VESDA ECO Detector by Xtralis Product Guide
17898_05 Installation 17
When a junction/terminal box (also known as a passive tap) is used to connect an
RS485 device, such as an ECO, to the bus then the branch must not be longer than
3m.
Using a “repeater” or “signal amplifier” or “active tap”, the cable lengths can be
extended, but each length between repeaters is limited to the 1200m length
restriction and must be terminated correctly.
Figure 8 Modbus Topology
The number of devices on each section between repeaters is the same as for a
standard bus, i.e. 32 “standard loads”, but the user must remember to account for
the repeater at each end in that total number, i.e. actual number of devices is 30
“standard loads”. The total number of devices on the overall the bus connection is
not affected by the use of “repeaters” or “signal amplifiers” as this is limited by the
maximum number of addresses allowed by the Modbus specification.
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