Confusion about fan speeds

My six corsair fans and my h100i cpu cooler seem perfectly controlled via Corsair Commander Pro. Fan speeds according to iCUE usually 1.000 - 1.500 RPM when I'm not gaming and pump around 1980 RPM

 

According to BIOS (but also according to iCUE) I have a CPU fan which goes around 3400 RPM. I don't understand this. I only have the above mentioned six corsair fans, two of which are installed in the H100i platinum system, so where does the motherboard get's the cpu fan from?

 

Maybe I should mentioned that the two fans in the h100i are controlled via the commander pro - they are not attached to the h100i.

That signal comes from the cooler. It provides a fan tach signal based on the pump to prevent a CPU Fan warning on boot. Also, in the event of a complete pump failure, you won't get any signal ... which will give you the CPU Fan warning.

Adding to the above, a "revolution" on a pump is not the same as 1 turn around on a fan. Most pumps have a numerical divider that turns their actual revolutions back into a number we expect. 2 is a common divider for a lot of pumps. I don't have a Platinum cooler and I don't know if the doubling is on the cooler or motherboard end, but if you cut the value in half it should be about right. Also note the motherboard and iCUE may not poll the device at the same time and that may be one of the reasons they don't exactly match. Another is a pump speed is a prediction, rather than a continuously rolling average or count over the last 60 seconds. Tiny differences get multiplied out creating the appearance of frequent change that may not really exist. Finally, I don't know about GA boards, but my Asus models drive me nuts with their coded sensor values. Most of them wind up wrong in iCUE. I deleted the motherboard "CPU fan" value from my dashboard. It's all over the place. There is no reason to use that when iCUE can communicate directly with the pump and display an accurate value.