For many years, technology has made many processes in the normal life of humans and of course in the industrial world. A property that was initially invented for industrial applications, but later due to its high power and acceptability, its applications have expanded more and more. Yes, we mean PLC. But what exactly is a PLC?
What does plc stand for?
PLC stands for Programmable Logic Controller in Latin, which means programmable logic controller. It means a controller that is programmable and you can write various control programs on it.
But what exactly is PLC and what is its use?
He said that PLC is a special type of computer designed for reliable operation in specific industrial conditions. Conditions such as very high temperatures, humidity, dryness and dust. PLCs are designed to automate industrial products. Things like the production line in a manufacturing plant, processes in ore factories or clearinghouses…
What are PLC members?
As it has been said, the use of PLC leads to better management of an industrial machine. The use of PLC makes the traditional methods of managing machines obsolete, and human labor is no longer needed, and these machines work automatically using PLC commands.
Another advantage of plc is easy troubleshooting. In industrial systems, for troubleshooting a system, different parts had to be examined. Meanwhile, with the help of plc, this work is intelligently recognized, and the problem can be fixed faster.
Also, using this board can increase the efficiency of a production machine. and at the same time maintain the quality of the products. As a result, a successful project can be launched using this internal computer.
In general, the advantages of plc are:
1- The use of PLC reduces the volume of control panels.
2- The use of PLC saves a lot of money.
3- PLC does not have mechanical consumption, so in addition to longer life, it does not need periodic service and repairs.
4- PLC energy consumption is much less than relay circuits.
5- PLC does not create audio and electrical noises.
6- Troubleshooting control circuits with PLC is quick and easy and usually PLC itself has a troubleshooting program.
PLCs are designed to last in harsh industrial environments and conditions and are protected against heat, cold, dust and moisture. A PLC has a microprocessor that is programmed using a computer language. The program is written in a computer and transferred to the PLC through a cable.
For the first time, PLC was used in the automotive industry and this device replaced relays and timers. In the PLC system, the output results in response to the input conditions must be produced in a limited time. If there is no proper response in the defined time, unwanted operation will happen in the system.
The range of manufactured PLCs starts from small PLCs with about a dozen I/Os that are compact with a processor, to modular rack-mountable PLCs that have thousands of I/Os and are often networked. They are connected to other PLCs and to SCADA.
PLCs have many characteristics, but the most commonly used ones are:
1. The number of digital and analog inputs and outputs
2. Number of timers
3. Number of counters
4. Number of auxiliary relays
5. Programmable memory volume
6. The speed of execution of orders
PLCs usually have industrial communication ports that can be used to communicate with other devices. This accelerates the exchange of information and allows more precise control to the PLC. Today, the use of PLC in industries and factories is increasing, and industrial electricians must know how to use it. In fact, every system needs control. There are 2 types of control in industrial systems.
1. Hardware (electric control circuits)
2. PL systems (which are divided into 2 parts):
1. DCS control systems
2. IPC personal computers
PLC components
Each PLC consists of two parts:
1. Hardware
2. Software
PLC hardware
The hardware of PLC includes CPU MEMORY, INPUT/OUTPUT, power supply and programming module.
PLC hardware includes the following:
1. Power supply unit
2. Central processing unit
3. Memory: RAM (includes maintenance of flags, timers, counters and user programs) and permanent memory (EEPROM, EOROM)
4. Input terminals: digital inputs and analog inputs
5. Output terminals: digital outputs and analog outputs
6. Processor communication module
7. Interface module: input image and output image
8. Power supply module
The following figure shows an overview of the structure of a PLC:
• CPU
In order to prevent errors, the CPU continuously checks the PLC controller and performs functions including logic functions, computer interface and many other functions.
• MEMORY
It is fixed data that is used by the CPU. The ROM system stores data permanently for system operation. RAM stores information about inputs and outputs, values of timers, counters and other internal equipment.
• I/O section
Receives and sends inputs and outputs of field equipment, such as sensors and switches.
• Power supply
PLCs have an isolated power supply. But most PLCs work with 220V AC or 24V DC power supply.
Programming Device
This device is used to send the program to the processor memory. The program is first entered into this device and then transferred to the PLC memory.
System Buses
Buses are ways to pass digital signals inside the PLC. There are 4 bus systems in PLC as follows:
• Data bus, which is used by the CPU to transfer data in different elements.
• The control bus transmits signals related to internal control functions.
• The address bus sends the address of the positions to access the data. • The system bus helps the I/O ports and the I/O unit communicate with each other
