The output signal from the sensor of a measurement system or the signal
from the control unit might have to be processed in some way to make it
suitable to operate the next element in the control system. For example,
the signal may be too small and have to be amplified, be analogue and
have to be made digital, be digital and have to be made analogue, be a
resistance change and have to be made into a current change, be a
voltage change and have to be made into a suitable size current change