The 499ACL is a family of membrane covered amperometric sensors used for measuring free chlorine, total chlorine, and monochloramine. The Free Chlorine Sensor, 499ACL-01, does not require sample pre-treatment or expensive reagents to maintain. The Total Chlorine Sensor, 499ACL-02, eliminates the need for pH correction with a standard reagent sampling system. The Monochloramine sensor, 499ACL-03 does not use reagents or sample pre-treatment for measurement. All three sensors have an easily replaceable membrane that does not require special tools.