plc and automation for ece department students

plc and automation first unit

1. 191ECEM PLC and Automation UNIT I PROCESS CONTROL & AUTOMATION

2. Process control Introduction to Process Control Control is the organization of a function for a specific purpose. Control systems (which change with time) are information processing devices that receive information, act on it, and generate an output . These systems are integrated and, as such, require a systems approach Process control systems meet three main needs: (1) minimizing and regulating the influence of external disturbances, (2) guaranteeing a stable process, and (3) optimizing process performance.

3. Process control There are two categories of control systems: servomechanisms and regulators . Servomechanisms change an output variable; regulators hold an output variable constant even if the input variable changes. Typical servomechanisms are those used for missile guidance or steering. Most chemical or petroleum process control systems are regulators. A chemical application that resembles a servomechanism is a program-controlled batch process using a preset pattern.

4. Process Control Feed forward Process Disturbances Manipulated Variables Heat exchanger Flow rate and temperature of liquid entering tubes Steam pressure for shell side Drum boiler Steam flow and feedwater flow Feedwater flow Distillation column Feed flow rate and composition Reboiler steam pressure and reflux Continuous-flow stirred tank reactor Inlet concentration and temperature Product removal rate an

5. Servo mechanism Servomechanism Servomechanism is an automatic closed loop control system. A  servomechanism, sometimes shortened as servo, is used for error-sensing of negative feedback to correct the performance of a mechanism . A servo system primarily consists of three basic components - A controlled device. A output sensor.  A feedback system

6. Servo mechanism

7. Servo mechanism A servo motor is basically a DC motor along with some other special purpose components that are a DC motor, a potentiometer, gear arrangement and a intelligent circuitry . As we know, a small DC motor will rotate with high speed but the torque generated by its rotation will not be enough to move even a light load. At the initial position of servo motor shaft, the position of the potentiometer knob is such that there is no electrical signal generated at the output port of the potentiometer. This output port of the potentiometer is connected with one of the input terminals of the error detected amplifier.

8. Servo mechanism servomechanisms force the robot arm to follow a path from point A to point B. This is done by con- trolling the speed of motors driving the arm and the angles of the arm parts . The strategy for servomechanisms is similar to that for process-control systems, but the dynamic differences between regulation and tracking result in differences in design and operation of the control system.

9. CONTROL SYSTEM EVALUATION The variable used to measure the erformance of the control system is the error, e ( t ) , which is the difference between the constant setpoint or reference value, r, and the con- trolled variable, c ( t ). e(t ) = r - c(t ) Control System Objective In principle, the objective of a control system is to make the error in Equation (1) exactly zero, but the control system responds only to errors (i.e., when an error occurs, the control system takes action to drive it to zero). Conversely , if the error were zero and stayed zero, the control system would not be doing anything and would not be needed in the first place. Therefore , this objective can never be perfectly achieved, and there will always be some error . The question of evaluation becomes one of how large the error is and how it varies in time. A practical statement of control system objective is best represented by three requirements: The system should be stable. The system should provide the best possible steady-state regulation. The system should provide the best possible transient regulation

10. Stability

11. Steady-State Regulation The objective of the best possible steady-state regulation simply means that the steady- state error should be a minimum . Generally, when a control system is specified, there will be some allowable deviation, ±¢c , about the setpoint . This means that variations of the variable within this band are expected and acceptable. External influences that tend to cause drifts of the value beyond the allowable deviation are corrected by the control system. For example, a process-control technologist might be asked to design and implement a control system to regulate temperature at 150°C within ±2°C . This means the set- point is to be 150°C, but the temperature may be allowed to vary within the range of 148° to 152°C.

12. Transient Regulation What happens to the value of the controlled variable when some sudden transient event occurs that would otherwise cause a large variation? For example, the setpoint could change. Suppose the setpoint in the aforementioned temperature case were suddenly changed to 160°C. Transient regulation specifies how the control system reacts to bring the temperature to this new setpoint . Another type of transient influence is a sudden change of some other process vari able. The controlled variable depends on other process variables. If one of them suddenly changes value, the controlled variable may be driven to change also, so the control system acts to minimize the effect. This is called transient response. Evaluation Criteria The question of how well the control system is working is thus answered by (1) ensuring stability, (2) evaluating steady-state response, and (3) evaluating the response to setpoint changes and transient effects. There are many criteria for gauging the response. In general, the term tuning is used to indicate how a process-control loop is adjusted to provide the best control.

13. One of the measures of control system performance is how the system responds to changes of setpoint or a transient disturbance

14. In cyclic or underdamped response, the variable will exhibit oscillations about the reference value.

15. Analog Control True analog control exists when all variables in the system are analog representations of an- other variable. Figure shows a process in which a heater is used to control temperature in an oven. In this case, however, the heater output, Q, is an analog of the excitation volt- age, V Q , and thus heat can be varied continuously. Notice that every signal is an analog: V T is an analog of T; the error E is an analog of the difference between the reference, V ref , and the temperature voltage, V T . The reference voltage is simply the voltage that would result from measurement of the specified reference temperature, T ref .

16. Digital Control- Supervisory Control Figure shows how a supervisory computer would be connected to the analog heater control system of Figure(previous slide) Notice how the ADC and DAC provide interface between the analog signals and the computer.

17. Digital Control- Direct Digital control The ADC and DAC provide interface with the process measurement and control action. The computer inputs a digital representation of the temperature, N T , as an analog-to-digital conversion of the voltage, V T . Error detection and controller action are determined by software. The computer then pro-vides output directly to the heater via digital representation, N Q , which is converted to the excitation voltage, V Q , by the DAC.

18. Types of Automation :   Basically we have three types of automation namely are    Fixed Automation Programmable Automation Flexible Automation Now let’s understand all the automation-:    Fixed Automation –   Fixed automation is nothing but the sequence of various operations that remains fixed, and can’t be scheduled customized by the user this type of automation is mainly used in mechanical industry to carry out the desired job.  In short, we can say that fixed automation is “A sequence of operations fixed by the system configuration”. 

19. Programmable Automation –   Programmable automation can be used to change the sequence of any operation based on the requirements specified by the user. It has made it to the front end of the user interface by providing various operations to the user to edit the sequence as per the requirements.  In short, we can say that Programmable Automation is “Ability to change the sequence of operation”.    Flexible Automation –   The automation type which has the property of both the automation Fixed as well as the programmable this type of automation known as flexible automation. Flexible automation has the ability to produce a variety of sequences that are not just limited to one static type of automation.  In short Flexible automation can be defined as “Ability to produce variety of sequences”. 

20. Industrial Automation Systems

21. Elements of Industrial control

22. Sensor system Analog electronic signal conditioning followed by Digital processing Diagnostics/calibration/configuration Communication Signal protection and transmission

23. Actuator System Electronic signal processing Electrical power amplification Electro-hydraulic/pneumatic/mechanical Feedback control for precision Auxiliaries for lubrication/cooling/filtering Remote operation and safety (operating circuit breaker which is a powerful machine) Energy optimization

24. Automatic control loop Controls analog continuous process variables closed loop control Track/hold set point/ (follow the set point). The set point is not constant it should hold it) Reject disturbance Generic PID/special purpose Tunable Dedicated digital RTS (microprocessor based system) Comparatively inexpensive

25. Supervisory Controller operation Set point computation (Impact on energy, quality, production volume) Start up, shutdown, emergency operations Control reconfiguration/tuning Performance monitoring/diagnostics Operator interface Domain dependent (physical model based Hard/soft real time Expensive

26. The production control has the following jobs and characteristics Process scheduling Material handling Maintenance management Inventory management Quality management Resource optimization technology

27. The production control has the following jobs and characteristics Process scheduling Material handling Maintenance management Inventory management Quality management Resource optimization technology

28. Effects of modern developments in automation on global competitiveness Automation – the key to competitiveness, growth AND jobs Technology always brings change and often replaces tasks, but over the long-term it creates jobs through growth and the new skills needed.  Steve Brambley from GAMBICA , the Trade Association for Instrumentation, Control, Automation and Laboratory Technology in the UK , shares his thoughts on negative headlines and why automation investment is creating jobs in the sector

29. Automation technology Throughout history, people have expressed concern about technology replacing jobs, from the early days of mechanisation in weaving and agriculture, through to office computers and automated factories . It is true that some tasks are automated and also true that some jobs are displaced, no disagreement there. However , in every wave of technological development, there has never been a large-scale increase in unemployment. Following a literature review of over 80 studies in this field, we have concluded that the net effect over time is that more jobs are created by technology than displaced – managed properly, the concern is not thousands of people out of work, but how best to reskill and re-deploy those affected.

30. Industrial digitalisation The UK is in a strong position to be at the forefront of industrial digitalisation , variously known as Industry 4.0, smart manufacturing or Internet of Things amongst other names . The vision is for manufacturers to benefit from production techniques that enable low-cost small batch sizes, localised manufacturing and mass customisation . To make this a reality, we need to encourage a business culture change – to get industry and government partnering in long-term, strategic thinking around investment and growth.

31. Productivity & growth Repeatability and accuracy are areas where technology helps to reduce errors and waste. Real-time control helps processes to use less energy and create less pollution. These are all benefits that contribute to productivity and growth, not downsizing. Further , many UK jobs have been and continue to be safeguarded by automation, especially where competition between sites in multi-national companies means that productivity is used as a measure for considering the next country to make an investment in. At a broader, national level, growth of jobs in the manufacturing sector leads to increased employment in the supply chain too. Indirectly, this will also boost service providers, from logistics, IT and payroll to hotels, taxis and caterers. The danger is that scaremongering headlines create a false narrative on the impact of automation on jobs. Such a misunderstanding of the bigger picture could be a barrier to the UK taking leadership in the new industrial revolution.