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Photoelectric Smoke Alarms
Photoelectric-type smoke alarms for use as an alert device connected to a Watchdog monitoring appliance, with a solid state piezo signal to warn and alert to the presence of threatening smoke
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Photoelectric smoke alarms / sensors
for Watchdog environmental monitoring systems
Photoelectric-type smoke alarms for use as an alert and relocate device in residential and commercial applications.
Each smoke alarm has a solid state piezo signal to warn and alert to the presence of threatening smoke.
Watchdog photoelectric smoke alarms are designed to detect the smoke that results from an actual fire. Consequently, it is uncommon cigarette smoke or normal cooking smoke to cause an alarm.
Watchdog smoke alarms operate on the photoelectric light scatter principle. The unit's sensing chamber houses a light source and a light sensor. The darkened sensing chamber is exposed to the atmosphere and designed to permit optimum smoke entry from any direction while rejecting light from outside the smoke alarm.
The light source is an infrared (invisible) LED which pulses every 8 seconds. The light sensor is a photodiode matched to the light frequency of the LED light source.
Under normal conditions, the light generated by the pulsing infrared LED is not seen by the light sensor, as it is positioned out of the direct path of the light beam. When smoke enters the sensing chamber, light from the pulsing LED light source is reflected by the smoke particles onto the photodiode light sensor.
At the first sighting of smoke, the device is put into a pre-alarm mode. This is indicated by a rapidly flashing LED on the face of the smoke alarm. Once the light sensor confirms smoke for 2 consecutive pulses inside the chamber, the light sensor produces the signal necessary to trigger the alarm and sound the electronic horn.
This technique of verifying the smoke condition, combined with a 5-to-1 signal-to-noise ratio, substantially reduces the possibility of nuisance alarms.