Construction of RTD
The RTD elements nearly always require insulated leads attached. At temperatures below about 250 ºC PVC, silicon rubber or PTFE insulators are used. Above this, glass fiber or ceramic are used.
The measuring point, and usually most of the leads, requires a housing or protective sleeve, often made of a metal alloy which is chemically inert to the process being monitored.
Selecting and designing protection sheaths can require more care than the actual sensor, as the sheath must withstand chemical or physical attack and provide convenient attachment points.