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7
ELECTRICAL
DESCRIPTION
The detector is designedto
be connected to a twowire
loop circuit carryingboth
data and a 17V to 28Vdc
supply. The detector is
connected to theincoming
and outgoing supplyvia
terminals L1 andL2 in the
mounting base. A remote
LED indicator requiringnot
morethan 4mA at 5V may
be connected between+R
and-R terminals. An earth
connectionterminal is also
provided, althoughthis is
not required for the
functioning ofthe detector.
Whenthe device is energised
the ASICs regulatethe flow
of powerand controlthe data
processing. The ionisation
chambers are energisedand
the ultra low leakagesensor
ASIC provides a conditioned
analogue signalto the
analogue to digital(A/D)
converter withinthe
communicationsand
processing ASIC. When
smoke enters theionisation
chambersthroughthe integral
gauze, the voltageat the
sensingelectrodeincreasesto
producean analoguesignal.
An A/D conversionof the
signal from the ionisation
chambersis carried out once
per second or wheneither
the detector or preceding
addressis beinginterrogated.
Whenever the deviceis
interrogatedthis data is sent
to the control equipment.
EN54 thresholdalarm levels
are calibratedwithin the
processing ASIC. If the
device is not addressed
within 1 second of its last
polling and the analogue
value is greater than 55 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 calibratedto
give an analoguevalue of
25±7countsin cleanair. This
value increases with smoke
density. A count of 55
correspondstothe EN54alarm
sensitivitylevel. See Fig 3.
Counts of 8 or less indicate
faultconditions. Countlevels
between 45 countsand 55
countscan be usedto provide
an early warningof fire.
ENVIRONMENTAL
CHARACTERISTICS
XP95ionisation smoke
detectorsare designedto
operatein a wide variety of
environments(See Figs4 to
6). Thereare only small
effectsfrom temperature,
humidity,atmospheric
pressureand wind. Detectors
are wellprotected against
electromagnetic interference
overa wide frequency range.
The XP95ionisation detector,
likeall ionisation detectors,
has somesensitivity to air
movement(wind). The
extentto which the analogue
valuewill change depends
on thewind speed and on
the orientation of the
detector relativeto the wind
direction. Relativelysmall
changesin wind direction
can causesignificant changes
in analoguevalue.
Fig.3 Typical response characteristics - XP95 Ionisation Detector
Fig.4 Typical temperature response - XP95 Ionisation Detector
Fig.5 Typical pressure response - XP95 Ionisation Detector
Fig.6 Typicalwindspeed response- XP95IonisationSmoke Detector