MIL-PRF-62546C
3.3.3 Performance. The OFSA shall be capable of detecting hydrocarbon mist or surface
fires, differentiating between large and small fires and providing an appropriate output response.
Response to a large or small fire shall be an output signal "A" at connector pin C and/or D
(see table III). Signal "A" is defined as 10 to 30 volts direct current (Vdc), source output
impedance less than or equal to 2000 ohms, load output impedance less than or equal to
20,000 ohms; Quiescent conditions: 1 Vdc maximum, input impedance ( source and load) greater
than or equal to 20,000 ohms. Specific response requirements are given in subsequent
paragraphs.
3.3.3.1 Response characteristics. The OFSA shall respond to radiation stimuli as
indicated in the following paragraphs.
3.3.3.1.1 Field of view (FOV). The FOV of the OFSA shall be, as a minimum, a
90 degree (°) solid cone. Anywhere within the FOV the OFSA shall meet the response
characteristic requirements specified herein. (see 4.3.3.2)
3.3.3.1.2 Thresholds. The OFSA shall respond to two discrete energy threshold levels: A
lower energy threshold, small fire, and a higher energy threshold, large fire.
3.3.3.1.2.1 Small fire. The OFSA shall generate a SMALL FIRE SIGNAL on pin D
(see table III) within 5 seconds (s) and as long as fire exceeds threshold (see 4.3.3.3).
3.3.3.1.2.2 Large fire. The OFSA shall generate a LARGE FIRE SIGNAL on pins C and
D (see table III) within 5 s and for as long as fire exceeds threshold (see 4.3.3.4).
3.3.3.1.3 BITE characteristics. Upon receipt of a BITE signal on pin E (see table III),
the OFSA shall generate optical stimuli to perform a complete functional self test (see 3.3.1). If
the OFSA is functioning properly and the optical window(s) does not require cleaning, the OFSA
shall generate FIRE signals for less than 5 millisecond (ms) on pins C and D within 5 s after start
of BITE signal. If the OFSA is not functioning properly or requires window cleaning, it shall not
generate output FIRE signals from a BITE signal (see 4.3.3.5).
3.3.3.1.4 Response time. At all temperatures between -17 and 71 °C (1 and 160 °F), the
OFSA shall respond to radiation and provide the appropriate signal(s) within the following times
(see 4.3.3.6):
Time (ms)
a. Type I OFSA
4
b. Type II OFSA
3
3.3.3.1.5 Penetration response time. The OFSA shall respond within the time specified
in 3.3.3.1.4, to a hydrocarbon fire ignited subsequent to and resulting from penetration of steel
and aluminum armor by threat munitions (see 4.3.3.8).
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