Stator RTDs, which are sometimes referred to as slot RTDs or stick RTDs, are the sensor of choice for monitoring motor/generator health. Technical papers and trade articles have proclaimed the advantages stator RTDs have over temperature sensing methods used to measure temperature in rotating machinery.
Perhaps stator RTDs’ most significant advantage is that:
All other sensor types…including thermocouples, thermistors, and thermostats… can only measure the temperature at a ‘point’ or ‘spot’ within the length of a motor slot. Even if the element is embedded in a traditional Stator laminated “stick” body, it is only sensing temperature at a specific “point” within the stator slot where it is installed. Stator RTDs can be produced in just about any length and they include a specially designed element called an “Averaging RTD” sensor. These averaging RTD elements extend throughout most of the body length of commercial Stator RTD sensors. The result of this design is that stator RTDs give a much more qualitative assessment of the temperature condition within a motor or generator.
Stator Winding RTDs have additional benefits over ON/OFF devices in that they provide continuous sensing. This provides ‘advanced warning’ without unnecessary shutdowns or tripouts.
A final consideration is that RTDs performance (i.e. resistance change per degree) degrades very little over time. The result is that one is seldom fooled by faulty readings from an old RTD. Some other temperature measurement technologies...most notably thermistors... have not been able to match this claim. "Troublesome readings" from an older thermistor installation can be the result of an aging thermistor and not a motor in need of attention.