Use of PLC in Industrial Automation

Use of PLC in Industrial AutomationPresented ByS Aloka PatroReg. No-13020034Department Of E&TC, VSSUT, Burla

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Manual Control:

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Behind the Invention:The Hydrometric Division of the General Motors Corporation specified the design criteria for the first programmable controller in 1968. The primary goal was to eliminate the high costs associated with inflexible, relay controlled systems.The specifications required a solid-state system with computer flexibility able to,survive in an industrial environment, be easily programmed and maintained by plant engineers and technicians, and be reusable3

What is it ?PLCs can be thought of in simple terms as industrial computers with specially designed architecture in both their central units (the PLC itself) and their interfacing circuitry to field devices (input/output connections to the real world). They are capable of storing instructions, such as sequencing, timing, counting, arithmetic, data manipulation, and communication, to control industrial machines and processes.

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What does the PLC consist?The Central processor unitThe power supply unitThe programming unitThe memory unitThe I/O interfacing Circuitry5

Operation:The operation of a programmable controller is relatively simple. The input/output (I/O) system is physically connected to the field devices that are encountered in the machine or that are used in the control of a process. These field devices may be discrete or analog input/output devices, such as limit switches, pressure transducers, push buttons, motor starters, solenoids,etc. The I/O interfaces provide the connection between the CPU and the information providers (inputs) and controllable devices (outputs).

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I/O Module:

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PLC I/Os:The PLC I/Os can be Analog or digital based upon the device.The AC modules and DC modules are not quite different though all the present day devices have sensors and sensors work on DC signals.The outputs may be a relay, transistor or a TRIAC.9

Switching:

When an input command comes from a field device, the signal goes to the DI or AI card, where it powers up the LED and through optical coupling/switching the Transistor is switched on & the signal goes to the PLC processor module through communication interface module via profibus cables.

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Memory Section:The total memory system in a PLC is actually composed of two different memories: The executive memory The application memoryThe executive memory is a collection of permanently stored programs that are considered part of the PLC itself.The application memory provides a storage area for the user-programmed instructions that form the application program.

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Program Scan:This process of reading the inputs, executing the program, and updating the outputs is known as the Scan. The scanning process is repeated over and over in the same fashion, making the operation sequential from top to bottom. Sometimes, for the sake of simplicity, we call the solving of the control program the program scan and the reading of inputs and updating of outputs the I/O update scan.

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Scanning Time:A typical PLC has repetitive cycle of operations. First the PLC sequentially scans the input devices and updates memory table as per the states of the inputs. Then it executes a control programming. After the execution it updates the memory table indicating whether output devices should be ON or OFF. This time comes around 3 to 100 milliseconds.13

PLC Communication:A PLC communicates with its interfaces using certain ways i.e.;Extension modules Remote I/O modules Serial communication modules(RS-232,RS-485)Parallel communication(IEEE 488)General twisted pair cables Ethernet cables

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Communication:15

How to program a PLC:To program a PLC we need to know some of the basic languages i.e., Functional Block DiagramLadder LogicStructured TextInstruction ListSequential Flow Chart16

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Ladder Logic:18

Functional Block Diagram:

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Merits:Rugged and designed to withstand vibrations, temperature, humidity, and noise. Have interfacing for inputs and outputs already inside the controller. PLCs are easily programmed and have an easily understood programming language.22

Future Research:Till now communication within a PLC hasnt been wirelessly done, so importance is given on making it wireless. Though a PLC needs more no of cables to be erected, it should be of prime concern for us to reduce the no. of cables for erection.23

References:www.jsl.comwww.google.co.in

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25Thank you