Control engineering has evolved notably over time, from the period the systems depended entirely on humans to an era that now involves electricity to drive the processes. Programmable Logic Controllers (PLC), developed in the 19670s by General Motors (GM), have brought several outstanding features, including reduced maintenance costs, easy programming, reliability, flexibility, among other benefits. Here are the components that make the PLCs perform their functions.
What is PLC?
A PLC is a software- and hardware-powered minicomputer used to aid industrial control operations. According to National Electrical Manufacturers Association (NEMA), PLCs are digitally operating electronic instruments. They use programmable memory to internally store instructions for executing particular functions such as arithmetic, counting, sequencing, and timing to regulate different types of processes or machines. They can either operate in a digital or analog setting.
PLCs are common across various industrial processes, where they help control small system configurations, complex processes, DCS, and SCADA systems.
Components of PLCs
A PLC operates through several interconnected components to receive input from different sensors, decide according to its programming, and respond (through outputs) according to the instructions. Here are the main elements that make up a programmable logic controller.
1. Power Supplies
The power supply offers the essential levels of voltage the PLC requires to function. It typically changes AC voltage from the mains to a low DC depending on the power requirements of the processor, plus other connections in the communication, input, or output modules. The supply may also be required to charge the PLC’s internal battery to avoid memory loss if the system goes off. Most programmable logic controllers have 24VDC or 230VAC.
2. Input/output (I/O) Sections
The input/ output section (I/O) acts as the essential sensing organs of the PLC system. The input receives incoming signals from the external sensors such as pressure or proximity switches (typically at a higher voltage) and changes them to low-voltage digital hints before sending them to the processor.
On the other hand, the output section receives low-voltage digital signals from the processing unit and converts them into high-power hints. These high-voltage signals from the output section drive the industrial functions, including lighting, rotation, heating, movement, and other operations.
3. Processor Sections
The processor, also referred to as the central processing unit (CPU), acts as the brain of a PLC. It examines the input signals and their levels, compares the data to the PLC’s memory, then controls the output devices according to the program’s instructions.
The CPU also contains a memory unit that keeps the instructions required to run the programs, and examines the inputs and outputs continuously, and adjusts them according to the recent programming.
4. Programming Section
The programming section enables inputs into the controller via a keyboard. It provides the processor with accurate, step-by-step directions on interpreting inputs and relaying the instructions to the outputs. As such, the programmer communicates all the information the processor needs, including when to load, begin timing, clear, set, enter, or move.
This process takes place through programming devices that come in varying sizes, functions, and capabilities. PLCs come with several benefits to manufacturing industries. They ease most processes, offer flexibility, reliability, and an excellent opportunity for them to grow.
