Technical data

XP95 Optical Smoke Detector s Part Number 55000-600/620/660
OPERATING
PRINCIPLES
The XP95 optical detector
uses the same outer case
as the ionisation smoke
detector and is distinguished
by the indicator LED which
is clear in standby and red in
alarm. Within the case is a
printed circuit board which
on one side has the light
proof labyrinth chamber with
integral gauze surrounding
the optical measuring system
and on the other the address
capture, signal processing and
communications electronics.
An infrared light emitting
diode within its collimator is
arranged at an obtuse angle to
the photo-diode. The photo-
diode has an integral daylight-
blocking filter.
The IR LED emits a burst of
collimated light every second.
Fig.7 Top section - XP95 Optical Smoke Detector
In clear air the photo-diode
receives no light directly from
the IR LED because of the
angular arrangement and
the dual mask. When smoke
enters the chamber it scatters
photons from the emitter IR
LED onto the photo-diode
in an amount related to the
smoke characteristics and
density. The photo-diode
signal is processed by the
optical ASIC and passed to
the A/D converter on the
communications ASIC ready
for transmission when the
device is interrogated.
ELECTRICAL
DESCRIPTION
The detector is designed to be
connected to a two wire loop
circuit carrying both data and
a 17V to 28V dc supply. The
detector is connected to the
XP95 OPTICAL SMOKE DETECTOR
incoming and outgoing supply
via terminals L1 and L2 in the
mounting base. A remote
LED indicator requiring not
more than 4mA at 5V may
be connected between the
+R and -R terminals. An earth
connection terminal is also
provided.
When the device is energised
the ASICs regulate the
flow of power and control
the data processing. The
optical ASIC is controlled by
the communications ASIC
and pulses the IR LED. The
signal from the photo-diode
is processed by the optical
ASIC and transferred to the
communications ASIC where it
is then stored. When smoke
enters the chamber the
photo-diode signal increases.
The information to the A/D
converter is updated once
per second or when either
the monitor or the preceding
address is interrogated.
Whenever the device is
interrogated this data is sent
to the control equipment.
EN54 threshold alarm levels
are calibrated within the
processing ASIC. If the device
is not addressed within one
second of its last polling and
the analogue value is greater
than the EN54 alarm level the
alarm flag is initiated and the
device address is added to the
data stream every 32 polling
cycles from its last polling
for the duration of the alarm
level condition, except when
the alarming device is being
interrogated. This can provide
a location identified alarm
from any device on the loop
in approximately two seconds.
The detector is calibrated
to give an analogue value
of 25±7 counts in clean air.
This value increases with
smoke density. A count of
55 corresponds to the EN54
alarm sensitivity level. See
Fig. 9.
ENVIRONMENTAL
CHARACTERISTICS
The XP95 optical smoke
detector is unaffected by
wind or atmospheric pressure
and operates over the
temperature range -20°C to
+60°C. See Fig. 10.
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