ABB AC 800M User Manual page 74

Bus length and speed
The maximum length of the line is restricted by the type of explosion protection and
the drop in current over the bus line. The drop in current may result in a further
limitation to the number of subscribers.
The time required for a complete cycle of data exchange depends essentially on the
transmission rate, the number of subscribers and the size of the measurement
(Value) and status values to be transmitted cyclically. Delay times, which arise
through the Linking Devices and the field devices itself, must be taken into
consideration as well.
For detailed information about power consumption and delay times, please read
the specific user manuals of the field devices.
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Section 3 Fieldbus Topologies
3BDS009029R5001 B