Xylem WQL-pH pH DATALOGGERS - Manual (Page 31)

WQL-pH Calibrating for pH measurements
105 ba75821e01 10/2009
5 Calibrating for pH measurements
Why calibrate? During the operation of a pH electrode, the slope and asymmetry of the
electrode change with time. Calibrating determines the current slope and
asymmetry (zero point) of the electrode and stores them in the logger.
When to calibrate? Always calibrate:
z During the initial commissioning
z Before starting a logging job
z After installing another electrode
Calibration procedure, AutoCal :
AutoCal is a fully automatic single-point or two-point calibration using the datasets for
buffer solutions selected in the Buffer sets menu.
The buffer solutions are automatically recognized. Depending on the setting
(see page 116), the PC program displays the relevant nominal buffer value
or the current electrode voltage in mV. The calibration can be terminated after
the first buffer solution. This corresponds to a single-point calibration. For
this, the instrument uses the Nernst slope (-59.2 mV/pH at 25 °C) and
determines the asymmetry of the electrode.
AutoRead When calibrating with AutoCal, the AutoRead function is automatically
activated. The AutoRead function checks the stability of the measured pH
and temperature signal. The stability has a considerable effect on the
reproducibility of the measured value.
The current AutoRead measurement can be terminated at any time
(accepting the current value).
Note
In the delivery condition, the WQL-pH logger is equipped with default
calibration values (see chapter 10 R
ESETTING THE LOGGER ). To achieve
accurate measured values it is essential to calibrate with the electrode before
logging.