Ocean Optics CHEM2000 Operating Manual And User Manual - page 15
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Relative Irradiance
Selecting this mode switches the spectral window into Relative Irradiance Mode. The reference
spectrum must be made in Scope Mode with a blackbody of known color temperature. (CHEM2000-
UV-VIS users cannot make relative irradiance measurements because the light source that comes with
the system is not a blackbody source with a known color temperature.) A dark spectrum is usually
obtained by preventing light from entering the fiber that connects to the spectrometer. (See the
Experiment Tutorial
beginning on page 27.) Relative irradiance spectra are a measure of the intensity
of a light source relative to a reference emission source. Relative irradiance is calculated by the
following equation:
S
λ
- D
λ
I
λ
= B
λ
(
R
λ
- D
λ
)
where B is relative energy of the reference calculated from the color temperature in Kelvin, S is the
sample intensity at wavelength
λ
, D is the dark intensity at wavelength
λ
, R is the reference intensity
at wavelength
λ
.
Concentration
Concentration is the amount of a specified substance in a solution. Graphs of absorbance vs.
concentration are known as Beer’s Law plots. These are calculated by first measuring the light that is
absorbed from a series of solutions with different known concentrations. The length of the sample --
such as the path length of our cuvette holder -- and the wavelength chosen for monitoring the amount
of light absorbed, are constants. Then a linear plot derived from the scans of these standard solutions
with known concentrations is obtained. The plot is then used to determine the unknown concentrations
of solutions. (See the
Experiment Tutorial
beginning on page 27.)
The absorbance of a solution is related to the concentration of the species within it. The relationship,
known as Beer’s Law, is:
A
λ
=
ε
λ
c
l
where A is the absorbance at wavelength
λ
,
ε
is the extinction coefficient of the absorbing species
at wavelength
λ
, c is the concentration and
l
is the optical pathlength.
Cursor Function Bar
+
Sign
When the + is selected, the pointer becomes a crosshair symbol, enabling you to drag the cursor around
the graph.
Magnify Symbols
When the magnify symbol is selected, you can choose from among 6
magnify functions. The function chosen will remain in use until another
magnify icon or the crosshair symbol is selected. Clockwise, beginning with
the top left symbol, the magnify icons perform the following functions:
1. magnifies a specific area by clicking and dragging a box around an area
2. zooms in on the horizontal scale, but the vertical scale remains the same
3. zooms in on the vertical scale, but the horizontal scale remains the same
4. zooms in approximately one point vertical and horizontal, click once or press continuously
5. zooms out approximately one point vertical and horizontal, click once or press continuously
6. reverts to the last zoom function
Cursor Diamond
To move the cursor left or right in small increments in the graph area, click on the left and right
sections of the move cursor diamond. The top and bottom sections of the diamond will send the
cursor to the next or previous channel in your system. (The CHEM2000 and CHEM2000-UV-
VIS are single channel systems. However, additional channels can be purchased at any time.)