YSI 9500 Photometer - Manual (Page 4)

4
OPERATING PRINCIPLE
The YSI 9500 direct-reading photometer is an instrument that measures color
intensity. Light is passed through a test tube containing the sample solution, and
then through a colored filter onto a photodetector. Filters have been chosen so that
light of a specific wavelength is selected. When the solution is completely colorless,
all of the light passes through the sample. With colored samples, light is absorbed
and that which passes through the sample is proportionately reduced.
In 9500 test procedures, the direct-reading photometer is used to measure the color
which is produced when chemical reagents are reacted with the sample. In these
tests, the color intensity produced is proportional to the concentration of the
parameter under test.
The photometer is pre-programmed with calibrations for each test parameter.
Different test procedures are carried out at different wavelengths to optimize the
sensitivity of each test. The required wavelength is selected automatically by
the instrument.
The calibrations are accessed by entering a unique program number at the
start of each test procedure. This enables the instrument to select the
appropriate wavelength filter automatically and allows the photodiode
response to be converted to a concentration reading. The instrument thus
displays a direct-reading of the test result.
The photometer is ideally suited for general analytical applications. The
instrument can be used as a laboratory or field photometer for standard
analytical methods or for comparison of colored solutions.
For general analytical applications, Transmittance (test program 0), or
Absorbance (test program 1) can be chosen.
Power Supply
The photometer is designed to be powered either from alkaline batteries or via the
USB socket. To use mains power, the instrument is connected using the USB
Connection Cable plugged to the Mains Adapter. Alternatively, if the USB
connection cable is plugged to a computer, power will be drawn from the computer.
These items are sold separately.
The photometer features a battery indicator – see ‘System Mode’ functions and scroll
down to Battery Level. A minimum voltage of 3.0V is needed to operate the
photometer.
In addition to the above feature, a battery-warning message will appear automatically
on the display when the battery voltage becomes low. The batteries should be
replaced as soon as possible after the warning message appears.