Xylem handylab pH 11 - Manual (Page 19)

handylab pH 11 Operation
19 ba75366e04 01/2011
4.3 Calibrating
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 displayed. Calibration
determines the current values of the asymmetry and slope of the electrode
and stores them in the measuring instrument.
Thus, you should calibrate at regular intervals.
When to calibrate? z After connecting another electrode
z after a voltage interruption, e. g. after changing the batteries
You can select between 3 calibration procedures:
AutoCal TEC is specially adapted to the SI Analytics technical buffer solutions as a fully au-
tomatic two-point or three-point calibration. The buffer solutions are auto-
matically recognized by the measuring instrument. Depending on the
instrument setting (see section 4.4 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 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.
AutoCal DIN is specially adapted to the permanently programmed buffer solutions in ac-
cordance with DIN19266 as a fully automatic two-point or three-point cali-
bration. The buffer solutions are automatically recognized by the measuring
instrument. Depending on the instrument setting (see section
4.4 C
ONFIGURATION ), the instrument displays the relevant buffer nominal val-
ue 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 de-
termines the asymmetry of the electrode.
ConCal This function is a conventional two-point calibration using two buffer solu-
tions (pH 7.0 ± 0.5 and any other buffer solution) or a single-point calibra-
tion using any buffer solution and 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 (accept-
ing the current value) by pressing <RUN/ENTER>.