Apollo Smoke Detector XP95 Betriebsanweisung PDF herunterladen (Seite 8)

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reference and smoke

chambers, the sensing

electrode converts variations

in chamber current into

voltage changes.

When smoke particles enter

the ionisation chamber, ions

become attached to them

with the result that the

current flowing through the

chamber decreases.

This effect is greater in the

smoke chamber than in the

reference chamber, and the

imbalance causes the

sensing electrode to become

more positive.

The analogue voltage at the

sensor electrode is

converted to a digital format

which is processed to

provide an analogue value

for transmission to the

control panel when the

device is polled.

Ionisation smoke detectors

are supplied in individual

packing with a red lid

serving as a dust cover

which can be left in place

after fitting to prevent

ingress of foreign material

until commissioning of the

system takes place. At this

point the covers must be

removed.

DISCOVERY IONISATION SMOKE DETECTOR

Discovery Ionisation Smoke Detector ▲ Part Number 58000-500

OPERATING

PRINCIPLES

The Discovery ionisation

smoke detector has a

moulded white

polycarbonate case with

wind-resistant smoke inlets.

Inside the case is a printed

circuit board which has the

ionisation chamber mounted

on one side and the signal

processing and

communications electronics

on the other.

The ionisation chamber

consists of a reference

chamber contained inside a

smoke chamber (Figure 2).

Fig.2 Sectional view - Discovery Ionisation Smoke Detector

Mode Alarm Minimum time

threshold to alarm

y value (sec)

1 0.45 5

2 0.45 30

3 0.70 5

4 0.70 30

5 1.0 5

Compensation rate complies with EN54–7:2000

Table 1 Ionisation detector operating modes

Address Buttons

10V on Foil Holder

Radioactive Foil

Case Moulding

Lid Moulding

LED

Smoke Chamber

0V

Inner Cover

Inner Chamber

PCB

LED

The outer smoke chamber

has inlet apertures fitted

with insect resistant mesh.

The radioactive source

holder and the smoke

chamber form positive and

negative electrodes

respectively. An Americium

241 radioactive source

mounted within the

reference chamber

irradiates the air in both

chambers, producing

positive and negative ions.

A voltage across the

electrodes produces an

electric field.

Ions are attracted to the

electrode of the opposite

sign to their own charge;

many recombine but a

small electric current flows

between the electrodes. At

the junction between

1 2 3 4 5 6 7 8 9 10 11 12 13 ... 27 28

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