Woodward EGCP-2 - Inter-Control Communications (RS-485 Network); Figure 3-25. RS-485 and RS-422 Termination Diagrams

EGCP-2 Engine Generator Control Package Manual 26076
46 Woodward
76
77
485
(+)
RS-485 Termination
485 (-
)
24
3
SW4-1
+5
Vdc
SW4-2 SW4-3
121.
5
24
3
78
Shiel
d
RS 422/485
Transceiver
81
82
RS-422 Termination
24
3
SW3-1
+5
Vdc
SW3-
2
SW3-
3
80
Shiel
d
85
422 TxD (-
)
422 RxD
(+)
422 RxD (-
)
84
422 TxD
(+)
121.
5
24
3
RS 422/485
Transceiver
83
VIS-108a
00-06-20
Figure 3-25. RS-485 and RS-422 Termination Diagrams
For detailed wiring diagrams pertaining to the RS-422 network of the EGCP-2
controls, please consult the plant wiring diagram in this manual.
Inter-control Communications (RS-485 Network)
The EGCP-2 uses a proprietary communication structure to share information
between multiple EGCP-2 controls. This structure allows accurate load sharing,
status, and command messages to be exchanged between up to 8 controls. The
network uses RS-485 protocol over a standard twisted shielded pair to link the
EGCP-2 controls at terminals 76(+) and 77(–) with 78 the shield.
NOTE
When EGCP-2 controls are installed with a distance of 1000 m or greater
between them, additional measures should be taken to ensure solid
communications. The wire gauge of the communications link should be
upgraded to 0.5–0.8 mm² (18–20 AWG) where larger sizes are used for longer
distances. The larger size wire will exhibit smaller voltage drop. If
communications errors are observed, terminal 80 can be connected from
control to control using 1.0 mm² (16 AWG) wiring. Making this connection
will force all communications transceivers to the same reference.
As shown in Figure 3-25, the EGCP-2 uses Switch 4 (4-1, 4-2, and 4-3) to
terminate the 485 network. Switches 4-1, 4-2, and 4-3 will be closed (pushed
DOWN toward the PC board, see Figure 3-4) for proper 485 network
terminations. Proper network termination will ensure robust inter-control
communications.