assemblies have gained in popularity over the years as improvements in research, engineering and manufacturing techniques have been made. UL Recognized NTC thermistors in the XGPU2 category helps save equipment manufacturers time and money when applying for safety approvals for their end product. DO-35 hermetically sealed glass encapsulated thermistors can operate up to 250°C which gives them an advantage in many applications when UL is requested for a sensing element. History The first NTC thermistor was discovered in 1833 by Michael Faraday, who reported on the semiconducting behavior of silver sulfide. Faraday noticed that the resistance of silver sulfide decreased dramatically as temperature increased. (This was also the first documented observation of a semiconducting material.) Because early thermistors were difficult to produce and applications for the technology were limited, commercial production of thermistors did not begin until the 1930s. A commercially viable thermistor was invented by Samuel Ruben in 1930. See also Resistance thermometer Thermocouple Iron-hydrogen resistor Stretch sensor References External links The thermistor at bucknell.edu Calculation of Steinhart-Hart Coefficients for Thermistors at sourceforge.net "Thermistors & Thermocouples:Matching the Tool to the Task in Thermal Validation" – Journal of Validation Technology Heating, ventilation, and air conditioning Resistive components Sensors Thermometers