Woodward EGCP-2 - Inter-Control Communications (RS-485 Network); Figure 4-19. Changing the Priority of a Slave Unit

Manual 26086 EGCP-2 Engine Generator Control Package
Woodward 93
The network priority of the priority 2 and 3 units are switched so now the unit with
network address #3 is priority 2, and network address #2 is priority #3. After a
time delay of less than 5 minutes, the #3 network address (priority 2) unit is
started by the master and paralleled to the bus. Now all three units are on line.
See Figure 4-18. The master recognizes the proper on/off sequence for the new
priority settings, and will sequence off network address #2 unit when system load
levels fall below 25%. See Figure 4-19.
MAINS
MAINS FAILURE DETECTED
OR RUN WITH LOAD AT MASTER
NEXT ON 2
G
NETWORK ADDRESS #1
NETWORK PRIORITY #1
NEXT OFF 3
NETWORK PRIORITY #3
NETWORK ADDRESS #2
G
ADDRESS: 1 2 3
MASTER SEQUENCING SCREEN
OPER. X X X
MASTER 1
PRIORITY 1 3 2
SYSTEM LOAD = 50%
NETWORK PRIORITY #2
NETWORK ADDRESS #3
G
VIS-124
00-04-27
Figure 4-19. Changing the Priority of a Slave Unit
System load levels have dropped below 25%, and the master has sequenced
network address #2, priority #3 unit off line. The master has fully recognized the
priority change, and the new priority settings are in effect.
The above examples are typical sequencing functions of the EGCP-2. Isolated
bus applications were shown for clarity. The EGCP-2 is capable of automatic
sequencing while in parallel with the mains in the process control, or process
control soft transfer operating modes. The examples shown above for priority
changing and its effects are accurate in mains parallel multiple unit process
control modes as well.
Inter-control Communications (RS-485 Network)
The EGCP-2 uses a proprietary communication structure to share information
between multiple EGCP-2 controls in a system. This communication structure
allows accurate load sharing, status, and command messages to be exchanged
between up to 8 units. The network uses RS-485 protocol over a standard
twisted shielded pair to link the units in the system together. The end units of the
network must have the proper network termination switches selected at Switch
Location 4. Switches 1, 2, and 3 must be closed to ensure robust inter-control
communications, and prevent reflected data from propagating on the network.
The information on the RS-485 network is for communications between controls
only and must not be interfaced in any way with external devices. There is an
RS-422 port on the EGCP-2 which is used to monitor and control the units
remotely.