30
SECTION 2, continued
14. Remove the sample cell from the cell compartment.
15. The display will show “S3” (with the 3 flashing) and “800 FNU” or
the value of the S3 standard for the previous calibration. If the value
is incorrect, edit using the arrow keys.
16. Fill a clean sample cell to the line with well mixed 800 FNU
StablCal Standard or 800 FNU formazin standard. Insert the sample
cell into the cell compartment by aligning the orientation mark on
the cell with the mark on the front of the cell compartment. Close
the lid.
17. Press
READ. The instrument will count from 60 to 0 (67 to 0 if signal
average is on), measure the turbidity and store the value. The
display will increment back to the S0 display. Remove the sample
cell from the cell compartment.
18. Press
CAL to accept the calibration. The instrument will return to
measurement mode automatically.
Note: If calibration errors occurred during calibration, error messages will
appear after CAL is pressed (See Section 5.4 on page 57).
2.4.3.1 Preparing User-selected Formazin Dilutions
The formazin solutions should span the entire range of the instrument.
Hach recommends preparing three standards:
• 10–30 FNU
• 90–110 FNU
• 700–900 FNU
The standards must have a difference of at least 60 FNU.
In addition, a blank made from the dilution water should be prepared.
Prepare the formazin standard solutions from the well mixed 4000 FNU
stock solution as specified in Section 2.4.2.4 on page 26 and dilution
water as specified in Section 2.4.2.2 and Section 2.4.2.3 on page 25.
Make the standards immediately before use and discard them after
calibration is done.
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