A generic design of ladder algorithm for automation of backwash water treatment plant

This paper is about development of PLC software for control and automation of a water treatment system which is called "Backwash Water Treatment Process". The algorithm developed in this paper may be used to develop PLC based software for any control process. Developed Software is based on the filter backwash sequence which determines the time to backwash and the time to stop backwashing the filter and the quantity of Aluminum sulfate Al-2 (SO4)(3) to be added. The decision is based on data acquired from limit switches, level switches/sensors, counters and timers. The logic sequence is designed to minimize production down time when a unit was off line due to backwashing and ensured that the primary sludge tank had sufficient capacity to accept the dirty backwash water. The algorithm is developed by considering filter backwash sequence, the I/O table developed for all input and output devices obtained by assigning the corresponding INPUT and OUTPUT number to these devices considering the particular programmable controller, developed timing diagram showing the length of occurrence of process (I/O) signals, flow chart developed for the control process and using CX-Programmer software supporting predominant ladder programming language for CQM1 PLC used as Master PLC and CPM2A-60 CDR PLCs used as slave PLCs for control of a water treatment system "backwash water treatment process. CQM1 is meant for advanced control system operations requiring 16 to 192 I/O points per PLC. CX-Simulator software was used for simulating software developed by CX-Programmer.