What Are the Different Types of Programmable Logic Controller?

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  • Written By: Jordan Weagly
  • Edited By: Angela B.
  • Last Modified Date: 14 August 2019
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Many types of programmable logic controller are often used in manufacturing, industry, and even amusement park rides. The different types can include ladder logic, traditional programming, state logic, human-machine interface, and remote terminal units. Most of these controllers are defined by the physical configuration of hardware, as well as the types of software or programming languages used. Programmable logic controller hardware is often built to withstand intense weather or physical wear, and software is often made to be somewhat elastic to accommodate many different situations. As a result, the various controllers are often designed for manufacturing and automation systems.

Ladder logic is considered to be one of the most common programmable logic controller types. In these systems, relay logic hardware is often automated and maintained using programmable logic. This makes this type useful in industrial systems, because many functions can be maintained with minimal human interaction. Additionally, ladder logic might be combined with multiple forms of programmable controllers to create advanced systems.

Traditional programming logic controllers often use common computer languages, such as BASIC, to input commands and maintain a system. This type often includes some level of human interaction. Logic controllers using traditional programming also might be used to control relay-based systems or factory manufacturing processes that must be flexible.


State logic is often considered to be one of the flexible types of programmable logic controller. By building a computerized model of a real-world task, programmable state logic controllers are often used to assist with tasks that might change quickly. State logic allows for simulation of decision-making, because the state of a program will often change based on input and output data. Many types of programmable logic systems can be modeled using state logic.

Human-machine interfaces often combine the different controllers to allow for automation and routine human interaction. These systems may rely on input commands or provide data to users when requested. This type is often more advanced than fully automated systems, because various programming languages are often needed to facilitate consistent interaction.

Remote terminal units are generally designed to provide a static function. They are often used remotely and can provide a consistent stream of data despite harsh environmental or data-processing conditions. These systems are often designed to function without much human interaction, which can make them ideal for monitoring when compared to other control systems.


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With the advances that have been happening in logic controllers and Artificial Intelligence software over the last several years, we may be getting close to seeing true thinking machines. An interesting site to visit is MIT’s Humanoid Robotics Group. The research there is fascinating going back to before the year 2000.

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