7
How many refl ective beam detectors can be
connected to a loop?
Although the refl ective beam detector is loop
powered, the total current drawn is considerably
higher than a standard point detector. 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
resistance, device loading and fi re control panel
specifi cation.
Each refl ective beam detector draws approxi-
mately 9mA from the analogue addressable loop
and, unless proven by calculation*, it is recom-
mended that not more than ten beam detectors
be powered from each loop.
The reflective beam detector is fitted with a
negative bi-directional short circuit isolator. For
details of these please refer to Apollo PIN sheet
PP2090.
*Depending upon the type of panel used, the
resistance of cable and the total loop load, it may
be possible to install in excess of 10 beam detec-
tors 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 in-
tended design. A loop
voltage drop calcula-
tion program, known as
‘Loop Calculator’, has
been developed by
Apollo for use by system
designers and is avail-
able as a free down-
load from the Apollo
website (www.apollo-
fi re.co.uk).
INSTALLING BEAM DETECTORS
General
Position the beam detector to give good access
for alignment and servicing.
Set sensitivity (obscuration level) and address
before making electrical connections. Route
cables away from other electrical cables and
switchgear.
Switch refl ective beam detectors to ‘operating
mode’ (mode switch on the back of the detector)
before they are connected to the loop to avoid
excessive current draw on the loop.
Setting the obscuration level
Set the beam detector to one of the three ob-
scuration levels shown in Table 2 below. This is
done with DIL switches 3 and 4 on the back of
the detector (Fig 3).
To alter the obscuration level while power is ap-
plied change the beam detector to ‘alignment
mode’ before altering the DIL switch setting.
Change it back to ‘operating mode’ after-
wards.
Obscuration level in %
Typical application
DIL switch segments
1 2 3 4
25
Offi ces, small premises,
non-smoking clean
areas, eg, museums,
theatres
X
X
ON
OFF
35 (Default setting)
Factories, warehouses
X
X
OFF
ON
50 Hostile
environments
only, eg, mills, foun-
dries
X
X
OFF
OFF
12 Do not use.
Possible future require-
ment.
X
X
ON
ON
Table 2 Obscuration levels
