Article Content
• Introduction
• Background
• PLC definition
• PLC manufacturers
• PLC Programming software
• How it works
• Advantages & Disadvantages of PLC
• Application of PLC
• Ladder logic
• Conclusions and Recommendations
Introduction
The Programmable Logic Controller (PLC) has revolutionized the automation industry. Today PLCs can be found in everything from factory equipment to Automobiles, but prior to 1968 the programmable controller didn’t even exist. Instead what existed was a unique set of challenges that needed a solution.
Background
• Before the days of the PLC the only way to control machinery was through the use of relays.
• For example, to control an electric motor, a relay could be attached between the power source and the motor. A control could be enforced when the motor is getting power by either energizing or de-energizing the relay.
• There could be several motors in one factory that need to be controlled, so what do you do? You add lots of relays.
• So factories started to amass electrical cabinets full of power relays
• To effect any changes, electricians would have go through the herculean task of rewiring each relays ”Five hours to find it and five minutes to fix it”
• In 1968 the Hydramatic Division of the General Motors Corporation specified the design criteria for the first programmable controller.
GM Hydra-Matic Mandate
The GM Hydra-Matic Mandate for PLC are as follows:
• Less wiring/User friendly
• Cost effective
• Extensive I/O capability
• Robust and able to withstand extreme operating conditions
• Extraordinary processing time
PLC Pioneers
• Dick Morley’s company Bedford Associates in Massachusetts proposed something called a Modular Digital Controller (MODICON).
• The MODICON 084 brought the world’s first PLC into commercial production.
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