Applications; Components; How It Works - ECD FCA-22 Instruction Manual

General Description
Application
The FCA‐22 is designed for use in drinking water, industrial cooling and rinse water or other samples of
fresh water that use chlorine in the range of 0‐20 ppm as a disinfectant. Chlorine exists in water as a pH
dependent mixture of hypochlorous acid and hypochlorite ion. The sum of these two components is
referred to as Free Chlorine, sometimes Residual Free Chlorine.
Organic chlorine compounds and chloramines, Bound Chlorine, are not detected by the FCA‐22. Other
measurement techniques are required for samples containing these bound chlorine chemicals. Bound
Chlorine plus Free Chlorine equals Total Chlorine. The FCA‐22 does not measure Total Chlorine.
Parts
The FCA‐22 is a complete system for measuring Free Chlorine. The panel mounted system includes a
Constant Head Flow Controller (CHFC), Free Chlorine sensor (FCS) and Flow Cell, pH sensor (PHS10) and
Flow Cell and the C22 Analyzer. Simply supply power to the C22 Analyzer and plumb the sample line in
and the drain line out and the FCA‐22 is ready to use.
How it works
The Free Chlorine Sensor (FCS) is an amperometric sensor with a PTFE membrane, gold cathode and a
silver/silver chloride anode.
The C22 analyzer applies a fixed voltage across the electrodes and measures the current flow.
Hypochlorous acid (HOCl) diffuses through the PTFE membrane and is reduced (gains electrons) by the
gold cathode to chloride ion. Silver on the anode is oxidized (donates electrons) to silver chloride
completing the current loop. With stable temperature and sample flow, the current flow is proportional
to the free chlorine concentration.
Many competitive chlorine sensors require service on a monthly or bimonthly basis. The FCS uses a large
surface area anode, combined with a large volume of electrolyte and a small cathode to provide
operational cycles of up to a year without refilling. The replaceable PTFE membrane is also designed for
long term stability. A special support grid maintains a constant tension between membrane and the
cathode minimizing effects caused by varying pressures and flow. Replacing the PTFE membrane and
recharging the electrolyte is easily accomplished without the use of tools.
The CHFC maintains a constant sample flow to the pH and Chlorine flow cells. Pressure regulators and
rotameters are not needed to maintain a constant flow rate, the CHFC provides trouble free sample
conditioning between 10 and 80 gal/hr.
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FCA‐22 Instruction Manual