5
How many XP95 beam detectors can be
connected to a loop?
Although the Apollo Beam Detector is loop powered,
the total current drawn by the beam detector compo-
nents combined is considerably higher than a standard
point detector (equivalent to approximately 40 point
detectors). For this reason care must be taken when
designing an analogue loop, bearing in mind the effects
of voltage drop—a consequence of loop cable resist-
ance, device loading and control panel speci
fi
cation.
Each beam detector set (consisting of transmitter, re-
ceiver and interface) draws approximately 16mA from
the analogue addressable loop and, unless proven by
In buildings with pitched roofs or ceilings the maximum
distance either side of the beam
in the apex only
may
be increased by 1% for each degree of ceiling pitch
up to a maximum of 25% (Fig 2).
Example: Roof pitch = 20°
Span of beam = 15m
15m + (15 x 20%) = 18m
There must be a clear line of sight between the trans-
mitter and receiver at all times. If there is any doubt
about the correct mounting of detectors in a particular
installation, the position may be de ter mined by smoke
tests.
All in stal la tions must conform to locally applicable
stand ards and codes of practice.
A ceiling or roof with a slope in excess of 3.5° should
be regarded as a pitched roof.
*calculation, it is recommended that
not more than
fi
ve beam detector sets are powered from each loop
or, alternatively, eight interface/ receiver combinations
when the transmitter head is independently powered
from a remote power supply.
Beam detectors must be protected by short-circuit iso-
lators. For details of these please refer to Apollo PIN
sheet PP2090. For calculation purposes the interface
should be considered as 12 point detectors and the
transmitter 7 point detectors.
*Depending upon the type of panel used, the resist-
ance of cable and the total loop load, it may be pos-
sible to install in excess of 10 beam detector sets on
a single analogue addressable loop. A mathematical
calculation to assess the worst case loop voltage drop
should be performed prior to installation in order to
prove the intended design. A loop voltage drop calcula-
tion program, known as ‘Loop Calculator’, has been
developed by Apollo for use by system designers and
is available as a free download from the Apollo web
site (www.apollo-
fi
re.co.uk).
10˚
7.5m
7.5+8.25m
8.25+7.5m
20˚
18m max
7.5 + 7.5 + 3.m
20˚
7.5m
15m
0.5m
Roof pitch = 20˚
Span of beam = 15m
15m + (15 x 20%) = 18m
Fig 2
Positioning detectors under different types of sloped or pitched roofs
