Weidmuller Transclinic 8i+ Bedienungsanleitung Seite 57

Function
RS–485 standard B
Modbus standard D1
Weidmüller
The RS–485 cable used to wire this equipment must fulfill the following specifications:
• Shielded twisted pair with 1.5 or 2 pairs (preferably 1.5 pairs)
• Braid shield, not foil shield
• 120 Ω characteristic impedance
• Cross section of individual wires 0.2 mm
The following are two examples of proper RS–485 cable:
• Belden: 3106 A
• Lapp Cable Unitronic Bus LD 2×2×0.22 (part number 2170204)
Modbus terminology:
• The Transclinic is a slave and a server from the viewpoint of the Modbus standard.
• A Scada or the program running in a PLC/datalogger is a client from the viewpoint
of the Modbus standard.
• A RS–485–to–Ethernet converter or the hardware of a PLC/datalogger is a master
from the viewpoint of the RS–485 standard.
Guidelines for RS–485 field wiring of this equipment when installed inside PV
combiner boxes:
• The RS–485 bus topology must be a daisy chain.
• Short stubs (< 2 meters) are allowed inside the combiner boxes.
• Even though the RS–485 standard allows up to 1200 meters bus length at low bit
rates (i.e. 9600 bps and 19200 bps), we recommend staying below 500 meters.
• Each end of the bus requires a 120 Ω 10 % ½ W termination resistor between D+
and D– (see the RS-485 wiring diagram). One end of the bus will be the RS–485
master (which may or may not include an internal termination option) and the other
end will be inside the combiner box farthest away from the master (in terms of
RS–485 cable distance).
58
Non-inverting pin
D+
Inverting pin
A
D0
D–
(AWG24) or larger
2
Reference pin
C
common
C