Sensors

This chapter first describes thermocouples starting from the famous experiments by Seebeck and Thomson. The basic concepts of thermocouples are described such as hot and cold junctions, the Seebeck coefficient, and thermocouple ‘types’ are explained. This chapter also explains what the ‘cold junction compensation’ is and the law of intermediate temperatures is illustrated. Resistance temperature detectors (such as Pt-100) are described, and the necessity of accurate resistance measurements is explained (the ‘4-wire method’). The measurement of extremely high and extremely low temperatures is covered at the end of Sect. 3.2. Section 3.3 introduces the versatile strain gauge principle and its many applications. It is also explained why strain gauges are (almost) always connected to a Wheatstone bridge and how it can be used to measure a wide range of physical quantities (like force, pressure, liquid level, torque, etc.). Piezoelectric crystals and Hall sensors are explained and light sensors (photodiodes, position-sensitive detectors, and photomultipliers). In the particle detector section, channeltrons and microchannel plates are explained and in the final Sect. 3.9, the most common vacuum gauges are presented.