Post by Professor Lake Shore on Jan 31, 2017 16:29:13 GMT -5
With negative temperature coefficient (NTC) temperature sensors, is higher resistance better?
For both germanium and Cernox RTDs, there is a common misconception that a higher resistance equates to a “better sensor,” if that is interpreted to mean a sensor that has better resolution or better accuracy (i.e., lower uncertainty). It is important to understand that concepts of resolution and accuracy are largely meaningless if applied only to the temperature sensor. These concepts become meaningful only when discussed in the framework of the electronics used to measure their resistance. Many instrumentation subtleties affect low temperature thermometry measurements, including the excitation mode and how the instrument switches between resistance ranges. Ultimately, the excitation level and resistance range determine the electronic resolution and accuracy which, in turn, determine the temperature resolution and accuracy. Since for a given NTC thermometer type, higher resistance implies higher sensitivities, it would be expected that the higher resistance thermometers should yield better resolution and accuracy. But as explained more thoroughly in this application note, this is not the case in general. The “best” sensor in terms of temperature resolution and accuracy is somewhat random in that it depends on which resistance range the instrument is forced to operate. Overall, the low resistance samples perform as well as the high resistance samples, and the differences that do occur are generally less than a factor of two.