IDL 101
STRUCTURE OF THE BUS TOPOLOGY
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HB_IDL101_E_V222.doc
Gantner Instruments Test & Measurement GmbH
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Figure 4.4 Line structure with branches
4.3. Number of Parties
The RS485 interface permits the simultaneous connection and operation respectively of a maximum of 32 bus users per
bus segment. Further bus segments can be constituted via bi-directional repeaters, and thus the number of bus users
can be raised to max. 127.
4.4. Transmission Speed and Line Length
The transmission speed with the
Datalogger IDL 101
can be adjusted for each protocol. The permissible line lengths
depend on the transmission speed. With transmission speeds lower than 93.75 kbps these line lengths amount to 1,200
m (3,900 feet) per bus segment; with 187.5 kbps the line length is reduced to 600 m (1,900 feet) per bus segment
(specifications according to USA-standard EIA RS422-A). Thus with lower baud rates and with 3 repeaters topologies
with a dimension of max. 4.8 km (3 miles) can be set up.
transmission line length
speed without repeater with 3 repeaters
≤
93.75 kbps
max. 1,200 m (3,900 feet) max. 4.8 km (3 miles)
187.5 kbps max. 600 m (1,900 feet) max. 2.4 km (1.5 miles)
Table 4.1 Interrelation between transmission speed and line length
Notice:
These specifications refer to bus cables with a conductor cross section of 0.22 mm² and a permissible signal
attenuation of max. 6 dB referred to the overall length. According to previous experience the line length can be twice as
long if a two-wire circuit with a conductor cross section of at least 0.5 mm² is used.
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