A Tutorial on Thermal Sensors in the 200th Anniversary of the Seebeck Effect

Two noteworthy events associated to the physics of thermal sensors were demonstrated and announced in 1821, exactly two hundred years ago. The first event was the Seebeck effect, which led to the development of thermocouples. The second was the study of the thermal dependence of the resistivity of pure metals, which led to the design of resistance temperature detectors (RTD). Sensors’ science and technology has experienced remarkable advances in the last decades, but these two types of thermal sensors, whose physics were announced 200 years ago, are still nowadays the main sensor technology in many industrial applications that require the measurement of extreme temperatures. In such a $200^{th}$ anniversary, this tutorial aims to explain the operating principle, subtypes, input-output characteristic, limitations, and new trends under research of the four main types of thermal sensor: RTDs, thermistors, silicon sensors, and thermocouples. These are also compared with each other, highlighting the main advantages and disadvantages of each sensor technology.