Help me write a lookup table for fan speed control

[google8]

I use PWM to control fan speed.
The fan will return a tacho to represent the factual speed(RPM).

The lookup table will contain the to be used PWM settings for the
requested speed. The speed needs to be converted as the PWM output is not
linear with the voltage of the connected fan. Depending on the load of the
fan the to be used PWM characteristics will differ.

But I don't know how to write a lookup table.
Do I must to try every PWM to corresponding RPM?
So, I want to know the fan how to give the factual RPM.

Thanks advanced.


I use PID algorithm to control fan speed.
So first I must write a PWM lookup table and a tacho lookup table.

My question is how to write these tables.

 

[google8]

fan speed control

Who can help me?

Added after 1 hours 30 minutes:

I use PID algorithm to control fan speed.
So first I must write a PWM lookup table and a tacho lookup table.

My question is how to write these tables.

I chage the fan speed according to the temperature.

The lookup table will contain the to be used PWM settings for the requested speed. The speed needs to be converted as the PWM output is not linear with the voltage of the connected fan. Depending on the load of the fan the to be used PWM characteristics will differ.

The lookup table can be used to make the conversion between the received tacho pulses and the corresponding fan speed. Note that this is the conversion table for 500ms tacho pulse measurement.