11.PMAT M-03

11.PMAT M-03 - PROCESS CONTROL The process of recognizing...

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Unformatted text preview: PROCESS CONTROL The process of recognizing the state of the process at all The times, analyse the information according to the set rules & guidelinens & accordingly actuate the control elements is referred to as process control. elements Process the Recognising Actuate the Information the Status Control elements Rules & Guidelines In the control of process all these actions can be In taken manually with human involvement or in a semiautomatic or fully automatic manner. semiautomatic AUTOMATION Automation is basically the delegation of human Automation control functions to technical equipment aimed towards achieving. towards •Higher productivity •Superior quality of end product Superior •Efficietn usage of energy & raw materials •Improved safety in working conditions •………..Etc. HISTORY OF PROCESS CONTROL & AUTOMATION PLC CONTROL ELECTRONIC CONTROL HARD WIRED CONTROL MANUAL CONTROL HISTORY OF PROCESS CONTROL & MANUAL CONTROL AUTOMATION In this all actions related to process control & In automation are taken care by the operators. automation One of the major drawback of this method is the likely One human errors & consequently its effect on quality of the final product. the The manual control has its own limitations with regard The to mass production techniques & hence this method cannot provide the consumer with quality goods at an affordable price. The safety or efficient use of raw material & energy are all subject to the correctness & accuracy of human action. accuracy HISTORY OF PROCESS CONTROL & AUTOMATION HARD WIRED LOGIC CONTROL This was considered to be first step towards automation. Here the contactor & relays together with timers & Here counters were used in achieving the desired level of automation. automation. Although this method served the purpose for many Although years, it had certain limitations as listed below : years, •Bulky & Complex Wiring •Involves lot of rework to implement changes in control logic •The work can be started only when the task is fully defined & this leads to longer project time. defined HISTORY OF PROCESS CONTROL & AUTOMATION ELECTRONICS CONTROL With the advent of electronics, the logic gates started With replacing the relays & auxiliary contactors in the control circuits. control The bimetalic & motorized timers were replaced by The electronic timers…..etc. electronic With incorporation of these changes, we got the With Reduced benefits of : •Reduced space requirements benefits •Energy saving Energy •Less maintenance & hence greater Less reliability reliability •………….etc. HISTORY OF PROCESS CONTROL & AUTOMATION ELECTRONICS CONTROL However even with electronics, the implementation of However changes in the control logic as well as reducing the project lead time was not possible. project This method of control & automation was also popular This for quite some time. for HISTORY OF PROCESS CONTROL & AUTOMATION PROGRAMMABLE LOGIC CONTROLLER With the coming of microprocessor & associated With peripheral chips, the whole process of control & automation underwent a radical change. automation Instead of achieving the desired control or automation Instead through physical wiring of control devices, in PLC it is achieved through a program or say software. achieved As the desired Logic control is achieved through a As ‘program’, these controllers are referred to as Programmable Logic Controllers. Programmable HISTORY OF PROCESS CONTROL & AUTOMATION PROGRAMMABLE LOGIC CONTROLLER The Programmable Controllers have in recent years The experienced an unprecedented growth as universal element in industrial automation. It can be effectively used in applications ranging from simple control like replacing small number of relays to complex automation problems. automation ADVANTAGES OF PLC REDUCED SPACE PLC are fully solid state & hence extremely compact as PLC compared to hard – wired controller where in electro – mechanical devices are used. mechanical ENERGY SAVING Average power consumption is just 1/10th of power consumed by an equivalent relay logic control. consumed EASE OF MAINTENANCE # Modular replacement. # Easy Trouble Shooting. # Error diagnostics with programming unit. ADVANTAGES OF PLC ECONOMICAL # Considering one time investment ; PLC is most Considering economical system. economical # Cost of PLC recovers within a short period (Low pay Cost back period). back GREATER LIFE & RELIABILITY # Static devices hence lesser number of moving parts, Static reduces wear & tear. reduces ADVANTAGES OF PLC GREATER LIFE & RELIABILITY # In the case of hard wired logic, the control hardware In is either electromechanical or pneumatic & therefore it is more prone to faults due to wear & tear of moving parts resulting in lesser ON TIME of the system. parts ADVANTAGES OF PLC TREMENDOUS FLEXIBILITY # To implement changes in control logic no rewiring is To required so considerable time is saved. required # PLC can carry out complex function such as PLC generation of time delays, counting, comparing , arithmetic operations etc. arithmetic # “ On line ” (I.e. without disturbing the process ) as On well as “ Off line ” programming is possible. well # High processing speed & great flexibility in the High processing of both analog & digital signals. processing # Suitability for closed loop tasks with several loops & Suitability high sampling frequencies. high APPLICATION OF PLC SYSTEMS # In Industry , there are many production tasks which In are of highly repetitive nature. Although repetitive & monotonous, each stage needs careful attention of operator to ensure good quality of final product. operator # Many times, a close supervision of processes cause Many high fatigue on operator resulting in loss of track of process control. process # Under all such conditions we can use PLCs Under effectively in totally eliminating the possibilities of human error. BUILDING BLOCKS OF PLC SYSTEM The PLC mainly consists of a CPU, memory areas, The and appropriate circuits to receive input/output data. and We can actually consider the PLC to be a box full We of hundreds or thousands of separate relays, counters, timers and data storage locations. counters, BUILDING BLOCKS OF PLC SYSTEM Do these counters, timers, etc. really exist? Do No, No, They don't "physically" exist but rather they are simulated and can be considered software counters, timers, etc. timers, These internal relays are simulated through bit These locations in registers. (more on that later) locations BUILDING BLOCKS OF PLC SYSTEM BUILDING BLOCKS OF PLC SYSTEM What does each part do? INPUT RELAYS These are connected to the outside world. They physically exist and receive signals from switches, sensors, etc. Typically they are not relays but rather they are transistors. they BUILDING BLOCKS OF PLC SYSTEM What does each part do? INTERNAL UTILITY RELAYS INTERNAL These do not receive signals from the outside world nor do they physically exist. They are simulated relays and are what enables a PLC to eliminate external relays. There are also some special relays that are dedicated to performing only one task. Some are always on while some are always off. Some are on only once during power-on and are typically used for initializing data that was stored. BUILDING BLOCKS OF PLC SYSTEM What does each part do? COUNTERS COUNTERS These again do not physically exist. They are simulated counters and they can be programmed to count pulses. Typically these counters can count up, down or both up and down. up, Since they are simulated they are limited in their counting speed. Some manufacturers also include high-speed counters that are hardware based. We can think of these as physically existing. Most times these counters can count up, down or up and down. BUILDING BLOCKS OF PLC SYSTEM What does each part do? TIMERS TIMERS These also do not physically exist. They come in many varieties and increments. The most common type is an on-delay type. Others include off-delay and both retentive and non-retentive types. Increments vary from 1ms through 1s. BUILDING BLOCKS OF PLC SYSTEM What does each part do? OUTPUT REALYS OUTPUT These are connected to the outside world. They physically exist and send on/off signals to solenoids, lights, etc. They can be transistors, relays, or triacs depending upon the model chosen. DATA STORAGE DATA Typically there are registers assigned to simply store Typically data. They are usually used as temporary storage for math or data manipulation. BUILDING BLOCKS OF PLC SYSTEM What does each part do? DATA STORAGE DATA They can also typically be used to store data when They power is removed from the PLC. Upon power-up they will still have the same contents as before power was removed. Very convenient and necessary!! RELAYS Now that we Now understand how the PLC processes inputs, outputs, and the actual program we are almost ready to start writing a program. But first lets see how a relay actually works. After all, the main purpose of a plc is to replace "realplc world" relays. world" A typical industrial relay RELAYS We can think of a relay as an electromagnetic We switch. Apply a voltage to the coil and a magnetic field is generated. This magnetic field sucks the contacts of the relay in, causing them to make a connection. These contacts can be considered to be a switch. They allow current to flow between 2 points thereby closing the circuit RELAYS Let's consider the following example. Let's Here we simply turn on a bell (Lunch time!) whenever a switch is closed. We have 3 real-world parts. A switch, a relay and a bell. Whenever the switch closes we apply a current to a bell causing it to sound. RELAYS Notice in the Notice picture that we have 2 separate circuits. The bottom (blue) indicates the DC part. The top (red) indicates the AC part. RELAYS Here we are using a dc relay to Here control an AC circuit. That's the fun of relays! When the switch is open no current can flow through the coil of the relay. As soon as the switch is closed, however, current runs through the coil causing a magnetic field to build up.This magnetic field causes the contacts of the relay to close. Now AC current flows through the bell and we hear it. Lunch time! ...
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