AUMA MATIC AMExB 01.1 Instructions Manual page 12

Actuator controls AUMA MATIC AM/AMExB/AMExC
Modbus
3.10 Bus cables
Figure E: Example: Modbus with one segment
Controls (master)
2-wire cable
Modbus board
Connection
Board
12
Only cables according to the recommendations of EIA 485 standard may be
used for Modbus wiring.
A maximum of up to 32 Modbus devices may be connected in one segment.
If more stations are to be connected to one Modbus network, several
segments must be connected with repeaters.
The bus cable must be laid at a distance of at least 20 cm from other cables.
It should be laid in a separate, conductive, and earthed cable trunking.
It must be ensured that there are no potential differences between the indivi-
dual devices on the Modbus (perform a potential compensation).
The max. cable length without repeater amounts to 1,200 m (independent of
the baud rate).
Cable recommendation for Modbus
Characteristic impedance:
Cable capacity:
Core diameter
Core cross section:
Loop resistance:
Screening:
35 to 165 Ohm, at a measurement
frequency of 3 to 20 MHz.
< 30 pF per metre
> 0.64 mm
> 0.34 mm², corresponds to AWG 22
< 110 Ohm per km
copper shielding braid or shielding braid and
shielding foil
Bus termination
switched on
AUMA MATIC
Modbus
Short instructions
Bus termination
switched on