In all conventional closed-loop control systems' flow diagrams I have seen, the feedback signal is taken directly from the output variable, but sometimes the output variable is not the same quantity being compared with the setpoint quantity (e.g. speed as an output and voltage as a setpoint).
For example, a motor speed-control system would have the speed of the axle as the system's output, but in the system's flow diagram the feedback signal would still be taken directly from the output.
If this is correct, how can you represent such a change in quantity as a transfer function? And as this seems illogical to me, is there any other way to represent this system?
Please look at the following image for a visual representation of the example:
https://pasteboard.co/HjndbVn.jpg
EDIT:
Example 2: What if the control output (speed) of the motor translates into the rotation of the vehicle; for example, if the right wheel speeds up and left wheel speeds down the vehicle will turn left. But we use optical sensors to detect a black line that the vehicle should follow.
How do we relate the motor's speed to the sensed voltage on a flow diagram and how would we find its transfer function?
Thank you!