Monitoring low speed fan

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Monitoring low speed fan

Postby kristsp » Sun Mar 19, 2006 8:59 pm


I have Intel D845EBG2 Motherboard with Arctic-Cooling Silent CPU cooler/fan fitted. Fan has its own temp probe on cooler and adjusts speed according to cooler (and CPU therefore) temperature. The problem is - when fan speed drops below 1000 rpm, fan readout disappears from hwmonitor screen - as if fan is not present at all. However, I am able to see fan speed readout (~ 600 - 700 rmp when CPU is idle) in SiSoft Sandra motherboard information screen and Intel motherboard monitor utility (but Intel utility also tends to 'loose' fan readout at low speeds).

Is this limitation of hardware sensor or could be fixed in software side?

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Postby author » Mon Mar 20, 2006 6:55 am

It is due to method of measuring fan speed by most sensors chips: the chip counts fixed predefined freq ticks between pulses from the fan. But the range of this count is limited to one byte (0-255) in most cases. So, if the fan speed is too low, counter will always equal to 255. To solve the problem, base freq may be divided to power of two (2,4,8, etc), but for most sensor upper limit is four. So, for most cases, minimum sensible speed is about 1000-1300 rpm.
Newest chips allow set divisor to 8 or even 64 especially for low speed fans, but it is very uncommon yet.
Hmonitor as universal program that should work for most configurations, always set the divisor to 4, to allow compatibility with most sensors and able to read fan speeds in the range 1000-10000 rpm.
But for those chips that allow higher divisors, hmonitor uses value 8, allowing to read speed from about 500 rpm.

So, much probably, your problem can be fixed in software, but i need to have detailed h/w report from your system.
Please, read the docs and FAQ and send the report to official support e-mail address.
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