What is the steady state difference between the control point and the set point called?

The steady state difference between the control point and the set point is referred to as "offset." This term specifically describes the condition where there is a persistent discrepancy between the desired operational levels (the set point) and the actual levels achieved (the control point) in a control system.

Offset occurs in various systems due to factors such as load changes, sensor inaccuracies, or control loop tuning issues, leading to a consistent bias that prevents the system from reaching its ideal state. Recognizing offset is crucial for effective control system management, as it can indicate the need for adjustments to the control parameters or equipment.

In contrast, deviation generally refers to any difference from a target but may not imply a steady state, gain is related to how much the output response of a system changes with changing input, and drift refers to a slow change in the parameters of a system over time, which is more dynamic and not necessarily indicative of a steady state. The clarity in definitions helps in understanding the nuances of control systems in practical applications.