32
SECTION 2, continued
12. Insert the cell into the cell compartment.
13. The display will show the S2 icon (with the 2 flashing) and
100 FNU or the value of the S2 standard for the previous
calibration.
14. Edit the standard concentration using the arrow keys.
15. 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. Remove
the sample cell from the cell compartment.
16. Thoroughly mix the 700 to 900 FNU standard, then fill a clean
sample cell to the line with the standard. Insert the cell into the cell
compartment.
17. The display will show the S3 icon (with the “3” flashing) and
800 FNU or the value of the S3 standard for the previous
calibration.
18. Edit the standard concentration using the arrow keys.
19. 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
instrument will increment back to S0. Remove the sample cell from
the cell compartment.
20. Press
CAL. The instrument will store the new calibration data and
return the instrument to the measurement mode.
Note: If calibration errors occurred during calibration, error messages will
appear after CAL is pressed.
2.4.4 Using Gelex
®
Secondary Turbidity Standards
Note: Store Gelex standards at room temperature. Do not allow to freeze or exceed 50
°C.
Gelex Secondary Standards (included with 4474000 only) are
particulate suspensions similar to formazin primary standards in light
scattering characteristics. FNU values on the Gelex standards indicate
the range for which they should be used. Due to minor variations in
glass and individual instrument optical systems, the true value of the
Gelex standards must be determined against formazin in the same
instrument they will be used with for later calibration checks.
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