modelling simulink block diagram

I'm using simulink to model the following:

U(s) ------> 2s+6 ------> X(s)

So the input U(s) multiplied by (2s+6) gives the output X(s). Now my problem is which block in simulink allows me to write (2s+6)? Should it be a gain? But then gain blocks require a numerical value, and this 2s+6 obviously has s. How do I do this. THanks.

Answer 1

[Anuj]

Go to simulink lobrary and type transfer fcn.

[Holaar]

but transfer fcn must be a fraction form. There must be something in the denominator. And if I set the denominator to 1, and try to set the numerator to 2s+6, it says "order of the denominator must be greater than the numerator".

[Anuj]

s in numerator means differntiation, you can use derivative block multiplied by 2 and then add 6 to get 2s+6.

[Holaar]

ok so du/dt = s. What about s^2? I just link up two derivative blocks? THanks a lot

Answer 2

[Azzi Abdelmalek]

Try this approximation:

(2s+6)/(0.0000001s+1)