When an alarm clears (i.e., the parameter returns to the normal range from an abnormal range), the return to normal conditions should be indicated by visual and audible means.
Additional Information:
Ringback, alerting the operator when a parameter returns to normal, should not be required for all alarms but should be required when it is important that the operator know immediately when the deviation has cleared, or when the deviation is not expected to clear for some time. Such cleared alarms should provide a positive indication by initiating audible and visual signals. Techniques that may be employed include: a special flash rate (one-half the normal flash rate is preferred, to allow discrimination); reduced brightness; or a special color. Cleared alarms should have a dedicated, distinctive audible signal, which should be of finite and relatively short duration.