Functions
Basic Operation
An ultraviolet-detector tube within the D284 absorbs very weak ultraviolet (UV) light such as that emitted from a flame and produces an electrical current. The detector's electronic circuitry translates this current into an alarm signal. A counter-current prevents alarm signals from single‑pulse UV sources such as lightning or cosmic flares. Additionally, the circuit is tuned to respond only to wavelengths from 185 nm to 300 nm.
 
Coverage Area
The D284's response depends on both the size of the fire and the distance from the fire to the detector; therefore the effective coverage area varies. Very small fires must have a duration of at least 7 sec if within 12 ft (3.7 m) of the detector and a duration of 30 sec if within 12 ft to 25 ft
(3.7 m to 7.6 m) of the detector.
 

Relative Humidity	up to 95%, non-condensing at +104°F (+40°C)
Temperature (operating)	+14°F to +122°F (-10°C to +50°C)
Color	Ivory
Dimensions (diameter x H)	4 in. x 2 in. (10.2 cm x 5.1 cm)
Material	ACS plastic (acrylonitrile-chlorinated PE-styrene)
Contact Rating	260 mA at 24 VDC
Alarm Current	0.25 mA at 24 VDC
Standby Current	0.2 mA at 24 VDC
Normal Voltage (operating)	24 VDC
Range Voltage (operating)	17.6 VDC to 27.7 VDC
Detection Angle	120° conical
UV Sensitivity	185 nm to 300 nm