The CellaTemp® PA 21 is a digital pyrometer with fibre optics for the measurement of temperatures between 300 and 2000 °C. The pyrometer is equipped with a separate pyrometer sensor. The pyrometer is equipped with a separate optical measuring head and a light guide. The light guide and measuring head are insensitive to interference from electromagnetic radiation and can be used in ambient temperatures up to 250 °C without cooling. The variant with separate optical measuring head has advantages especially in confined spaces.