Cable And Bus Termination Rs-485; Can Interface; Cable Recommendations; Termination - Beijer Electronics X2 control 7-B2 Installation Manual

NOTE
It is very important to make sure that the 24 V feed in the external insulation unit
is not connected to one of the communication outlets. If it does not have 100%
insulation against the 24 V feed, disturbances and grounding currents from the 0 V on
the 24 V side disrupt the communication.
Using this type of unit solves one problem but creates a larger problem! A
substandard installation may work now, but problems may arise when other devices
are connected.

7.7. Cable and Bus Termination RS-485

• If maximum transfer distance and maximum transfer speed is needed, shielded and twisted pair
cable should be used. The mutual capacitance may not exceed 52.5 pF/m, and the cable area
should be at least 0.25 mm
• 0 V, the reference voltage for communication should be included in the cabling. With two-way
communication use two pairs; one pair for communication and one pair for 0 V.
• The shield must be grounded at one end. The other end is usually grounded, but with longer
distances or when there is a difference in the ground potential, the shield should be connected to
the ground via 0.1 μF / 250 V film capacitor to prevent ground current in the braided shield. Some
manufacturers recommend that the shield be grounded at each node. Various manufacturers have
different systems for bus termination.
Depending on the recipients' design, the bus wires may be on the same level or require pull-up
or pull-down to ensure that no faulty signals are detected when the bus is in resting mode (all
transmitters are disconnected).

7.8. CAN Interface

7.8.1. Cable Recommendations

• Use shielded, twisted pair cable to improve noise immunity and to reduce radiated emissions.
Characteristic impedance: 120 Ohm (typical)
Propagation delay: 5 ns/m
Mutual capacitance: 40 pF/m (typical, wire to wire)
• Recommended cable cross section:
Bus length 0-40 m: 0.25-0.34 mm² (AWG23,AWG22), 70 mOhm/m
Bus length 40-300 m: 0.34-0.6 mm² (AWG22,AWG20), < 60 mOhm/m
Bus length 300-600 m: 0.5-0.6 mm² (AWG20), < 40 mOhm/m
Bus length 600-1000 m: 0.75-0.8 mm² (AWG18), < 26 mOhm/m
• GND should be included in the cabling to provide a reliable reference Ground for each CAN node
(potential equalization). Use two wire pairs; one pair for communication and one pair for GND. Do
not use the cable shield to connect GND.

7.8.2. Termination

• To achieve the best signal integrity, noise immunity and reliable bus performance, the CAN network
must be terminated at its two most distant CAN nodes with 118Ohm... 130Ohm resistors. The
recommended resistor value is 120 Ohm/1%/0.25W on each end.
• Place the termination resistor near the CAN bus connector (as close as possible).
• This product has no integrated termination resistors. They must be added externally.
Beijer Electronics, MAEN215
2
(AWG 24).
27
Additional Installation Tips
2023-09