Innotech Omni C14, Installation Instructions Manual

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Omni Installation Instructions
Page 58 © Mass Electronics Pty Ltd 2017 Edition 1.2 dated 20.08.2018
4-3.5 Innotech Subsystem Wiring Considerations
The maximum number of devices that can be connected on one section of Comms cable is 32. This
limit is set by the characteristics of the RS-485 ICs. To increase the number of nodes or devices on a
system, an Innotech Repeater IR11 or IR12 should be used.
In practice, the maximum length of cable is determined by the quality of the signals. The signal will
be degraded by using cable which does not meet the RS-485 cable specification and by installing
the cable in locations where it is subject to interference from other cables and equipment. In severe
cases, it may not be possible to have 32 nodes on one section of cable, or to match the defined
maximum cable length.
The two ports on an Innotech Repeater IR11 or IR12 module reside on different sections of the system
and each section can have up to the maximum of 32 nodes. With a one repeater, a total of 64 nodes
can be connected on the system. A repeater can be connected at any point on the network providing
bus topology is maintained.
4-3.5.1 Omni Comms Wiring Connections
There are a number of rules that apply to the comms connection of an Omni System network:
• The screen must be continuous.
• Only one point earthed on the screen.
• Even if a network has a number of devices with a soft earth
1
, one hard earth
2
is still required on
that network.
• The Net and Global networks should have the same length cable run and path.
• If a Innotech Repeater is installed, each side of that repeater is a separate network and each
requires a bonded earth connection on the screen.
• There are no End of Line termination (EOL) requirements on the primary network.
1. Hard Earth - A bonded, hard or clean earth is defined as a low impedance earth point with little or no chance of
conducted noise either already present or likely to be created when bonded to a circuit. For Innotech’s reference
we also explicitly mean there is no potential difference to true earth.
2. Soft Earth - A soft earth is where there is a path to earth via a circuit. This provides a tie to earth so potential
differences are minimised. This path has higher impedance than a bonded earth. Soft earth is often used in 24 V
supplied devices. The ‘tie to earth’ is in fact a ‘tie to 0 V’ because there is no dedicated earth terminal available. It
is therefore expected that the 0 V is earthed near the supply transformer.
4-3.5.2 BACnet MS/TP Wiring Considerations
BACnet MS/TP uses RS-485 for communication and allows up to 32 devices to be installed on a single
network no longer than 1219m (4000 ft).
Different Baud rates can be used but this will change the physical length of the network. If using a
baud rate of 115,200, the maximum length is approximately 600m (1968ft). At 76,800 baud rate the
maximum length is approximately 1219m (4000ft).
Device numbers allowed per network length may be limited when using third party devices.