As you know, the main prerequisite for doing any work is to have accurate information about that subject. In the discussion of choosing, checking prices, buying, and getting to know more about the types of PLCs, the following information is included so that you, dear visitors of the specialized website of Dematheheez (an official member of the Heating and Air Conditioning Dealers Association), can use these tips. With enough information, choose and buy suitable PLCs in bulk for your living or work environment.
Introduction and User Manual of PLC
In simple words, PLC is a device that can program an operation that can provide the desired data as input to the device to process it and finally control or display the outputs. The use of PLC has caused many of the conventional wirings in relay control circuits to be eliminated. It can be said that PLC is a programmable computer that is very easy to work with. By knowing the simple principles and basic logic, you can analyze and understand the basis of its work. These devices are like the electrical command circuit of a controller, but unlike them, they are logical. Join us in introducing and checking the performance of PLC types in the rest of this article.
What is PLC?
PLC or programmable logic controller (PLC: Programmable Logic Controller) is an industrial digital computer with different applications used in industrial processes that require simple troubleshooting and reliable and accurate control. Among the industrial processes in which PLC is used, we can mention production processes, assembly line control, and robotic devices.
Structure of PLCs
Each PLC consists of five main parts:
The central processing unit (CPU): The processing unit includes a central processing unit and its memories, which, taking into account the state of the inputs, executes the programs stored in the PLC and, based on that, gives the command to activate the desired output. To provide the CPU with a unit that connects various internal and external parts.
Memory: Memory is used to store programs and information. PLC memory includes both ROM and RAM.
ROM or permanent memory (Read Only Memory) includes the operating system, applications, and driver programs. The information of this chip is embedded in it by the manufacturer and cannot be changed or erased during CPU operation, even when CPU power is cut off.
RAM, or random access memory, is a semiconductor chip that stores written programs and user work information.
Memories use long-life batteries, EEPROM, and flash memory methods
Power Supply: This unit is responsible for the AC voltage from the system electricity, which provides safety against input voltage fluctuations and noise in industrial environments.
Input and output (I/O) unit: This unit communicates the PLC with the outside world.
Programming tool (Programmer): It is used to write a program and transfer it to the PLC memory, which includes a keyboard and a screen and is connected to the central unit as a separate unit through a wire.
All these five parts are placed in one unit in small PLCs, and in larger PLCs, each is placed in a separate unit.
Buying PLCs
In the specialized HVAC group of Damatajhiz, all the PLCs are only sold in bulk. Therefore, if you want to wholesale any of these products, feel free to contact us.
Types of PLC
PLCs are classified in terms of memory, size, number of inputs and outputs, etc. In the review and evaluation of PLCs, other features such as the processor, the simplicity of the programming language, the execution time of a cycle, the ability to develop, etc., should be considered.
Small PLCs: The memory size of this type of PLC is one kilobyte and consists of 40 input and output lines. These devices are a suitable alternative to traditional controllers, and their programming is done by ladder or symbolic commands.
Medium PLCs: These PLCs have 128 input and output lines, and their memory size is 4 KB. These PLCs have a modular structure with the possibility of easy expansion and modification. Their type of programming language is a ladder, symbolic or graphical commands.
Large PLCs: The memory of this type of PLC is more than 4 kilobytes, and they have more than 128 input and output lines. Large PLCs are used in cases where the number of inputs and outputs is large. Also, this type of PLC is used for complex control operations and directing several small PLCs. The programming of these types of PLCs is usually written using high-level languages.
PLC types in terms of hardware
Each PLC manufacturing company produces four different models of PLCs with unique and specific names for their manufacturing company. These four general models of PLC devices are:
Rack PLC
Expandable PLC (Modular PLC)
One-piece PLC (Compact PLC)
Mini PLC
Types of PLC in terms of appearance
Integrated PLC: Small PLCs are usually designed and built as compact or integrated, meaning that the power supply and CPU and the input and output modules are integrated and considered a unit. This type of PLC can maintain only 1000 program lines, but they have space to connect additional input and output programs.
Modulator PLC: In this type of PLC, unlike the integrated type, the user can choose the input and output modules of the same family according to their needs and put them together, including separate power supply cards. CPU, input, and output are required in number, respectively, installed on the RACK and inside the SLOTS slots.
The role of PLC in industrial automation
The ability to read all types of digital, analog, and high-frequency inputs and display them
The ability to transfer commands to systems and output components such as engines, electric valves, industrial monitors, etc.
Very high response speed and accuracy
Safety, accuracy, and high flexibility
Tiny and practical dimensions
The possibility of connecting to the network according to the latest standards
Networking of PLCs and the possibility of managing them with a central computer
Better control of production processes
Ease of work for the operator
The built-in troubleshooting functions of the PLC system make it very easy to diagnose and troubleshoot the system.
Because PLCs do not have mechanical depreciation, they have a longer life and will not need periodic repairs and services.
Application of PLC in industrial industries
PLCs are used in various industries, some of which are designed and manufactured for special applications such as hazardous environments, which are often explosion-proof. The price of explosion-proof and EX PLCs is higher than other PLCs with similar features. Some of the applications of PLCs in various industries are:
Heavy industries: industrial coolers, automatic control systems, devices, and equipment used for melting metals. Plastics industries: melting and injection molding machines, air blowing systems for plastic production and analysis Machine industries: danger notification and warning systems, wood industries, packaging industries, systems used in metal welding, drilling systems, etc. Construction services: automatic lighting systems, elevators, air control, air conditioning, etc. Chemical industry: mixing systems, devices combining materials with different proportions, etc. Automotive industry: paint spraying systems and body shaping by automatic presses, connecting parts, testing car parts and equipment, automatic drilling operations, etc. Food industry: centrifuge systems, extraction and packaging systems, etc.
Essential factors in choosing the suitable PLC
Type of nutrition
Memory size
Number and type of flags and timers
number of counters
Accuracy and speed of the project
Number of inputs and outputs
load type (output current and voltage)
SCAN TIME program execution speed
Device operating program type
Types of PLC based on manufacturer (brand)
Germany SIEMENS PLC (SIMATIC S5, S7)
Omron plc Japan
PLC ABB Switzerland-Sweden
Allen Bradley America plc
PLC Schneider Electric
France Telemecanique plc
Japan Mitsubishi PLC
FATEK TAIWAN PLC
Delta China plc
Korea LG plc
Among the most famous PLC brands, we can mention Delta PLCs, made in Taiwan, Siemens PLCs from Germany, Omron from Japan, and Allen Bradley from America, each of these PLCs is designed with its programming and has been built.
Types of PLC programming methods
PLC programming is done in various ways, and three methods are used to display the PLC program; we will introduce these languages in the following:
Ladder Programming (LAD): The program structure of this method is similar to relay circuits, and the program is shown as connection symbols and relay control circuit screw systems. Programming by flow chart method (CSF) or function facet display (FBD): rectangular symbols are used in this method, and regional action is displayed in each rectangle. Programming using the written method or list of sentences (STL): In this programming language, commands and key sentences are used to write the program, and each statement has two parts, an operator and an operand.
Abbreviations in PLC
Standard abbreviations used when working with a PLC:
ASCII: American Standard Letter System for Information Interchange
BCD: binary decimal system
CSA: Canadian Standards Association
I/O: Distributed DIO
EIA: Electronics Industries Association
EMI: Electromagnetic interference
HMI: Human-Machine Interface
IEC: International Electrotechnical Commission
IEEE: Institute of Electrical and Electronics Engineers
I/O: inputs or outputs
ISO: International Organization for Standardization
LL: Ladder logic
LSB: Least Significant Bit
MMI: Man-Machine Interface
MODICON: Digital Modular Controller
MSB: Maximum significant bit
PID: Proportional Integral Derivative (Feedback Control)
RF: Radio frequency
I/O: Remote RIO
RTU: Remote Terminal Unit
SCADA: Data acquisition and supervisory control
TCP/IP: Transmission Control Protocol/Internet Protocol
Four steps in PLC operation
Input Scan: Detects the status of all input devices connected to the PLC. Program Scan: The program logic created by the user is executed. Output scan: All input devices connected to the PLC are energized or de-energized. Internal operation: This phase includes communication with programmable terminals, internal diagnostics, etc.
In the PLC group, the reference site and store of Damatajhiz, you can view the information and prices of Siemens brand PLCs for review and selection.
In addition to a valid business license from the heating and air-conditioning trade union, Damatajhiz has an electronic trust symbol and has been operating its store site since 2013 in Tehran's head office.
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