From 86e403695bd499529c1b83fb1e5ec68fbd8d2008 Mon Sep 17 00:00:00 2001 From: "Mark D. Studebaker" Date: Sun, 25 Apr 1999 23:52:37 +0000 Subject: [PATCH] update. Clarify that w83782d/783s support both thermistors and diodes but must be configured for one or the other. git-svn-id: http://lm-sensors.org/svn/lm-sensors/trunk@425 7894878c-1315-0410-8ee3-d5d059ff63e0 --- doc/temperature-sensors | 46 ++++++++++++++++++++++++++++++++++------- 1 file changed, 38 insertions(+), 8 deletions(-) diff --git a/doc/temperature-sensors b/doc/temperature-sensors index 709a05cc..374ece87 100644 --- a/doc/temperature-sensors +++ b/doc/temperature-sensors @@ -2,17 +2,19 @@ Termistor and Transistors as Temperature Sensors ------------------------------------------------ Temperature measuring chips that use external sensors generally are designed to use either thermistors or -transistors. +transistors. Check the driver documentation in doc/chips +or the actual data sheets to determine which. -Exceptions are the Winbond W83782D and W83783S which claim -to be able to use both, however it isn't clear how -to configure these to use transistors. +Exceptions are the Winbond W83782D and W83783S which can use either. +These chips default to termistors but can be configured to use +Pentium II / Celeron diodes or 3904 transistors. +Thermistors are about 10 times more sensitive than +diodes or transistors at room temperature. Thermistors ----------- - (summarized from http://www.thermometrics.com/htmldocs/ntcapp.htm - most thermistor companies don't have much on their web sites but Thermometrics has a comprehensive guide) @@ -38,15 +40,16 @@ A = - B / T**2 So by the last equation, a thermistor with a Beta of 3900 will change resistance about 4.4% for 1 degree change at 25C (298K). -For a beta of 3423 as recommended in the 782D data sheet the change is 3.8%. +For a beta of 3435 as recommended in the +Winbond W83782D data sheet the change is 3.8%. For thermistors, resistance (= voltage for a constant current) is exponentially related to temperature. -Transistors --------------- +Transistors / Diodes +-------------------- To use a transistor as a sensor, hook the base of an NPN transistor (such as the 3904) to the collector. @@ -67,3 +70,30 @@ For diodes, voltage is linear with temperature. +Winbond W83782D and W83783S +--------------------------- +These chips default to thermistors with Beta = 3435. +Each sensor on the chip can be individually set to be +a diode, transistor, or thermistor. +If the temperature reading changes much less than expected, +the sensor type probably needs to be changed to a diode. +See doc/chips/w83781d for details. + + +Summary +------- +Thermistors are about 10 times more sensitive than +diodes or transistors at room temperature. + +Thermistors change resistance exponentially with respect to temperature. +Diodes and transistors change voltage linearly with respect to temperature. + +Sensors built into chips (including Pentium II / Celeron processors) +are always diodes/transistors because that's what's on a chip +already - transistors. + +External, discrete sensors can be either diodes/transistors or +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.