User Manual

Optical pH Sensors | User Manual

3 SENSOR CALIBRATION

3.1 General Informations

The pH calibration has to be repeated periodically, depending on the individual

application (e.g. required accuracy, temperature of the sample, life-time of the sensor,

substances in sample). It is advisable to perform a 2-point calibration before every

measurement using freshly prepared buffer solutions.

The calibration of optical pH sensor differs from other measurements methods, as the

calibration points are NOT in the dynamic range of the sensor. This is due to the function

principle.

Optical pH sensors can be 2-point calibrated and pH offset adjusted.

• 1-point calibration (required): Calibration of the completely protonated sensor at

highly acidic conditions. Recommended before every measurement. pH has to be

lower than pH 3.

• 2-point calibration (highly recommended): Additional calibration of the completely

deprotonated sensor at highly basic conditions. Recommended before every

measurement. pH has to be higher than pH 10. The 2-point calibration is required

for the pH Minisensor.

• pH-offset adjustment (for complex medium): Adjustment of the turning point of the

sensor in highly complex medium (individual sample, see image below). This offset

pH has to be in the dynamic range (e.g. between pH 6.5 and 7.5 for a pH 7 sensor).