MIL-PRF-49446B(CR)
4.5 Test methods.
4.5.1 Detector-Dewar defects. The detector array shall be checked for defects. Failure to
meet requirements of 3.5.1 shall constitute failure of this test.
4.5.2 Time constant. Measurement shall be performed on two (2) elements of the array
each separated by at least 20 elements. This time constant is defined as the time required for the
element response to reach 63 percent of its steady state value when irradiated by a 7.5 to 12
micrometer source which produces a signal-to-noise ratio not greater than 100:1. This time
constant shall be considered equal to the time constant defined by the high frequency rolloff of
the noise spectrum of the detector. Any measurement technique consistent with these definitions
shall be considered acceptable. Failure to meet requirements of 3.5.2 shall constitute failure of
this test.
4.5.3 Sensitive area. The physical area of 0.0960 by 0.0144 inch or greater shall be
determined by optical microscope examination or equivalent measurement method.
Measurement shall be made on two (2) elements of the array each separated by at least 20
elements prior to the integration of the Dewar window with the Detector-Dewar. Failure to meet
requirements of 3.5.3 shall constitute failure of this test.
4.5.4 Crosstalk. Measurements shall be made on four (4) elements of the array. The
crosstalk shall be measured under the following conditions:
a. An element shall be irradiated by a 7.5 to 12 micrometer source having a signal 20
times greater than the noise level for the element. The image of the source shall fall
entirely within the area of the detector element.
b. The signal level of the element adjacent to and on the same ground path of the
irradiatedelement shall be measured. The element under test shall meet the
requirements of 3.5.4. Failure to meet requirements of 3.5.4 shall constitute failure of
this test.
4.5.5 Blackbody detectivity. Noise measurements shall be made on each element of the
array under the following conditions: The detector cooled to 77 ±3 K with LN2, 295, ±5 K
background temperature and equivalent noise bandwidth of 9 kHz ±200 Hz with low frequency
3dB point (high pass) no greater than 80 Hz. Using the results of these measurements, the results
of the 500 K blackbody responsivity measurements, and the nominal detector size (see 6.3.7), the
500 K blackbody detectivity for each element of the array shall be calculated. Failure to meet
requirements of 3.5.5 shall constitute failure of this test.
4.5.6 Detector resistance. The resistance of each element of the array shall be measured.
Failure to meet requirements of 3.5.6 shall constitute failure of this test.
4.5.7 Responsivity. Blackbody responsivity of each element of the array may be
measured with the Dewar cooled with LN2 to 77°K, ± 3° K. Nominal element size (see 6.3.7)
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