D20/D200 Redundancy; Failover Sequence - GE D20 Installation And Operation Manual

GE Energy
Familiarization
, continued
D20/D200 D20/D200 equipment redundancy requires:
Redundancy •
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
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 Serial
Communications
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 If the Active CCU fails:
Sequence
1. The Standby CCU detects the failure through the inter-CCU communications
2. The Standby CCU commands the RS-232 Switch Panel to switch over all
3. The RS-232 Switch Panel switches all serial field connections to the Standby
General
Full
Panel is 15 mA. The maximum power requirement on the +12 V input during
operation is 230 mA.
. . . . .
CCU A
(Active)
link.
serial connections.
CCU, which now becomes the Active CCU.
Installation and Operations Guide
To Field
Equipment
. . . . .
RS-232 Switch Panel
RS-232 Switch
Monitor and
Control
Inter-CCU
Communications
994-0078-2.00-7
D20/D200
CCU B Serial
. . . . .
Communications
CCU B
(Standby)
39