HOME
Model
R200V
Reflectometer
Transmissometers
Other
Tutorials
Other
Graham Products
About
Us
|
|
At the
right is the Model R200V as shown on
our Reflectometer Web Page. This instrument is provided with a reflectance
standard -- in this case one with reflectance of 99.65% In this image,
the protective cover slide is shown in the withdrawn position as required
to calibrate used the instrument. But we're getting ahead of ourselves.
Let's start at the beginning.
The Model R200V should
be turned on for about 20 minutes before attempting to use it. This
allows the electronic circuit to become thermally stabilized as required
for consistent measurements.
Two initial operations are
required before taking reflectance measurements of samples. First, it is
necessary to set the "zero" for the instrument. Then the instrument is
set to read the reflectance value which the Reflectance Standard provides. |
| The image at the right shows
the instrument with the cover slide closed to protect the reflectance standard
housed beneath. Note that the meter does not read zero because the
black anodized finish on the cover slide does reflect some light back into
the Reflectometer head.
In order to set zero, it
is necessary to have a surface which reflects no light. The top surface
of the instrument even though black anodized actually still reflects a
very substantial amount of light -- here shown to be 2.72%
Rather than providing a "Black
Sample" -- which is very difficult to maintain, the Model R200V is provided
with an aperture to prevent any light from reaching the black anodized
surface. |
 |
 |
In the image at the left,
the operator's hand is shown closing the aperture to block the test beam
from leaving the optical head and preventing any of the light from reaching
the optical sensor inside.
With the aperture closed
(below) the readout will typically show somewhere around 0.1 to 0.2% before
adjusting the zero -- below showing 0.13%
The operator adjusts the
"SET
O" control to bring the readout down close to 0.00%
 |
| At the right
we see the readout showing 0.02% which is actually a pretty good approximation
to zero since the last digit is constantly fluctuating +/- 1 digit.
If the Reflectometer has
been allowed to come to thermal equilibrium the zero setting should normally
persist throughout the day, but it is always a good idea to perform an
occasional check to see that nothing has changed, .
Such zero drift usually varies
with ambient conditions such as temperature, but is independent of the
ambient lighting conditions, whether the aperture is closed or open.
If the level of drift from zero becomes too large, simply reset zero as
described above.
It is recommended that the
instrument be turned on at the beginning of the day and allowed to stabilize
at least 20 minutes before taking readings. The longer the instrument
is operating, the more stable the readings become. |
|
 |
In order to calibrate the
instrument, the operator moves the protective slide to one side exposing
the reflectance standard beneath as shown in the image at the left.
With the cover slide withdrawn
the reflectance standard is exposed to the test beam. Note, that
in this case, the readout shows 99.49% before the calibration procedure
|
| The operator
adjusts the "SET STANDARD" control to give the required reflectance
reading, in this case, 99.65% -- the calibration data provided by
the manufacturer of the reflectance standard.
With the Reflectometer calibrated
to read 99.65% as shown in the image below, the cover slide may now be
replaced and the instrument is ready to measure reflectance! |
 |
|
Making
a reflectance measurement does not require any further manipulation of
controls. Simply place the sample beneath the optical head, as shown
below, and take the reading directly from the meter -- in this case 86.67%
It is easy to make 6 to 10 reflectance measurements per minute.
Occasionally,
throughout the day, the operator should go through these procedures to
ascertain that both the zero setting and the calibration setting remain
constant. Small variations from either (+/- .02%) do not significantly
affect the actual reflectance reading of the test piece.
Graham
Optical Systems would be happy to discuss your requirements for an instrument
to measure your samples. We can provide instruments to measure either
specular reflectance (as shown here) or diffuse reflectance.
If
you have specific requirements not met by the Model R200V, please contact
us. Specials are usually not very expensive to provide. |
| Making
a reflectance measurement does not require any further manipulation of
controls. Simply place the sample beneath the optical head, as shown
below, and take the reading directly from the meter -- in this case 86.67%
It is easy to make 6 to 10 reflectance measurements per minute.
Occasionally,
throughout the day, the operator should go through these procedures to
ascertain that both the zero setting and the calibration setting remain
constant. Small variations from either (+/- .02%) do not significantly
affect the actual reflectance reading of the test piece.
|
 |
|
STEP
|
OPERATION
|
| Warmup |
At least
20 minutes warmup time -- the longer the instrument has been operation,
the more stable it will become! |
| Closing
Aperture |
Before
setting zero or calibrating, close the aperture as described above |
| Setting
Zero |
Set ZERO
using the Control.
A reading of +/- 0.1% to
+/- 0.2% is adequate. |
| Opening
Aperture |
Reopen
the aperture in preparation of setting the zero |
| Uncovering
Reflectance Standard |
Uncover
the Reflectance Standard making sure that you do not touch it or scratch
its surface. It should be kept covered whenever not in use,
It may be cleaned by passing a light jet of "canned air" over the surface.
Do not allow a direct jet of compressed air or gas strike the surface since
it can cause misting and may compromise e the standard's accuracy. |
| Setting
Standard Reflectance |
Adjust
the "Set Standard" control so that the readout shows the value supplied
with the Reflectance Standard.
Again an accuracy of +/-
0.1% to +/- 0.2% is adequate. |
| Protecting
Reflectance Standard |
The Reflectance
Standard must be protected from contact with other surfaces. Touching
the surface with the fingers can permanently alter the reflectance, and
thus compromise the calibration. |
| Measuring
Reflectance |
To measure
reflectance simply place the test piece under the optical head. The readout
shows the reflectance as %R |
| Rechecking
Zero and Calibration |
Throughout
the day, the operator should occasionally recheck that the Instrument read
Zero and the correct calibration value. |
For
Further Information, call Gordon Graham today at (818) 700-1263 or send
an email to the address below.
GRAHAM OPTICAL
SYSTEMS, 9530 Topanga Canyon Blvd., Chatsworth,
CA 91311
Phone
(818) 700-1263 FAX (818) 700-1627
E-mail: graopt@ix.netcom.com
Copyright
© 2008 Graham Optical Systems All Rights Reserved
This
page last updated June 16,2008
|
