6 Operation
K-375 / K-376 / K-377
Operation Manual, Version E
71
Setpoint colorimetric sensor
It is necessary to determine the Setpoint every day
before starting sample determinations, and when
the method is changed or fresh chemicals are used
to adjust the device to the current conditions.
Before the Setpoint determination a Preheating
should be performed to heat up the system.
We recommend a determination of 3 Setpoint
cycles before a determination is started. The last
Setpoint is used as endpoint for the following deter-
minations.
Select whether the Setpoint cycle should be
performed via the KjelSampler or not and the
number of cycles. Set the concentration of the
boric acid used, the indicator and the method. The
selected method for Setpoint determination must be
identical to the method used for sample determina-
tion.
The Setpoint should fulfill the following criteria:
Deviation between the last two Setpoints should not
be more than ±20 mV.
If Sher indicator is used, you should work with a
wavelength of 610nm, in which case the setpoint is
in the range of 300 - 500mV.
If bromocresol green/methyl red indicator is used,
you should work with a wavelength of 640nm, in
which case the setpoint is in the range of 300 -
500mV.
NOTE
To obtain good results, the optical sensor should be
used with the setup described in Section 7.2.6. To
prevent accumulations of air bubbles on the optical
sensor, clean the optical sensor regularly and keep
it in the wash solution when not in use.
All Setpoint measurements are stored in Result
Groups
Setpoint
Method must be identical to the determination
method used for the samples and blanks.
