Introduction to the Central Processing Unit (CPU) of PLC

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 the features of different plc inputs and output modules. In today’s tutorial, I am going to explain to you a detailed article on the 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 the 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 work. 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 use 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 work.
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 enhances 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 the 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.

The function of key switch of the PLC CPU

• The key switch of plc’s CPU provides three main functions 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 to 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 the 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 programming changes.

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 the 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 progress 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 that 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 supervising and functioning with stationary-sensitive components and units.
  • Be grounded physically by moving a conductive body before supervision of static-sensitive types of machinery.
  • Always try to dress a wristband that 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, use 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

Faqs

• What is the role of CPU in PLC?

The CPU is the central processing unit of the PLC. It is used for executing the program, reading input signals, and producing output signals. The CPU is the brains of the PLC and controls all of its operations.

• What is the processor section of a PLC?

The processor section of the PLC is where the CPU is located. It also contains the memory, which stores the program and data. The processor section is called the heart of the PLC and is responsible for all of its processing operations.

• What is the difference between CPU of PLC to computer CPU?

The basic difference between the CPU of a PLC and the CPU of a computer is that the PLC CPU is made to be more rugged and reliable. PLC CPUs are also able to work in harsh environments, like in high temperatures or vibrations.

• Does a PLC have a processor?

Yes, a PLC has a processor. The processor is the central processing unit of the PLC and provdies executing the program, reads input signals, and generates output signals.

• What is a CPU of the PLC executes two different programs?

A CPU of the PLC that executes 2 different programs is known as a dual-core CPU. Dual-core CPUs have 2 processors that can run 2 different programs at the same time. It can be useful for applications that need a lot of processing power, like machine vision or motion control.

• How to choose a CPU for PLC?

There are some factors to consider when selecting a CPU for a PLC, like the number of inputs and outputs, the amount of memory, and the processing speed. Certain requirements will changes based on the application.

• Is the central processing unit the brain of PLC?

Yes, the CPU is the brain of the PLC. It is used for controlling all of the PLC’s operations, like reading input signals, executing the program, and producing output signals.

• Is PLC a processor or controller?

A PLC is a controller that uses a processor to execute its programs. The processor is the part of the PLC that executes the instructions in the program.

• What is the difference between CPU and a central unit?

The CPU and the central unit are 2 different parameters that are sometimes used interchangeably. But, there is some difference between the two. The CPU is the actual processor that applies the instructions in the program. The central unit is the complete PLC, like the CPU, memory, and I/O modules.

• Is A CPU the same as a compiler?

No, a CPU is not like a compiler. A compiler is a program that transforms a high-level language program into a low-level language program that can be executed by the CPU. The CPU is the part of the computer that actually applies the instructions in the program.

• What is the CPU operating cycle of PLC?

The CPU operating cycle of a PLC is the sequence of steps that the CPU follows to apply a program. The cycle normally consists of the follow these points

1. Read input signals.
2. Execute the program.
3. Generate output signals.
4. Wait for the next scan cycle.

• What are the sub parts of CPU in PLC?

The sub-parts of the CPU in a PLC are:

• processor: This is the actual chip that executes the instructions in the program.

• Memory: It stores the program and data.

• registers: These are temporary storage locations for data.

•  control unit: It controls the operation of the CPU.

• What are the three operating modes of the CPU of a PLC?

The 3 operating modes of the CPU of a PLC are:

• Run mode: it is the normal operating mode of the PLC. The program is executed in this mode.

• Program mode: This mode is used to load or modify the program existing in the PLC.

• Monitor mode: It is used to view the status of the PLC and its inputs and outputs.

• What are the two main CPU makers?

The 2 main CPU makers for PLCs are Intel and Motorola. Intel CPUs are common in the USA, while Motorola CPUs are commonly used in Europe.

• What are the names of the two types of CPU?

The 2 types of CPU are the microcontroller and the microprocessor. The microcontroller is a small size and less powerful CPU that is normally used in small PLCs. The microprocessor is a larger and more powerful CPU that is used in larger PLCs.

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.