13-12-2012, 06:27 PM
Programmable Logic Controller (PLC) and Sensors
Programmable Logic Controller.ppt (Size: 1.91 MB / Downloads: 153)
Introduction
A programmable logic controller (PLC) or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, or light fixtures.
Where ever there is a need to control devices the PLC provides a flexible way to "softwire" the components together.
A PROGRAMMABLE LOGIC CONTROLLER is a control system that continuously monitors the status of devices connected as inputs. Based upon a user written program, stored in memory, it controls the status of devices connected as outputs.
NEMA DEFINATION
According to National Electrical Manufacturers Association(NEMA) in 1978 :
“A digitally operating electronic apparatus which uses a programmable memory for the internal storage of instructions for implementing specific functions, such as logic, sequence, timing, counting, and arithmetic, to control through digital or analog i/o, various types of machines or process.”
Disadvantages of a classic control panel
Large amount of work required connecting wires
Difficulty with changes or replacements
Difficulty in finding errors; requiring skillful/experienced work force
When a problem occurs, hold-up time is indefinite, usually long