3 calibrating, Calibrating – Xylem handylab pH 12 User Manual
Page 20
Operation
handylab pH 12
20
ba75368e04
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 When the sensor symbol flashes:
– after the calibration interval has expired
– after a voltage interruption, e. g. after changing the batteries
Calibration interval
The calibration interval (Int 3) is set to 7 days in the factory. You can select
the interval in the range of 1 ... 999 days (see section 4.6 C
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 4.6 C
), 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
4.6 C
), 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
Displaying
calibration data
Each time the instrument is switched on, the calibration data are shown on
the display for a short time (see section 4.1 S
). In order to view the calibration data, switch the measuring instru-
ment off and switch it on again.