PLC Hardware: A Detailed Description with Component Examples

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Both hardware and software elements make up a PLC (Programmable Logic Controller). The actual elements that make up a PLC system are referred to as PLC hardware. The PLC’s operating system and application program, on the other hand, are kept in the memory of the PLC and are referred to as its software.

The actual elements that make up the whole PLC system are refer to as PLC hardware. Each piece of PLC hardware is create to carry out a certain function. A PLC system cannot function properly without all of its hardware parts.

To create a custom PLC system, the bulk of PLC vendors have created hardware and software components. It follows that PLC hardware components vary depending on the manufacturer and are typically not compatible with hardware from other PLC brands.

1. PLC Processor (CPU)

Every PLC system has a CPU at its core. It is perhaps the most significant Allen Bradley PLC hardware element. The PLC processor may also go by the names PLC controller or PLC CPU (Central Processing Unit). Whichever name you give this PLC hardware component, it is the engine that drives the PLC system and does all the logic calculations and data processing.

The PLC processor may be included into the PLC unit or may be purchase separately. The processor for fixed PLC types is typically includ inside the PLC itself. While the PLC processors for modular and distributed PLC types are contained within different modules.

The Allen Bradley ControlLogix 5580 controller, the Mitsubishi Melsec-Q Processor CPU (Q03UDECPU), the Delta AHCPU560-EN2 processor, and the Omron CJ2M-CPU1 and CJ2M-CPU3 controllers are a few examples of PLC processor modules.

There are three essential parts in the PLC processor:

  1. PLC CPU (Central Processing Unit)
  2. PLC Memory
  3. PLC Programming port

Major PLC CPU functions

  • accepts status data from a variety of input devices
  • putting the program into action
  • The process or machine activity will handle properly.
  • It performs several logic operations.
  • provides the necessary output signal to operate the devices in the output field, such as control valves and relay coils.

2. PLC Power Supply

A PLC power supply’s primary function is to transform the available power supply voltage into a voltage that the PLC processor (CPU) and other PLC modules can use. The most popular input voltages for PLC power supplies are 120VAC, 240VAC, a wide range of AC voltages (such 85-265VAC), and 24VDC. Whereas 24DC and 5VDC are the most often use PLC power supply outputs.

PLC power supplies come in three different categories:

  • Power supply for integrated PLC
  • PLC power supply module
  • Remote PLC power supply

The PLC processor includes an integrated PLC power supply. The PLC processor houses the PLC power supply in fixed type and certain modular type PLCs. While being independent from the PLC processor, the PLC power supply module is housed on the same PLC rack. Although the PLC processor is hard wired to a distant PLC power supply that is positioned away from the PLC rack.

3. Input/Output (I/O) modules:

The PLC input and output modules serve as a common interface in an industrial PLC system between field devices and the PLC processor (CPU). Typically, a terminal strip connects the field devices to the PLC inputs and outputs. As a PLC input and output interface, communication modules with fieldbus protocols like Ethernet IP, Profinet, etc. can also be utiliz.

The input and output interface of a PC (Personal Computer) connects peripheral devices to the computer. Examples of input devices include the keyboard and mouse, while a USB port serves as an example of an input interface. An example of an output device is a monitor, and an example of an output interface is the monitor port.

PLC input devices such pushbuttons, limit switches, proximity sensors, temperature transmitters, pressure transmitters, level transmitters, encoders, etc. are linked to a PLC’s inputs. Relays, motor contactors, VFDs (Variable Frequency Drives), solenoid valves, proportional valves, indicator lights, sirens, and other PLC output devices are linked to the PLC outputs.

Types of PLC Input and Outputs

Analog and digital signals are the two primary PLC input and output signal types (discrete). The PLC processor receives measurements of the outside field conditions from both analogue and digital inputs (CPU). Moreover, field devices are activate through command signals send from the PLC processor (CPU) through analogue and digital outputs.

The following are the primary differences between PLC analogue I/O and digital I/O:

  • Signal Format
  • Signal Wiring
  • Signal Processing

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4. Communication interface

With a communication interface, PLCs may connect with several devices. A cable connection to devices like other PLCs, remote I/O drops, fieldbus devices, touch displays, programming PCs, and servers is made possible through the communication interface’s communication ports. Larger and more complicated applications could need the use of many communication interfaces.

The PLC communication interface may be present as communication modules or as embedded communication ports on the PLC processor. When several communication interfaces are require, it’s rather typical to have both additional communication modules install in the rack and integrate communication ports on the PLC processor. In conclusion, PLC hardware and software elements collaborate to build a reliable and adaptable automation system that can carry out complicated control activities and react to changes in industrial processes in real-time.

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