Kidde's OFD utilizes the 4.3 micrometer (µ) infrared band to sense fires. Infrared energy generated by the excitation of CO2 molecules in a hydrocarbon fire impinges upon the sensor, which in turn produces a micro volt electrical signal. This signal is then amplified to a level that allows it to be processed. The OFD utilizes digital signal processing circuitry to discriminate between the flicker from fire and background infrared sources such as a hot engine for engine compartment applications. It will also discriminate against non fire sources such as natural and manmade light.
An optional OFD design incorporates built in test (BIT) for complete detector functionality. This is accomplished by incorporating an infrared source within the sensor case. To initiate the BIT function, a 28 VDC signal is applied to the test input of the detector. At this point, the infrared source pulses heat to the sensor which in turn causes the detector to output an alarm signal.
The 4.3µ OFD has been qualified to the requirements of MIL F 23447 and is FAA TSO C79 approved. This design protects the Sikorsky S 76, S 92, and the RAH 66 Comanche.