Programmable logic controller
What is a plc
A programmable logic controller (PLC) or program controller is a digital computer used to automate the electro-mechanical process. This factory adjustment line can be used to control machinery, recreation rides, or lighting fixture, etc. in the automation of electromechanical processes. PLC is used in many industries and machines. Unlike a normal computer, the PLC is designed for multiple input and output systems, wide temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs that control machine operation are typically stored in battery-supported or static memory. A PLC is an example of a real-time system because output results must be presented in a timeframe in response to input conditions, otherwise the result will be an irregular operation.
PLC was invented in response to the needs of the American automotive manufacturing industry. Programmable logic controllers were initially adopted by the automotive industry, where software modifications changed the rewiring of a rigid wiring controlled panel when the product model was changed.
Prior to PLC, control, sequence and safety matching for the manufacture of automobiles was accomplished by the use of logic hundreds or thousands of relays, cam timers and drum sequencer and dedicated closed loop controllers. The process of updating such facilities to replace the annual model took a lot of time and cost, as the electorates had to re-wire each relay individually.
In 1968, GM Hydramatic (General Motors' Automatic Transmission Division) issued a request to propose electronic changes for hard-wired relay systems. The winning proposal came from Bedford Associates of Bedford, Massachusetts. The first PLC, 084, was specified as it was the result of the Choracian project of Bedford Associates. Bedford Associates started a new company dedicated to the development, manufacturing, sales and new product: Medicon, which was an abbreviation for modular digital controller. One of the people working on the project was Dick Morley, known as the father of PLC. The Medicon brand was sold to Gold Electronics in 1977, and was later acquired by the German company AEG, and then by its current owner, French Schneider Electronic.
One of 084 models initially built is now on display at Medicon's headquarters in North Andover, Massachusetts. When the unit was retired after nearly twenty years of uninterrupted service, it was given to Medicon by GM. Until the appearance of 984, Medicon used 84 monikers at the end of its product range.
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The automotive industry is still one of the largest users of PLC.
Early PLC relays were designed to replace logic systems. These PLCs were schematic in "Ladder Logic", which strongly resembles a diagram of relay logic. This program marking was chosen to reduce the training demands of existing technicians. Other early PLCs used a stage of instruction list programming, which was based on a stake-based logic solver.
The main difference from other computers is that PLCs are armored for severe conditions (eg dust, moisture, heat, cold) and have facilities for extensive input / output (I / O) systems. They connect the PLC to the sensor and the promoter. PLC limit switches read analog process variables (such as temperature and effect) and state of complex placement systems. Some use machine vision. On the promoter side, PLC electric motors, pneumatic or hydraulic cylinders, magnetic relays, solenics or analog outputs, operate. The input / output system may be formed in a simple PLC, or the PLC may have external I / O parameters that are connected to the computer network plugged into the PLC.
PLCs are well adapted to a range of automation functions. These are typically industrial processes, in construction where the cost of building and maintaining the automation system is higher than the total cost of automation and where some changes to the system will be expected during its working period. The PLC consists of investment / output devices compatible with industrial pilot devices and controls; A little electrical design is required and the design problem focuses on describing the desired sequence of operations. PLC applications are typically highly customized systems so the price of a clustered PLC is lower than the price of a uniquely customized controller design. On the other hand, in the case of surplus-produced materials, customized control systems are economical due to the low price of the components, which can be chosen optimally rather than as a "normal" solution and where non-recursive engineering costs in thousands or millions of units. Extends.
Digital or discrete signals behave as binary switches and easily generate an on or off signal (1 or 0, true or false, respectively). Push buttons, limit switches, and photoelectric sensors provide a discrete signal. Examples of devices. Discrete signals are sent using either voltage, or power, where a specific range is assigned as ON and the second OFF. For example, a PLC may possibly use 24 V DC I / O, with values above 22 V DC indicating ON, values below 2VDC off, and intermediate values uncertain. Initially, the PLC had only discrete I / O.
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For example, suppose a facility needs to collect water in a tank. When needed, water is drawn from the tank by another system and our example system is required to manage the water level of the tank.
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