CHEMOTRONIC III
20
solution measured by the automatic calibration procedure. The factor can be varied
between 90 % (clear) and 10 % (hazy).
This adjustment is particularly of interest for solutions which show a slight turbidity
only or those with a turbidity range. The standard test program is adjusted for
automatic calibration, as it eliminates the necessity of turbidity standards. The
setting of P
2
= 20 % of P
1
(Ac20).
6.6. External calibration
Ec
is a global calibration for all test programs by means of turbidity standards. Both
P
1
and P
2
must be calibrated by standard solutions, valid for all test programs.
6.7. Turbidity calibration standards
In turbidity measurements, primary turbidity standards are required as these are
the only certified standards. By diluting a primary turbidity standard a secondary
standard can be made for actual use. The derived turbidity value is traceable to the
original primary standard. It is accepted that dilutions are less stable and cannot be
used over a longer period of time (max. 1 week). The definition of turbidity units is
based on the polymer suspension FORMAZIN. A FORMAZIN primary turbidity
standard is specified for 4000 Nephelometric Turbidity Units (NTU). A wide range of
secondary standards can be made by dilution with distillated water (see calibration
procedure). A 4000 NTU turbidity standard is stable for long period of time (max. 1
year). Titration of FORMAZIN has proven to be the fastest and most convenient
means of an accurately working turbidity standard.
Summary of Contents for HEMOTRONIC III
Page 54: ...CHEMOTRONIC III 54 Appendix...
