7.1.3 Indexing the calibration cuvettes
Purpose of indexing
The cuvettes of the standard solutions have a min‐
imum manufacturing tolerance. This manufacturing
tolerance results from the manufacturing process
and is unavoidable.
Index and mark the position on the cuvette with the
lowest turbidity value (lowest NTU value) to mini‐
mise the effect of this manufacturing tolerance on
the calibration process.
Use the marking rings supplied to mark the index
points. These marking rings are supplied with the
calibration kit packaging. Place this marking ring
around the plastic lid of the respective cuvette.
NOTICE!
Display resolution
We recommend setting up the sensor in the “Com‐
missioning/Display resolution” menu to achieve the
following resolutions for the purpose of indexing
– 1000 NTU: No digit after the decimal point on
the display
– 10 NTU: Two digits after the decimal point on
the display
– 0.02 NTU: Four digits after the decimal point
on the display
NOTICE!
Freezing of the standard solution
Do not allow the standard solutions to freeze. Not
even for short periods of time.
Handling the standard solutions
n
Gently shake the standard solution 1000 NTU before using it
for calibration.
n
All standards need to be poured from the storage bottle into the
cuvette before use. The contents of the cuvette can then be
used for 24 hours.
n
Do not use the standard solutions after their expiry date.
The following steps permit the repeatable indexing of standard sol‐
utions:
1.
Insert the standard solution into the optical chamber if the
device is operating in AUTO mode.
2.
Slowly rotate the standard solution in the optical chamber
one complete revolution (360 º).
While slowly rotating the standard solution, observe the tur‐
bidity measured and determine the position of the cuvette
with the lowest value.
3.
Position the standard solution at the point with the lowest tur‐
bidity value and place the indexing ring on the cap of the
standard solution so that the pointer of the indexing ring
points directly forward.
Indexing the standard solutions with
their cuvettes
Operation
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