Emerson XM670, Инструкция по установке и эксплуатации

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40 • XM679K I&O Manual 026-1218 Rev 4
it.
22.4.Wiring Types
Emerson specifies Belden #8761 shielded twisted pair
cables for use as MODBUS wiring (or Belden #82761
and Belden #88761 for plenum installations).
For MODBUS network wiring of XM670 - XM679
controllers to E2, Belden #8641 (
Emerson

P/N 135-8641
) is the recommended wire type to use.
If the recommended cable is not available in your
area, be sure the wiring meets or exceeds the
following specs:
Shielded? Yes
Conductor Type Twisted Pair
Gauge 18 - 24 AWG
Capacitance between
signal wires
31 pF/ft or less

(9.45 m) or less
Capacitance between
signal and shield
59 pF/ft or less

(17.98 m) or less
Maximum Length
4000 ft/18 to 22 AWG

(1219.2 m)

2500 ft/24 AWG

(762 m)
Nominal Impedance 120W±50W
22.5.MODBUS Termination
Blocks
Because the XM670/XM679 device has no on-board
means of termination, use the MODBUS termination
block (
P/N 535-2711
) for termination that can be
wired to the end of the cable segment using the three-
pin connector. Wire the two signal wires to the
outside terminals, and connect the shield to pin 38 of
the device, keeping the exposed shield wire length as
short as possible (3 inches ideal maximum length).
Figure 22-9 - Network Summary Screen
Figure 22-10 - MODBUS Termination Block (P/N 535-2711)
FROM LAST
DEVICE
AT END OF
DAISY-CHAIN
SHIELD WIRE
(CONNECT TO
OF DEVICE)
PIN 38
TO TERMINAL DEVICE