Question

Why are unit step, unit ramp and impulse called standard test signals

Answer 1

Usually the input signals to control systems are not fully ahead of time. In most cases these signals may be random in nature,r.g., in radar tracking system, the position and speed of the target to be tracked may vary in random fashion.

It is thus difficult to express the actual input signals mathematically by simple equations. The characteristics of signals which severely strain a control system are a sudden shock, a sudden change, a constant velocity and a constant acceleration.