ProMinent DULCOMETER pH/mV/Pt 1000 Mode D'emploi page 43

Glossary of terms
Redox potential
The redox potential is dependent on the sum of reducing and oxidizing
substances present in the water – or in simple terms – it is the measurement of
the disinfection strength in water. The higher the concentration of oxidizing
substances, the higher the redox potential (oxidation = disinfection).
Hypochlorous acid is the decisive oxidant in swimming pools. The
contaminants present in water reduce this level.
Temperature and pH value have the following effects on the redox value:
Rising temperature high redox potential
Rising pH value low redox potential (by use of chlorine)
There is no clear relationship between disinfectant concentrations and redox
potential. It has been determined that at a redox potential of 750 mV,
microorganisms are eradicated or deactivated in seconds. At less than 600 mV
the disinfecting time can take minutes or hours.
Calibration (of probes)
As all pH probes will deviate from the theoretical values it will be necessary to
recalibrate the zero point and slope value of the probe from time to time.
A single point calibration is normally carried out using pH 7 buffer solution, i.e.
zero point calibration.
In case of a two-point calibration, a second value is to be selected to adjust
the slope. The second value is dependent upon the actual measurement range
(alkaline or acid).
In swimming pools, a zero point calibration will suffice. The sensor function
must nevertheless be checked from time to time with a pH 4 or pH 10 buffer
solution. As the measurement is carried out around the zero point, moderate
errors in the slope values are insignificant.
Age and dirt will alter the probe slope value.
Zero point
This refers to the voltage measured at the terminals of a pH probe when
immersed in a solution of pH value 7. The zero point of the probe is altered by
aging and dirt.
The zero point of pH probes is theoretically 0 mV; in practice, good
performance is achieved with a probe having a zero point between ±60 mV.
New probes have a maximum zero point variation of ±30 mV.
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ProMinent
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