Special Features Of The Loop Structure Redundancy - AUMA AUMATIC AC 01.2 Manual

Description of the data interface
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station, this repeater functions enables the setting up of redundant Modbus RTU
field systems in loop structure.
Figure 3: Redundant loop
Only a two-wire fieldbus cable is required between the actuators as fieldbus cable.
Modbus RTU is used as data protocol. All actuator controls have two Modbus
RTU-485 channels. The settings of the Modbus interface apply to both channels.
Please refer to the separate operation instructions for SIMA master station for further
information regarding the setting and operation of the SIMA master station made by
AUMA.

Special features of the loop structure redundancy

The two channels of the actuator controls are galvanically isolated from each other.
The Modbus RTU data telegrams from the SIMA Master Station are received by the
actuator controls via one channel and are forwarded to the next device by means of
the repeater function of the second channel.
The galvanic separation creates RS-485 loop segments with max. permissible cable
length of 1,200 m per SIMA master station. 247 AUMA actuators may be connected
per loop. In theory, Modbus RTU networks with cable lengths up to approx. 290 km
can be implemented.
Figure 4: Redundant loop (normal operation)
The Modbus communication to the actuators is maintained in the event of a cable
fault as the galvanic isolation prevents the transmission of a fault from one loop
segment to the neighbouring loop segment. As long as only one loop segment fails,
the communication to the other actuators is maintained via the remaining segments.
Actuator controls
AC 01.2/ACExC 01.2 Modbus RTU