wtw Multi 350i, Operating Manual

Page: 32 / 108

Operation Multi 350i
30
4.4.5 pH calibration
Why calibrate? pH electrodes age. This changes the asymmetry (zero point) and slope
of the pH electrode. As a result, an inexact measured value is dis-
played. Calibration determines the current values of the asymmetry
and slope of the electrode and stores them in the measuring instru-
ment. Thus, you should calibrate at regular intervals.
When to calibrate?
!
After connecting another electrode
!
When the sensor symbol flashes:
– after the calibration interval has expired
– after a voltage interruption (empty batteries)
Buffer sets for
calibration
You can use the buffer sets quoted in the table for an automatic calibra-
tion. The pH values are valid for the specified temperature values. The
temperature dependence of the pH values is taken into account during
calibration.
Note
The buffers are selected in the sensor menu (setting, Calibration type ,
see section 4.4.4).
Buffer set Name on the
display pH values at
25 °C
Technical buffer solutions TEC 2.00
4.01
7.00
10.01
NIST/DIN buffer solutions NIST/DIN 1.679
4.006
6.865
9.180
12.454
(user-defined single-point or two-
point calibration) ConCal pH 7.0 ± 0.5
and any other
buffer solution