Aug 27, 2019 In many cases, a programmable logic controller allows all of the relays and timers within a factory system to be replaced by a single controller. Modern PLCs deliver a wide range of functionality, including basic relay control, motion control, process control and complex networking. They also can be used in a distributed control system (DCS). MasterLogic Programmable Logic Controller (PLC) is a modular, scalable rack-based industrial controller delivering powerful performance in a control application. It is applied in various processing applications in industries such as oil and gas, steel, cement, power, food and beverage and delivers a blend of power, performance and efficiency.
Contents.Introduction What is a Programmable Logic Controller (PLC)? A Programmable Logic Controller, or PLC, is more or less a small computer with a built-in operating system (OS). This OS is highly specialized and optimized to handle incoming events in real time, i.e., at the time of their occurrence.The PLC has input lines, to which sensors are connected to notify of events (such as temperature above/below a certain level, liquid level reached, etc.), and output lines, to which actuators are connected to affect or signal reactions to the incoming events (such as start an engine, open/close a valve, and so on).The system is user programmable. It uses a language called 'Relay Ladder' or RLL (Relay Ladder Logic).
![Plc Plc](/uploads/1/2/5/6/125658685/154634546.jpg)
![Control Logic Plc Control Logic Plc](/uploads/1/2/5/6/125658685/592349633.jpg)
The name of this language implies that the control logic of the earlier days, which was built from relays, is being simulated.Some other languages used include:. Sequential Function chart. Functional block diagram. Structured Text. Instruction List. Continuous function chartA programmable logic controller, PLC, or programmable controller is a digital computer used for automation of typically industrial electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures.
PLCs are used in many machines, in many industries. PLCs are designed for multiple arrangements of digital and analog inputs and outputs, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed-up or non-volatile memory. A PLC is an example of a 'hard' real-time system since output results must be produced in response to input conditions within a limited time, otherwise unintended operation will result.Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was mainly composed of relays, cam timers, drum sequencers, and dedicated closed-loop controllers. Since these could number in the hundreds or even thousands, the process for updating such facilities for the yearly model change-over was very time consuming and expensive, as electricians needed to individually rewire the relays to change their operational characteristics.Digital computers, being general-purpose programmable devices, were soon applied to control industrial processes. Early computers required specialist programmers, and stringent operating environmental control for temperature, cleanliness, and power quality. Using a general-purpose computer for process control required protecting the computer from the plant floor conditions.
An industrial control computer would have several attributes: it would tolerate the shop-floor environment, it would support discrete (bit-form) input and output in an easily extensible manner, it would not require years of training to use, and it would permit its operation to be monitored.
PLCs are useful tools for repeatable processes because they have no mechanical parts and they can gather information. Each central processor unit continually through an input scan, program scan, output scan and housekeeping mode, repetitively performing a single task while monitoring conditions. The information the 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 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 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.