Group4

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Group 4

• Venumadhav Navuluri
• Gopinath Pochareddy
• Vandan Chennamadhavani
• Kishore Jeeligula

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Patents, Software and Hardware for PID Control

• An Overview and Analysis

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Overview

• PID stands for Proportional, Integral,
  derivative." These three terms describe the basic
  elements of a PID controller .
• In a typical PID controller these elements are
  driven by a combination of the system command and
  the feedback signal from the object that is being
  controlled

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Block Diagram for a Basic PID
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Patents

• Patented Tuning methods rely on identification of
  Plant dynamics.
• Non-excitation method denoted by NE.
• Excitation method denoted by E.

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Identification Methods for tuning

• Excitation type is used during plant setup and
  also to set initial parameters.
• Time- or frequency domain method.
• Non-Excitation type is used during normal
  operations.

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Identification Methods for tuning

• Time-domain Pseudorandom binary sequence
  applied in an open-loop fashion.
• Frequency domain Usually uses a relay like
  method,where plant undergoes self controlled
  oscillation.

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Tuning

• Tuning a controller involves setting the
  proportional, integral, and derivative values to
  get the best possible control for a particular
  process.
• You might see a need for a loop to be tuned if it
  responds slowly, or if it oscillates too much, or
  if it has a steady-state error and most
  definitely if its unstable.

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Tuning Methods Adopted

• Advacontrol Tuner,IMC Tune,Protuner32,
• The IMC or lambda tuning method is the most
  widely adopted tuning method in commercial PID
  software packages.
• A tuning method based on achieving smooth set
  point response - guarantees stability, robustness
  and no overshoot.

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Tuning Methods Adopted

• Most of these packages require a time-domain
  plant model before the controller can be
  designed.
• The widely adopted plant model is the first order
  with delay given by
• G(s) Ke-Ls/(1 Ts)
• K process gain, T process time constant
• L process dead time or transport delay.

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Benefits of Lambda Tuning

• The method provides smooth control over a large
  range.
• It allows coordinated tuning of cascaded control
  strategies, loops that are interactive and that
  require identical response times.
• The manual bump test identifies control element
  problems that will degrade control loop
  performance.

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Example of Lambda Tuning

• A process with a gain of 1, dead time of .2
  minutes and time constant of 10 minutes. The fast
  lambda tuning (lambda10 min) for this process
  yields
• Proportional Band 100 Integral 10 min/rep

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Results for lambda Tuning
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Results for Lambda Tuning

• The resulting set point and load responses are
  shown as green lines in the above figure.
• The setpoint response is smooth and does not
  overshoot. Neither does the response to a load
  upset.
• And the output to the controller is also smooth
  with no overshoot, ensuring long valve life.

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Software Packages

• PID tuning software combines various design
  methods within a single package.
• It allows a practitioner with control knowledge
  or plant information to tune a PID controller
  efficiently and optimally.
• IMCTune and CtrlLAB, are general control system
  softwares with good PID capabilities.

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Software Packages

• Packages can interface directly with generic
  data-acquisition hardware for online control,
  such as the LabVIEW PID Control Toolset.
• Microsoft Windows is currently the most supported
  platform.
• MATLAB is a popular software environment used in
  offline analysis.

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PID Hardware Types and Applications

• Although analog-interfaced PID controllers exist,
  commercial hardware modules are mainly digital.
• These modules run on a dedicated computer, which
  can implement features found in PID software
  packages.

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Tuning Methods in Hardware Modules

• The majority of hardware systems employ a
  time-domain tuning method, while a minority rely
  on frequency-domain relay experiments.
• Automated tuning is implemented through either
  tuning on-demand with upset or adaptive tuning.

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Tuning Methods in Hardware Modules

• Tuning-on-demand with upset is a self-tune,
• autotune, or pretune.
• It typically determines the PIDcontroller
  parameters by introducing a controlled
  perturbation in the process.
• It then uses measurements of the process
  response to calculate appropriate controller
  parameters.

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Tuning Methods in Hardware Modules

• Adaptive tuning is sometimes known as self-tune,
  autotune, or adaptive tune.
• A controller constantly monitors the process
  variable for oscillation around the setpoint.

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ABB controllers

• ABBs uses a formula-based tuning method, termed
  Easy-Tune.
• This controller approximates the process with a
  first-order plus delay model.
• For oscillatory processes, this provides two
  autotuning options, quarter-wave and minimal
  overshoot.

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ABBs Control Efficiency Monitor
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ABBs Control Efficiency Monitor

• This device measures six secondorder-
• like key-performance indicators
  
  
  
  
  
  independently to set PIDs for
  oscillatory processes.
• Although y1 0.9y2, the signal y1 is
  nevertheless monitored to determine
• t approach.

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Yokogawa Modules

• The module consists of two main parts, namely,
  the setpoint modifier and the setpoint selector.
• Delivers both a short rise time and low
  overshoot.
• The setpoint modifier first models the process
  and functions as an expert operator, bypassing
  PID control.

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Yokogawa Modules Operation

• Operates in 3-Modes
• Mode-1Designed for overshoot suppression when
  the process output approaches a new target
  setpoint by observing the rate of change.
• Mode- 2Ensures high stability at the setpoint
  while sacrificing response time to a setpoint
  change.

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Yokogawa Modules Operation

• Mode -3Provides a faster response to a setpoint
  or load change with a compromise in stability.

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Conclusion

• Many PID patents focus on automatic tuning for
  process control,starting from conventional or
  intelligent system identification.
• The system identification functionality is seen
  more in hardware modules.
• Software packages are mainly focused on offline
  design.

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Conclusion

• The major difficulty appears in delivering an
  optimal transient response.
• At present there exists no standardization of PID
  structures.
• Modularization around standard structures should
  help improve cost effectiveness of PID control
  and maintenance.
• Digital PIDs are widely used in consumer
  electronics
• and mechatronic systems