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Which type of smoke detector system uses filament lamp?
Ion type
Phote electric type
Both
None of this
Phote electric type
A photoelectric smoke detector uses a light source, typically a filament lamp or LED, and a light-sensitive sensor (photodiode or phototransistor) housed in a chamber. When smoke particles enter the chamber, they scatter the light beam, causing it to strike the sensor and trigger the alarm.
A photoelectric smoke detector uses a light source, typically a filament lamp or LED, and a light-sensitive sensor (photodiode or phototransistor) housed in a chamber. When smoke particles enter the chamber, they scatter the light beam, causing it to strike the sensor and trigger the alarm.
I=I0тАЛтЛЕeтИТ╬▒L тАФ Beer-Lambert law describing light attenuation (relevant for obscuration-based sensing)
╬ФIтИЭNтЛЕ╧Г тАФ Change in current is proportional to the number density (N) and scattering cross-section (╧Г)of particles
The principle is based on the Tyndall effect or light scattering. A beam of light is emitted from a filament lamp across a sensing chamber. Under clear conditions, the beam does not hit the sensor directly. When smoke enters, it scatters the light, directing a portion onto the photoelectric sensor, which generates a current to actuate the alarm circuit.
Photoelectric detectors are more sensitive to smoldering fires with large smoke particles.
The filament lamp acts as the light transmitter in older conventional models.
Modern detectors often replace incandescent filament lamps with infrared LEDs to improve durability and power efficiency.
They operate on either light-scattering or light-obscuration principles.
High sensitivity to large-sized smoke particles from smoldering fires.
Lower rate of false alarms compared to ionization types in high-humidity environments.
Susceptible to interference from insects or dust accumulation in the sensing chamber.
Less effective than ionization sensors for fires involving fast-burning materials with small particles.
Residential fire alarm systems.
Commercial building smoke detection.
Server rooms and data centers.
| Feature | Ionization Type | Photoelectric Type |
|---|---|---|
Sensing Mechanism | Alpha particle ionization | Light scattering/obscuration |
The term 'Photo electric' is often written as 'Photoelectric'.
Ionization types use a radioactive source (typically Americium-241) to ionize the air, not a lamp.
B is correct тАФ Photoelectric type detectors use a light source, traditionally a filament lamp or LED, to detect smoke particles via light scattering.
In competitive exams, remember that ionization detectors use radiation, while photoelectric detectors use optical sensors; both are fundamental parts of the life safety fire protection syllabus.