PROCESS CONTROL

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PROCESS CONTROL AUTOMATION

• BY
• SOBUKOLA, O.P. (PhD)/KAJIHAUSA, O.E. (MRS)
• Department of Food Science Technology,
• University of Agriculture, PMB 2240, Abeokuta,
  Nigeria.
• sobukolaop_at_unaab.edu.ng

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Grading

• Continuous Assessment Test CAT - 20
• Examination - 70
• Attendance - 10
• Total - 100

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Course Outline

• Lecture 1- Introduction
• Lecture 2- Control Systems
• Lecture 3- Measuring and Detecting Elements
• Lecture 4- Control Actions
• Lecture 5- Frequency response Analyses
• Lecture 6- Computer-based Systems

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LECTURE ONE

• INTRODUCTION
• Automatic control has played a vital role in the
  advance of engineering and science. In addition
  to its extreme importance in space-vehicle
  systems, robotic systems and the like, automatic
  control has become an important and integral part
  of modern manufacturing and industrial processes.

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• - A process is the transformation of a set of
  inputs, which may be material, actions, methods
  and operations into desired outputs in the form
  of a product.
• - Control - means measurement of the performance
  of a process and the feedback required and
  corrective actions where necessary.
• - Automation Automation means reductions in the
  use of direct labour during food processing.

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• Advantages of Automation include
• Consistency and accuracy in the positioning of
  moving parts of an equipment.
• A more consistent product.
• The more economic use of existing plant by saving
  of fuel/and or electrical energy.
• The release of skilled personnel for other
  productive work .
• Reduction of physical effort with consequent
  reduction of fatigue and boredom
• Improved working conditions.

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• Limitations of automation
• Initial cost is high
• power fluctuations,
• Lack of skilled personnel etc.
• Basic steps in process control are
• Measurement of the process variable
• Evaluation and comparison with desired level and
  
• Control of the required level of the parameter
  involved

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LECTURE TWO

• Definition of some terms in process control
• Controller A device that measures a variable
  condition (Temperature, pressure, humidity,
  moisture content) like thermostats, humidistat or
  pressure controllers.
• Control system consist of controller,
  controlled device and source of energy or input.
• Controlled device it reacts to the signal
  received from a controller and varied the flow of
  the controlled agents. Valve, damper, electric
  relay or a motor driving a pump, fan etc.
• Control agents the medium being manipulated by
  the action of controlled device e.g. air or gas.

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• Controlled variables are system parameters
  which are under control e.g. Temperature,
  pressure, humidity etc.
• Manipulated variable is the quantity or
  condition that is varied by the controller so as
  to affect the value of the controlled variable.
• Plant This may be a piece of equipment or a set
  of machine parts functioning together, the
  purpose of which is to perform a particular
  operation.
• Disturbances A disturbance is a signal that
  tends to adversely affect the value of the output
  of a system.

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• CONTROL SYSTEMS
• Self controlled systems
• Pneumatic system
• Hydraulic system
• Electrical system
• Electronic System

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LECTURE THREE

• MEASURING AND DETECTING ELEMENTS (SENSORS)
• They are the main interfere between the control
  system and process. In food processing, they are
  required for incoming material selection
  material waste control process quality control
  packaging inspection equipment
  maintenance/failure prediction, environmental
  control.

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• Block diagram
• A control system consist of a number of
  components that perform certain factors which are
  represented by block diagram in control
  engineering.
• It is a pictorial representation of functions
  performed by each component and of the flow of
  signals.
• It depicts the interrelationships that exist
  among the various components.

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• Open loop control system Those systems in which
  the output has no effect on the control action.
  In other words, in an open loop control system
  the output is neither measured nor fed back for
  comparison with the input.
• Feedback/Closed loop system- The term closed-loop
  control always implies the use of feedback
  control action in order to reduce system error.

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LECTURE FOUR

• CONTROL ACTIONS
• The relationship between the deviation and the
  signal sent from the controller to the correcting
  unit determines the control action.
• Most control actions derive their names on the
  basis of mathematical or functional relationship
  between the output and the error.
• An automatic controller compares the actual value
  of the plant output with the reference input
  (desired value), determines the deviation, and
  produces a control signal that will reduce the
  deviation to zero or to a small value.
• The manner in which the automatic controller
  produces the control signal is called the control
  action.

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• Industrial controllers are usually classified
  according to their control actions
• Two step Action or on-off controllers
• Proportional Action
• Integral Control Action
• Proportional plus integral control Action
• Proportional plus derivative control Action
• Proportional plus Integral plus derivative
  control actions

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• Frequency response of controller
• A controller may be regarded as an amplifier.
  For sinusoidal input signals, a controller with
  proportional action only gives an output
  proportional to the input, but in phase
  opposition to it, whatever the frequency may be.

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LECTURE FIVE

• FREQUENCY RESPONSE ANALYSIS
• Frequency response Is the relationship between
  output signal and input signal when the
  sinusoidal input is a component or system is
  varied over a wide range of frequencies.
• When the plant and the controller are connected
  together to form a closed loop, we have a system
  similar to a voltage amplifier with feedback
  mechanism.

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• The input to the controller is a signal
  representing the output condition of the process
  and the output of the controller is fed into the
  process.
• The process may be broken down into a series of
  individual stages, called transfer stages and
  time lags due to the finite time taken for
  signals to travel from one point to another.
• As the frequency of the input signal is increased
  the angle of lag increases, the largest possible
  lag for a signal stage being 90o.
• The attenuation also increases as frequency is
  increased. Attenuation is the production of an
  output signal smaller than the corresponding
  input.

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• Frequency response of controller
• A controller may be regarded as an amplifier.
  For sinusoidal input signals, a controller with
  proportional action only gives an output
  proportional to the input, but in phase
  opposition to it, whatever the frequency may be.
• Transient response and stability
• It is time variation of the output signal when a
  specified step input signal or disturbance is
  applied. The transient response of a speed
  control system is illustrated by the shape of the
  speed/time graph immediately following the sudden
  application of load or a sudden change in the
  desired speed setting.

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LECTURE SIX

• Computer-based systems
• The increasingly widespread use of
  microprocessor-based process controllers over the
  last twenty years is due to their flexibility in
  operation, their ability to record (or log)
  data for subsequent calculations and the
  substantial reduction in their cost.
• Computers can not only be programmed to read data
  from sensors and send signals to process control
  devices, but they can also store and analyse data
  and be connected to printers, communications
  devices, other computers and controllers
  throughout a plant.
• They can also be easily reprogrammed by
  operators to accommodate new products or process
  changes.
• Examples of the different types of computer
  controlled systems are described below.

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• Programmable logic controllers (PLCs)
• A significant development in process control
  during the 1980s was the introduction of PLCs.
• They are based on microcomputers, and have the
  same functions as relays, but with vastly greater
  flexibility.
• Historically, they were first used to replace
  relays in simple repetitive applications, but the
  greater power was quickly used to develop other
  functions, including recipe storage, data
  transfer and communications with higher level
  computers.

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• Types of control systems
• The different combinations in which PLCs and
  larger computers can be linked together in an
  integrated control system can be described in
  three categories
• 1. dedicated systems
• 2. centralised systems
• 3. distributed systems.

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• Neural networks
• Where complex relationships exist between a
  measured variable and the process or product, it
  has not yet been possible to automate the
  process.
• Recent developments of expert systems or
  neural networks may have the potential to solve
  such problems.
• These are able to automatically deduce complex
  relationships and also to quickly learn from
  experience.