What You Need to Know About Programmable Logic Controllers

What You Need to Know About Programmable Logic Controllers

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The manufacturing industry is poised to grow by 20% in the next five years. It means that the need for industrial automation will continue to grow along with this trend. At the forefront of the manufacturing industries is the Programmable Logic Controllers (PLC), which helps govern most of their functions.

This vital component monitors the processes and functions of various forms of industrial machinery and streamlines the operations of different types of machinery to make the manufacturing process more efficient.

For most of us who have a vague idea of the inner workings of the manufacturing industry, we will share here some of the things you need to know about the Programmable Logic Controller or PLC for short.


Programmable Logic Controllers Were Invented at the End of the First Millennium

The first PLC was invented in the late 1960s by Richard Morley to perform the same functions as relay logic systems and to address the problem of clutters of wires, terminal blocks, and relays. Another problem of relay systems at the time is the recurring failure of the system and the subsequent manufacturing delay it causes. Technicians also had a hard time troubleshooting numerous relays to fix the problem. 

In 1968, General Motors presented a design for the development of a “standard machine controller” that includes full logic capabilities, durable, expandable, and can reduce machine downtime.

By 1971, engineers at Allen-Bradley completed the first reproducible design of a machine controller called the “Programmable Logic Controller”. The Allen-Bradley PLC became a popular automation device in the automobile sector, and later other industry sectors began adopting PLCs into their processes.

Today, Allen-Bradley remains among the top PLC manufacturers together with other notable manufacturers such as Siemens, Mitsubishi Electric, ABB, Schneider Electric, Hitachi Industrial Equipment Systems, and other big names in PLC brands.

The competitive PLC market has allowed various industries to select and buy PLCs online or offline, depending on their processes and machinery specifications. With various industries and sectors aiming to boost their production by automating most of their processes, the demand for PLCs and the PLC market will continue to grow in the next few years.

The PLC manufacturing industry is relatively young but is making great strides in enhancing its capabilities to meet the complex demands of other manufacturing industries. PLCs are expected to take on more industrial workloads and streamline more industrial processes soon.

Modern PLC Applications Systems are Versatile

We have mentioned earlier that the PLC manufacturing industry is relatively new, but the applications of PLC systems are already extensive in such a short time. PLC systems are found nearly everywhere – from car washes, elevators, and traffic lights to the manufacturing, food, and beverage industries. As long as there are machines that perform repetitive functions and processes, there are PLC application systems behind their efficient operations.

Simply defined, a Programmable Logic Controller or PLC is a computing device that is designed for use in various industrial operations. It is no wonder why it is often described as the workhorse of industrial automation because of its increasing number of applications in different industries.

Basic Operation of PLC Systems

As discussed earlier, many industries have relays or devices that turn machines on and off. Relays are more complex and time-consuming to operate than PLCs and require a long operational downtime when reconfigured. Panel relay switches take up a lot of space, have high power consumption, and generate heat and soot that reduce machine efficiency.

Introducing a PLC system into industrial machines reduces downtime by at least 16% and reduces power consumption and space concerns. Regarding durability concerns, PLC systems are designed to be robust and capable of withstanding harsh conditions such as severe heat and cold, excessive moisture, and extreme dust accumulation. 

PLCs generally follow the following basic operational steps listed below.

  1. Input Scan – PLC takes a snapshot of all input devices connected to it and solves their operation logic. It determines if the input card is ON or OFF and stores the information in a data table in its memory. 
  2. Logic Execution (Execute Program) – PLC then scans and executes a user-created application program one instruction at a time using its stored memory copy of the inputs in the ladder logic program. Using the stored information from the input scan, the PLC then decides if an input or output should be turned ON/OFF.
  3. Output Scan – the outputs are updated using temporary values from memory during the ladder scan completion. The PLC scans and updates the inputs in the first step and the results of the execution step to energize/de-energize the outputs. PLC begins the cycle again by performing a self-check for faults.

The logic scan, which is performed by PLCs in the background, uses ladder logic programs modeled after relay logic. Each element in the relay logic will switch as fast as possible but will be examined by PLC one at a time in a fixed sequence, usually following a top-to-bottom pattern.

PLC Programming Language

A PLC program is written or created by a user and stored in the PLC system’s memory to produce specific and accurate output control signals. PLC programming has its language and is governed by grammar, syntax, and vocabulary for the proper interpretation and execution of the central processing unit (CPU).

There are five programming languages used in PLCs, and PLC manufacturers use different programming languages and introduce variations to these languages.

  1. Ladder logic – it is the most commonly used PLC language. It uses symbols that indicate counters, timers, opening, and closing relays, shift relays, and mathematical operations. Users can arrange the symbols into a specified program routine, depending on the type of machine operation.
  2. Function block diagram (FBD) – this programming language depicts functions as blocks that connect input and output variables. Interconnected control systems use FBD to describe their algorithms and logic.
  3. Structured text (ST) – it is a high-level programming language characterized by sentence commands. Programmers using ST can use conditions and inputs like “SQRT”, “repeat/until”, or “if/else/then” to create PLC programs.
  4. Instruction list (IL) – it is a low-level, non-graphical programming language. It resembles assembly language programming, having functions and variables defined by a simple list. Its PLC operation includes jumping to a program label and calling or returning from separate functions. 
  5. Sequential function chart (SFC) – it is a graphical programming language used for complex control systems. It can divide large and complicated programming tasks into smaller and more manageable subtasks. It is done by representing a task as a sequence of functions or states.
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We are entering a new industrial phase where more operations are automated. We hope that the bits of information we shared here can shed light and improve our understanding of the industries around us, especially the manufacturing sector.

Knowing more about the inner workings of the machines that create products and devices for us can help us appreciate their importance in our lives.

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