wtw inoLab 740, Operating Manual

Page: 101 / 274

Ion concentration
101
7.3 Calibration for ion-selective measurements
Why calibrate? Ion-selective electrodes age and are temperature-
dependent. This changes the slope. Calibration determines
the current slope of the electrode and stores it in the
measuring system.
Thus, you should calibrate before each measurement and at
regular intervals.
Note
For calibration, use tempered standard solutions with a
temperature that differs by a max. of
±
2 °C from the
temperature of the test sample.
When to calibrate? l Before any concentration measurement if possible
l
After connecting another electrode
l When the sensor symbol flashes after a voltage
disconnection, e.g. battery change
ISECal This is the conventional two-point or three-point calibration
procedure that uses 2 or 3 freely selectable standard
solutions. The concentration expected in the measurement
determines the concentration of the calibration standards to
be selected.
AutoRead The calibration procedure automatically activates the
AutoRead function. In order to accept the current measured
value without waiting for the end of the AutoRead function,
simply press
g
.
Display
TP Error
If you are using a temperature probe, any temperature
deviation (
±
2 °C) of the standard solutions that is too large
is signaled by the display indicator, TP Error .