APPLLICATIONS OF PLC: Proper application of a PLC begins with an economical justification analysis. The batch process in chemical, cement, food and paper industries are sequential in nature, requiring time or event based decisions. PLCs are being used more and more as total solutions to a batch problem in these industries rather than just a tool. In batch process savings are developed principally from reduced cycle time and scheduling. Cycle automation provides rigid control enforcement to eliminate human errors and to minimize manual interventions. Increased efficiency in scheduling is to be expected with maximum utilization of equipment and reduction of fluctuating demands on critical equipment. In large process plants PLCs are being increasingly used for automatic start up and shutdown of critical equipments. A PLC ensures that an equipment can not be started unless all the permissive conditions for safe start have been established. It also monitors the conditions necessary for safe running of the equipment and trip the equipment whenever any abnormality in the system is detected. The PLC can be programmed to function as an energy management system for boiler control for maximum efficiency and safety. In the burner management system it can be used to control the process of purging, pilot light off, flame safety checks, main burner light off and valve switching for changeover of fuels.
ADVANTAGES OF PROGRAMMABLE CONTROLLER
- Very fast
- Easy to change logic i.e. flexibility
- Reliable due to absence of moving parts
- Low power consumption
- Easy maintenance due to modular assembly
- Facilities in fault finding and diagnostic
- Capable of handling of very complicated logic operations
- Good documentation facilities
- Easy to couple with the process computers
- Analog signal handling and close loop control programming
- Counter, timer and comparator can be programmed
- Ease operator interface due to colourographic and advisory system introduction