User Manual

Optical pH Sensors | User Manual
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readings is activated. The compensation temperature will be displayed in the
corresponding channel row of the main window.
AquapHOx: The AquapHox devices have a temperature sensor included for automatic
temperature compensation. The temperature sensor is factory 2-point calibrated.
Pico-pH:
The Pico-pH OEM module does not include an Pt100 temperature sensor. This
sensor (Item No. TSUB21-NC) needs to be soldered on the device. Please refer to the
Pico-pH manual for more information.
NOTE: The Pt100 temperature sensor may have an offset which needs to be
determined manually and calibrated first. To calibrate the Pt100 sensor please
see the Appendix.
2.2.2 Salinity
The optical pH sensors show a cross sensitivity to the ionic strength of the medium.
Ionic strength is a function of the concentration and charge of all the ions in a solution
and is an important parameter for pH measurements. Theoretically, the ionic strength of
a sample can be calculated, but from a practical point of view, other indicators can
provide a rough estimate of the ionic strength, such as using the concentration of all
compounds or conductivity data.
The sensors are specified for measurements between 20-500 mM ionic strength.
Response time and accuracy at lower or higher salinities may differ from the specified
value which was determined at 150mM Ionic strength.
For compensation of the effect, the salinity [g/l] must be entered in the sensor settings
and during a pH calibration (please note that the ionic strength can differ between the
calibration buffer and the medium of the measurements).