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4
Operating principle (see block diagram Fig. 3)
2 ASIC
9
13
12
7
23
20
22
NTC
Fire & Security Products
Siemens Building Technologies Group
The PolyRex detectors DOTE1152 measure the smoke density as well as the am-
bient temperature. The temperature sensor signal can be evaluated either differen-
tially and/or absolute. The smoke sensor is based on the scattered light principle. An
infrared light emitting diode (IRED) transmits brief, intensive light pulses into the
scattering chamber. The receiving element "sees" the scattering chamber but not the
transmitter. The smoke that has penetrated into the scattering chamber scatters the
light beam produced by the transmitter. As a result some of the light reaches the re-
ceiver. The generated receiver signal is processed by the electronic circuitry.
The microprocessor (µP)
performs the signal processing and classifies the events into different danger levels
and function states. Also the communication with the control unit is controlled by the
µP. Numerous detector characteristics are stored in the non–volatile µP memory
(255 byte EEPROM). These can be read out and modified at any time by authorized
specialists. The content of the non–volatile memory is checked automatically in in-
tervals of approx. 15 minutes.
In the customer–specific integrated circuit (ASIC),
are implemented. Centrally located is the sequence control.
other functions, a current pulse in the light transmitter
µP. The light receiver
into the sensor chamber.
This current is amplified and integrated
filter
5
very selectively passes only signals on the correct frequency and phasing
(interference signal suppression). The sample/hold stage
gnal and stabilizes it until the µP has read the value. The level check unit
the signals for possible overamplification. Gain Control
ment of the detector and the sensitivity setting. On request, the test unit
a test signal to the receiver input so that the overall amplification of the signal path
can be monitored (part of the selftest).
10
3
4
5
6
8
21
Fig. 3
Block diagram DOTE1152
1
controls the various measurement and test sequences,
12
produces a synchronous signal current of smoke penetrates
4
in the integrator. The multiple coincidence
µP
1
11
ADC
ADC
ADC
I/O
2
the sensor–specific functions
3
It produces, among
13
, which is monitored by the-
6
further amplifies the si-
8
is used for coarse align-
14 LI
18
15
17
16
Isolator only
Detector
in DOT1152
Socket
CO
25
24
7
monitors
9
transmits
+
B
D
F
19
E
A
–
C
Control unit
7
e4070e
10.2002
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