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【范围】
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This ARP describes methods for measuring the visual performance of direct view cathode ray tube
displays used in aircraft flight decks and cockpits. Procedures may vary depending upon the type of
display (for example, monochrome, color shadowmask, beam index, etc.), but all types are
considered.
1.1 Purpose:
This ARP describes the methods to be used in measuring those performance characteristics
important for color and luminance use in direct view airborne electronic display systems.
1.2 Field of Application:
This ARP defines three classes of tests. Each class of test is applicable to the different phases of a
product’s life: for example, engineering development (Class 1), production/quality assurance
(Class 2), and field service or flight readiness (Class 3). The test requirements for each of these
phases differ and hence the test procedures for each test class may differ. Each procedure in this
ARP is Class 1 unless otherwise stated.
1.2.1 Classes of Tests: Class 1, Laboratory Tests - Tests in this class are most appropriate in an
engineering laboratory environment or as part of a certification program. The test in this class are
the most rigorous and are performed by highly skilled personnel. The objective of tests in this class
is to verify the design and, hence virtually every parameter is measured as accurately as possible.
Set-up time, test time and test equipment cost are of less concern than in the other classes of tests
because the Class 1 tests are not expected to be performed often.
The procedures described are designed to employ basic laboratory instruments. However, these
procedures do not exclude the use of task-specific instruments that are designed to perform the
same measurements.
Class 2, Production/Quality Assurance - Tests in this class are most appropriate for acceptance or
end item tests, or both. The objective of this test class is to verify that every display has been
manufactured/repaired within specified requirements. These tests may be performed often so test
time and test equipment cost are significant considerations.
Class 3, Maintenance/Flightline Readiness - Tests in this class are most appropriate for field
service and flight line functions. The objective of tests in this class is to verify that the display has
not degraded to below minimum required performance levels. These tests may be performed often
by semi-skilled personnel in an environment where equipment must be highly portable and simple
to operate. For tests in this class, set-up and test time must be held to a minimum.
1.2.2 Categories of Tests: The test procedures of this ARP are divided in to three categories:
Geometric: Linear measurements
Luminance: Visible light intensity measurements
Color: Spectral measurements of visible light
1.2.3 Procedure Constraints: The test procedures in this ARP are designed to be performed under the
following constraints:
1. Only visible presentations on the display can be measured.
2. No internal electrical measurements of the display can be made by external electronic test
equipment (except through interface connectors provided for that purpose).
1.3 Measurement Equipment:
1.3.1 Equipment Type, Accuracy and Calibration:
1.3.1.1 Photometric Equipment: All photometric equipment shall meet the following requirements:
1.3.1.1.1 Photometer Calibration: The photometer shall be calibrated using methods that are traceable
to NBS standards.
1.3.1.1.2 Photometer Sensitivity: The full-scale sensitivity shall be 1.0 fL or less with a measuring
aperture size no greater than 75% of the sample to be measured.
1.3.1.1.3 Photometer Accuracy: The measured luminance of an NBS traceable luminance standard
shall be within ±2% of the standard’s certified luminance.
1.3.1.1.4 Photometer Sensitivity and Accuracy Verification: The full-scale sensitivity and accuracy of the
photometer shall be verified using an NBS traceable standard of luminance set to a luminance
value less than or equal to 1.0 fL and also equal to the known full-scale sensitivity value of one
of the photometer ranges. Using a measuring aperture size no greater than 75% of the sample
to be measured, the photometer’s full scale sensitivity shall be within ±2% of the value stated
for the NBS traceable standard.
1.3.1.1.5 Readout Resolution: The photometer shall have a digital readout with a resolution better than
or equal to 0.1% of full scale (3-1/2 digits).
1.3.1.1.6 Photometer Optics: The optics shall have the capability of providing a field coverage of
between 50 and 75% of the sample to be measured while maintaining the 1.0 fL sensitivity
requirement.
1.3.1.1.7 Viewing System: The photometer viewing system shall be capable of aligning the measuring
aperture with the sample to be measured to within 5% of the dimensions of the area being
covered in both x and y axes.
1.3.1.1.7.1 Viewing System Verification: A black card, with a hole in the center, shall be placed in front of
a light source in such a manner that the smallest aperture of the photometer optics covers the
hole when viewed through the viewing system. The card shall be moved back and forth in
one axis orthogonal to the axis of the photometer until a peak reading is obtained. The
distance (A) the card was moved from its original position to the peak position shall be
recorded. The card shall be placed back in its original position and then moved back and forth
in the axis orthogonal to the axis of the first movement and orthogonal to the axis of the
photometer until a peak reading is obtained. The distance (B) the card was moved shall be
recorded. The viewing system of the photometer shall be considered to be aligned accurately
if both A and B are less than or equal to 5% of the dimensions of the area being covered by
the measuring aperture.
1.3.1.1.8 Polarization Error: The polarization error of the photometer shall be no greater than 1.0%.
1.3.1.1.8.1 Polarization Error Verification: The polarization error shall be checked by placing a linear
polarizer in the optical path between a standard lamp and the photometer and then
measuring the luminance. The polarizer shall be rotated 45 degrees and another
measurement shall be made. The polarizer shall be rotated another 45 degrees and a third
measurement shall be made. The photometer shall be considered as having passed the
polarization error test if the difference between the three readings is lower than or equal to
1.0%. Throughout the test, the alignment of the standard lamp with respect to the polarizer
shall not be changed.
1.3.1.1.9 Photodetector Saturation: The photodetector of a photometer must be linear, within ±1%, over
the luminance range of use.
To test for photodetector saturation, place several decades of neutral density filters of known
attenuation, or other means of known optical attenuation between the light source and the
photometer. As the attenuators are removed, one at a time, the photometer response should
change in proportion to the calculated attenuation of the optical filters. If the response does not
change proportionally, then photodetector saturation has occurred. The system sensitivity
should then be adjusted either electrically or optically (using neutral density filtering) until the
change is proportional. This adjustment may require recalibration of the photometer.
1.3.1.1.10 Colorimetry: When colorimetric capability is required, the photometer shall be calibrated for the
accurate measurement of the three primary and any secondary CRT colors. A means shall be
available for the establishment of color correction factors for the photometer. The correction
factors shall be established by measuring a source whose CIE 1931 x, y or 1976 u′ v′ values
are known and whose spectral distribution is similar to the sample to be measured. Then, using
the procedure provided by the manufacturer of the photometer, a correction factor shall be
established for the sample after measuring the known source and establishing the colorimetric
corrections resulting from the deviation between the source’s known coordinates and the
results of the photometer’s measurements. These factors are applicable only to samples of
similar spectral distribution to the source of known CIE 1931 x, y or 1976 u′ v′ coordinates.
(See 4.3.3 for transformations between CIE 1931 and 1976 coordinates.)
As applied to electronic displays such as CRTs, this means that a colorimeter correction factor
must be determined for each type of CRT with a given phosphor set and optical filter and that
correction factor is not applicable to any other CRT type.
1.3.1.2 Spectroradiometer: If a spectroradiometer is to be used for any procedure in this document, it
shall meet the following requirements:
1.3.1.2.1 Spectral Response: The spectroradiometer shall have sufficient sensitivity to permit
measurement of radiance levels equal to or lower than those listed in the following table and
shall have a minimum spectral coverage of 400 to 720 nm with 380 to 760 nm preferred. The
values listed below are for spectral bandwidths of 5 nm and a signal to root-mean-square noise
ratio of 100:1 (for proper colorimetric measurements). The spectroradiometer meets the
sensitivity requirements when the values listed below can be measured using an optical
configuration that provides measurement intervals equal to, or less than, the bandwidth.
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1.3.1.2.2 Spectral Responsivity: The spectroradiometer shall be calibrated for radiance within six
months prior to making a measurement. The calibration shall be traceable to NBS standards
and shall be performed at wavelengths and intervals consistent with the measurements to be
made. Calibration factors shall be supplied for any spectroradiometer configuration (optical,
mechanical, etc.) needed to perform measurements listed in this document or the capability of
the user to establish these calibration factors shall be documented.
1.3.1.2.3 Wavelength Accuracy and Repeatability: The wavelength accuracy shall be within an
uncertainty no greater than 1 nm. The accuracy is the difference between the wavelength
actually being measured and the indicated wavelength. Wavelength repeatability shall be
within ±0.5 nm.
1.3.1.2.3.1 Wavelength Accuracy and Repeatability Verification: Verification of wavelength accuracy
shall be performed by using a source of known emission lines that has at least one line
between 400 to 475 nm (blue), one between 500 to 600 nm (green) and one between
650 to 750 nm (red). A spectral bandwidth configuration no greater than 1 nm is suggested
for this test. The test may be performed using the spectroradiometer under automatic control
of a computer. If this is used, the spectroradiometer shall be moved in increments less than or
equal to one tenth of the bandwidth through the known emission lines. The test shall be
performed at least twice for each emission line. The average deviation between the true and
calculated centroid for each emission line may be no greater than 1.0 nm. This technique is
recommended as it takes into account any wavelength correction inherent in the system’s
software. The system shall be considered to have passed the repeatability test if, for each
scan made, the measured peaks are within 0.5 nm of each other.
Although not recommended, the test may also be performed by a manual scanning technique
that provides the same accuracy and bandwidth as specified. The monochromator shall be
positioned to obtain the peak reading at the wavelength of each of the known emission lines.
The wavelength of the measured peak reading shall be recorded. The test shall be performed
at least twice for each known emission line. The average deviation between the true and
measured emission lines shall be no greater than 1.0 nm. The system shall be considered to
have passed the repeatability test if, for each line tested, the measured peaks are within
0.5 nm of each other.
1.3.1.2.4 Precision: The spectroradiometer shall have precision equal to or better than 0.1% of full scale
on any measurement range.
1.3.1.2.5 Zero Drift: During any given spectroradiometric scan, the maximum zero drift shall be less
than 0.2% of the full scale reading on the most sensitive range, after the appropriate warm up
period. A capability shall be provided to allow zero drift to be checked before any given
spectroradiometric scan.
1.3.1.2.6 Linearity: Within any given measurement scale, the linearity shall be ±1% of the full scale
value. The linearity between any two measurement scales shall be ±2%.
1.3.1.2.6.1 Linearity Verification: The linearity of the spectroradiometer shall be verified within six
months prior to making a measurement. A source which covers the applicable dynamic range
of the spectroradiometer and can be precisely optically or mechanically varied in intensity
shall be used. The linearity shall be checked at a specific wavelength (to be determined by
the contractor) which shall not be varied throughout the linearity check. The inverse square
law may be used when a precision photometric bench is utilized. Dimming of the lamp
through electronic means is unacceptable. The light source shall be adjusted so that a full
scale reading is obtained on the spectroradiometer’s most sensitive range. The source shall
then be increased in 5 x increments relative to the initial setting until the applicable dynamic
range of the spectroradiometer has been covered. The output of the spectroradiometer shall
not deviate from the output of the source by more than ±1% on any scale or by greater than
±2% between measurement scales.
1.3.1.2.7 Stray Light: The stray light characteristics of the spectroradiometer shall not adversely affect
the accuracy of the spectroradiometer. In general, the measured stray light using the technique
described below shall not exceed 0.01%.
1.3.1.2.7.1 Stray Light Verification: Stray light accuracy shall be verified within a six month period prior
to taking a measurement. This can be accomplished by measuring the relative intensity of a
known tungsten light source at a selected low wavelength. Then when an optical filter, with a
sharp cut-off above that wavelength is placed in the light path and the measurement
repeated, the relative energy should be some small percentage of the initial measured value.
If that value is excessive, the false reading is an indication of stray light impinging on the low
wavelength sensor of the instrument.
Stray light accuracy can be verified by using a 2.5 mm thick piece of Schott GG 475 filter (or
equivalent) and a tungsten source operating at 2856 Kelvins. The measurement shall be
made at 400 nm. Position the spectroradiometer to 400 nm. Measure the source and record
the relative intensity. Without disturbing the position of the source or spectroradiometer, place
the filter in the light path. Record the relative intensity. Use the following formula to determine
stray light:
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The spectroradiometer meets the stray light requirement if the value for L
s
is less than or
equal to 0.01%.
1.3.1.2.8 Spectroradiometer Optics: See 1.3.1.1.6.
1.3.1.2.9 Spectroradiometer Viewing System: See 1.3.1.1.7.
1.3.1.2.9.1 Spectroradiometer Viewing System Verification: See 1.3.1.1.7.1.
1.3.1.2.10 Spectroradiometer Accuracy: The spectroradiometer shall be capable of measuring spectral
radiance to within ±5% of that of an NBS traceable standard of spectral radiance at each 5 nm
wavelength interval throughout the spectroradiometer’s spectral coverage. When measuring
an NBS traceable standard of color temperature or chromaticity, the spectroradiometer shall
yield 1976 CIE UCS chromaticity coordinates u’, v’ to within ±0.007 of the certified values.
1.3.1.2.11 Diffuse Reflectance Standard: The diffuse reflectance standard is required for certain
measurement procedures. It shall have a lambertian reflecting surface with reflectivity greater
than 97.5% from 380 to 760 nm. The reflecting surface is recommended to be at least
2 x 2 inches. Such standards are made of barium sulfate or Halon, a fluorocarbon plastic. The
quality of the white surface must be carefully inspected for cleanliness and homogeneity just
prior to use.
1.3.1.2.11.1 Reflectance Standard Verification: The reflectance standard shall be calibrated within a six
month period prior to use. The standard shall be calibrated using techniques traceable to the
NBS.
1.3.2 Units of Measurement:
1.3.2.1 Linear Measurement Units: The units of linear measurement used in this procedure are as
follows:
millimeter (mm)
nanometer (nm)
inch (in)
Mil (that is, thousandths of an inch)
These units are related by the following equations:
25.4 mm = 1 in
1 nm = 1 x 10
-9
meters
39.37 mils = 1 mm
1.3.2.2 Luminance Units: Luminance is the metric of measurement of light radiating or reflecting from a
surface such as the face of an electronic display (see 4.2.1.1). The units of luminance used in
this procedure are the foot-lambert (fL) and the nit or candela per square meter (cd/m
2
). To
convert between these units, use the following equations:
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1.3.2.3 Illuminance Units: Illuminance is the metric of measurement of light from a source such as the
sun, that impinges upon a surface such as the face of an electronic display. The units of
illuminance are the footcandle, lux, or lumen/square meter. To convert between the unit systems,
use the following equations:
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1.4 Monochrome/Multicolor Displays:
Monochrome CRT displays have phosphor screens that are uniform over fairly large areas.
Multicolor CRT displays usually have a structured phosphor screen to achieve multicolor
performance. Test procedures for monochrome displays often are not applicable to displays with
structured phosphor screens. Hence, the applicability of each test procedure will be identified as
follows:
(u) - Uniform screen (that is, monochrome, penetron, etc.)
(P) - Patterned screen (that is, shadowmask, beam index, etc.)strRefField
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