CANOPEN Field Bus

Types of Bus Cables

For CANOPEN, only bus cables with characteristics as recommended in ISO 11898 are to be used. The requirements for the bus cables depend on the length of the bus segment. Regarding this, the following recommendations are given by ISO 11898:

Length of segment [m]	Bus cable (shielded, twisted pair)			Max. baud rate [kbit/s]
	Conductor cross section [mm²]	Line resistance [W/km]	Wave impedance [W]
0…40	0.25…0.34 / AWG23, AWG22	70	120	1000 at 40 m
40…300	0.34…0.60 / AWG22, AWG20	< 60	120	< 500 at 100 m
300…600	0.50…0.60 / AWG20	< 40	120	< 100 at 500 m
600…1000	0.75…0.80 / AWG18	< 26	120	< 50 at 1000 m

Attention

:strong:Risk of telegram and data errors!

The use of wrong cable type and quality could lead to limitations in cable length, causing telegram and data errors.

Attention

:strong:Risk of damaging the terminating resistor!

A bus-line short-circuit to the 24 VDC power supply can cause damage by exceeding the power rating of the terminating resistor.

Attention

:strong:Risk of telegram and data errors!

Miss- or unterminated data lines can cause reflections on the bus, leading to telegram and data errors. For maximum cable length and transmission rate, the bus must always be terminated on both ends with the characteristic impedance of the cable type.

Attention

:strong:Verification of termination (Make sure the power supply on all CAN nodes is turned off)!

To verify the termination, the DC resistance between CAN_H and CAN_L can be measured. The value should be between 50 W and 70 W.

Check for correct resistor values, short circuits and correct number of terminating resistors, if the measurement is showing deviations.

Installation Hint

Note

Ensure that the termination and FE connection will not be removed when removing CAN modules from the bus.

Note

Branches are not allowed in a CAN network. Stubs should be avoided or kept as short as possible (< 0.3 m).

Note

When connecting the cable take care to use one dedicated twisted pair for the CAN signals (CAN_L and CAN_H) and another free wire for CAN_GND. CAN_GND must be connected as reference, to avoid common mode problems causing telegram errors.

Note

Keep the CAN bus wiring away from electrical disturbance and close to earth potential to minimize interference.

CAN Bus, connection and wiring

For more Information on CANOPEN/DEVICENET field bus see CM578-CN - CANOPEN Master.