Control,Instrumentation,and Design

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Control,Instrumentation,and Design

• Presented
• by
• Pavan Kumar Amirineni
• Ravi Kanth Mukkala
• Kalyan Velicheti
• Brahmaiah Chowdhary
• Devendar Gandra

2
Presentation outline

• Introduction
• Control system architecture
• Digital control
• Signal classification in control systems
• Feedforward control
• Instrumentation and design

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Introduction.

• Controller
• It is a functional unit which makes system to
  respond in a desired manner.
• Types of controllers
• Analog controllers
• Digital controllers

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Analog controllers

• How analog controlling is done?
• On/Off switches controller acts like a
  conventional switch
• PID actions
• Lead and lag compensation networks

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Analog controllers contd..

• Limitations
• Cost factor
• Noisy
• Complex circuitry
• Reliability
• Adaptability
• Accuracy
• Data storage
• Linear assumptions

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Control system architecture

Ref signal
O/P signal
Components of a typical analog system
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Architecture contd..

• Signal conditioning block
• The main function of signal condition block is to
  suppress the unwanted noise present in the signal
  and reduce the error
• Methods amplifying, modulation and filtering
• Lock in amplifiers, charge amplifiers, power
  amplifiers, linear amplifiers, tracking filters,
  low pass and high pass filters etc are present in
  SCB
• Actuators
• Actuator actuates signals to the plant
• Dc motors, stepper motors, relays and valves

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contd

• Sensors
• Sensors are used for measuring process response
• Ex Thermocouples, potentiometers, differential
  transformers
• Additional components
• Power supplies
• surge protection units

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Digital Control

• In digital control processing has to be
  synchronized with plant operation and actuation
  requirements.
• Digital control computers consists of
• Processor
• Memory
• Input/output devices
• Digital control systems make use of digital
  instruments and additional processors for
  actuating , signal-conditioning, or measuring
  functions as well.

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Contd

• For example
• Stepper motor that responds with incremental
  motion
• steps when driven by pulse signals can be
  considered
• a digital actuator.
• A two position solenoid is a digital (binary)
  actuator.

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Block diagram of direct digital control system
Ref signal
O/P signal
DAC
plant
Drive system
ADC
address
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Description

• Analog measurements and reference signals have to
  be sampled and encoded prior to digital
  processing with in the controller.
• The drive system of a plant typically takes in
  analog signals.
• If more than one output signal is measured , each
  signal will have to be conditioned and processed
  separately.
• For complex processes with a large number of
  input/output variables and with various operating
  requirements, direct digital control is difficult
  to implement.

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Advantages

• Less susceptible to noise or parameter variation
  in instrumentation .
• Very high accuracy and speed.
• Repetitive tasks can be handled well.
• Complex control laws and signal conditioning
  methods can be programmed.
• Large amounts of data can be stored .

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Advantages contd

• Data can be stored or maintained for longer
  periods .
• Fast data transmission is possible over long
  distances.
• Easy and fast data retrieval capabilities.
• Uses low operational voltages.
• Low overall cost.

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Signal classification

• A digital control system can be loosely
  interpreted as one that uses a digital computer
  as a controller.
• Analog signals are continuous in time. They are
  represented as functions of the continuous time
  variable.
• Sampled data are pulse amplitude-modulated
  signals. A pulse amplitude-modulated signal is
  generated through a sample and hold operation.

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Signal classification contd.

• An important advantage of sampling is that
  expensive equipment can be shared among many
  signals.
• Sampled data consist of sequence of numbers.
• Digital data are coded numerical data. The code
  itself determines the actual value of a
  particular unit of digital information.

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Identifying control system types
Signal category Description
Analog signals Sampled data Digital data continuous in time. Pulse amplitude-modulated signals. Information carried by pulse amplitude. Coded numerical data. Typically generated by digital processors, digital transducers and counters.
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Significance of the sampling period

• Sampling period has to be sufficiently large so
  that required processing and data transfer can be
  done during that time for each control step.
• On the other hand, sampling period should be
  small enough to meet control band-width and
  process dynamic requirements.
• Shannons sampling theorem states that in a
  sampled signal, the Nyquist frequency fc , is
  given by half the sampling rate.
• fc 1/(2?T)

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Feedforward Control

• Def- Feedforward control system is defined as
  the process variables are measured, and
  anticipated disturbances are compensated for
  without waiting for changes in the controlled
  variable to be visible.
• Feedforward control suits better for tracking
  rapid changes in the reference.

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Feedforward Vs Feedback control systems

• In feedback control unknown outputs are measured
  and compared with known inputs to generate
  control signal.
• In feedforward control, unknown inputs are
  measured and that information along with desired
  inputs is used to generate control signals that
  can reduce errors due to these unknown inputs or
  variations in them.

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A Feedback Loop That Uses Feedforward Control

• 
  
  Disturbance input
• Ref
  
  
• I/P
  
  O/P

Measurment For Feed forward
Controller
Plant
Measurment For Feedback
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A Natural Gas Home Heating System
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Block Diagram Representation

• w1
  w2 w3
• Temp set point
  
  room temp
• I/P
  
  O/P

Controller
Furnace
Sensor-Transducer
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Contd

• W1 Water flow rate.
• W2 Temperature of cold water into the furnace.
• W3Temperature outside room temperature.

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Advantages of feedforward control

• Feedforward control signal can be introduced
  gradually to improve existing controller.
• Improves rapid reference tracking

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Instrumentation and Design

• Basic constituents of a control system
• Plant
• Signal measurement
• Drive system
• Signal Conditioning
• Controller
• Instrumentation, means identification of various
  instruments or hardware components with respect
  to their functions, operation, and interaction
  with each other and the proper selection and
  interfacing of these components for a given
  application.

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Design

• Design is the process of
• Selecting suitable equipment to accomplish
  various functions in the control system.
• Developing the system architecture.
• Matching Interfacing these devices.
• Selecting the parameter values, depending on the
  system characteristics to achieve desired
  objectives.
• Identification of key design parameters, modeling
  of various components, and analysis are often
  useful in the design process.

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Future Discussions

• Sensors and actuators
• Analog and digital devices
• Applications such as automated manufacturing and
  robotics, transit vehicles
• Dynamic testing and process control

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Questions
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• Thank you