YSI 9300 Photometer - Manual (Page 16)

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The BLANK TUBE is a test tube filled only with the water being tested only. It
is important to use the actual water to be tested to provide a true comparison
for the test results.
The term 'SAMPLE TUBE' is used to describe the tube containing the water
sample to which the reagents have been added in accordance with the
appropriate test instructions. This tube is used to take the photometer
reading.
Light Cap
A light cap is provided with the photometer. This cap fits over the test
chamber and prevents stray light reaching the photodiode.
It is NOT necessary to use the light cap when using the photometer indoors or
under shaded outdoor light. The light cap should be used when working outside
in strong sunlight. The light cap is also recommended when carrying out
turbidity-based tests such as the cyanuric acid test, under bright or variable
lighting conditions. Test instructions indicate when the light cap should be used.
Getting the Best Results
Success in obtaining accurate and consistent test results will depend on the
care with which test procedures are carried out. Always follow the test
instructions carefully and observe the stated standing periods and
temperature conditions where applicable.
Wipe test tubes free from condensation before placing in the photometer.
Test tubes should always be kept in a clean condition. Wash and dry the test
tubes carefully after use. Dirty tubes may be soaked in a mild detergent
solution if necessary. Tubes which become stained or scratched should be
discarded and replaced.
Taking Test Readings
Press key. The instrument displays the ‘Choose a Test’ menu box, with the
last test program used highlighted as the active line.
The cursor will flash on the [OK] symbol of the ‘options menu' at the bottom
of the screen. Press [OK] to accept this program.
To choose a different test program, either use the  and  keys to scroll
through the menu options, or use the numeric keys to enter the Phot number
of the desired test. The four most recently used tests are listed at the top of
the ‘Choose a Test’ screen for convenience. Press [OK] to accept the selected
program.