What is a Programmable Logic Controller?

A PLC (Programmable Logic Controller) is a type of small industrial computer that receives data via inputs and sends instructions via outputs. The device makes decisions based on the logic functions and controls system functions proggramed in PLC system. Programmable logic controllers are used in all industries to automate critical industrial processes and control the operation of machines.

How does a PLC work?

A PLC takes input data (e.g. sensor signals). Then an appropriately programmed microprocessor, analyses this information in a cyclic manner. The controller verifies these commands in the order in which they were written in the programme and then creates a so-called output image. The outputs of a PLC can control a wide variety of devices, including motors, solenoid valves, lighting, switchgear or safety switches.

PLC construction

PLCs consist of components such as:

• central processing unit (CPU)

• digital inputs

• analogue inputs

• digital outputs

• analogue outputs

• power supply module

• communication module

• memory

What are the 3 types of PLC (programmable logic controllers)?

By size:

• compact controllers – consist of one module

• compact controllers that can be expanded with additional modules, e.g. JUMO variTRON 300

• modular controllers – with several modules, used in automation systems for the control of process and production lines, e.g. JUMO variTRON 500

By outputs:

• relay output

• transistor output

• triac output

Why is PLC used? Application of programmable logic controller

Programmable logic controllers are widely used in various industries to have complex process control. They are used wherever production is predictable enough to be automated. These versatile microprocessor devices are designed to control, among other things, the operation of machines on assembly lines in factories, lighting, food packaging, machine tools or pumping stations in sewage treatment plants.

One of the reasons why programmable logic controllers are so popular is their modularity. This means that you can mix different types of input and output devices best suited to your application.

PLC programming

Programmable logic controllers can be programmed using a standard computer and PLC programming software.

The 5 most popular types of programmable logic controllers Programming Languages are:

• Ladder Diagram (LD)

• Sequential Function Charts (SFC)

• Function Block Diagram (FBD)

• Structured Text (ST)

• Instruction List (IL)

Ladder logic programming

Ladder logic programming is a graphical programming language. In this programming language, all elements are represented using diagrams. It is simpler for the average programist and easier to learn than the average classical controller programming language.

Which programmable logic controllers to choose?

Choosing the wrong PLC for a particular application can result in, among other things, problems in its interaction with other equipment or difficulties in installation in the machine. How to avoid these problems and choose the correct programmable logic controller?

1. Determine how many and which inputs/outputs you will use in your project, including whether they will be analog inputs (voltage or current), temperature or pulse inputs and transistor or relay outputs.

Note: When you have chosen the appropriate number of input and output circuits, add about 15% more to it. This will avoid problems when the installation is expanded in the future.

1. Check how much space you have for the controller

2. Decide which functions you need

3. Ensure that the controller supports the communication protocol to communicate with your other devices

4. Verify the number and type of ports on the controller, and verify the possibility of expansion with additional ports

Any doubts? Contact us – together we will choose the right device for your application.