122 . Spectrum Two N User's Guide
Appendix 5: Calibration Procedure for Optical
Attenuators
Calibration of optical attenuators involves collecting spectra with and without the attenuator
in the optical path and computing the corresponding attenuator correction factor. In order to
prevent detector saturation a sample will need to be present in the optical path such that in
the absence of the attenuator in the optical path the detector is within the linear range of
operation. Calibration of attenuators is required when the attenuator is required to collect a
background scan but is not required for collection of sample scan or a different attenuator is
used for collection of background and sample scans. If the collected spectra are not
corrected for the use of an optical attenuator the resulting spectrum will not be an accurate
representation of the sample’s optical properties. The calibration procedure for the optical
attenuator is as follows:
1. Place sample in sample compartment and collect a Background scan.
Sample of choice should be sufficiently absorbing such that the detector is not saturated
without use of the optical attenuator. When the attenuator is in place sufficient light
must be transmitted to collect a spectrum.
2. After collection of Background scan, place the optical attenuator in the designated
holder. Do not remove the sample from Step 1 from the sample compartment.
3. Collect a Sample scan with sample and optical attenuator in the optical path.
4. Process the resulting Sample scan to units of % Transmittance.
The resulting % Transmittance spectrum is the actual percent transmittance value of
the optical attenuator. For samples having significantly absorbing spectral features, the
percent transmittance of the optical attenuator should be taken as the value at
maximum signal.
=
%
100
Correction of a singlebeam spectrum for the use of an optical attenuator is
accomplished using the following equation:
=
Physical deformations of the optical attenuator will impact its optical properties. If the
optical attenuator becomes deformed, the purchase of a new attenuator is
recommended.
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