(APPENDIX IV) CAN COMMUNICATIONS |
PAGE 93
Table 2
Characteristics of the cable depending on the number of nodes
Length of bus
Number of nodes
32
64
100
100 m
0.25 mm
2
0.25 mm
2
0.25 mm
2
250 m
0.34 mm
2
0.50 mm
2
0.50 mm
2
500 m
0.75 mm
2
0.75 mm
2
1.00 mm
2
Cable Resistance
<21 mΩ
<18.5 mΩ
<16 mΩ
To connect the different nodes to the network an unshielded twisted pair cable is
required. As an exception, inside for the connection between the measurements
and visualization module of the control unit, an untwisted cable can be used.
In very noisy environments and with high electromagnetic interference (EMI)
shielded twisted cable can be used with the shield connected to earth of the
installation. Another technique for improving immunity to electromagnetic
interference is to replace the CAN terminator of the node for two 62Ω resistors
and install a bypass capacitor between the CAN resistance and battery negative.
Fig.2
Protection technique against electromagnetic noise:
Decoupling capacitor
NOTE
The existing impedance must be measured when all the equipment is no longer working
or does not have physical access to the network. For more information, please see the
ISO 11898 specification and the different notes that apply in this respect.
Fig.1
CAN bus topology
12.3 WIRING
The CAN network requires wiring dependent on the distance, baud rate and
number of nodes connected to the bus.
Table 1
Characteristics of the cable depending on the length
Length of bus
Characteristics of the cable
Length/resistance ratio
Cross-section
0 m..40 m
70 mΩ/m
0.25 mm
2
..0.34 mm
2
AWG23, AWG22
40 m..300 m
<60 mΩ/m
0.34 mm
2
..0.6 mm
2
AWG22 , AWG20
300 m..600 m
<40 mΩ/m
0.4 mm
2
..0.6 mm
2
AWG20
600 m..1 Km
<26 mΩ/m
0.75 mm
2
..0.8 mm
2
AWG18
CAN Bus line
node 1
node n
Bus Line
