B&B Electronics GW-7433D - Manual - Manual (Page 16)

2.1.4 Terminator resistor settings
In order to minimize reflection effects on the CAN bus line, the CAN bus
lines have to be terminated at both ends by two terminal resistances. Based on
the ISO 11898-2 spec, each terminal resistance is 120Ω (or between
108Ω~132Ω). The length related resistance should have 70 mΩ/m. Users
should check the resistances of their CAN bus, before they install a new CAN
network as figure 2.5.
Figure 2.5 Terminator resistor
Moreover, to minimize the voltage drop on long distance, the terminal
resistance should be higher than the value defined in the ISO 11898-2. Table
2-4 may be used as a reference.
Bus Length
(meter)
Length Related
Resistance (mΩ/m)
Cross Section
(Type)
Terminal
Resistance (Ω)
0~40 70 0.25(23AWG)~
0.34mm2(22AWG)
124 (0.1%)
40~300 < 60 0.34(22AWG)~
0.6mm2(20AWG)
127 (0.1%)
300~600 < 40 0.5~0.6mm2
(20AWG)
150~300
600~1K < 20 0.75~0.8mm2
(18AWG)
150~300
Table 2-4: Relation between bus cable and length
GW-7433D MODBUS TCP/RTU to CANopen Gateway User Manual 16
(Version 2.0.0, Jul/2011)