Siemens SITRANS F Series Operating Instructions Manual page 38

Connecting
5.4 Integrating the FST030 with Modbus system
Topology
The device supports a two-wire electrical interface in accordance with EIA/TIA-485 standard.
An RS485 Modbus configuration without repeater has one trunk cable, along which devices are
connected, directly (daisy chaining) or by short branch cables.
Note
Multidrop examples in this document show a trunk cable with short branch cables.
Maximum cable lengths
The end to end length of the trunk cable must be limited. The maximum length depends on the
baud rate, the cable (gauge, capacitance or characteristic impedance), the number and types
of loads on the daisy chain, and the network configuration.
Note
Maximum branch cable length
Branch cables must be short, never more than 20 m.
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Operating Instructions, 08/2018, A5E37367739-AD
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SITRANS FST030 (Modbus)