Block diagram of PLC | Types of PLC

Programmable logic is like a controller computer in which all basic functions of the same type of computer are the same. Programmable logic controllers are mainly used in industrial operations. The programmable logic controller is shown in the block diagram.

Programmable logic controller

The following are the major blocks of programmable logic controllers -

Processor - All programmable logic controllers have a central processing unit (CPU). This microprocessor supervises and controls the internal action. In this way, the CPU resolves the programs of the users and updates the storage of the output. It performs various logic and securing functions hence it is known as PLC Controller. During the program execution, the processor reads the inputs and takes their values, with the control application activating the outputs according to the program or Disables. The ladder network is thus resolved. Once the logic is resolved, the processor updates the output. In this, the process of reading the input, implementing the control application program and updating the output is known as scan. PLCs are classified by scan time. The scan time is usually in the range of 1 to 100 milli-seconds. Z.80,8086,9900,6800. Some CPUs from the 286,386 and 486 microprocessor families are used.
Memory – Logic programs, sequencing and other input / output operations are included under memory. The storage capacity of PLC memory varies from 1Kb to 64 Kb. PLC can be divided into system memory (operating system) and application memory. In this way system programs store ROM and application programs in RAM
Programming Device – The PLC is programmed through a programming device. Programmers or operators can enter and edit program instructions and data through a programming device. Basic components of a programming device are keyboard, visual display, microprocessor and communication cable. The PLC is separated from the cabinet so that its parts can be divided between different controllers. Different PLC manufacturers provide different types of devices. These devices can be handheld programming units or personal computers or industrial programming terminals. The programming device is usually connected to the troubleshooting system at the time of programming. Otherwise, it is disconnected from the programming device. Some of the important functions of a programming device are as follows -

(A) Generating and transferring user programs from memory in PLCs
(B) Debugging the startup of user programs and control systems
(C) Performing installation diagnostics

(A) Handheld programming Unit - Handheld programmers are innovative and portable units which are commonly used to program small PLCs. Most of these units are portable with a large display and a separate keyboard and calculator. Usually their display is LED or LCD matrix and the keyboard of this type of device consists of alphanumeric keys, programming instructions keys and special function keys etc. In addition, it is mainly used for inputting and editing of control programs. Programmable controls are also used for testing, checking and monitoring of programs.
Handheld programming unit
Industrial programming Terminal - The Industrial Programming Terminal is an intelligence device that provides control editing programs as well as program editing functions. It is independent of functional programmable controllers. Industrial programs typically have their own internal memory and cathode ray tubes (CRTs) used to make alter and monitor programs. CRT is a powerful tool for programming because control programs cannot be modified and displayed without attaching them to a programmable controller. The industrial programming terminal is shown in Fig.
Industrial programming terminal
Personal Computer – Modern changes in programming terminals are called personal computer types. All the features of industrial terminals, such as program editing and storage, etc. come inside the personal computer, but some other features, such as automatic program, printout and local area network, are added by them. Any programmable in the network to LAN, programmer or engineer Allows access to controllers so that any device can be monitored or controlled from the network. In this type of function, small portable computers, laptops etc. are used in programming of PLC
Personal Computer
Input Module - The input module acts as a link between the field input devices and the CPUs of the PLCs. There is a terminal block to connect the input wiring of each module to each individual field input device. The main function of the input module is that it takes the input signal of the field device and converts it to a signal level to which the CPU relates. Could work and isolate this signal electrically and send it to the CPU via the backplane. Input modules in particular have 8, 16 or 32 input terminals. An input module is an electronic circuit that interfaces the PLC with the field input devices of the CPU
Output Module - The output module acts as a link between the CPU and field output devices of the PLC. Each module has a terminal block to connect the output wiring to different field output devices. The main function of the output module is to isolate and electrically control the CPU's control signal and activate or deactivate the output field device to turn on or off. In particular, the output module has 8, 16 or 32 output terminals. The output module is an electronic circuit connected to the field output devices of the central processing unit of the PLC
Power supply - The power supply converts the AC line voltage into the DC line voltage to power electronic circuits in a programmable controller system. This power supply incorporates rectifiers, filters, regulator voltages, etc. to supply the correct amount of voltage and current to the system. 280V AC by power supply The line voltage is converted to DC line voltage. The power supply for the PLC is added to the processor, memory and input / output modules under single housing and can also be a separate unit connected by the cavity Power supplies are manufactured for high temperature and humidity as PLC is used in industrial environments. It is used to remove the electrical noise present in the signal lines of AC power or industrial plants so that the noise does not cause inaccuracy in the control system.