ASTM D589-97 pdf free.Standard Test Method for Opacity of Paper (15° Diffuse Illuminant A,89 % ReflectanceBacking and Paper Backing)
Arrange the instrument to per-mit the beam of light exiting the specimen aperture toilluminate a wall perpendicularly 0.6 to 1.2 m (2 to 4 ft) awayfrom the instrument.The filament image observed should be ina good state of focus and centered in the beam. If not,reposition the lamp or optics in accordance with the manufac-turer’s instructions.When a sheet of paper is laid over the specimenaperture to inspect the distribution of light in the aperture, thecircular light spot should be (a) centered in the aperture,(b)nearly fill the aperture but should not be in contact with theedge of the aperture (there should be a clearance of about 2.5mm between the edge and the boundary of the light spot), and( c) the boundary of the light spot should be as sharp and as freeof color as possible. After the optics have been adjusted,usually it is necessary to adjust the lamp only for subsequentchecks of the optical system.The alignment and state of focusof the lamp should be checked before each standardization ofthe instrument.The lenses should be cleaned to minimize thelight scattered into the integrating cube. Cleanliness of theoptical system may be tested by comparing the zero readingobtained with the lamp on and the black body placed over thespecimen aperture to the reading with the lamp of. Thereshould be very little difference.The instrument shall incor-porate a photometric measurement system which measuresreflectance in direct proportion to the light energy incidentupon the sample within 0.2 % of full scale throughout theentire range of measurement. Photometric linearity errors arenormally associated with the photocell or electronics, or both.A means of measuring photometric linearity is described inTechnical Information Sheet 0804-06 (old number 018-5).A1.2 Adjustment of the White Backing
The adjustment of the white backing to conform tothe requirement that it have an absolute reflectance of 0.89 (under the conditions of actual test with a test specimen orstandard in place) may be carried out by means of opal glass orpaper standards evaluated for opacity.
Adjustment by Means of Opal Glass or PaperStandards: Clean the opal glass standard by washing it with amild soap solution,rinsing it with water，and drying it with alent-free non-abrasive towel. Read the opacity of the calibrated area of the opalglass or paper standard.If this opacity reading conforms to thevalue of opacity certified for the standard within 0.3 %，thewhite backing may be regarded as correctly adjusted.If the reading departs from the certified value ofopacity by more than 0.3 %，adjust the distance between thewhite surface and the standard.Too high an opacity readingmeans that the distance must be decreased; too low a readingmeans that it must be increased.Check the adjustment by means of standards ofdifferent opacities. Adjust the white backing so that theopacimeter will read within 0.3 %of the assigned standardvalues throughout the range interest.ASTM D589 pdf download.