GE Energy
D20/D200
Installation and Operations Guide
General 994-0078-2.00-7
Full
39
Familiarization
, continued
D20/D200
Redundancy
D20/D200 equipment redundancy requires:
•
A second CCU (Central Control Unit, a term used to describe the D200 multi-
processor system), and
•
One or more RS-232 Switch Panels.
Note:
The quiescent current of the +12 V power supply input on the RS-232 Switch
Panel is 15 mA. The maximum power requirement on the +12 V input during
operation is 230 mA.
Through a toggle switch on the RS-232 Switch Panel, you designate one of the
CCUs as the Active unit. If the Active unit hardware or software fails, the Active
CCU is automatically switched offline, and the Standby unit is switched through to
the field equipment (i.e., it is made Active).
The RS-232 Switch Panel is not equipped with EMI protection circuitry. If the
connection length exceeds 3m, a Serial Surge Protection Panel (GE item number
540-0249) or equivalent protection device should be installed.
The following diagram illustrates a redundant D20/D200 system, with CCU A
active:
CCU A
(Active)
CCU B
(Standby)
RS-232 Switch
Monitor and
Control
Inter-CCU
Communications
To Field
Equipment
CCU A Serial
Communications
CCU B Serial
Communications
. . . . .
. . . . .
. . . . .
RS-232 Switch Panel
See “Redundant D20/D200 Systems” on page 83 for:
•
Requirements for implementing a redundant D20/D200 system
•
Instructions for physically assembling a redundant D20/D200 system
Failover
Sequence
If the Active CCU fails:
1. The Standby CCU detects the failure through the inter-CCU communications
link.
2. The Standby CCU commands the RS-232 Switch Panel to switch over all
serial connections.
3. The RS-232 Switch Panel switches all serial field connections to the Standby
CCU, which now becomes the Active CCU.
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