Xylem VARIO WATERPROOF PH METER - Manual (Page 22)

Operation VARIO pH
22 ba75373e04 07/2006
4.4 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.
Thus, you should calibrate at regular intervals.
Note
The calibration data are stored in the short pH electrode or DIN adapter and
read out by the meter.
When to calibrate? z During the initial commissioning of the meter or sensor
z After connecting a different electrode to the adapter
z After the calibration interval has expired (when the sensor symbol flashes)
Calibration interval We recommend to take 14 days as a guide value for the calibration interval
(the interval between two regular calibrations). The calibration interval (Int) is
set to 14 days in the factory. You can select the interval in the range of 1 ...
999 days (see section 4.4.3).
Buffer sets You can use the buffer sets quoted in the table for an automatic calibration.
Use any one, two or three buffer solutions of a buffer set in a sequence of
your choice. The pH values apply to the quoted temperature values. The
temperature dependency of the pH values is taken into account when
calibrating.
Calibration points Calibration can be performed with one or two or three buffer solutions (single-
point, two-point or three-point calibration). The meter determines the
following values and calculates the calibration line as follows:
Buffer set Name on the
display pH values at 25 °C
WTW Technical buffer
solutions TEC 2.00
4.01
7.00
10.01
NIST buffer solutions NIST 1.68
4.01
6.87
9.18
12.45