• Proportional (P mode)
– increase in gain increases P mode contribution
– Provides an immediate reaction to magnitude of measurement change to minimize
peak error and integrated error for a disturbance
– Too much gain action causes fast oscillations (close to ultimate period) and can make
noise and interactions worse
– Provides an immediate reaction to magnitude of setpoint change for P action on Error
to minimize rise time (time to reach setpoint)
– Too much gain causes falter in approach to setpoint
• Integral (I mode)
– increase in reset time decreases I mode contribution
– Provides a ramping reaction to error (SP-PV) to minimize integrated error if stable (since
error is hardly ever exactly zero, integral action is always ramping the controller output)
– Too much integral action causes slow oscillations (slower than ultimate period)
– Too much integral action causes an overshoot of setpoint (no sense of direction)
• Derivative (D mode)
– increase in rate time increases D mode contribution
– Provides an immediate reaction to rate of change of measurement change to minimize
peak error and integrated error for a disturbance
– Too much rate action causes fast oscillations (faster than ultimate period) and can make
noise and interactions worse
– Provides an immediate reaction to rate of change of setpoint change for D action on
Error to minimize rise time (time to reach setpoint)
– Too much rate causes fast oscillation in approach to setpoint