What is difference between noise and disturbance in control system?

Here d = disturbance & n = noise

• 'Noise' generally refers to measurement noise, possibly Gaussian noise generated in a sensor. 'Disturbance' is normally some unwanted variation of a control signal, for example a step change in ambient conditions. – Chu Mar 3 '17 at 9:17
• "d" is multiplied by "P" hence it has to be different to "n". – Andy aka Mar 3 '17 at 9:59

3 Answers

According to your image, disturbance acts on a controller output, while noise acts on a process output.

Take a moving vehicle for example - obstacle on the road would be a noise, and some (unexpected) event in the engine, gas tank etc. (in a car itself) would be a disturbance.

• ....and the transfer functions y/d resp. y/n will be different. – LvW Mar 3 '17 at 8:28
• @Marko Gulin Thanks for answer. Can you tell me what are the differences between noise & disturbance in general? – basic123 Mar 3 '17 at 8:45
• The main difference is where they act on a system (before or after a process). Both disturbance and noise are (usually) unpredictable, and they are usually modelled as a stochastic process. – Marko Gulin Mar 3 '17 at 10:14

Noise $n$ affects your meassurements of $y$, so that instead measuring $y$ you will measure $y+n$. Disturbance affects the generation and not the meassurement of the variable $y$.

MrYouMath's answer is the most accurate. In a Control System, Disturbance is what you make the control system for in the first place, it can be anything that alters the functionality of whatever you are working with. If it's a car, you could say that a disturbance is an obstacle in the road, or if it's a washing machine, it could be a weight overload. Noise here refers to electrical noise, it's an alteration in the output which in that particular control system that your image shows, is mitigated with a feedback loop