Maintenance
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optek-Manual--1004-2003-02--AF45-US-2011-01-04
www.optek.com
9.6 Reference filter and certificates
The reference filters with the nominal values 0.45 CU, 0.9 CU, and 1.8 CU are
available as standard. The reference filters are enclosed in a filter holder FH03
and are supplied in a storage box (filter protector).
The expected measuring result (validation value) for the required measuring
wavelength is assigned to these reference filters at optek. It slightly differs from
the measuring result of the merely spectral absorption due to differences in the
beam path. The validation value is documented in a test certificate and is in ad-
dition to that given on the filter holder. When using a reference filter in various
sensors, the measured values may fluctuate within a tolerance of +/- 0.03 CU.
The measuring results with a specific sensor are normally reproducible
within +/- 1%.
Moreover, the reference filters' spectral absorption is measured in a certified
laboratory at characteristic wavelengths. These measured values are based on
reference standards established by the PTB (Physikalisch-Technische
Bundesanstalt, the national metrology institute in Germany) and the NIST
(National Institute of Standards and Technology in the USA). They allow
monitoring and traceability of the reference filters. These measured values are
collected in a calibration certificate.
The materials of the reference filter guarantee stable validation values to a high
degree when stored and handled properly. The revalidation deadline for the
filters depends on the user's requirements.
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