There were two types of temperature-taking technologies at play in our testing of digital thermometers: thermocouple and thermistor. In thermocouple thermometers, the mechanics are housed in the unit’s body and connected to a sensor in the tip of the probe by a very thin wire. In thermistor models, the sensor and mechanics are located entirely at the tip of the probe.
We spoke with Dr. Scott Bergeson, a professor in the Department of Physics and Astronomy at Brigham Young University, about the differences between the two styles. He told us that thermocouples are made by connecting (or “coupling”) two thin wires made of different kinds of metals. The connection causes a tiny voltage to appear, and higher temperatures cause the voltage to increase.
Thermistors, on the other hand, determine temperature by reading how electrons move in a semi-conductor material. In this case, a small voltage is applied to the material and it pushes the electrons. The temperature is then calculated based on how easily the electrons move in response to the voltage.
Bergeson said thermocouples can respond to changes in temperature more quickly because thermal conductivity is faster in metal, which thermocouples use. Thermocouples also work over a wider range of temperature; in Bergeson’s lab, he has some that read up to 1,000 degrees. But when accuracy is paramount, he said he typically uses a thermistor, because while the range is usually smaller, the changes in temperature are easier to measure. In the kitchen we don’t need as high a level of sophistication. Even though they measure temperature differently, we found fast and accurate thermometers in both styles.