Configuration - Knick
Configuration - Knick
Configuration - Knick
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pH Value Calculation<br />
pH value calculation by means of dual conductivity measurement<br />
When monitoring boiler feed water in power plants, the pH value can be<br />
calculated by means of a dual conductivity measurement. For that purpose,<br />
the boiler feed water conductance is measured before and after the cation<br />
exchanger. This commonly used method of indirect pH value measurement<br />
does not require much maintenance and has the following advantage:<br />
Normal pH measurement in ultrapure water is very critical. Boiler feed water<br />
does not contain many ions. This requires the use of a special electrode,<br />
which must be calibrated constantly and the service life of which is generally<br />
rather short.<br />
Function<br />
Two sensors are used to measure the conductivity before and after the cation<br />
exchanger. The pH value is inferred from these two conductivity values<br />
according to the calculation formulas shown below:<br />
Cation<br />
exchanger<br />
Cond measuring<br />
point A<br />
Cond measuring<br />
point B<br />
H 2 O<br />
Sensor A<br />
TC: NH3 / NaOH<br />
Sensor B<br />
TC: HCl<br />
Calculation Block<br />
pH<br />
Calculating the concentration of sodium hydroxide solution /<br />
pH value:<br />
COND A – 1/3 COND B<br />
c(NaOH) =<br />
pH = 11+log[c(NaOH)]<br />
243<br />
34
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