User's Manual

Radio/Serial Telemetry Module User Manual
Page 10 © March 2000
Chapter Two INSTALLATION
2.1 General
The 905 module is housed in a rugged aluminium case, suitable for DIN-rail mounting. Terminals are
suitable for cables up to 2.5 sqmm in size.
Normal 110/220/240V mains supply should not be connected to any input terminal of the
905 module. Refer to Section 2.3 Power Supply.
Before installing a new system, it is preferable to bench test the complete system. Configuration
problems are easier to recognise when the system units are adjacent. Following installation, the
most common problem is poor communications on the radio channel or the serial channel. For radio
modules, problems are caused by incorrectly installed aerials, or radio interference on the same
channel, or the radio path being inadequate. If the radio path is a problem (i.e. path too long, or
obstructions in the way), then higher performance aerials or a higher mounting point for the aerial
may fix the problem. Alternately, use an intermediate 905 module as a repeater.
For serial modules, poorly installed serial cable, or interference on the serial cable is a common
problem.
The foldout sheet 905 Installation Guide provides an installation drawing appropriate to most
applications. Further information is detailed below.
Each 905 module should be effectively earthed via a "GND" terminal on the 905 module - this is to
ensure that the surge protection circuits inside the 905 module are effective.
2.2 Aerial Installation (905U units only)
The 905 module will operate reliably over large distances. The distance which may be reliably
achieved will vary with each application - depending on the type and location of aerials, the degree
of radio interference, and obstructions (such as hills or trees) to the radio path. See the 905
Installation Guide for expected ranges in your country. Where it is not possible to achieve reliable
communications between two 905 modules, then a third 905 module may be used to receive the
message and re-transmit it. This module is referred to as a repeater. This module may also have
input/output (I/O) signals connected to it and form part of the I/O network - refer to Chapter 4
Configuration of this manual.
An aerial must be connected to each 905 module using the BNC female connector which protrudes
though one of the end plates.
To achieve the maximum transmission distance, the aerials should be raised above intermediate
obstructions so the radio path is true “line of sight”. Because of the curvature of the earth, the
aerials will need to be elevated at least 5 metres above ground for paths greater than 5 km (3 miles).
For short distances, the modules will operate reliably with some obstruction of the radio path.