An example of a high-power transistor has a current of 15 amps with a max voltage of 60V. Allen-Bradley termed their new device the "Programmable Logic Controller" patent 3, over the then accepted term " Programmable Controller ".
The completed program looks like a ladder but in actuality it represents an electrical circuit. Using a general-purpose computer for process control required protecting the computer from the plant floor conditions.
Scan time[ edit ] A PLC program generally loops i. Some PLCs enforce a strict left-to-right, top-to-bottom execution order for evaluating the rung logic. Diagnosis and communication is used in many different disciplines with variations in the use of logics, analytics, and experience to determine "cause and effect".
That much is obvious right. Hence, a programmable logic controller is a specialized computer used to control machines and processes. These symbols are interconnected by lines to indicate the flow of current through relay like contacts and coils. A Programmable Logic Controller, or PLC for short, is simply a special computer device used for industrial control systems.
If a discrete input is energized, the memory bit is a 1, and a "normally open" contact controlled by that bit will pass a logic "true" signal on to the next element of the ladder. 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.
If enabled until setpoint is reached then the timer output goes true, and stays true until the input enable line goes false. Besides the ones and zeros it is important to understand how these bits are packaged into codes like BCD and Gray codes.
An industrial control computer would have several attributes: Modicon used the 84 moniker at the end of its product range until the made its appearance.
Other engineering firms developed their own versions of this device, and it eventually came to be known in non-proprietary terms as a PLC, or Programmable Logic Controller. The winning proposal came from Bedford Associates of Bedford, Massachusetts.
Instead, digital computers fill the need, which may be programmed to do a variety of logical functions. Fortunately for them the prospect of computer control was rapidly becoming a reality for large corporations as themselves.
The elimination of these "sneak paths" is either a bug or a feature, depending on programming style. What Is a PLC. A relay can switch ac or dc modules because they are non-polarized. Since many industrial processes have timescales easily addressed by millisecond response times, modern fast, small, reliable electronics greatly facilitate building reliable controllers, and performance could be traded off for reliability.
The new system drastically increased the functionality of the controls while reducing the cabinet space that housed the logic. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact.
These controllers eliminated the need for rewiring and adding additional hardware for each new configuration of logic. That is, you can mix and match the types of Input and Output devices to best suit your application. One of the advantages of implementing logical control in software rather than in hardware is that input signals can be re-used as many times in the program as is necessary.
Their programming language is easily understood, so they can be programmed without much difficulty. A Delay-OFF timer activates immediately when turned on, counts down from a programmed time before cutting off, and is cleared when the enabling input is off. The function, represented by blocks, connects input and output variables.
Direct current dc input modules connect to sourcing or sinking transistor type devices.
This is a rather simple example but in a larger system with many switchs and lights and a host of other devices all interacting with each other this kind of flexibility is not only nice but imperitive.
This instruction is true logic 1 when the hardware input or internal relay equivalent is NOT energized.
To this end you are welcome to comment on each section by registering as a user and clicking the "add a comment" link at the bottom of the page. Once the water level rises enough so that the "High Level" switch is off openedthe PLC will shut the inlet to stop the water from overflowing; this is an example of seal-in latching logic.
PLC serial ports transmit and receive data as voltages. In some software packages, it is also possible to view and edit the program in function block diagrams, sequence flow charts and structured text. PLCs work with inputs, outputs, a power supply, and external programming devices. The components that make a PLC work can be divided into three core areas.
To meet these challenges the PLC was developed with several key attributes. Systems and processes requiring “on/off” control abound in modern commerce and industry, but such control systems are rarely built from either electromechanical relays or discrete logic gates.
Instead, digital computers fill the need, which may be programmed to do a variety of logical functions. Definition of programmable logic controller (PLC): Microcomputer embedded in or attached to a device to perform switching, timing, or machine or process control tasks.
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A programmable logic controller (PLC) is an industrial solid-state computer that monitors inputs and outputs, and makes logic-based decisions for automated processes or machines. 1. The image. A Programmable Logic Controller, or PLC, is a ruggedized computer used for industrial automation.
These controllers can automate a specific process, machine function, or even an entire production line. The programmable logic controller, or PLC, is ubiquitous in process and manufacturing industries today.
Initially built to replace electromechanical relay systems, the PLC offers a simpler solution for modifying the operation of a control system. A PROGRAMMABLE LOGIC CONTROLLER (PLC) is an industrial computer control system that continuously monitors the state of input devices and makes decisions based upon a custom program to control the state of output devices.
Almost any production line, machine function, or process can be greatly enhanced using this type of control system.Write a definition of a programmable logic controller