West Control Solutions KS 800 CANopen Interface Manual - Manual (Page 45)

KS 800 CAN-Interface
11.4 Cable parameters
ISO 11898-2 defines some DC or AC parameters for the cables which can be used in CAN bus
networks (typically, pairwisely twisted cables with defined electrical properties are used). The
important AC parameters are 120 Ohm cable impedance and a nominal _propagation delay_ of
5 ns/m ! Recommendations for the bus cables and terminating resistors are given in the following
table:
Bus-length Bus-cabel (Z: 120 Ohm, tp: 5ns/m Terminating-
resistance
Max. Bit-rate
Spec.
resistance
Cabel-size
0 ..40 m 70 mOhm/m 0,25mm², 0,34mm²
AWG 23, AWG 22
124 Ohm, 1% 1 MBd
@ 40m
40 m .. 300 m <60 mOhm/m 0,34mm², 0,6mm²
AWG 22, AWG 20
127 Ohm, 1% * ) > 500 kBd
@ 100m
300 m .. 600 m <40 mOhm/m 0,5mm², 0,6mm²
AWG 20
127 Ohm, 1% * ) > 100 kBd
@ 500m
600 m ..1 km <26 mOhm/m 0,75mm², 0,8mm²
AWG 18
127 Ohm, 1% * ) > 50 kBd
@ 1 km
* ) With very long cables, a higher value for the terminating resistor (150 .. 300 Ohm) is useful for
reducing the attenuation.
Further recommendations for CAN networks (especially large ones):
Galvanic isolation is necessary with very long bus cables (e.g. 400m).
A separate ground line is purposeful.
The voltage drop (potential difference) between the transceiver ground potentials should
be low (smaller than 2 V, supply voltage from power supply in the middle of the cable).
The total input resistance of bus nodes should be > 500 Ohm.
Any tap lines should be as short as possible to prevent/reduce reflections, e.g. 6m @
500kbit (DeviceNet). < 1 m with higher bit rates !
For further information, refer to ODVA (DeviceNet), CiA (CANopen), various chip manufacturers
and Internet.
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