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AQ-00073-000, Rev. 7 17

standard are identical. Therefore, the efficiency factor for radiation reflected from each sample

will be the same. If the geometric scattering properties of the sample differ greatly from those of

the reference, significant systematic errors may be introduced into the measurements. Therefore,

the geometric scattering properties of the sample and the reference should be matched as closely

as possible.

Although your PerkinElmer spectrometer may be a double beam instrument, the RSA-PE-20 is

a single beam accessory such that combined operation is in dual beam spectrometer mode. The

value of

for your system does not change from background correction to sample scan.

Single Beam Substitution Error Correction

The single beam substitution error, sometimes known as single beam sample absorption error, is

the systematic, predictable, and non-random error inherent in single beam integrating spheres

measuring reflectance or transmittance. The error is caused by the difference in the throughput

of the sphere when the reference makes up a portion of the sphere wall and when the sample is

substituted for the reference. In integrating spheres which are designed for dual beam spectrom-

eters, it is not possible to place both the reference beam and the sample beam into the sphere at

the same time. These dual beam spectrometers employ a beamsplitter to divide the instrument’s

beam between the sample and reference channels.

Thus, even though the dual beam spectrometer has two beams, it is still only possible to utilize a

single beam integrating sphere accessory. Unfortunately, single beam integrating spheres are

subject to substitution errors during sample measurements which must be corrected to obtain

accurate results.

In reflectance measurements the throughput and corresponding measured reflectance is usually

lower when the sample is present since a reference material of high reflectance is used. In trans-

mittance measurements the throughput and the measured transmittance is usually higher when

the sample is present since an open port is typically used as a reference. With spectrometers that



Physical

Reference



Reference Detector

(optional)

Sample Beam

Reference Beam



Sample



Reference Detector

(optional)

Sample Beam

Reference Beam

Background Scan Sample Scan

Figure 9. Operation of a dual beam spectrometer.

Brand	Labsphere
Model	RSA-PE-20
Category	Laboratory Equipment
Language	English

Labsphere RSA-PE-20 User Manual

Table of Contents

Questions and Answers:

Labsphere RSA-PE-20 Specifications