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01-01-2011, 05:27 PM
AUTOMATION17.doc (Size: 1.8 MB / Downloads: 71)
Automation is the use computers to control industrial machinery and processes replacing human operators .It is a step beyond mechanization where human operators are provided with machinery to help them in their jobs .Thus, Automation is the self driven process based on suitable logics . The most visible part of automation can be said to be industrial robotics .Some advantages are repeatability ,tighter quality control and waste reduction ,integration with business systems, increased productivity and reduction of labor .some disadvantages are high initial costs and increased dependence on maintenance.
What is Industrial Automation?
• One of the most important developments in modern technology.
• Optimum consumption of energy and raw material.
• Optimum co-ordination and co-operation between mechanical and electrical counterparts.
• Performance of a task with the application of least physical efforts.
Automation is required because of
• Shorter throughput times.
• Shorter set-up times.
• Stock reduction.
• Higher productivity.
• Better capacity utilization.
The main difference from other computers is that PLCs are armored for severe conditions (dust, moisture, heat, cold, etc) and have the facility for extensive input/output (I/O) arrangements. These connect the PLC to sensors and actuators. PLCs read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems. Some even use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays or solenoids, or analog outputs. The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a computer network that plugs into the PLC.
Different types of automation tools exist:
• DCS: Distributed Control Systems
• PLC: Programmable Logic Controller
• HMI: Human Machine Interface
• SCADA: Supervisory Control and Data Acquisition
• Higher availability.
• Shorter process change times.
• Stability and accuracy of control.
• Greater reliability and equipment life.
• To add flexibility to process
PROGRAMMABLE LOGIC CONTROLLERS
A PLC ( Programmable Logic Controller) is a device that was invented to replace the necessary sequential relay circuits for machine control. The PLC works by looking at its inputs and depending upon their state, turning on/off its outputs. The user enters a program, usually via software, that gives the desired results.
A digitally operating electronic apparatus which uses a programmable memory for the internal storage of instructions by implementing specific functions such as logic sequencing, timing, counting, and arithmetic to control, through digital or analog input/output modules, various types of machines or processes.
The digital computer which is used to perform the functions of a programmable controller is considered to be within this scope. Excluded are drum and other similar mechanical sequencing controllers.” Control engineering has evolved over time .in past humans was the main method for controlling system .More recently electricity has been used of control and early electrical control was based on relays .These relays allow power to be switched on and off without a mechanical switch.Controls. PLCs have been gaining popularity on the factory floor and will probably remain predominant for some time to come.
• Most of this is because of the advantages they offer. Flexible and can be reapplied to control other systems quickly and easily.
• Computational abilities allow more sophisticated control.
• Trouble shooting aids make programming easier and reduce downtime.
In the 1960s and 1970s, industry was beginning to see the need for automation. Industry saw the need to improve quality and increase productivity. Flexibility had also become a major concern. Industry needed to be able to change processes quickly to meet the needs of the consumer.
• There was always a huge wiring panel to control the system.
• Inside the panel there were masses of electromechanical relays.
• These relays were all hardwired together to make the system work.
• Hardwiring means that an electrician had to install wires between the connections of the relays.
• An engineer would design the logic of the system and electricians would be given a blueprint of the logic and would have to wire the components together.
• That the engineer made a few small errors in his/her design.
• That the electrician may have made a few errors in wiring the system.
• That there are few bad components in the system.
• The only way to see everything was correct was to run the system.
• Troubleshooting was done by running the actual system. This was a very time-consuming process.
• No product could be manufactured while the wiring was being changed and system had to be disabled for wiring changes. This means that all the production personnel associated with that production line were without work until the system was repaired.
• The control system was based on mechanical relays.Mechanical devices are usually the weakest links in the systems. Mechanical devices have moving parts
• that can wear out. If one relay failed, the electrician might have to troubleshoot the whole system again. The system was down again until the problem was found and corrected.
• Another problem with hardwired logic is that if a change must be made, the system must be shutdown and the panel rewired. If a company decided to change the sequence of operations (even a minor change), it was a major expense and loss of production time while the system was not producing parts.
NEED FOR PLC
• Due to the disadvantages of the hardwired control panels industry saw the need to replace them and introduce PLCs.
• Increased competition to manufacturers to improve both quality and Productivity.
• Flexibility, rapid changeover and reduced downtime became important.
• Industry realized that a computer could be used for logic instead of hardwired relays. Computer could take the place of huge, costly, inflexible, hardwired control panels.
• If changes in the system logic or sequence of operations were needed, the program of the computer could be changed instead of rewiring.
• Imagine eliminating all the downtime associated with wiring changes.
• Imagine being able to completely change how a system operated by simply changing the software in the computer.