Free chlorine, chlorine dioxide and ozone measuring cells
November 2003
Analytical Instrumentation & Environmental Monitoring
Jumo's membrane-covered, amperometric measuring cells are used to determine the concentration of free chlorine, chlorine dioxide or ozone in aqueous solutions (such as in drinking or pool water as well as in service, process or cooling water). The cell for free chlorine can be applied to determine the following inorganic chlorination agents: chlorine gas, electrolytically produced chlorine, sodium hypochlorite, calcium hypochlorite or chlorinated lime.
The cell for chlorine dioxide is available for measuring chlorine dioxide in chlorite/chlorine and chlorite/hydrochloric acid plants. By using the cell for ozone, it is also possible to measure electrolytically produced ozone, for example. The disinfectant (Cl2, ClO2, O3) diffuses through the sensor membrane into the electrode chamber filled with electrolyte, which contains the gold cathode and the silver/silver chloride anode. Since the sensor operates in the diffusion limiting-current range, every disinfectant molecule that reaches the cathode surface is immediately reduced.
A corresponding reaction takes place at the anode. The electrical current produced by the electrode reaction is proportional to the disinfectant concentration in the solution and serves as a measurement signal, after the appropriate conversion and calibration. In the course of calibration, only the slope has to be calibrated (reference value of DPD determination). Membrane-covered cells from Jumo do not require calibration of the zero point.
The integral electronics of the cells provides a temperature-compensated 4 to 20 mA current signal. Calibration is performed through a connected instrument - indicator, controller, recorder, PLC, etc. The measuring cells can be directly interfaced to a suitable indicator/control instrument.
For more information contact Anastas Schnippenkotter, ASSTech Process Electronics & Instrumentation, 011 794 7057.
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