Proportional control system: Calculating the change in offset

[James FC]

Homework Statement

I'm having trouble worki out the transfer function of the block. Whats confusing me is the input of O2 input of 50. If that wasn't there I know the transfer function would be Oo/Oi=G/1+GH.

Homework Equations

The Attempt at a Solution

 

[LvW]

The answer is simple: You have two input sources. Hence, we can define two different transfer functions (one of the sources is set to zero).