TEGAM’s Fast Response Temperature Probe – When Time Is of the Essence!
GENEVA, OH, September 1, 2019
What does “Fast Response” mean for a thermometer temperature probe? To someone measuring a pot of water being brought to a boil in their kitchen, it might mean “1 minute.” To a person measuring a cooked piece of meat coming out of an oven on a moving conveyor belt in a production facility, it means something quite different.
Time constant and response time are often confused. You might think that a temperature probe with a 1-second time constant is fast but… you have to understand the math involved.
The thermal time constant indicates the time required for a temperature sensor to respond to a change in its ambient temperature. When the ambient temperature is changed from T1 to T2, the relationship between the time elapsed during the temperature change t (sec.) and the sensor temperature T can be expressed by the following equation.
τ (tau in sec.) in the equation denotes the thermal time constant. The temperature change rate at n times (x) the constant τ (sec.) is as follows, showing that the sensor body temperature reaches its ambient temperature approximately within 7 times the constant.
According to the formula, it takes 1 time constant to reach 63.2% of total temperature, 3 time constants to reach 95% of the final temperature, and 7 time constants to reach 100%.
If you are measuring food on a moving conveyor belt (typical speed is 65 ft/minute – walking speed) then you need to walk with the probe in the food for 7 time constants to get a 100% temperature reading. Now the 1-second time constant begins to look slow, as you have to walk along the conveyor belt for 7 seconds to get a good reading! That’s at least 7.6 feet. Doing that all day can wear out a pair of sneakers as well as knees quickly.
This is the response time of the TEGAM Fast Food Temperature Probe.
At about 2.5 sec this probe hits the 99% mark so the final reading which is 5 time constants so 2.5/5 = this probe has a 0.5 second time constant.
What goes into building a fast-response temperature probe? It is actually what “does not” go into it --- mass. To get fast response, you need good thermal conductivity and minimal mass, while more durability typically requires more mass. The TEGAM fast response temperature probe (Model # 9T797MTCPVC36) uses a small diameter, high-strength SS tube inside a larger tube to give it the durability needed and yet still provide the low mass at the measuring tip. The tip is 0.067” while the shaft it 0.125”. We can manufacture this style of probe with the tip as small as 0.040”.
The smaller the tip, the faster the response time, but durability also suffers. If you need fast response and durability, check out the TEGAM fast-response temperature sensor. We also recommend Type T thermocouple probes because they have twice the accuracy of a type K thermocouple, which is important in the food industry for numerous reasons like health & safety as well as for product quality. See all our thermocouple probes, RTD probes and thermistor probes by following the preceding links, please.
Take a look at our Temperature Probe Selection Guide infographic here for more edification.
Lastly, feel free to reach-out and contact TEGAM with any specific questions or queries you may have on our temperature probes and digital thermometers, thanks.
Dan Jackson, Thermometry Products Manager