Changeset 425 for lm-sensors/trunk/doc/temperature-sensors
- Timestamp:
- 04/26/99 01:52:37 (10 years ago)
- Files:
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- lm-sensors/trunk/doc/temperature-sensors (modified) (4 diffs)
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lm-sensors/trunk/doc/temperature-sensors
r317 r425 3 3 Temperature measuring chips that use external sensors 4 4 generally are designed to use either thermistors or 5 transistors. 5 transistors. Check the driver documentation in doc/chips 6 or the actual data sheets to determine which. 6 7 7 Exceptions are the Winbond W83782D and W83783S which c laim8 to be able to use both, however it isn't clear how 9 to configure these to usetransistors.8 Exceptions are the Winbond W83782D and W83783S which can use either. 9 These chips default to termistors but can be configured to use 10 Pentium II / Celeron diodes or 3904 transistors. 10 11 12 Thermistors are about 10 times more sensitive than 13 diodes or transistors at room temperature. 11 14 12 15 13 16 Thermistors 14 17 ----------- 15 16 18 (summarized from http://www.thermometrics.com/htmldocs/ntcapp.htm - 17 19 most thermistor companies don't have much on their web sites but … … 39 41 So by the last equation, a thermistor with a Beta of 3900 will change 40 42 resistance about 4.4% for 1 degree change at 25C (298K). 41 For a beta of 3423 as recommended in the 782D data sheet the change is 3.8%. 43 For a beta of 3435 as recommended in the 44 Winbond W83782D data sheet the change is 3.8%. 42 45 43 46 For thermistors, resistance (= voltage for a constant current) … … 46 49 47 50 48 Transistors 49 -------------- 51 Transistors / Diodes 52 -------------------- 50 53 To use a transistor as a sensor, hook the base of an NPN transistor 51 54 (such as the 3904) to the collector. … … 68 71 69 72 73 Winbond W83782D and W83783S 74 --------------------------- 75 These chips default to thermistors with Beta = 3435. 76 Each sensor on the chip can be individually set to be 77 a diode, transistor, or thermistor. 78 If the temperature reading changes much less than expected, 79 the sensor type probably needs to be changed to a diode. 80 See doc/chips/w83781d for details. 81 82 83 Summary 84 ------- 85 Thermistors are about 10 times more sensitive than 86 diodes or transistors at room temperature. 87 88 Thermistors change resistance exponentially with respect to temperature. 89 Diodes and transistors change voltage linearly with respect to temperature. 90 91 Sensors built into chips (including Pentium II / Celeron processors) 92 are always diodes/transistors because that's what's on a chip 93 already - transistors. 94 95 External, discrete sensors can be either diodes/transistors or 96 thermistors. Generally, sensor chips are designed to be connected 97 to one or the other and cannot be configured. The Winbond 98 W83782D/W83783S chips are exceptions, they can be 99 configured for either.
