Duplex Sensor: What is a duplex temperature sensor?

Duplex temperature sensors consist of a pair of temperature sensors within a single enclosure. For example, a duplex thermocouple would have two pairs of thermocouple conductors in a single sheath. Similarly, a duplex RTD sensor would have two RTD elements at its hot end instead of a single element. The main reason for such a configuration is to enable redundancy if one of the sensors fails. Duplex sensors cost more, but certain applications benefit from the redundancy gained.