hello, i need to know how can i find the transfer function for a plant:
-a fan that moves with variable speed
-a PID controlller that controllers the fan speed according to a temperature sensor that senses the temperature of the component.

I have been working for a week on this project but i hit this obstacle..i do not know how to move from the physically realizable system to this new system in the s domain.... please help
PS: I do not plagiarize

 

from what I remember to go from the time domain to the s-domain you have to use laplace transforms... and if your time domain equation or plant doesn't "align" with the "standard" laplace transforms then you need to factor it such that it does... if that doesn't work... off the top of my head on don't know what to tell you other than google may be your best friend.

 

It is a long time ago. I hope i remember well enough.

If you can't derive the model mathematically, you might do some measurements.
You might find out the transfer function if you can apply a test signal to the input and measure the output.

Here: voltage and speed

Typically such test signals are:
- a step signal at the input
- a sinusoidal function which is wobbled through the frequencies