Temperature sensor was first developed, the most widely used type of sensor. Temperature sensor's market share considerably more than the other sensors. From the early 17th century people began to measure temperature. In semiconductor technology with the support of this century have developed a semiconductor thermoelectric couple sensors, PN junction temperature sensor with integrated temperature sensor. Correspondingly, according to the interaction with matter, and have developed a acoustic sensor, infrared and microwave sensors.
Conductor of two kinds of different materials, such as connected together at some point, the junction heating, will appear in their unheated parts of the potential difference. This potential difference of the value associated with a temperature not heating parts, and the two conductors of the material concerned. This phenomenon can be found in a wide temperature range, if accurately measured the potential difference, unheated parts of the measured ambient temperature, you can know exactly the temperature of the hot spot. Because it requires two different conductor materials, so called "TC". Thermocouples made of different materials used in different temperature ranges, their sensitivity can vary. Sensitivity refers to the hot spot temperature of thermocouple 1 c, the output voltage variation. For most metal support thermocouple, this value is about 5~40 microvolt/℃.
Thermocouple sensor has its own advantages and disadvantages, its sensitivity is lower, vulnerable to the effects of environmental interference signal, effects are susceptible to temperature drift of the preamplifier and is therefore not suitable for measuring small changes in temperature. Due to sensitivity of thermocouple temperature sensor has nothing to do with the thickness of the material, made of very fine material can be made into temperature sensors. Also because of the production of thermocouples has good ductility of metallic materials, this subtle temperature element has a very high response rate, rapid process of change can be measured.