Xylem handylab pH LF 12 - Manual (Page 23)

handylab pH/LF 12 Operation
23 ba75370e03 11/2009
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 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 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 SI Analytics technical buffer solutions as a fully
automatic two-point calibration. The buffer solutions are automatically rec-
ognized 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 corresponds to a single-point
calibration. When doing so, 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 DIN 19266 as a fully automatic two-point calibration. The op-
erating sequence of the AutoCal DIN calibration corresponds to that of the
AutoCal TEC calibration. The calibration can only be terminated after the first
buffer solution (single point calibration).
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, 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 (accept-
ing the current value) by pressing .
Displaying the
calibration data
You can view the data of the last calibration on the display. The proceeding
is described on page 53.
Printing the
calibration
record
The calibration protocol contains the calibration data of the current calibration.
You can transmit the calibration protocol to a printer via the serial interface
(see page 55).