IEC 62651:2013 describes the requirements for thermocouples suitable for nuclear power plant (NPP) applications. Thermocouples are widely used in NPPs with other temperature measurement devices such as resistance temperature detectors. They are simple and robust and have some specific characteristics (range of measurement and maximum temperature) which make them uniquely suitable for some measurements. The requirements given in this standard for thermocouples include design, materials, manufacturing, testing, calibration, procurement, and inspection.