Browse Definitions :
Definition

programmable logic controller (PLC)

A programmable logic controller (PLC) is a small, modular solid state computer with customized instructions for performing a particular task. PLCs, which are used in industrial control systems (ICS) for a wide variety of industries, have largely replaced mechanical relays, drum sequencers and cam timers.

PLCs are useful tools for repeatable processes because they have no mechanical parts and they can gather information. Each central processor unit (CPU) continually loops through an input scan, program scan, output scan and housekeeping mode, repetitively performing a single task while monitoring conditions. The information the controller gathers can be used as feedback to guide needed changes and improvements to processes, some of which can be performed automatically according to the device’s coding.

PLCs take up less space, perform more complex tasks and are more customizable than the mechanical technologies they have replaced. They are known for their ability to operate continuously without maintenance and have had a great impact on digitizing a great many industries, particularly manufacturing. The first PLC, for example, was invented by Dick Morley in 1969 for General Motors and performed uninterrupted for 20 years before being retired.

Five programming languages are used to code PLCs, as specified by International Electrotechnical Commission (IEC) 61131. They are Ladder Logic, Function Block Diagram (FBD), Structured Text (ST), Instruction List (IL) and Sequential Function Chart (SFC). Should significant code changes be required and the PLC's memory is embedded, the controller can be recoded in place. When the PLC's memory is not embedded on the circuit board and significant code changes are required, the memory can be removed from an exterior slot on the PLC and replaced without requiring the assistance of a programmer on site. 

This was last updated in March 2016

Continue Reading About programmable logic controller (PLC)

Networking
  • firewall as a service (FWaaS)

    Firewall as a service (FWaaS), also known as a cloud firewall, is a service that provides cloud-based network traffic analysis ...

  • private 5G

    Private 5G is a wireless network technology that delivers 5G cellular connectivity for private network use cases.

  • NFVi (network functions virtualization infrastructure)

    NFVi (network functions virtualization infrastructure) encompasses all of the networking hardware and software needed to support ...

Security
  • Advanced Encryption Standard (AES)

    The Advanced Encryption Standard (AES) is a symmetric block cipher chosen by the U.S. government to protect classified ...

  • operational risk

    Operational risk is the risk of losses caused by flawed or failed processes, policies, systems or events that disrupt business ...

  • risk reporting

    Risk reporting is a method of identifying risks tied to or potentially impacting an organization's business processes.

CIO
  • Risk Management Framework (RMF)

    The Risk Management Framework (RMF) is a template and guideline used by companies to identify, eliminate and minimize risks.

  • robotic process automation (RPA)

    Robotic process automation (RPA) is a technology that mimics the way humans interact with software to perform high-volume, ...

  • spatial computing

    Spatial computing broadly characterizes the processes and tools used to capture, process and interact with three-dimensional (3D)...

HRSoftware
  • OKRs (Objectives and Key Results)

    OKRs (Objectives and Key Results) encourage companies to set, communicate and monitor organizational goals and results in an ...

  • cognitive diversity

    Cognitive diversity is the inclusion of people who have different styles of problem-solving and can offer unique perspectives ...

  • reference checking software

    Reference checking software is programming that automates the process of contacting and questioning the references of job ...

Customer Experience
  • martech (marketing technology)

    Martech (marketing technology) refers to the integration of software tools, platforms, and applications designed to streamline ...

  • transactional marketing

    Transactional marketing is a business strategy that focuses on single, point-of-sale transactions.

  • customer profiling

    Customer profiling is the detailed and systematic process of constructing a clear portrait of a company's ideal customer by ...

Close