• Many furnaces and kilns use thermocouples for temperature sensing.four image by thierry planche from Fotolia.com
  
  Temperature sensors are one part of a thermometer, gauge or temperature control device. Sensors detect changes in temperature, which the device then reads, calculates the change, converts it to degrees and displays it. Devices like thermostats act on the change by turning another device on or off to regulate the temperature being monitored. The materials temperature sensor devices are made of, and how they respond to temperature changes, determine their type.
  
  

Thermistors

• The resistance of semiconductor material inside thermistors changes when the temperature changes. The resistance falls as the temperature rises in a way that is predictable enough to be correlated to degrees. Thermistors commonly used in appliances and other household items that measure and respond to temperature changes. Their upper range is 500 degrees F. They are very sensitive compared to other sensors like the thermocouples or resistance temperature detectors. They have a medium to fast response time when sensing changes in temperature.
  
  

Resistive Temperature Devices

• Resistive temperature detectors (RTD) are another type of resistance sensor. As temperature rises their resistance rises. The rise in resistance can be correlated to degrees. An RTD can measure temperatures from -400 degrees F to 1200 degrees F and is highly accurate. These temperature sensors are widely used in industry for measuring surface and fluid temperatures.
  
  

LM35

• The LM35 is more accurate than a thermistor and it puts out higher voltage than a thermocouple, minimizing the possibility that the voltage needs to be boosted. It is made to be included in an integrated circuit on a circuit board. Its voltage correlates to the Celsius temperature scale, and it is highly accurate without any calibration. It also uses very little power, so it does not heat up. When included in circuits LM35s trigger events such as activating a relay when certain temperatures are reached.
  
  

Thermocouples

• Thermocouples have a wide range of operating temperatures. While a typical household oven uses a thermistor temperature sensor, a kiln has to use a thermocouple because of its higher operating temperature. Thermocouples sense temperature changes that cause the two dissimilar materials joined inside it to create voltage. Usually, the device the thermocouple is connected to reads the voltage and converts it to a temperature reading.
  
  Common thermocouple types are Type K, Type T and Type N. Type K operates at temperatures between -452 degrees F to 2300 degrees F. Type T handles temperatures between -418 degrees F and 1562 degrees F. Type N measures temperatures from -436 degrees F to 2354 degrees F. The types are determined by the kind of metals used in the thermocouple. Different metals produce different electrical charges when they expand or contract from temperature changes.