Jb. Fowler et al., High-accuracy aperture-area measurement facilities at the National Institute of Standards and Technology, METROLOGIA, 35(4), 1998, pp. 497-500
The uncertainty in the measurement of aperture area can limit high-accuracy
radiometric and photometric measurements. Relative total uncertainties in
some measurements have now been determined at or below the 0.1% level, maki
ng substantially smaller aperture-area measurement uncertainties necessary.
The National Institute of Standards and Technology (NIST) has recently imp
lemented an absolute aperture-area measurement facility and a relative aper
ture-area measurement facility; the two facilities together are designed to
determine aperture areas with low uncertainty. The absolute instrument mea
sures the aperture-area using optical edge detection, along with high-preci
sion positioning of the optical edge relative to the sensor, resulting in a
n expected relative combined standard uncertainty of less than 10(-4). The
relative instrument uses optical flux transfer to compare aperture areas an
d also has an expected relative combined standard uncertainty of less than
10(-4). The absolute instrument will be used to measure the area of standar
d apertures for use with the relative instrument.