Logic controllers are programmable logic devices

Logic controllers are programmable logic devices


Definition of a PLC

Programmable logic controllers (PLCs) are essentially miniature computers that contain both hardware and software for controlling industrial equipment. 6ES7326-1BK02-0AB0 is primarily used for automating industrial electromechanical processes, such as controlling machinery on factory assembly lines, amusement rides, or food processing. A variety of digital and analog inputs and outputs can be provided, as well as resistance to vibrations and impacts, extended temperature ranges, and immunity to electrical noise. PLCs are composed of two basic sections: the central processing unit (CPU) and the input/output (I/O) interface system.

Explaining the CPU

Through its processor and memory system, the CPU controls all system activity. In order to control logic, monitoring, and communications, the CPU contains a microprocessor, memory chip, and other integrated circuits. It has several modes of operation. The CPU will accept changes to the logic downloaded from a PC when it is in programming mode. In run mode, the CPU executes the program and executes the process. The CPU performs an execution of the control program that has been stored in its memory system after it processes input data from connected field devices (e.g., switches, sensors, etc.). PLCs are dedicated controllers, which means they will run the same program over and over again. The time it takes for one cycle through the program to complete is called scan time, and takes only a few hundredths of a second, depending on the program. As well as storing the program, the CPU’s memory also tracks the status of the I/O and stores values.


Interface System for Input/Output (I/O)

Physically connected to field devices, the input/output system serves as the interface between the CPU and its information providers (inputs) and controllable devices (outputs). The CPU will then make any necessary output changes (output scan) after it processes the input data (input scan). An input scan, a program scan, an output scan, and a housekeeping scan comprise the four basic steps in the operation of a PLC. All of these steps are repeated continuously.

Input Scan – Checks the state of all input devices connected to the PLC

Runs the logic created by the user in the program scan

Scan of PLC output devices – Energizes or de-energizes all connected devices

Communication with programming devices and internal diagnostics are part of housekeeping

A PLC is typically equipped with a wide range of I/O modules that can accommodate all kinds of sensors and output devices. With discrete input modules, such as proximity sensors, photoelectric sensors, limit switches, or push buttons, the presence or events of objects can be detected. Loads such as motors, lights, and solenoids can be controlled via discrete output modules. Process instrumentation such as flow, pressure, temperature, and level transmitters can be connected to analog input modules. Based on the devices’ electrical specifications, these modules can interpret the signal and present a value within a certain range. Loads requiring varying control signals, such as panel meters, variable frequency drives, and analog flow valves, will be controlled with analog outputs. PLCs also offer specialized modules, such as high-speed I/O and motion control, as well as serial or Ethernet communication.

With a Programmable Logic Controller, the most important benefit is the ability to repeat or change the operation or process while collecting and communicating vital data. Programmable Controller applications are bought by people with very different needs. The right PLC for the job must consider a number of factors, including cost, power, speed, and communication.


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