What metrics are used to evaluate control loop performance?

Key metrics include: IAE/ISE/ITAE (Integral of Absolute/Squared/Time-weighted Absolute Error) - overall error measures; Standard deviation of controlled variable (should be near measurement noise if well-tuned); Percentage time in auto (availability); Variance ratio (actual vs minimum achievable variance); Valve travel (excessive travel indicates issues); Oscillation index; and Controller mode statistics. Harris index compares actual variance to minimum variance achievable with dead time constraint. Good performance: low variability, stable output, reasonable valve movement, high time in auto.