# What is the purpose of the transfer function in PID?

In a SciLab project wherein they build a PID controller they include a CLR/continuous transfer function between the output of the PID and the multiplexer, which was used to combine the step and the PID output for the graph. I was curious as to what the transfer function was supposed to do and what purpose it served in the project?

-
It's rather bad style to ask two closely related questions and not to link them to each other. –  joriki Dec 22 '11 at 1:04
@joriki I linked them together –  Bob Dec 22 '11 at 1:19
Can you state in precise mathematical terms your question? –  Manos Dec 22 '11 at 4:55
@Manos Well, the continuous transfer function in SciLab is in the format of (4)/(s^2 + s), where 4 is the numerator of a fraction, and s^2 + s was the denominator. That's what they created in the video. I know if you don't have the function it gives an error stating "algebraic loop"... –  Bob Dec 22 '11 at 5:39
The project simulates a PID controller for a specific process, namely the process whose transfer function is $\frac{4}{s^2 + s}$.