The Model 499ACL-01 sensor is intended for the continuous determination of free chlorine (hypochlorous acid plus hypochlorite ion) in water. The primary application is measuring chlorine levels in drinking water. The sensor can also be used to monitor dechlorination processes. The sensor requires no acid pretreatment and can measure free chlorine in samples having pH as high as 9.5. In some cases, samples having pH as great as 10.0 can be measured. For high pH applications, consult the factory. The linear range of the sensor is 0 to 10 ppm. For determination of higher levels of chlorine, consult the factory.
The 499ACL-01 is a membrane-covered amperometric sensor. The sensor consists of a porous membrane stretched tightly over a platinum cathode. A silver anode and an electrolyte solution complete the internal circuit. During operation, free chlorine (hypochlorous acid plus hypochlorite ion) diffuses from the sample through the membrane. A polarizing voltage applied to the cathode completely reduces free chlorine to chloride ion. The reduction produces a current, which the analyzer measures. The current is directly proportional to the rate at which free chlorine diffuses through the membrane, which is ultimately proportional to the concentration of free chlorine in the sample.
The sensor requires no sample pretreatment. Amperometric free chlorine sensors measure hypochlorous acid, not hypochlorite ion. Because the fraction of free chlorine present as hypochlorous acid decreases as pH increases, sensor current drops with increasing pH. To maintain sensitivity, competing sensors require pretreatment of the sample with acid to convert hypochlorite to hypochlorous acid. The 499ACL-01 sensor needs no sample pretreatment. It can readily measure free chlorine in samples having pH as high as 9.5. For samples having pH between 9.5 and 10.0, consult the factory. The analyzer automatically applies a pH correction factor to the raw sensor signal.