What is a PLC?

What is a PLC and how does it work? You will get the answer in this basic article. A PLC (Programmable Logic Controller) is a specialized computer used for controlling and automating of industrial processes. It acts as the brain of automation systems and can be programmed to perform a variety of tasks, from simple control functions to complex automation scenarios.

PLCs vary from small simple PLCs with, for example, eight inputs and four outputs. They can be obtained from a few thousand DKK, to larger PLCs, which are built in modules that can be expanded indefinitely and control complex process plants. They can easily cost DKK 50-60,000.

A PLC can also be built into a frequency converter as, for example, the brand Peter Electronic does. If you need to be able to log data and see trend curves on large process plants, you typically use a SCADA plant.

The structure of a PLC

PLCs typically consist of a processor, input and output modules, and its memory. Input modules register signals from sensors, while output modules control actuators or other devices. The processor processes the programming logic and controls the inputs and outputs accordingly. PLCs are programmed using different programming languages where "ladder" is the easiest one to learn.

An example of a simple program to start/stop a conveyor belt could be:

  • When you press start on input 1, the output must switch on so that the conveyor belt runs. 
  • While the belt is running, output 2 must flash, so that a lamp warns that the belt is running.
What is a plc

Where is a PLC used?

PLCs are used in a wide range of industries such as manufacturing facilities, energy supply, transportation and more. Their versatility makes them ideal for automating processes. The advantages of PLC technology are fast and reliable control, easy modification of the program without hardware changes, and the ability to monitor and diagnose the state of the system in real time. As mentioned above, PLCs can be obtained from small compact units to modular units which can be expanded "infinitely".

For large process plants, where there is a need to be able to see historical data and display trend curves, SCADA plants are often more flexible, but also much more extensive to program.

Choosing the right PLC

Did you get an answer to what a PLC is? You can read more about the history of the PLC on Wikipedia.

Should you buy a PLC for your company? At PRO-CONSULT, we guide you to purchase the right one PLC. PRO-CONSULT has 35 years of experience with industrial electronics, and are experts in, among other things, PLCs.