mirror of
https://github.com/lm-sensors/lm-sensors.git
synced 2026-10-20 11:29:31 +00:00
Jean Delvare
35a5a7dbce
be found, fallback to /etc/sensors.conf. This allows for an old libsensors and a new libsensors to be installed in parallel, and each one has its own configuration file. One important change here is that the default configuration file will be installed as /etc/sensors3.conf by "make install". git-svn-id: http://lm-sensors.org/svn/lm-sensors/branches/lm-sensors-3.0.0@4990 7894878c-1315-0410-8ee3-d5d059ff63e0
100 lines
2.9 KiB
Plaintext
100 lines
2.9 KiB
Plaintext
Fan reading problems and solutions
|
|
----------------------------------
|
|
|
|
If you aren't getting the expected readings on your fans,
|
|
try the following:
|
|
|
|
- Do you get a fan reading in the BIOS or using a different OS?
|
|
If not, you may not have a fan with a tachometer output.
|
|
Look and see. Fans with tachometer outputs have at least 3 wires.
|
|
Fans with only 2 wires cannot, in general, report their speed.
|
|
|
|
- Try experimenting with the fan divisor settings:
|
|
|
|
|
|
Fan Divisor Settings
|
|
--------------------
|
|
|
|
Fan Divisor Minimum RPM Maximum RPM
|
|
----------- ----------- -----------
|
|
1 5314 1350000
|
|
2 2657 675000 default on most chips
|
|
4 1328 337500
|
|
8 664 168750
|
|
16 332 84375 not supported on most chips
|
|
32 166 42187 ""
|
|
64 83 21093 ""
|
|
128 41 10546 ""
|
|
|
|
Pick a divisor so that the nominal RPM is about 50%
|
|
above the minimum. This is a good compromise between
|
|
margin and accuracy. Note that most chips only support
|
|
fan divisors of 1, 2, 4, and 8.
|
|
|
|
If you have a 0 RPM reading some or all of the time,
|
|
increase the divisor until you get good readings.
|
|
|
|
If you have a nominal reading less than 1.25 times the
|
|
minimum, increase the divisor to give you margin
|
|
so that you will not get spurious alarms.
|
|
|
|
If you have a nominal reading more than 3 times the
|
|
minimum, decrease the divisor to provide better
|
|
accuracy.
|
|
|
|
|
|
How to change fan divisors
|
|
--------------------------
|
|
|
|
Put an entry "set fanN_div X" in the appropriate section of
|
|
/etc/sensors3.conf and run 'sensors -s'
|
|
(N is the number of the fan, and X is the divisor you want).
|
|
|
|
|
|
Further details
|
|
---------------
|
|
|
|
Fan divisors are quite confusing.
|
|
|
|
Sensor chips count fan speed by using the fan signal
|
|
to gate an 8-bit counter driven by a 22.5 kHz clock.
|
|
So the _higher_ the counter value, the _slower_ the fan,
|
|
and vice versa.
|
|
|
|
The term 'fan divisor' is a misnomer because it doesn't divide
|
|
the fan signal, it divides the 22.5 kHz clock.
|
|
Thus you _increase_ the divisor if you have a slow fan.
|
|
|
|
The drivers account for the 'fan divisor' in their calculation
|
|
of RPM. So changing the fan divisor will NOT change the
|
|
nominal RPM reading, it will only affect the minimum and maximum
|
|
readings and the accuracy of the readings.
|
|
|
|
The actual formula is RPM = (60 * 22500) / (count * divisor)
|
|
|
|
The readings are most accurate when the fan speed is low
|
|
(i.e., close to the minimum possible RPM reading).
|
|
As fan speed gets closer to the maximum possible RPM reading,
|
|
the reading becomes quite inaccurate. Fortunately, most computer
|
|
fans do not approach 1,000,000 RPM !
|
|
|
|
|
|
Fan readings 2X too high
|
|
------------------------
|
|
|
|
This is rare, but can happen. This is typically caused by a fan which
|
|
outputs 4 pulses by revolution, instead of the standard 2.
|
|
|
|
As we learned above, you can _not_ fix this by changing
|
|
the fan divisor. You must add entries into the appropriate
|
|
section of /etc/sensors3.conf:
|
|
|
|
compute fanN @/2, 2*@
|
|
|
|
(N is the number of the fan)
|
|
|
|
|
|
|
|
------------------
|
|
Copyright (c) 2000-2004 Mark D. Studebaker
|