ICP DAS USA I-7540D - Manual (Page 15)

2.3 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 2-4.
Figure 2-4: 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.
Table 2-4: Relation between bus cable and length
Bus Cable Parameters
Bus
Length
(meter)
Length Related
Resistance
(mΩ/m)
Cross Section
(Type)
Terminal
Resistance
(Ω)
0~40 70
0.25(23AWG)~
0.34mm 2 (22AWG)
124 (0.1%)
40~300 < 60
0.34(22AWG)~
0.6mm 2 (20AWG)
127 (0.1%)
300~600 < 40
0.5~0.6mm 2
(20AWG)
150~300
600~1K < 20
0.75~0.8mm 2
(18AWG)
150~300
i-7540D CAN-Ethernet Gateway User’s Manual (Version 1.4, April/2008) 15