Editing Resistance thermometer (section)

==Construction==
[[File:Rtdconstruction.gif]]

These elements nearly always require insulated leads attached. [[PVC]], [[silicone rubber]] or [[polytetrafluoroethylene|PTFE]] insulators are used at temperatures below about 250&nbsp;°C. Above this, glass fibre or ceramic are used. The measuring point, and usually most of the leads, require a housing or protective sleeve, often made of a metal alloy that 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.

The RTD construction design may be enhanced to handle shock and vibration by including compacted magnesium oxide (MgO) powder inside the sheath. MgO is used to isolate the conductors from the external sheath and from each other. MgO is used due to its dielectric constant, rounded grain structure, high-temperature capability, and its chemical inertness.