The First Programmable Logic. Controllers (PLCs). • Introduced in the late 's. • Developed to offer the same functionality as the existing relay logic systems. Programmable logic controllers (PLCs) have been used in industry in one form or another for the past twenty over years. The PLC is designed as a replacement. installation of an S PLC. •. Connect a simple discrete input and output to an S •. Select the proper expansion module for analog inputs and outputs.

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Lecture 1, Introduction to PLCs, LECTpdf Lecture 3, PLC Addressing and Basic Instructions, LECTpdf Lecture 5, PLC Timer Functions, LECTpdf. Lecture – PLC Programming Basics. MME – Fall 4 of Processor Memory Organization. Advanced ladder logic functions allow controllers to. Programmable Logic Controller (PLC) is a microprocessor based system that uses programmable memory to store instructions and implement functions such as.

A processor appears only once in a PLC and it can be either a one-bit or a word processor.


One bit processors are adequate for dealing with logic operations. PLCs with word processors are used when processing text and numerical data, calculations, gauging, controlling and recording, as well as the simple processing of signals in binary code are required.

The principle of operation of CPU can be briefly described as fallow. The CPU accepts reads input data from various sensing devices, executes the user program from memory and sends appropriate output commands to control devices.

This power supply can be housed in the CPU unit or may be a separately mounted unit, depending on the PLC system manufactures. The CPU contains various electrical parts and receptacles for connecting the cables that go to the other units as well as to operational key switches.

Typical operation key switch positions are.

Off: system cannot be run or programmed. Run: allow the system to run, but no program alterations can be made. And also used for interfacing between output devices e.

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The input information is transfer to the processor through input module and output information from the processor to load is transform through output module. And also to provide isolation from processor to output devices.

For isolation modules use the opto coupler. Input devices such as push buttons, limited switches, sensors and selector switches are hard-wired to terminals on the input modules.

Output devices such as small motor, motor starters, solenoid valve, and indictor lights are hard wired to the output modules. Input interface modules accept signals from the machine or process devices e. The simplified circuit and block diagram of input modules is shown in fig.

PLC Programmable Logic Concept

They are basically used to control automated systems in industries. They are one of the most advanced and simplest forms of control systems which are now replacing hard wired logic relays at a large scale.

Programming Logic Controller PLC Advantages: Before getting into details about PLCs, lets us know 3 reasons why PLCs are being widely used these days They are user friendly and easy to operate They eliminate the need for hard wired relay logic They are fast It is suitable for automation in industries.

The input from the sources is connected to the PLC through the input connector rails.

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The output section or output module can be a motor or a solenoid or a lamp or a heater, whose functioning is controlled by varying the input signals. It can be a hexagonal or an octal microprocessor. It carries out all the processing related to the input signals in order to control the output signals based on the control program. Programming Device: It is the platform where the program or the control logic is written.

It can be a handheld device or a laptop or a computer itself.

Power Supply: It generally works on a power supply of about 24 V, used to power input and output devices. Memory: The memory is divided into two parts- The data memory and the program memory.

The program information or the control logic is stored in the user memory or the program memory from where the CPU fetches the program instructions.That is an open-loop because the sprinklers will turn on no matter the feedback in this case. Counter will be reset and operation repeats until PB2 is pressed. These lamps will turn on and off automatically when the sensor detects the brightness of light.

Understanding a Programming Logic Controller (PLC)

This is also called the controlled system. When the contactor coil is de-energized, gravity or a spring returns the electromagnet core to its initial position and opens the contacts.

Since a contactor is required for a higher load.

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