What does the term 'deviation' refer to in control systems?

The term 'deviation' in control systems specifically refers to the difference between the controlled variable and the set point. In a typical control system, the set point is the desired value that the system aims to maintain, while the controlled variable is the actual value being measured. When the actual value does not match the desired set point, there is a deviation, indicating how far off the controlled variable is from where it should ideally be. This measurement is crucial because it helps determine the necessary adjustments required to bring the system back into alignment with the desired set point, allowing for effective regulation and control of processes.

Understanding deviation is fundamental in control theory because it directly influences control actions. For instance, in temperature control systems, if the thermostat indicates a temperature higher than the set point, the deviation would be positive, signaling the system to reduce cooling. In contrast, when the controlled variable is lower than the set point, the deviation would be negative, prompting an increase in heating. By monitoring this difference, control systems can adjust their performance to maintain stability and efficiency.