Failover Sequence; Required Components - GE D20MX User Manual

CHAPTER 3: CONNECTING TO DEVICES AND NETWORKS

Failover sequence

Required components

D20MX HARDWARE USER'S MANUAL
Figure 21: RS-232 Switch panel
A pair of LEDs marked CCU A and CCU B indicate which of the D20 units is currently active.
If the hardware or software of the active unit fails, it is automatically switched offline and
serial connections to the field are transferred to the standby unit. A toggle switch on the
RS-232 switch panel can be used to switch the D20 devices between active and standby
modes.
If the active D20 unit fails, the following actions occur:
1. The standby D20 unit detects the failure through the lack of a heartbeat signal on the
ping cable or through a status change on the watchdog cable.
2. The standby D20 unit attempts to pull the RS-232 switch panel to assume the active
state.
3. The RS-232 switch panel transfers all serial field connections to the standby D20,
which then becomes the active D20.
To implement a redundant D20 system, you need the components: listed in Table 18.
Table 18: Redundant D20 system - required components
Component Function
RS-232 Switch Panel Communications switch.
Power Supply Power supply to power the RS-232 switch panel.
Input: 85 – 264 V AC or 90 – 350 V DC.
Watchdog Cable Connects D20 A to the RS-232 switch panel.
Assembly
Connects D20 B to the RS-232 switch panel.
Ping Cable Assembly Links both D20 units to facilitate a heartbeat message
that determines the status of the active unit.
RS-232 Serial Cable Connects the D20 to the RS-232 switch panel which is
then connected to external field devices.
Power/SysFail Cable Connects the RS-232 switch panel to D20 external power
supply.
Ground Cable Provides a ground connection for the RS-232 switch panel. 970-0182
Pins 4 on switch panel connectors J2 through J9 are tied together and to the panel's power
supply. Any loading from field devices on these pins will load the RS-232 panel power
supply and should be taken into consideration when sizing power supplies.
Power Indicator LEDs
Activ e/Standby Sw itch
GENERAL
PWR A
PWR B
CCU A
CCU B
CCU Indicator LEDs
Part Number
517-0247
580-0046
977-0160
977-0160
977-0122
977-0121
970-0161
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