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17.6 Backup unit management (Stand-by)
17.6.1
Introduction
In an installation made up of on units and stand-by units, there may be imbalances in the operating hours that cause the former
to age faster because of the failure to use the latter. In order to solve this problem, the local network (LAN) always rotates
between the units of the same group in order to even out the operating hours.
Basically, the rotation puts an active unit in stand-by and turns on a unit that was previously in stand-by.
17.6.2
Rotation management
The rotation of the reserve unit is managed entirely by the Priority unit and starts from the unit with the lower address, that is,
address 1, and works its way up.
The time-based rotation modes managed by the application are as follows, defined through parameter P26.31:
•
at hourly intervals;
•
at a set time every day;
•
at a set time and day every week;
•
at a set time and day the first week of each month.
The number of backup units can be set using the appropriate parameter P26.05 in the "LAN" Menu and varies from 0 (no
backup units) to N–1, with N equal to the number of units in the same group (all units in backup and only one in operation).
The configuration parameters for rotation are under the "LAN" menu, which can be accessed by entering the "Service"
password.
INFORMATION:
If the rotation time interval is set to zero, no further rotation takes place. Therefore the backup units remain
the same, activating only in case of the faults and alarms indicated in the following paragraphs.
INFORMATION:
Rotation of the backup units can be forced manually with the specific command in the "Manual" menu that
can be accessed with the "Service" password.
For reasons of safety, at least 10 minutes must elapse between each instance of manual forcing (this period
of time is fixed and cannot be changed).
The time remaining until the next instance of forcing is indicated in the forcing mask.
17.6.3
Reserve units activation mode
Units in stand-by interrupt their stand-by status. These units are activated in the following circumstances:
•
alarm that blocks one resource on one of the active units;
•
One of the active units is turned off from the user terminal;
•
Local LAN disconnection detected (including power feed disconnection of one or more units);
•
Exceeding the set room temperature and humidity limits.
As regards the first two bullet points, turning on the stand–by unit is entirely managed by the Priority unit.
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