Hach TL2350 Manuel D'utilisation De Base page 18

5. Apply a small
drop of silicone oil
from the top to the
bottom of the vial.
6.3 Turbidity measurement
For accurate turbidity readings use clean sample cells and remove air bubbles.
6.3.1 Measurement notes
Proper measurement techniques are important in minimizing the effects of instrument variation, stray
light and air bubbles. For accurate and repeatable measurements:
Instrument
• Make sure that the instrument is on a level, stationary surface that is free of vibration during the
measurement.
• The USEPA filter assembly is required for turbidity measurements reported for United States
Environmental Protection Agency (USEPA), National Primary Drinking Water Regulations
(NPDWR) or National Pollutant Discharge Elimination System (NPDES) permits.
• Turn the instrument on 30 minutes (Ratio on) or 60 minutes (Ratio off) before measurement. Keep
the instrument on 24 hours a day if the instrument is used regularly.
• Always close the sample compartment lid during measurement, calibration and verification.
• Remove the sample cell from the instrument and turn off the instrument if the instrument is stored
for an extended time period (more than a month).
• Keep the sample compartment lid closed to keep dust and dirt out.
Sample cells
• Always cap the sample cell to prevent spillage of the sample into the instrument.
• Always use clean sample cells in good condition. Dirty, scratched or damaged cells can result in
readings that are not accurate.
• Make sure that cold samples do not "fog" the sample cell.
• Store sample cells filled with distilled or deionized water and cap tightly.
• For the best accuracy, use a single sample cell for every measurement or a flow cell.
Note: As an alternative, matched sample cells may be used for measurements but do not provide as good of
accuracy or precision as a single indexed sample cell or flow cell. When using matched sample cells, align the
orientation mark on the sample cell with the reference mark on the sample cell holder.
Measurement
• Measure samples immediately to prevent temperature changes and settling. Before a
measurement is taken, always make sure that the sample is homogeneous throughout.
• Avoid sample dilution when possible.
• Avoid instrument operation in direct sunlight.
18 English
6. Use the oiling
cloth to apply the oil
equally to the
surface of the vial.
Remove most of the
oil. Make sure that
the vial is almost dry.
7. Put the vial in the
sample cell holder
with the triangle on
the vial aligned with
the reference mark
on the sample cell
holder. Push the lid
closed until a click is
heard.
8. Push Read. The
value and pass or
fail status shows.
The data is
automatically stored
in the instrument.