Hi friends, I hope all of you are fine. As you already know we have started a series of PLC articles. In last lecture, we discussed detailed articles on features of different plc inputs and output modules. In today’s tutorial, I am going to explain to you about detailed article on Introduction to the Central Processing Unit (CPU) of PLC. CPU stands for the central processing unit. In plc, it is like a brain it performs a function like human brain. It controls every activity of plc.

CPU of plc is like a personal computer CPU, which controls all functions of a computer. From receiving a signal to sending or control and logic function. Similarly CPU of plc control every function and circuitry of plc. It is the core part of plc without it plc is nothing, as there is no control system then how other devices can works. So in today’s article, we will discuss details about it.  So let’s get started with an Introduction to the Central Processing Unit (CPU) of PLC.

Introduction to the Central Processing Unit (CPU) of PLC

• The central processing unit of plc is constructed into a single element fixed PLC controller while modular frame categories normally usage a plug-in unit.
• A central processing unit, control system, and computer are all names used by different producers to signify a similar unit that performs similar tasks.
• CPUs differ in handling speed and storage choices.

• A computer unit can be distributed between two parts the central processing unit and the memory or storage unit.
• The central processing unit implements the programs and makes the decisions needed by the PLC to operate and communicate with other units.
• The memory unit by electronic means stores the PLC controller programs with other retrievable numerical data.

PLC Power Supply

• The PLC controller power supply delivers the essential power (normally five volts DC) to the CPU and input and output units connect into the back-plane of the frame.
• Power sources are existing in different ratings.
• The power source transformed 115V AC or 230V AC into the operating (direct current) voltage obligatory to the processor, memory or storage, and input and output electric circuits.
• PLC power source is usually built to endure temporary damages of power without upsetting the process of the PLC.
• The time for which plc can bear a loss of power is known as Holdup time, normally it ranges from ten ms to three seconds.

Difference Between PLC CPU and Computer CPU

PLC CPU	Computer CPU
The program used in this processor is intended to simplify manufacturing control.	This CPU is constructed only for general mathematical and computing working.
This processor implements the functioning scheme, control storage, controls inputs, assesses the operator logic program, and make suitable outputs.	While this CPU do just arithmetic logic functions and simple control functions.
The CPU of a PLC scheme can be consists of more than one processor. Which enhance its overall working speed.	Cpu of the computer contains only one processor.
Every processor of plc CPU has its own storage and instruction, which work instantaneously and independently.	This CPU has only one processor which do many functions alone.
Due to having multiprocessors the scanning of every processor is equivalent and liberated thus dipping the retort time.	Due to a single processor, these parameters did not happen in this CPU.
Error tolerant PLC schemes sustenance double CPUs for serious procedures. These schemes permit the operator to arrange the scheme with two processors, which permits transmission of a switch to the second CPU in the case of a CPU error.	we cannot use the CPU of a computer for such schemes.

Function of key switch of PLC CPU

• The key switch of plc’s CPU provides three main function which are described below.

 RUN Position

• This mode of key switch converts the CPU in the Running condition.
• It Implements the ladder logic program and operates output instruments.

• It Stops you from doing online programming changing.
• It Stops users from using programming or operative interfacing components to change the CPU style.

PROG Position

• This feature of a key switch converts the CPU in the Program condition.
• It Stops the CPU from a scan or implementing the ladder programming, and the regulator outputs are stops to works.
• It Permits operator to make program entrance and removal.
• It also Stops users from using a programming or operative interfacing instrument to change the CPU mode.

REM Position

• This feature of a key switch converts the processor in the distant style which can be either the Run, Program, or Test mode.
• It Permits us to alter the CPU mode from a programming or operative interfacing component.
• It Permits us to do online programing changing.

Features of PLC CPU

• These are important features of the PLC CPU that are explained here.
• The CPU also comprises circuits to link with the device that is programmable.
• Someplace on the unit, we will find a joint that permits the PLC to be linked to an exterior programmable expedient.
• The decision-making aptitudes of PLC CPUs go far away from simplest logic process.
• The CPU executes other tasks like time, calculating, latching, associating, indication control and complicated mathematics tasks.
• PLC CPU has varied continually due to progresses in computer equipment and larger response from different applications.
• Nowadays, CPU is quicker and has extra commands which are introduced in new models.
• As PLC are microchip constructed, they can be prepared to do jobs which a computer can also do.
• In count to their controlling purposes, PLC can interact with the (SCADA).

Precautions for PLC static devices           

• Numerous electrical apparatuses establish in CPUs and other kinds of PLC units are subtle to electrostatic voltages which can damage their working or harm them.
• The following stationary control actions should be monitored when supervision and functioning with stationary sensitive components and units.
  • Be grounded physically by moving a conductive body before supervision static-sensitive types of machinery.
  • Always try to dress a wrist band which offers a track to drain off any charge which can figure up through working.

• • Be cautious not to trace or touch the backplane connections or connector pinouts of the PLC scheme (permanently grip the circuitry passes by the border if probable).
  • Also, be cautious not to touch other circuitry machinery in a unit when you arrange or substitute its inner components.
  • When not in working conditions stock units in its static-shield container.
  • If accessible, usage a stationary safe working place.

I also have uploaded some related articles to plc you must read them for further learning.

• Introduction to PLC
• Working of PLC
• Parts of PLC
• Input and Output Section of PLC
• PLC Discrete Input and Output Devices
• Analog Input and Output Devices of PLC
• plc special inputs and outputs
• Features of PLC Inputs and Outputs

That all about the CPU of PLC each and everything has mentioned in this tutorial. If you have a query can ask in comments thanks for reading.