AWWA CSC91077

Automatic control of filter backwashing has a number of advantages, such as consistency of operation, time savings, and record keeping. This paper briefly describes a system designed to control 40 filters for the North Texas Municipal Water District. A programmable logic controller was used to control the modulating hydraulic actuated effluent valves. The system consists of eight PLCs, each controlling five filters. A ninth PLC provides monitoring and alarm outputs. The PLCs were linked in two ways so that the failure of the linkage or any single PLC would not prevent the normal operation of the remainder of the system. A brief description of the plant's control system is appended.