Operating principle

CL 91 can be used for measurement of concentration of both free chlorine and chlorine dioxide in waters. For chlorine dioxide measurements, specific reference should be made upon ordering the cell, as the sensitivity of the latter must be suited to the higher oxidizing capacity of the same dioxide. The residual chlorine meter utilizes an amperometric technique in compliance with the Standard Methods. Such technique consists in a special adaptation of polarography and is based on the principle that the diffusion current limit between two (polarizing and auxiliary) electrodes, is proportional to the concentration of an oxidizing substance.a continuous measurement of the free residual chlorine in mother waters. Its sensitivity to very small CL 91 carries out changes in the amount of chlorine and the rapidity of the response signal make it particularly suited as a process instrument, and thus compatible with indicators, recorders and PIQ controllers.

For all CL91 Plus models
pH: 0 - 14
redox: -1200 +1200 mmV

Operation

A continuous flow of water drawn from a conduit or a reservoir, enters the analysis cell through a connector at the bottom. The intake water must be so ajusted as not to present changes in its flowrate. To this end, the cell is provided with a flowmeter and a controller. CL 91 measures the free chlorine as hypoclorous ion HOCL. When water is present in the cell, the normal voltage differential between the two metals is cause for the electrodes to operate as a pile. Since the metal of cell "A" is behind the cell "B" (copper) in the voltage series, the latter acts as a sensitive pole generating a flow of current according to the following equation:

Consequently, the ions H+ move towards the electrode "A", and lay down to form immediately a thin layer of solution with a certain concentrotion gradient. Then the flow of electrons stops and the electrode is said to be polarized. The presence of free chlorine in the sample under test has a depolarizing function to avoid the accumulation of ions H+ on the measuring electrode, thereby allowing for a fresh inflow of electrons:  2HClO + 2H⁺ + 2e Cl₂ + 2H₂O

Functional Capabilities

Both CL 91 and CL 91 Plus may function also on waste waters, provided these are clarified and free from oily and greasy residues.
Actually, such impurities do not alter the measurement but, in spite of the self-cleaning system, they may clog the electrode (as do suspended materials) or cause it to become insensitive (as do oils and greases), and when this happens, a cleaning operation is in order. Although provisions have been taken to make this operation as simple as possible, when recurring impurities demand too frequent cleaning services, it is prefereable using the CL 91 or any other residual chlorine analyzer especially those of membrane and colorimetric types - as an instrument for monitoring use only and not for regulating functions.

CL 91 Plus perfomance

In addition to chlorine, the CL 91 Plus version allows measurements to be made of pH, redox and temperature. Through the use of GR 91 Controller in its version 3 (GR 913) these three parameters can be controlled and the pH and chlorine adjusted as well. This solution is mostly used in swimming pools where the control of all the three parameters - residual chlorine - pH - redox is required.

Control Box

As shown in the picture on the right, the measuring cells and other controlling and monitoring instruments of the line Sodi Scientifica may be housed within a sturdy box of anti-shock plastic material, provided with a front transparent door. The devices are fully factory-assembled and wired.

Download brochure:

CL91_03_B.pdf

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