14 - English
1. FUNCTION
1.8.1 Boundary wire
The signal strength on the boundary wire is constant at
a loop length of up to about 500 metres (1600 ft).
However, when the loop is longer than 500 metres
(1600 ft), the strength can start to depreciate even if it
may still be adequate. For installations where a longer
boundary wire of up to 800 metres is required, we
recommend a Signal amplifier (522 42 58-01), which is
available as an accessory.
The strength of the loop signal varies depending on the
distance to the wire. Directly by the wire the signal
strength is high. The strength then depreciates the
further you come from the wire. Outside of the loop the
signal is negative and its strength depreciates quicker.
The signal from the boundary wire is called the
A-signal. See the picture below for examples of high
and low signal strengths.
The strength of the A-signal also varies along the
boundary wire depending on the proximity to other
parts of the loop. The strength of the signal is affected
by the size of the working area, islands, heads,
passages and corners. The signal may also be
affected by magnetic objects in the ground or in
surrounding walls and buildings. The signal will
weaken in these areas. For example, a grassed area
on a concrete roof
.
In small installations or sub-areas, narrow passages
and out-turned corners the strength of the signal is
higher. In large installations, heads that point in
towards the area and in-turned corners the strength
of the signal is lower.
When the signal is amplified or weakened, it is normal
that low respective high signal strengths are not always
available along the entire length of the boundary wire.
Examples of high and low signal strengths
300
275
250
Narrow head =
low strength
In-turned corner =
low strength
Out-turned corner
= high strength
Propagation of the loop signal strength, seen from ground
level
Outside Inside
Wire
320
275
70
35m (100 ft)
Strength of the
A-signal
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