Word of the Day: programmable logic controller (PLC)

Word of the Day Daily updates on the latest technology terms |December 1, 2017

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 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.  Quote of the Day "Many PLCs allow encapsulation of instructions to create user-defined function blocks. This is a powerful tool that sophisticated users leverage to create simple, re-usable code." - Steve Blaine   Trending Terms IT/OT convergence industrial control system critical infrastructure controller nonvolatile storage programmable automation controller   Learning Center The real convergence of IT and OT: How much longer do we have to wait? In the industrial internet, we will see more and more OT and IT converge. This convergence will drive new industry technologies and services. A look at IoT platforms that rely on local intelligence IoT platforms provide local intelligence sitting between intelligent things and cloud applications. Here is a primer on local intelligence platforms and gateways. Nothing funny about SCADA and ICS security The state of industrial control system (ICS) security is being questioned by two researchers who say it has a negative impact on SCADA system security. The researchers found 1,000 vulnerabilities in ICS software in 100 days. Building a secure operating system with Roger R. Schell A secure computer system requires a secure operating system, according to Roger R. Schell, who discussed the Orange Book and class A1 systems with Marcus Ranum. Industrial IoT platforms proliferate while standards slowly percolate Learn why choosing industrial IoT platforms is complicated by the huge array of emerging standards for devices, middleware and the cloud. Writing for Business _______ are common in factory automation, building automation and material handling systems. a. PLC's b. PLCs Answer   Stay In Touch For feedback about any of our definitions or to suggest a new definition, please contact me at: mrouse@techtarget.com   Visit the Word of the Day Archives and catch up on what you've missed!   FOLLOW US About This E-Newsletter This e-newsletter is published by the TechTarget network. To unsubscribe from Whatis.com, click here. Please note, this will not affect any other subscriptions you have signed up for. TechTarget, Whatis, 275 Grove Street, Newton, MA 02466. Contact: webmaster@techtarget.com Copyright 2016 TechTarget. All rights reserved.