrial and Medical equipment I worked on and with, had Metal Therm Probes and had better be thermally isolated and highly accurate or there would be huge Costs to our clients from manufacturing inferior Product, Malfunctioning Control Systems and worthless Test Equipment. ------------------- Please make your Closing Statements and move on starting a New Thread on the subject if you wish to continue, in a civil manner of course...JJ”
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Spinning off from the above thread.
Here is a quick experiment to illustrate my point on that thread:
I wrapped some paper towel around the shaft of a typical probe thermometer about 1 ½” away from the tip. I poured 212F water just over the paper towel. In about 5 minutes, the tip measured temperature change from 76F to 89F.
I would assume that the temperature rise is mostly due to the metal conductivity of the shaft.
Imagine the situation of a thermometer probe in a 350F cooker, not 212F environment, for 4 to 5 hours or more into the meat, not 5 minutes, how much thermal distortion the conductivity of the metal can possibly introduce.
However, this does not mean probe thermometers are useless or not accurate, all it means is to have the best designed fastest electronics, and the smallest probe; the smaller the metal construction the better the thermal characteristics (note the probe size of Thermapen) and don’t take too long to take your measurements. Read the thermometer's spec and see how long it says for the thermometer to register a correct reading and don't take much long that that. Just MHO.
I have also done a lot of sous vide cooking. In sous vide, as you probably know, people are concerned with 1 degree accuracy.