Siemens SIMATIC PCS 7 OSx Operator's Manual page 131

SIMATIC PCS 7 OSx 4.1.2 Operator
Acknowledging Non-networked Alarm Tags If a tag configured for
alarming has a non-networked status attribute, such as a recipe area tag,
and the tag goes into alarm, the system does not clear the alarm
unacknowledged bit of the status word under the following conditions:
• The operator does not acknowledge the alarm, and
• The system transitions from the Operate state to the Offline state and
then back to the Operate state.
Typically, tags configured for alarming have networked status attributes,
and this situation does not occur. However, the status attribute for recipe
area tags is not networkable. For example, a recipe area tag goes into
alarm, and the operator does not acknowledge the alarm before the system
state transitions from Operate to Offline and then back to Operate again. If
an operator displays a graphic that contains the recipe area tag's status
attribute, the alarm unacknowledged bit for the attribute is on, even though
there are no current alarms to acknowledge for the recipe area tag.
When this situation occurs, the operator can ignore the setting of the alarm
unacknowledged bit.
5-7
Alarms