Appendix B - Sensing Current And Thermistor Selection - ILX Lightwave LDT-5525 User Manual

Introduction
Choosing the right sensing current depends on the range of temperature you want to measure and the resolution you
require at the highest measured temperature. To correctly set the SENSOR SELECT switch you must understand how
the thermistor and the LDT-5525 Temperature Controller interact, and how temperature range and resolution values
are inherent in the nature of thermistors.
Thermistor Range
Thermistors can span a wide temperature range, but their practical range is limited by their non-linear resistance
properties. At high temperatures, the thermistor resistance changes less for an equivalent temperature change at
lower temperatures (the thermistor becomes less sensitive). Consider the temperature and sensitivity figures in
Table B.1 below for a 10 K thermistor.
Appendix B
Sensing Current and Thermistor Selection
Thermistor Sensitivity at Various Temperatures
Temperature
-20°C
25°C
50°C
Table B.1 Thermistor Sensitivity
Sensitivity
5600 ohms/°C
439 ohms/°C
137 ohms/°C
B-1