Xylem pH/ION 3400i ION SELECTIVE ELECTRODE ANALYZER - Manual (Page 20)

Operation pH/ 3400i
20
4.3 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? z After connecting another electrode
z When the sensor symbol flashes
– (after the calibration interval has expired)
– after a voltage interruption, e. g. after changing the batteries
You can select one of 3 calibration procedures:
AutoCal TEC is specially matched to the WTW technical buffer solutions as a fully au-
tomatic two-point calibration. The buffer solutions are automatically
recognized by the measuring instrument. Depending on the instrument
setting (see section 4.8 C
ONFIGURATION ), the instrument displays the
relevant buffer nominal value or the current electrode voltage in mV.
The calibration can be terminated after the first buffer solution. This cor-
responds to a single-point calibration. When doing so, the instrument
uses the Nernst slope (-59,16 mV/pH at 25 °C) and determines the
asymmetry of the electrode.
AutoCal DIN is specially adapted to the permanently programmed buffer solutions in
accordance with DIN 19266 as a fully automatic two-point calibration.
The operating sequence of the AutoCal DIN calibration corresponds to
that of the AutoCal TEC calibration. The calibration can only be termi-
nated after the first buffer solution (single point calibration).
ConCal This function is a conventional two-point calibration using two buffer
solutions (pH 7.0 ± 0.5 and any other buffer solution) or a single-point
calibration using any buffer solution, which is used as a high-speed
method.
AutoRead When calibrating with AutoCal TEC and AutoCal DIN, the AutoRead
function is automatically activated.
The current AutoRead measurement can be terminated at any time
(accepting the current value) by pressing <RUN/ENTER>.
Displaying the calibra-
tion data
You can view the data of the last calibration on the display. The pro-
ceeding is described on page 48.
Printing the calibration
record
The calibration protocol contains the calibration data of the current cal-
ibration. You can transmit the calibration protocol to a printer via the se-
rial interface (see page 51).