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RSA-PE-18
INTRODUCTION......................................................................................................................1
INSPECTION PROCEDURE ..................................................................................................2
INSTALLATION.......................................................................................................................3
Removing the Lambda 18 Compartments .......................................................................3
Installing the Accessory...................................................................................................4
Optical Alignment............................................................................................................4
Energy Scan .....................................................................................................................6
OPERATING PROCEDURES.................................................................................................7
Background Correction - An Overview...........................................................................7
Measurement Procedure - 8°/Hemispherical Reflectance Factor....................................10
Measurement Procedure - Specular Subtraction..............................................................11
Measurement Procedure - Transmittance ........................................................................11
Measuring Large Samples ...............................................................................................12
OPERATING SUGGESTIONS................................................................................................13
Background Correction - Scan Parameters......................................................................13
Zeroline Correction..........................................................................................................13
Dry Nitrogen Purge..........................................................................................................14
Creating a Data File for Reflectance Standards...............................................................15
Optional Sampling Accessories .......................................................................................16
MAINTENANCE.......................................................................................................................21
General Information.........................................................................................................21
Mirror Cleaning Procedure ..............................................................................................21
TECHNICAL NOTES...............................................................................................................22
Measurement of Transmittance .......................................................................................22
Specular Subtraction ........................................................................................................22
Use of Proper Reflectance Standards...............................................................................23
RECOMMENDED READING.................................................................................................24
AQ-00148-000, Rev. 2
APPENDIX.................................................................................................................................25
Typical 8°/Hemispherical Reflectance Factor for an SRS-99 .........................................25
AQ-00148-000, Rev. 2
INTRODUCTION
The RSA-PE-18 is a six-inch (150 mm) diameter integrating sphere accessory to the
Perkin-Elmer Lambda 18 spectrophotometer. The integrating sphere is constructed from
Labsphere's proprietary Spectralon® material. The accessory allows diffuse reflectance
and transmittance measurements of materials.
The RSA-PE-18 is essentially an optical bench which includes double beam transfer
optics along with the integrating sphere. The integrating sphere provides sample
mounting ports for reflectance and transmittance measurements, a reference port for
reflectance standards, and a photomultiplier tube (PMT) detector with preamplifier.
Optional center-mounted sample holders permit reflectance measurements to be
performed for beam incident angles variable from 0° to 70°.
This manual is intended to provide installation procedures as well as measurement
procedures for the RSA-PE-18 accessory. The "Operator's Manual" of the Lambda 18
should be referenced in conjunction with this manual.
Cuvette Holder
Position
Attenuator
Positions
Lens Assembly
Position
Figure 1. Top View of RSA-PE-18 Accessory Showing Placement of Optional Components
AQ-00148-000, Rev. 2
1
INSPECTION PROCEDURE
The RSA-PE-18 was thoroughly inspected and calibrated before shipping and should be
ready to operate after completing the set-up instructions. It is packaged and shipped in a
reinforced cardboard carton. Carefully check the assembly after unpacking it for any
damage that may have occurred during shipping. If there is any such damage, file a claim
immediately with the involved carriers and contact the Labsphere Customer Service
Department at
(603) 927-4266.
AQ-00148-000, Rev. 2
2
INSTALLATION
Removing the Lambda 18 Compartments
Before the RSA-PE-18 can be installed the normal sample and detector compartments of
the Lambda 18 must be removed. The following tools are required:
(1) flat-head screwdriver (1) 3 mm hex driver
1.
Ensure that the Lambda 18 is powered OFF and disconnected from the line voltage
input.
2. Lift the cover to the detector compartment.
3. Detach the gray detector connector, as well as the chrome stepping motor connector,
by pulling straight back. The detector connector is often latched into position. To
unlatch, use the flat-head screwdriver to push the latching mechanism from right to
left.
4. Remove the detector compartment's sheet metal cover by removing the 3 mm hex
socket cap screws which hold it in place. Two of these screws are located at the rear
of the cover. The third is centrally located at an L-bracket on the lower front of the
cover.
5. Fully loosen, but do not remove, the four 3 mm hex socket cap screws located in
recesses at the corners of the detector compartment.
6. Grasp the detector compartment firmly and remove by carefully lifting the back end
first and then the front.
7. Lift the cover to the sample compartment.
8. Remove the beam path windows by grasping the edges of the magnetic window
mounts and pulling straight back.
9. Remove the 10 mm cuvette holders by loosening the eight Phillips screws located at
the corners of both holders and then lifting straight up.
10. Fully loosen, but do not remove, the four 3 mm hex socket cap screws located in
recesses at the corners of the sample compartment.
11. Remove the sample compartment by grasping firmly and carefully lifting straight up.
AQ-00148-000, Rev. 2
3
Installing the Accessory
1.
2.
3.
4.
5.
Ensure that the Lambda 18 is powered OFF and disconnected from the line voltage
input.
Slide the RSA-PE-18 assembly into the vacated compartment area until it sets firmly
onto the mounting studs of the Lambda 18 baseplate. The connector access holes
will align when the assembly is seated properly.
Secure the assembly by tightening the four (3 x 40 mm) captive socket cap screws
provided using the 3 mm hex driver. The screws fit through the access holes located
on the baseplate of the transfer optics enclosure.
Attach the detector connector to the Lambda 18. The PMT connector (the 11-pin
connector with a central Teflon sleeve) can be damaged quite easily. Insert this
connector gently, ensuring the pins are aligned with their receptor holes. If the
center sleeve becomes depressed or bent, the RSA-PE-18 will not initialize the
Lambda 18 properly and the PMT function will be impaired.
Secure the connector by sliding the latching mechanism from left to right.
CAUTION: DO NOT FORCE THE CONNECTOR!
Optical Alignment
The transfer optics of the RSA-PE-18 were factory pre-aligned prior to shipment.
However, it is generally good practice to ensure that misalignment did not occur in
transit.
1.
2.
3.
4.
AQ-00148-000, Rev. 2
Place one Spectralon standard (or other white reflectance standard) in the sample
reflectance port and one in the reference reflectance port.
Power ON the Lambda 18. Initialize the operating software.
Upon completion of the Lambda 18's self-test routine, the software should display a
wavelength of approximately 652 nm and report its status as READY. This indicates
that there was sufficient sample beam energy to perform the wavelength calibration
during initialization. Go to step 10).
If the instrument does not initialize, the message "wavelength calibration failed"
appears or the instrument status remains BUSY for an extended period, a
misalignment may have occurred.
4
Note: It is also possible that the PMT connector was not properly installed. Power OFF the
Lambda 18. Inspect the PMT plug to ensure that none of the pins are depressed into the
connector. Re-connect the PMT and power ON the Lambda 18 once again to attempt
initialization.
5.
6.
7.
8.
Power OFF the Lambda 18 and remove the RSA-PE-18 accessory.
Replace the standard sample and detector compartments.
Power ON the instrument and initialize the software. Note ignition of lamp D2.
Expect to see 652 nm displayed following a proper initialization.
Choose single beam operation (reference beam). Open the SLIT width to 5.0 nm.
Enter a PMT GAIN value of 0.1 (the minimum value). In Perkin-Elmer's UVCSS
software, one types the command SERV to select single beam operation. The PMT
GAIN value is set from the SCAN methods page. In UVDM software, simply open
the INSTRUMENT and SCAN windows to select single beam operation and to set
the PMT GAIN value.
CAUTION: DO NOT PROCEED IF UNABLE TO ACCESS SINGLE BEAM MODE AND
SET THE PMT GAIN TO THE MINIMUM VALUE.
9.
10.
11.
12.
13.
14.
15.
16.
AQ-00148-000, Rev. 2
With the Lambda 18 power remaining ON, remove the standard sample and detector
compartments and install the RSA-PE-18 accessory . Open the accessory cover.
GOTO a wavelength value of 0 nm. This should produce white light in the
instrument beams, visible when placing a piece of white paper in the beam paths.
(The sample beam is closest to the front of the Lambda 18 and has two mirrors as
transfer optics in the RSA-PE-18.)
Remove the plug at the top of the integrating sphere. View the rectangular images at
the sample and reference reflectance ports. The images should be approximately
centered on the white standards placed at each reflectance port.
If not centered, adjust the mirror alignment.
Align one mirror at a time. In the sample beam, place a small piece of white paper
over the face of the second mirror in the beam path.
Adjust the first mirror to align the beam cross-section on the second mirror. Turn
only one thumbscrew at a time.
Adjust the second mirror of the sample beam to center the image on the sample
reflectance port of the integrating sphere.
Repeat this procedure for the reference beam. Adjust one mirror at a time. Ensure
that the beam is centered on each subsequent mirror until a centered image appears
on the sphere port.
5
17. Replace the plug onto the top of the integrating sphere.
18. When alignment is complete, power OFF. Connect the detector if necessary. Close
the accessory cover. Repeat the initialization procedure.
Energy Scan
A single beam energy scan prior to sample measurements is recommended. The energy
scan provides an indication that the RSA-PE-18 is functioning properly with the Lambda
18 on which it is installed. The actual energy scan performed on a particular accessory is
included in shipment. The results of the following procedure should be similar. Actual
results are particular to each RSA-PE-18, the Lambda 18 on which the RSA-PE-18 is
operated, and the white standard used in the sphere sample port.
1.
2.
3.
4.
Choose single beam operation (sample beam). In Perkin-Elmer's UVCSS software,
type SERV to select single beam operation. Instrument parameters are set from the
SCAN methods page. In UVDM software, simply open the INSTRUMENT and
SCAN windows to select single beam operation and to set the instrument
parameters.
Place one Spectralon standard (or other white reflectance standard) in the sample
reflectance port and one in the reference reflectance port of the integrating sphere.
Set the wavelength range to start at 499 nm and end at 498 nm. Set the GAIN value
to 8.0 nm.
The LIVE DISPLAY should reveal an intensity value of 80.0 I at 499 nm. If the
value is too large, return to the SCAN parameters and decrease the GAIN value and
return to the LIVE DISPLAY. Conversely if the value is too small, increase the
GAIN value. Repeat this procedure until the optimum GAIN value is found to
produce the intensity value of 80 (+/- 2).
Note: If a SLIT value greater than 2.0 nm or a GAIN value greater than 11.0 is required to
obtain 80 I units, check the mirror alignment. If the RSA-PE-18 mirror alignment is
satisfactory, it may be that the optics of the Lambda 18 are in need of alignment or at least
servicing. See your local Perkin Elmer technical service representative.
5.
AQ-00148-000, Rev. 2
With satisfactory SLIT and GAIN settings obtained, run a scan over the wavelength
range of 850 nm to 200 nm. The result should look similar to the one in the
document that was included with shipment.
6
OPERATING PROCEDURES
Background Correction - An Overview
Prior to performing either reflectance or transmittance measurements, it is necessary to
perform an instrument background correction. This determines a 100% line for
measurement. White standard materials need to be placed in both the sample and
reference ports of the integrating sphere during background corrections.
Calibrated Spectralon® standards provide durable, reproducible working reflectance
standards. The calibrated standards are recommended for performing most background
corrections. If the standards become soiled, they may be rinsed with distilled water and
thoroughly dried. If the standards become badly contaminated, they may be lightly
sanded using 220-240 grit emery cloth under a stream of running water. This treatment in
no way affects the performance of the material. Typical reflectance data for an SRS-99
calibrated standard appears in Table A of the Appendix. The SRS-99 is not included with
the accessory unless it is ordered.
For transmittance measurements, both reflectance ports need only be filled with the (2)
USRS-99-010 uncalibrated Spectralon standards supplied with the accessory. The
background correction produces an absolute 100% T reference.
Any reflectance measurement using an integrating sphere is relative to the reference
standard used. This means that the 100% R line displayed on the Lambda 18 is incorrect.
Display data may even exceed 100% if the sample has a higher absolute reflectance than
the reference material. It is recommended that an SRS-99-010 calibrated Spectralon
standard or other calibrated reflectance standard be used in the sample port during the
background correction. Subsequent sample reflectance data are corrected by the actual
values reported in the calibration certificate for the SRS-99-010 standard. The following
derivation explains the correction.
In a double beam, ratio recording spectrophotometer, the background correction is
intended to balance the amount of energy in each beam. During the background
correction (Bc), the ratio of the sample beam energy (Es) to the reference beam energy
(Er) is recorded into instrument memory:
B c=
Es
Er
AQ-00148-000, Rev. 2
7
In a transmittance measurement, the transmittance of the sample (Ts) interrupts the
amount of energy in the sample beam, producing the following ratio:
EsT s
Er
The Lambda 18 displays a result which is this ratio divided by the background correction:
D ISPLA Y V A LU E=
EsT s 1
EsT s Er
*
=
* = Ts
Er B c Er Es
In a reflectance measurement using what is often referred to as a comparison type
integrating sphere, the reflectance of the sample (Rs) placed at the sample port interrupts
the sample beam energy and the reflectance of the reference material (Rr) placed in its
port interrupts the energy in the reference beam to produce the following ratio:
EsR s
ErR r
The Lambda 18 displays:
D ISPLA Y V A LU E=
EsR s 1
*
=
ErR r B c
EsR s Er R s
* =
ErR r Es R r
Therefore, the DISPLAY VALUE on the Lambda 18 must be multiplied by the known
reflectance of the reference material in order to obtain the actual reflectance of the
sample.
Please note that the method just described has used the reference port of the integrating
sphere for the reference material. The validity of the ratio used to describe the
background correction has a strict dependence. Two samples of matched reflectance
value must be used in each reflectance port during the background correction.
If matched samples are not available (which is often the case over a wide spectral range),
an alternative method places the reference material in the sample port during the
background correction. A matched white material is not necessary for the reference port.
AQ-00148-000, Rev. 2
8
The background ratio becomes:
B c=
EsR r
Er
The sample replaces the reference material and the following ratio results:
EsR r
Er
The Lambda 18 displays:
D ISPLA Y V A LU E =
EsR s
Er
*
1 EsR s Er R s
=
*
=
Bc
Er EsR r R r
Once again the DISPLAY VALUE is the ratio of the material reflectances. The
advantage of this method is that matched samples are not required for the background
correction. The method does require that the material placed at the reference port remain
in place for the sample measurement.
AQ-00148-000, Rev. 2
9
Measurement Procedure - 8°/Hemispherical Reflectance Factor
1.
Set all Instrument Parameters as desired.
Note: It is recommended that scans be recorded as %T (or %R if available) on the ordinate
scale. The SLIT should be set as wide as possible for the best signal-to-noise ratio
performance.
2.
3.
4.
Perform an instrument Background Correction (review III-A).
Place the sample to be measured in the sample port. Obtain the measurement data.
Multiply the instrument data by the reflectance of the standard reference material
used. For example:
DISPLAY VALUE Rr Rs
.650 x .985 = .640 (64% R)
Note: If the system you ordered included an SRS-99-010, the reference data for this
calibrated standard can be converted to a Lambda 18 data file in either UVCSS or UVDM
software using DWRITE function (see section IV-F). The Arithmetic functions of the
software can then be utilized to multiply spectra.
AQ-00148-000, Rev. 2
10
Measurement Procedure - Specular Subtraction
The integrating sphere of the RSA-PE-18 is fitted with a removable plug located at a port
which corresponds to an 8° angle of reflection (i.e.- the specular direction). The port is
adjacent to the sample transmittance port. The port may be fitted with a light trap to
exclude the specular (mirror-like) component reflected from a sample.
1.
2.
3.
4.
5.
Set all Instrument Parameters as desired.
Perform an instrument Background Correction (review III-A).
Replace the specular port plug with the light trap. The port features a detaining lever
which is keyed to properly secure both the plug and light trap when mounted.
Place the sample to be measured in the sample port. Obtain the measurement data.
Multiply the instrument data by the reflectance of the standard reference material
used.
Note: Measurements performed using specular subtraction light traps should always be
interpreted with caution. A light trap of finite size is not always effective for the complete
extinction of a broadened specular peak. Also, diffuse reflections distributed within a few
degrees of specular may inadvertently be excluded from measurements as well. Specular
exclusion from diffuse reflectance measurements is required in the colorimetry of glossy
sample surfaces as well as in Kubelka-Munk analysis of materials.
Measurement Procedure - Transmittance
1.
2.
3.
4.
Place a white standard material (USRS-99) in each reflectance port.
Set all Instrument Parameters as desired.
Perform an instrument Background Correction.
Place the sample to be measured in the sample port. Obtain the measurement data.
Note: When measuring the transmittance of large sized samples, ensure that the reference
beam is not obscured by any part of the sample. Samples up to 150 mm wide and 115 mm
high will fit inside the accessory enclosure.
AQ-00148-000, Rev. 2
11
Measuring Large Samples
The sample reflectance port of the integrating sphere is located on the extreme right-hand
edge of the accessory to accommodate the measurement of large objects. The hinged
sheet metal enclosure surrounding the port, as well as the port's sample holder, can be
removed to obtain access for large samples.
1.
2.
3.
Using a 3 mm hex driver, remove the three hex socket cap screws located beneath
the enclosure.
Using a 0.9 mm hex driver, loosen but do not remove the set screws in the flat plate
of the sample holder.
Remove the sample holder to expose the port frame.
Note: The sample surface should sit flush against the port frame to make a good light seal
with the port. If the sample does not make an adequate seal, cover the sample and port with a
dark cloth or darken the room. Ambient light from the room or even the Lambda 18 light
source compartment can add noise to the spectra or even saturate the PMT within the
integrating sphere.
To check the quality of the light seal, choose servo slit (PMT region) instrument
operation. Turn off the light sources of the Lambda 18 (via software). Increase the PMT
gain to a value near 20. GOTO a wavelength less than 860 nm (PMT region). Shine a
flashlight around the sample port area with the sample in place. If there is a rapid clicking
sound (the slit servo mechanism), there is a light leak. Note the location and improve the
light seal.
AQ-00148-000, Rev. 2
12
OPERATING SUGGESTIONS
Background Correction - Scan Parameters
It is suggested that the background correction scan start and end at wavelengths at least 5
nm beyond those desired for sample scans. This reduces scan noise at the extreme ends of
spectra obtained with the RSA-PE-18. Therefore, if the measurement range of interest is
300 nm - 850 nm, background correct from 295 nm - 855 nm.
Following a background correction, the Lambda 18 allows the scan range to be shortened
without requiring a new correction. However, if any other parameters are changed such
as scan speed, slit or gain values then a new background correction is required.
Zeroline Correction
An integrating sphere is sensitive to small-angle scatter from the sample beam coupling
optics. The scattered "halo" surrounds the sample port and has the effect of mixing a
small proportion of the sphere wall reflectance with that of the sample. This means that
the 0% R line displayed on the Lambda 18 can be incorrect. This is especially applicable
when using masking techniques to measure very small samples. The sample beam
illumination will overfill the mask aperture.
The "halo effect" can be measured after a background correction by placing a light trap in
the sample reflectance port. The light trap should approximate a sample of 0%
reflectance.
The actual sample reflectance factor, Rs, relative to the perfect diffuser is computed as
follows:
R s =R r*
SA M PLE -ZERO LIN E
100% -ZERO LIN E
Where Rr is the reflectance value of the white standard SAMPLE is the sample data
displayed on the Lambda 18 ZEROLINE is the data from the light trap measurement.
Note: The zeroline data need only be measured periodically. It should be re-measured after
changing Instrument Parameters or reflectance standards.
AQ-00148-000, Rev. 2
13
Dry Nitrogen Purge
The RSA-PE-18 may be equipped with a brass purge inlet connector located at the rear
quarter of the accessory. A dry nitrogen purge of the RSA-PE-18 is recommended if
spectra free from absorbance bands due to oxygen and water vapor are desired.
Both the Lambda 18 and the RSA-PE-18 should be purged concurrently. The nitrogen
source outlet should be fitted with a Y-connector. One branch of the Y-connector should
lead to the purge inlet of the Lambda 18 and the other to the inlet on the RSA-PE-18.
When purging is to begin, the RSA-PE-18 should be prepared by making sure all the
integrating sphere ports are empty, including the center mount access port at the top. The
instrument should then be initially purged for 10 minutes at a flow rate of about 10
L/min.
After the initial purge, the flow rate may be reduced to 6-8 L/min. When samples are
introduced into the RSA-PE-18 compartments, the nitrogen flow should remain on. After
the samples are mounted in place, the top port plug replaced, and the accessory cover
closed, the instrument should be allowed to purge for 5-10 minutes before the
measurement data is acquired. This should be repeated for each new sample.
Note: It is recommended that only high purity (>99.999%) dry nitrogen be used to purge the
RSA-PE-18.
AQ-00148-000, Rev. 2
14
Creating a Data File for Reflectance Standards
Reflectance data collected by the Lambda 18 using the RSA-PE-18 must be multiplied by
the reported reflectance values of the standard reference material used. Both UVCSS and
UVDM software packages feature arithmetic functions to multiply entire spectra. A data
file containing the reflectance standard's data which would be recognized by the
instrument software has to be created in ASCII format using MS-DOS™ line editor
commands or compatible software such as Lotus 1-2-3™, Excel™ or Wordstar™.
The most important aspect of the ASCII data file to UVCSS or UVDM is the file format,
especially for the header. The best approach is to take an existing data file and convert it
to ASCII format using the JCAMP command (the file will have a .DX or .DA filename
extension). This file can then be examined and edited by one of the software systems
previously identified.
It may be desirable to first create a "ready-to-edit" data file in UVCSS or UVDM which
would already contain relevant header information and data intervals. For example, run a
100% scan immediately following a background correction with the scan range and data
interval initially selected to correspond with the available reference data. Reference data
for wavelength intervals smaller than those reported in the accompanying calibration
certificate can be determined by interpolation. After editing the file's reflectance data at
each wavelength, substituting the values for the reflectance standard, save the file in
ASCII for mat (be sure to use the correct .DX or .DA filename extension). The file is
now ready to be converted back into the proper data file format for either UVCSS or
UVDM.
Please consult your software manual or your local Perkin Elmer technical applications
specialist for more assistance in editing instrument data files.
AQ-00148-000, Rev. 2
15
Optional Sampling Accessories
Center Mounted Samples - Variable Angle Reflectance
A center mounted sample holder is an optional accessory which places samples at the
center of the sphere enabling measurements of hemispherical reflectance as a function of
incident angle. The standard holder can accommodate samples up to 50 mm (W) x 31.75
mm (H) x 12 mm (D). See Figure 2. An optional clip style holder is also available for
thin flexible samples.
1.
2.
3.
4.
5.
6.
7.
AQ-00148-000, Rev. 2
Load the reflectance standard into the jaws with the reflecting surface even with the
front edge of the jaws. This will place the front surface at the rotational axis of the
sample holder. Tighten the jaws using the thumbscrew at the top.
Open the lid of the RSA-PE-18 and remove the top plug.
Carefully insert the sample holder into the vacated port. Align the mounting pins in
the holder with the holes in the port adapter.
Set the angle of incidence by the indicator inscribed on the rotary stage of the sample
holder. The 0° location indicates normal incidence (i.e.- the sample face is
perpendicular to the beam path).
Set all Instrument Parameters as desired.
Perform an instrument Background Correction.
Replace the reflectance standard with the sample to be measured in the sample
holder. Obtain the measurement data.
16
Figure 2. Center mounted Sample Holder
CAUTION: Care should be taken when handling the center sample holder. Do not handle
the coated surfaces with bare hands. In addition, take care when inserting or removing the
center mount from the integrating sphere. The center mount must be removed slowly, lifting
straight up to avoid damaging the interior of the integrating sphere.
When using the center mount sample holder for the reflectance of samples which also
transmit, the transmitted component must be extinguished. This can be accomplished by
backing the sample with a light trap or black felt cloth.
The specular subtraction port can also be used for center mounted samples. The specular
component corresponding to a sample beam incident angle of 16° is excluded by the light
trap placed at the specular subtraction port. (Please note that the specular subtraction port
excludes the 8° component for sample port measurements, section III-C).
At normal incidence (0°) the specular component retroreflects and is excluded
inadvertently by the sample beam entrance port of the integrating sphere.
Measuring The Reflectance of Very Small Samples - Small Spot Accessory
The cross section of the sample beam at the sample reflectance port is approximately 9
mm wide by 19 mm high. Samples surfaces should usually be large enough to fill the
entire sample port aperture or at least large enough to fill the beam cross section.
For sample surfaces smaller than the beam cross-section, a mask can be used to reduce
the port aperture to a size small enough to accommodate any sample. [A. Brunsting, R.S.
Hernicz and A.J. Dosmann, "Small Area Measurements of Diffuse Reflectance from 410
to 700 nm," Applied Optics 23(23), 4218-4225, 1984.]
AQ-00148-000, Rev. 2
17
Labsphere offers an additional optical assembly for reducing the beam cross-section at
the three sample locations on the integrating sphere. The assembly consists of a four
position wheel, three of which are fitted with various focal length lenses. The lenses are
fused silica to operate over the entire spectral range of the RSA-PE-18. The focal lengths
vary according to the sample position on which to reduce the beam size. The RSA-PE-18
also needs to be fitted with an iris diaphragm in each beam to further reduce the beam
cross-section.
Locate the holes in the baseplate for the two attenuators. See Figures 1 and 3. Align the
feet of one attenuator with one set of hole such that when the attenuator is fully open, the
adjustment handle points towards the back of the accessory. Carefully tip the accessory
to access the bottom panel of the accessory. Place the hex screw in the hole between the
two feet of the attenuator and tighten to secure the attenuator. Repeat with the second
attenuator.
Locate the holes in front of the entrance port of the sphere for the lens holder assembly.
See Figures 1 and 3. Align the feet of the lens holder assembly with the holes and
position the lens holder assembly such that the base of the assembly faces away from the
sphere. Tighten the hex screw from the top of the base plate to secure the lens holder
assembly to the accessory.
Attenuators
Lens Assembly
Figure 3. Top View of Accessory With Small Spot Kit
AQ-00148-000, Rev. 2
18
T
Figure 4. Lens Holder Assembly
If your RSA-PE-18 is equipped with the beam reducing optics, the following procedure
applies:
1.
2.
3.
GOTO a wavelength value of 0 nm. This should produce white light in the
instrument beams, visible when placing a piece of white paper in the beam paths.
Opening the slit width increases the brightness.
Place the sample to be measured in the appropriate sample holder of the integrating
sphere.
Turn the lens wheel so that the letter indicator at the top of the wheel corresponds to
the sample position.
Indicator
O
T
C
R
4.
5.
AQ-00148-000, Rev. 2
Sample Position
All, lens, normal beam
Transmittance, front of sphere
Center Mount
Reflectance, rear of sphere
Close the sample beam iris diaphragm until the beam cross section is contained
within the boundaries of the sample surface (i.e.-no overlap).
Adjust the reference beam iris to approximately the same diameter as the sample
beam iris. This balances the energy in both beams.
19
Note: The live display of the Lambda 18 can also be used, adjusting the reference beam iris
to obtain a reading of 100%T or 0A after first setting the sample beam iris for the sample to
be measured.
Cuvette Holders for the Sample and Reference Beam
Locate the holes in the baseplate in the reference beam path in front of the last mirror.
Align the dowels on the reference beam cuvette holder with the holes in the baseplate and
secure the assembly. See Figures 1 and 5. Place the sample cuvette in the cuvette holder.
The sample beam cuvette holder slides into the transmittance port holder.
Cuvette
Holder
Dowels
Figure 5. Cuvette Holder
Specular Light Trap
Raise the detaining lever and carefully remove the specular port plug. Gently insert the
specular light trap and secure with the detaining lever.
AQ-00148-000, Rev. 2
20
MAINTENANCE
General Information
When not in use, the RSA-PE-18 should be stored carefully in a controlled environment.
Dust and moisture may adversely affect its performance.
PRECAUTIONS
• Never disconnect or connect the detector cable with the instrument powered on.
• Do not remove the cover to the detector preamplifier electronics located underneath
the integrating sphere.
• Do not handle the photodetector or mirrors.
• Do not allow foreign objects to enter the integrating sphere.
• Clean dust and particulate debris out of the sphere using a very gentle air blower.
Mirror Cleaning Procedure
The transfer optics mirrors should never be touched or handled. However, the mirrors do
have a protective magnesium fluoride overcoat to allow cleaning if necessary. The
following procedure is recommended:
1. Remove mirror fixture.
2. Spray the mirror with Fantastic Spray Cleaner.
3. Rinse the mirror with distilled water.
4. Repeat until the water sheets off the mirror.
5. Blow dry with a stream of clean nitrogen.
6. Replace mirror fixture.
AQ-00148-000, Rev. 2
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TECHNICAL NOTES
Measurement of Transmittance
There are three types of transmittance measurements that can be performed using a
reflectance spectroscopy accessory; total, diffuse and regular transmittance. All
measurements follow a background correction with white reference materials in the
reflectance ports.
Total transmittance is performed with the sample in the transmittance port and the white
standards remaining in the reflectance ports. This includes the light transmitted through
the sample in all directions. Diffuse transmittance is performed by replacing the white
standard in the port diametrically opposite the sample with a black cavity light trap. This
excludes light transmitted in the regular sample beam direction, measuring only light
scattered through the sample. Regular transmittance is that portion transmitted through
the sample without scattering. Regular transmittance is calculated by subtracting the
diffuse transmittance from the total.
Specular Subtraction
The specular component or gloss refers to the mirror-like reflection from an otherwise
diffuse surface. This property of a surface is responsible for the degree to which reflected
high lights or the images of objects may be seen as superimposed on the surface. In color
measurement, the gloss only reflects back the color of the illuminating light source
without any color information about the bulk material.
In integrating sphere measurements of reflectance, two techniques for subtracting the
specular or gloss component are used. The sample beam can be incident at an angle
slightly off the normal to the sample port. A light trap can then be positioned at another
port across the sphere in the specular direction. In the other technique, the sample beam
can be incident normal to the sample surface. The specular component then retroreflects
back out of the sphere through the sample beam entrance port. This can make for a
simplified and more efficient integrating sphere design; fewer ports are required in the
sphere wall.
AQ-00148-000, Rev. 2
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Use of Proper Reflectance Standards
The use of proper standards is extremely important in obtaining consistent results in any
reflectometer. The term reflectance factor is often used when reporting reflectometer
values. The difference between reflectance factor and reflectance lies in the selection of
the reference. For the reflectance factor, the perfect reflecting diffuser is used as the
reference. The reference for the reflectance is the incident flux. In measurements with
any biconical geometry, the reflectance factor can exceed unity (100% R), whereas the
reflectance cannot. In any reflectometer, determination of the reflectance can be
approximated by measuring the incident flux with a standard of known reflectance.
It is also important to choose a standard with similar geometric reflectance characteristics
to the samples being measured. This preserves the reflective geometry of the
reflectometer between reference and sample readings.
Specular standards such as the NIST SRM 2003X or NIST SRM 2011 first surface mirror
should be used for measuring the reflectance of specular surfaces in integrating spheres.
Samples mounted on the surface behave as part of the sphere. Surfaces that require
specular standards would include mirrors as well as polished glass or metal surfaces.
Most other samples measured for reflectance will be predominantly diffuse in character.
These samples would include most paints, coatings, textiles, ceramics, and natural
materials. Recommended standards for measurement of diffuse reflectance include
Labsphere's Spectralon™ and Infragold™ Reflectance Standards.
Samples which are neither completely specular nor diffuse are more difficult to
adequately measure. Sometimes it may be desirable to compare these surfaces to both a
specular and a diffuse standard to obtain an average result.
AQ-00148-000, Rev. 2
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RECOMMENDED READING
Clarke, F.J.J. and J.A. Compton, "Correction Methods for Integrating Sphere
Measurements of Hemispherical Reflectance", Color Research and Application,
11 (4), 253-262, 1986.
Erb, W. and W. Budde, "Properties of Standard Materials for Reflection", Color
Research and Application, 4 (3), 113-118, 1979.
Goebel, D.G., "Generalized Integrating Sphere Theory", Applied Optics, 6 (1), 125-128,
1967.
Roos, A., C.G. Ribbing, and M. Bergkvist, "Anomalies in Integrating Sphere
Measurements on Structured Samples", Applied Optics, 27 (18), 3828-3832,
1988.
Springsteen, A.W., "Physical and Reflectance Properties of Spectralon Diffuse
Reflectance Materials," Labsphere Technical Note #4, 1989.
Weidner V.R. and J.J. Hsia. "Reflectance Properties of Pressed Polytetrafluoroethylene
Powders," J.O.S.A., 71(7) 856-861,1981.
Weinder, V. , Technical Document 250-8, "Spectral Reflectance Measurements"; U.S.
Dept. of Commerce Riblicalver, 1986.
Zwinkels, J.C., "Errors in Colorimetry Caused by the Measuring Instrument", Textile
Chemist and Colorist, 21 (2), 23-29, 1989.
AQ-00148-000, Rev. 2
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APPENDIX
Typical 8°/Hemispherical Reflectance Factor for an SRS-99
Wavelength (nm)
250
300
400
500
600
700
800
900
AQ-00148-000, Rev. 2
Reflectance
.973
.984
.991
.991
.992
.992
.991
.991
25