What is a PLC ( Programmable Logic Controller ) ?

A PLC is a type of simplified, ruggedized industrial computer. They are extremely reliable and easy to use. Which has been a key factor to their popularity. It was first invented by a group of engineers from the Hydramatic division of General Motors in 1968.

They can be used for basic digital on/off logic. But they can also run extremely critical processes involving complex algorithms. In some cases there will be dedicated PLCs just for safety. Pretty much anything you purchase at some point in its creation had a PLC involved. And as you read more here, you will see how they contribute to the product your purchasing.

PLCs can use different programming languages and forms of communication.

Common PLC programming languages:

• Ladder Diagram ( LD or Ladder Logic )
• Sequential Function Charts ( SFC )
• Function Block Diagram ( FBD )
• Structured Text ( ST )
• Instruction List ( IL )

Common PLC communication protocols:

• Ethernet IP
• Modbus
• Profibus
• ProfiNet
• DeviceNet
• RS – 232
• HART
• DH
• And many more! Just look it up. Most sites list about 33 of them. But I’ll save that for another lesson.

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