Siemens SIMATIC PCS 7 OSx Operator's Manual page 93

SIMATIC PCS 7 OSx 4.1.2 Operator
Keep the following considerations in mind when you decide to issue a
command.
Role_Change
• The operator needs to choose a supervisory station that is in sync to be
the new primary. If all stations are out of sync, choose the backup first,
then other supervisory stations, then operator stations. An operator
station cannot be the primary if a supervisory station is available.
If you set a station to the backup role immediately after the station
•
joins the system, you may experience a delay. At that time the station
must process incoming messages from other stations that were deferred
while the station was joining. The role change request has to wait its
turn to be executed.
• A primary role change can also lead to one or more stations being out of
sync with the new primary. This occurs when the system has not
completely propagated the data updates from a non-primary station to
all other stations before the role change. Resynchronize the affected
stations to ensure correct operation.
There is a brief period of time during a role change involving the
•
primary when there is no primary. This condition is indicated by the
station role code T (transition) in the Information area of the former
primary. Typically, the period of no primary is only a few seconds. For
example, a report that is scheduled to run may not run at that time,
but will run at the next repeat time for that report. A few seconds of
trend data may also be lost in the transition, or a BCL or RDT event
may be lost.
To minimize adverse effects to OSx functions, choose a time to change a
role when system activity is minimal. Plan a role change between shifts
to minimize the possibility that shift reports are running, before or
after a batch has run, and there are few or no unacknowledged alarms.
Do not issue a
•
Role_Change
after you issue a
still be in the process of synchronizing to the original primary.
Normally, the OSx system prevents you from selecting a new primary
during synchronization; however, under heavily loaded conditions, the
system may permit a role change to primary during the brief period of
time immediately after you select the
• If an alarm occurs in the controller during this period and OSx is in the
Operate state, the alarm icon and the alarm summary line do not flash.
However, the system writes the alarm to the alarm log and the alarm
summary. The operator needs to check for new alarms after a role
change involving the primary.
command to a new primary immediately
command for a station, since the station may
Re_Sync
Re_Sync
command.
2-11
OSx Station Control