In general a Control System is a collection of electronic devices and equipment which are in place to ensure the stability, accuracy and smooth transition of process or a manufacturing activity. It takes any form and varies from power plant to a semi-conductor machine. As a result of rapid advancement of technology, complicated control tasks accomplished with a highly automated control system, which may be in the form of Programmable Logic Controller (PLC) & possibily a host computer, etc. Besides signal interfacing to the field devices ( such as operator panel, motors, sensors, switches, solenoid valve and etc.), capabilities in network communication enable a big scale implementation and process co-ordination besides providing greater flexibility in realizing distributed control system. Every single component in a control system plays an importnat role regardless of size. For instance, as shown in Fig 1.1. the PLC would not know the happenings around it without any sensing devices. And if necessary, an area host computer has to be in place to co-ordinate the activities in a specific area at the shopfloor.
Fig 1.1
It could also be an application as small as a single PLC controlling a single or some output devices.
1. INTRODUCTION
Fig 1.2
Typical Programmable Logic Controllers-base Control System
Fig 1.2, is a typical application of a Gantry Robot Control Machine. It is used in a pick and place operation. The whole process sequence is controlled by a plc. The various input devices such as selecttor switches, push buttons, togle switches, snesors are connected to the input of the PLC via the input terminal block. The output devices such as the revolving light, indicators, relays, contactor and solenoid valves are connected too the output terminals of the PLC. The whole process is controlled by a ladder program loaded into the PLC CPU memory. The program will operation are also provided to allow operator to activate the machine manually by the switches, emergency push buttons for the purpose of safety in case you need to stop the operation abruptly. In this application. the control system operates as a stand-alone operation
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