Hach-Lange POLYMETRON 9245 User Manual - Manual (Page 19)

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Section 3 Analyzer Overview
3.1 Overview
The Polymetron 9245 Sodium Analyzer is a continuous on-line monitor for direct measurement
of sodium in power generation processes.
The measurement is based on a direct potentiometric technique using a highly sensitive sodium
glass electrode. The difference of potential between the glass electrode and the reference
electrode is directly proportional to the logarithm of sodium concentration as shown by the
Nernst law:
With:
• K
Na-S
: Selectivity constant of the ion S
• a
S
: Activity of the ion S
• Z
S
: Valency of the ion S
• E
D
: Diffusion potential (conductivity dependant)
The analyzer features low maintenance, automatic or manual process calibration and uses a
sodium-sensitive glass electrode together with a reference electrode to measure sodium
concentrations in a sample that has been previously conditioned to a pH > 10.5.
The pH value can be set to between 10.7 and 11.6 pH and is controlled by measuring the
conductivity of the conditioned sample.
External grab sample analysis is also available for this high-accuracy analyzer.
The physical system consists of two integrated units, the electronics control section and the
liquid handling section.