What is a PLC?

Published on 22 May 2022 Reading time : 2 Minutes

PLC stands for Programmable Logic Controller . These are electronic devices in the form of a digital computer. They are designed for controlling production processes and come in various shapes and sizes. For example, you have large ones that have 10,000 entrances and exits and require heavy racks to mount them. There are also small PLCs that fit in your pocket with only a few inputs and outputs.

A PLC contains a microprocessor that receives information via its inputs and then controls it via a number of outputs. Furthermore, a PLC is resistant to electrical noises and vibrations, which is necessary because they are often used where the system has to function under the constant influence of vibrations and noise. The PLC systems are often also protected against heat, cold, dust and moisture.

What is a PLC used for?

PLCs are used, among other things, to automate machines or production lines of factories. Because a PLC is programmed, the control of a machine is established, so it indicates what a machine has to do. It simply forms the brain of the machine. PLC systems are developed in such a way that they can withstand harmful external influences as mentioned above.

As mentioned before, a PLC consists of inputs and outputs and a CPU. It works in a continuous cycle as shown below. A PLC has two types of inputs:
Data entry from devices and machines:
– High/low, such as: pressure sensors and temperatures
– On/Off, such as: mechanical switches and buttons
Open/close, such as: pumps and values
Human-generated data inputs, such as: push buttons, switches, sensors from devices such as keyboards, touchscreens, remote controls, and card readers

A PLC is not programmed or adapted by everyone, this is work for specialists because small errors can disrupt a PLC system. PLCs are often tuned, adjusted or programmed by maintenance engineers. Software engineers devise PLCs or develop adjustments to PLCs.

Most companies use the PLC’s systems after they have been developed and installed on the machines. With a PLC system it is possible to localize faults if, for example, something no longer functions. This is considered for software, electrical and mechanical solutions.

PLCs and HMIs

PLCs often interact with HMI and SCADA applications, these applications make the collected data transparent on displays. The application checks the data and chooses whether adjustments need to be made to the PLC. If necessary, the application forwards this to the PLC, after which it implements the changes.

New products are constantly entering the market due to technical innovations such as industrial software or Programmable Automation Controllers or PACs. But the PLCs remain very popular despite the innovations because of their simplicity, usability and affordability. There are several PLC brands on the market and almost each brand requires separate training. At PartTracker we specialize in Siemens and Omron.

Difference between Siemens and Omron PLCs


* User-friendly
* Simple programming


* More features
* More complex programs
* More popular
* Better online materials (user manuals, samples and support website)

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