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)

Start the conversation

Send me notifications when other members comment.

Please create a username to comment.

-ADS BY GOOGLE

File Extensions and File Formats

SearchCompliance

  • regulatory compliance

    Regulatory compliance is an organization's adherence to laws, regulations, guidelines and specifications relevant to its business...

  • privacy compliance

    Privacy compliance is a company's accordance with established personal information protection guidelines, specifications or ...

  • data governance policy

    A data governance policy is a documented set of guidelines for ensuring that an organization's data and information assets are ...

SearchSecurity

SearchHealthIT

  • telemedicine (telehealth)

    Telemedicine is the remote delivery of healthcare services, such as health assessments or consultations, over the ...

  • Project Nightingale

    Project Nightingale is a controversial partnership between Google and Ascension, the second largest health system in the United ...

  • medical practice management (MPM) software

    Medical practice management (MPM) software is a collection of computerized services used by healthcare professionals and ...

SearchDisasterRecovery

SearchStorage

  • megabytes per second (MBps)

    Megabytes per second (MBps) is a unit of measurement for data transfer speed to and from a computer storage device.

  • zettabyte

    A zettabyte is a unit of measurement used by technology professionals and the general public to describe a computer or other ...

  • hybrid flash array

    A hybrid flash array is a solid-state storage system that contains a mix of flash memory drives and hard disk drives.

Close