diff --git a/doc/temperature-sensors b/doc/temperature-sensors index 374ece87..d8de2384 100644 --- a/doc/temperature-sensors +++ b/doc/temperature-sensors @@ -1,5 +1,5 @@ -Termistor and Transistors as Temperature Sensors ------------------------------------------------- +Thermistors and Transistors as Temperature Sensors +-------------------------------------------------- Temperature measuring chips that use external sensors generally are designed to use either thermistors or transistors. Check the driver documentation in doc/chips @@ -19,8 +19,9 @@ Thermistors most thermistor companies don't have much on their web sites but Thermometrics has a comprehensive guide) -NTC (negative temperature coefficient) thermistors -have a parameter B (beta), units are K (kelvin). +NTC (negative temperature coefficient) thermistors decrease their +resistance with an increase in temperature. +They commonly have a parameter B (beta), units are K (kelvin). B is the "material constant" of the thermistor and is a measure of the change of resistance with respect to temperature. It is the slope of the line graphing (ln R) vs. (1/T). @@ -46,6 +47,9 @@ Winbond W83782D data sheet the change is 3.8%. For thermistors, resistance (= voltage for a constant current) is exponentially related to temperature. +PTC (positive temperature coefficient) thermistors increase +in resistance with an increase in temperature. They are not +commonly used for accurate temperature sensing. Transistors / Diodes @@ -97,3 +101,7 @@ thermistors. Generally, sensor chips are designed to be connected to one or the other and cannot be configured. The Winbond W83782D/W83783S chips are exceptions, they can be configured for either. + + +------------------ +Copyright (c) 1999, 2001 Mark D. Studebaker