programmable logic controller

A Crash Course on Programmable Logic Controllers + Reviews of 4 Types Available!

Programmable logic controllers are used everywhere – from elevators, fans, and car washes to amusement rides, traffic signals, and industrial machines! But what is a PLC, and is it easy to use?

In this guide, we break down the components and features of a PLC, differentiate it from a common PC, teach you how to choose one, and review four programmable logic controllers available!

What Is a Programmable Logic Controller?

A programmable logic controller is a compact but tough industrial computer that helps automate repetitive industrial tasks to increase efficiency. It’s reliable and designed to handle the rugged conditions of a particular industry. We’ve listed below the specs of a PLC:

Components

  • The CPU or the brain of the PLC: processes input by following the programmed instructions and controls the output.
  • Input/Output Ports: input slots connect to the control panel while the output ports connect to motors, heaters, etc.
  • Power Supply: an external or internal power source that runs the I/O ports.
  • Programming Unit: a PC, tablet, or laptop where all instructions are provided and encoded.

Memory

In a PLC, two types of memory programs are stored:

  • RAM: data can be written and altered (eg: collected information from the output devices).
  • ROM: data cannot be written or altered (eg: information or code from the CPU’s control program).

Types

There are two types of PLCs available:

  • Compact/Fixed PLC: small in size, has I/O ports fixed by the manufacturer with no room for expansion, cost-effective, and best recommended for small applications and domestic purposes.
  • Modular PLC: large in size, has multiple modules that function independently of each other, along with different I/O ports that can be increased in number and it is most commonly used in industrial applications.

According to output, a PLC can be divided into:

  • Triac Output PLC
  • Relay Output
  • Transistor Output

A PLC is also divided up into three types according to size:

  • Nano PLC
  • Micro PLC
  • Mini PLC

Programming Languages

A PLC is controlled by a program that is encoded using a set of instructions. These instructions may be of two types:

1. Textual Language

  • Structured text (high-level language)
  • Instruction list (low-level language)

2. Graphical Language

  • Ladder Logic (simplest and most commonly used)
  • Sequential Function Chart (makes troubleshooting easy)
  • Function Block Diagram (programs multiple functions using many I/O ports)

In programmable logic controllers, graphical language is more commonly preferred over textual language as I/O ports can be varied (FBD), and the functions are greater and more sophisticated (Ladder Logic).

In addition, it’s actually easier and better to learn graphical programming languages than the textual ones as PLC projects usually require the knowledge of at least one to encode a program.

PLC programming languages are easy for beginners to learn and training can take anywhere between 40 hours to a complete week.

Advantages of Using Programmable Logic Controllers

A programmable logic controller can be used in many different industries and it benefits all of them. But how? Here are a few advantages of using programmable logic controllers:

  • A PLC works like a mini computer. It has completely revolutionized the industry of IoT. In a size four times smaller than a normal PC, a PLC manages to handle and automate industrial machinery, perform relay switching tasks, and process analog signals.
  • PLCs have omitted the need for hardwiring relay control circuits as it performs tasks without the need to modify, alter, or change the data.
  • A PLC has optimized the use of logic in control systems. Previously, large and expensive relay-based units were utilized which have now been compacted into a small PLC.
  • The usage of a PLC is reliable. It can transfer programs to download on multiple PLCs. The memory unit of a PLC monitors the logical program being sent and stored which eliminates the risk of logic wiring errors.
  • PLCs are flexible, i.e programs can be installed, created, modified, and even transferred easily. Also, the functionality of a PLC can be enhanced to perform better by adding extra modules.
  • PLCs are budget-friendly. In fact, they have completely taken over the relay control industry and now power the logic controls of many relay-based applications because they save costs.
  • A PLC is compatible with a variety of communication protocols. With the help of networking, it’s able to handle supervisory control, monitor devices, gather data, and process certain parameters.
  • PLCs are primarily designed for efficiency meaning they process input and control output not only at a steady rate but also at a higher speed. They function in real-time and this has primarily benefited the proceedings of bulk production industries.
  • PLCs rarely malfunction but when they do, it’s actually displayed by fault indicators which can then be easily troubleshot.
  • PLCs are engineered to work in the rugged industrial environment so they have better resistance to heat, durability against vibrations, and exceptional hold against dust. This increases their lifespan and saves industries billions of dollars in maintenance.
  • PLCs are user-friendly, i.e adolescents and adults alike can learn how to use it, program the mini-computer, maintain it, and create projects using it. The unit comes with a built-in program language plus some input and output ports.
  • PLCs are energy-efficient. Compared to relay-based control units, a PLC consumes only 1/10th of the power.

Industrial Applications of Programmable Logic Controller

Programmable logic controllers have a variety of uses and can be found in many different industries automating electromechanical processes so everything runs efficiently.

Wherever technology advances, the scope of PLCs grows. It can generally be found in:

Steel Industry

PLCs are used to control machinery on assembly lines

Automotive Industry

PLCs are used to assemble the automobile automatic transmissions

Energy Industry

Using a PLC minimises human operators and decreases chances of human error

Chemical Industry

PLCs are primarily used in city bridges and water stations

Travel Industry

PLCs are used to operate elevators and escalators

Also monitors security alert systems

Laundromats

A PLC is used to control large, industrial batches of washing machines

Also monitors closed loop textile shrinkage systems

Glass Industry

PLCs are used to control the ratio of material used

Also processes the manufacture of flat glasses

Cement Industry

PLC is used to control the ball milling and ensure the right quantity and quality of raw material is used in coal kilns and shaft kilns

Paper Industry

PLCs control the speed and direction of bulk printing machines

Production of newspapers and book pages is monitored by PLCs in offset web printing

Aerospace Industry

PLCs oversee the water tank quenching systems

Food Industry

A PLC is used to process the filling machine control system

Plastic Industry

PLCs are utilized in silo feeding systems

They direct the corrugation machine control system

Monitors injection moulding control systems

Medical Industry

PLCs are used to gather and transmit operating data in hospitals

All You Need to Consider When Buying a Programmable Logic Controller

When narrowing down your choices of a programmable logic controller, there are a few factors you should consider as the highest priority so the PLC you purchase is perfectly designed to suit your set up.

System Use Case

Every system is set up differently to perform a variety of functions. These functions essentially determine the type of PLC that will work best for your system. 

Speaking of setting up a system, if you’re building one up from scratch, make sure to match the PLC’s purpose to the task your system is going to carry out. 

If your system is already installed, match the PLC with the I/O ports and the task at hand.

Temperature Reliability

Programmable logic controllers are designed to work in harsh industrial conditions but they have a temperature limit in which they may fail to function. A PLC operates best within a range of 0°C to 55°C. Dust and excessive vibrations can also be harmful.

Number of I/O Ports

Besides the CPU, a PLC’s operation depends upon the input and output sources. The higher the number of I/O ports, the better it is for the functioning of the PLC. But the size of the PLC will increase too. Make sure it fits in the area in which you’re setting up the system.

Processing Speed

If you’re going down the multiple I/O ports route, make sure to match the speed of the CPU and the capacity of memory so the system runs smoothly. Also, if you’d like your system to run fast, process data, and update the output quickly then look for the scan time of the CPU.

Multiple Network Compatibility

If you’re looking to connect your PLC to a WiFi network or Bluetooth, make sure it’s compatible. Some PLCs come with slots to connect communication systems and a few need additional module support to communicate with the system.

Programming

A PLC runs on many different programming languages and if you’re a beginner at coding, look for PLCs that run on Ladder Logic. It’s the simplest form of program and takes less than a week to grasp the basics. The better the programming, the easier it’ll be to use, maintain, and repair the PLC.

The 4 Best Programmable Logic Controllers Reviewed

1. Walfront 24V PLC Control Programmable Logic Controller

The Walfront PLC is leading the industry with its highly flexible communication and relay system. It functions well for online download, monitoring, as well as program uploads. Its processing speed is unmatched by any of its competitors. 

The built-in 32-bit MCU stabilizes the performance of the PLC and optimizes the efficiency of systems.

Features:

  • Industrial-grade 32-bit MCU
  • Strong anti-interference
  • Fast speed
  • High-quality chip
  • Ladder Logic programming language
  • Supports HMI communication
  • Transmission baud rate is 9600
  • 8000 steps memory capacity
  • DC24V power supply voltage
  • Original password protection

Pros

  • Works great with GX-developer and a simple RS-232 USB cable

Cons

  • No program reading function

2. Walfront Programmable Logic Controller FX1N-14MR

Walfront is actually leading not just one industry, but multiple industries (textile, food, chemicals, printing, carpentry and more) with its out-performing PLC 14MR. 

It features a built-in 32-bit MCU that communicates well with other programs, downloads programs that can be super-encrypted, and supports GX-Developer with Ladder Logic diagrams.

No wonder it’s able to optimize the functioning of bulk production machines – it’s absolutely powerful!

Features:

  • Industrial-grade 32-bit MCU
  • Supports GX-Developer and GX Works2
  • Ladder diagram supported
  • Strong anti-interference
  • Super encryption
  • 8000 steps memory capacity
  • DC24V power supply voltage

Pros

  • Processes input data and executes output in seconds

Cons

  • The RS232 connection port is narrow

3. Garosa FX3U-32MT Programmable Logic Controller

The Garosa programmable logic controller is powered by speed and directed by control. Its I/O port count is incredible and it works with a wide range of industrial applications.

It’s portable, lightweight, and easy to operate. The high-quality materials used in its construction ensure that it’s going to last long and withstand extreme temperatures well. 

Features:

  • High speed
  • 16 input
  • 16 output
  • 24V power supply voltage
  • 1A power output current
  • Supports connecting touch and text screen
  • Transistor output
  • 6AD analog input
  • 2DA analog output

Pros

  • Great processing – downloads and installs programs fast and uninterrupted

Cons

  • Does not come with an instruction manual

4. Walfront FX1N-06MR Programmable Logic Controller

The Walfront Programmable Logic Controller 06MR is one of the best units available for vast industrial applications and even some small applications. It supports the monitoring and download of programs as well as reading of them.

Its power supply allows uninterrupted and quick processing. The PLC 06MR comes with a built-in timing circuit that ensures its long lifespan. Not to mention, the Walfront PLC is cost-effective too!

Features:

  • 10-28VDC power supply
  • Anti-interference processing
  • Built-in timing circuit
  • Instruction manual added
  • Small, lightweight construction
  • High-quality materials used

Pros

  • Has a long lifespan, does not require constant maintenance or troubleshooting

Cons

  • Hard to clean

Frequently Asked Questions:

Why is PLC used instead of PC?

A programmable logic controller or a PLC works like a mini computer but it is designed to be more reliable and easy to use in industrial applications. A PC usually cannot handle the rugged programming industrial machinery requires. Also, PLCs are easy to control, troubleshoot, and usually last longer.

Why is PLC used in automation?

A PLC essentially works like a mini computer. It’s programmed to learn a set of instructions and then make decisions on the input and output interface according to the program stored in its memory. This automates decision-making in repetitive processes that would otherwise be handled by a human at a slower pace. 

Which programming language is used in PLC?

Out of all five PLC programming languages (ladder logic, sequential function chart, structured text, instruction list, and function block diagram) ladder logic is most commonly used. It generally depends on the application, but since programmable logic controllers are mostly used in critical control systems of vast industrial machinery, ladder logic is the best programming language to use. 

Is PLC programming easy to learn?

Yes, learning the basics of PLC programming takes only about a week or two, or less if you already possess some knowledge or even experience of programming. It doesn’t matter what language is used, you can learn the skills of PLC programming in at most 40 hours – with training, of course.

Which PLC is best for beginners?

For beginners, a nano-sized PLC is most recommended as it’s easy to handle, has at least 4 high current relay outputs, and 10 to 12 digital outputs. It’s also easy to maintain, repair, and program for domestic or home automation projects. Not to mention, the power loss is minimal.

Which type of PLC is most suitable for domestic purposes?

A compact PLC is best recommended for small applications and domestic purposes as it’s easy to use, small in size, stores a fixed amount of data, and in case it starts to malfunction, can be repaired. Also, a compact PLC is inexpensive as compared to a modular PLC.

Brief Summary

Now that you’ve completed the crash course (we won’t test you, don’t worry) and have become well-versed in the world of programmable logic controllers, you can easily choose one that’s not only effective but efficient in performing its duties – saves money too!