PLCs were invented in the 60/70's for the automotive manufacturing industry. Since this time, they have developed into one of the most versatile tools used for industrial automation. A working knowledge of PLCs and other microprocessor based control systems are critical to technical personnel who are staying current with technology in industry.

Programmable Logic Controllers or PLC are the hub of many manufacturing processes. These microprocessor based units are used in processes as simple as boxing machines or bagging equipment to controlling and tracking sophisticated manufacturing processes. They are in virtually all new manufacturing, processing and packing equipment in one form or another. Because of their popularity in industry, it becomes increasingly more important to learn skills related to these devices. Click on the buttons to learn more about industrial automation and this invaluable tool.

The microprocessor or processor module is the brain of a PLC system. It consists of the microprocessor, memory
integrated circuits, and circuits necessary to store and retrieve information from memory. It also includes communications ports to other peripherals, other PLC's or programming terminals. Today's processors vary widely in their capabilities to control real world devices. Some control as few as 6 inputs and outputs (I/O) and others 40,000 or more. One processor can control more than one process or manufacturing line. Processors are often linked together in order to provided continuity throughout the process. The number of inputs and outputs PLCs can control are limited by the overall capacity of the PLC system
hardware and memory capabilities. The job of the processor is to monitor status or state of input devices, scan and solve the logic of a user program, and control on or off state of output devices.

RAM or Random Access Memory is a volatile memory that would lose it's information if power were removed..
This is why some processor units incorporate a battery back up. The type of RAM normally used is CMOS or
Complementary Metal Oxide Semiconductor. CMOS RAM is used for storage of the user's program (ladder logic diagrams) and storage memory.

ROM or Read Only Memory is a non-volatile type of memory. This means you don't need an external power source to keep information. In this type of memory, information can be read, but not changed. For this reason the manufacture sometimes calls this firmware. It is placed there for the internal use and operation of processor units.