When this happens, you must push the VENTILATION/BLOWER pushbutton switch and the VENTILATION/EXTRACT pushbutton switch: the OVRD legends come on. This causes the blower fan to stop, opens the conditioned-air inlet valve and opens the skin air-outlet valve not fully.
 All other valves close and the air goes overboard through the skin
 air-outlet valve. The extract fan stays energized.
 4. Power Supply
____________
 **ON A/C 001-049, 051-099, 101-105, 151-154, 201-207,
 (Ref. Fig. 004)

R **ON A/C 106-149, 155-199, 208-299, 301-399, 401-499,
 (Ref. Fig. 004A)
 **ON A/C ALL
 The smoke detection system gets the electrical power from the DC system of
 the aircraft.
 A. Circuit Breakers The smoke detection system gets 28VDC through this circuit breaker:
 -------------------------------------------------------------------------------FIN PANEL/LOCATION DESIGNATION BUS ATA REF. -------------------------------------------------------------------------------5HQ 49VU D05 AIR COND/AVNCS VENT/CTL 401PP 21-26-00 -------------------------------------------------------------------------------

 VENTILATION Panel 22VU and EMER ELEC PWR Panel 21VU
 Figure 003
 1EFF :  ALL  1  26-15-00 Page 6 
1  1  Feb 01/98
 1  1
 1CES  1

 Avionics-Compartment Smoke-Detection System - Power supply
 Figure 004

R 1EFF : 001-049, 051-099, 101-105, 151-154, 1 26-15-00Page 7 1201-207, 1May 01/05 1 1 1CES 1

 Avionics-Compartment Smoke-Detection System - Power supply
 Figure 004A

R 1EFF : 106-149, 155-199, 208-299, 301-399, 1 26-15-00Page 8 1401-499, 1Aug 01/05 1 1 1CES 1

 5. Interface_________ (Ref. Fig. 005)
 The avionics-compartment smoke-detection system has an interface with the following systems:
 -Avionics Equipment Ventilation System (Ref. 21-26-00),
 -
Electrical Power: AC Main Generation (Ref. 24-22-00),

 -
Electrical Power: DC Ancillary Equipment (Ref. 24-68-00),

 -Flight Warning Computer (FWC) (Ref. 31-52-00),
 -Annunciator Light Test and Dimming (Ref. 33-14-00),
 1EFF : ALL 1 26-15-00Page 9 1 1 May 01/05R 1 1 1CES 1

 Avionics-Compartment Smoke-Detection System - Interface Figure 005
 1EFF : ALL 1 26-15-00Page 10 1 1 Nov 01/01R 1 1 1CES 1

 6. Component Description
_____________________

R **ON A/C 001-049, 051-099, 101-105, 151-154, 201-207,
 (Ref. Fig. 006)
 A. Smoke Detector
 The smoke detector includes:
 -
a protective box with air inlets and electrical connectors,

 -
a cell/card assembly.

 (1) Protective box
 The protective box is a cylindrical box made of aluminium alloy. It is made of two half shells:
 (a)
 one half shell with:

 -two connectors (only one used),
 -the cell/card assembly,
 -and the identification plate.

 (b)
 another half shell which is connected to the outside by air inlets.

 (2) Cell/Card Assembly
 The cell/card assembly includes:
 (a)
 A cell assembly with:

 -
a measuring chamber contained in a cover. This cover allows air to flow into the cell. A protective grid is spot-welded in the cover.

 -
a detecting cell which contains a radio-active source.

 (b)
 An electronic circuit which analyses and processes the information from the cell.

 Smoke Detector - Description
 Figure 006

R 1EFF : 001-049, 051-099, 101-105, 151-154, 1 26-15-00Page 12 1201-207, 1May 01/05 1 1 1CES 1R **ON A/C 106-149, 155-199, 208-299, 301-399, 401-499,

 (Ref. Fig. 006A, 007)
 B. Principle
 The smoke detector is of the photo-electrical type. The smoke detection is based on the scattered light principle. The heart of the smoke detector is an optical measurement chamber that screens external parasite light but optimally detects light colored and dark smoke particles. The light source (IR LED), the light trap (or light stop) and the light receiver (photodiode) are arranged in such a way that the light from the emitter cannot directly reach the receiver. Only when smoke particles are present in the optical path, some of the scattered light reaches the photoreceiver and produces an electrical signal. A labyrinth enables the light trap to be efficient and prevent false alarms due to parasite light. The IR LED periodically transmits brief light pulses (0.4 ms) into the measurement chamber. The wavelength of the light is 880 nm (near infrared) in order to optimise the detection efficiency. When smoke particles are present in the optical path, the photodiode receives scattered light and converts it into an electrical signal, to be processed by the electronics.
　
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