A loop alarm detects faults in the control feedback loop by continuously monitoring process response to the control output(s).
When used, the controller starts an internal timer when the PID control output reaches saturation (0% or 100% power for single control type, -100% or +100% for dual control type).
Thereafter, if the output has not caused the process variable to be corrected by a predetermined amount ‘Q’ after time ‘T’ has elapsed, the alarm becomes active. When the process variable starts to move in the correct direction or when if PID output is no longer at saturation, the alarm is deactivated.