PLCs and Programming Options

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PLCs and Programming Options
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New Check goal is to maintain upstream water level
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Radial Gate
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Goal is to maintain water level. In order to
change the water level, we need to adjust the
flow through the gate.
How much should you adjust the flow? How
often? How long will it take the canal to
respond? What happens if something else causes
the flow to change?
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Algorithm

• For a given water level or flow error in the
  canal, how much should you adjust the gate
  opening?

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Different Algorithms

• Calculate the required gate move based upon the
  desired change in flow. Commonly called flow
  control. The challenge with this method is
  anticipating the desired/required flow change.

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More Algorithms

• Observe a water level at some location downstream
  from the gate, if the water level gets too low,
  open the gate, if it gets too high, close the
  gate. This method requires a way to adjust the
  flow going into the system. This method is
  commonly called downstream control. The
  challenge is determining how much should the gate
  be opened or closed and adjusting the flow into
  the canal.

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More Algorithms

• Observe the upstream water level and if it is too
  high, open the gate. If it is too low close the
  gate. Commonly called upstream control. This
  approach passes errors downstream. Again, how
  much should the gate be opened or closed?

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Module 6 of our algorithm flow chart
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New Check goal is to maintain upstream water level
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Hardware Selection

• Off the shelf vs Custom
• Data logger
• PLC
• RTU

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PCs vs. PLCs

• PCs
• Mac PCs
• Windows PCs
• Linux PCs

• PLC/RTU
• Perhaps 100s of different platforms.

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PCs vs. PLCs

• PCs
• C, C,
• Office Suite
• Excel
• Java

• PLC/RTU
• Each manufacturer has their own programming
  language.
• Sometimes the same manufacturer may have
  different languages for different PLCs.

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PCs vs. PLCsPortability!

• PCs
• If you have a fairly current operating system,
  you can run most windows applications on any PC
  made by any manufacturer.
• Kind of the same for Macs and Linux based PCs

• PLC/RTU
• Youve got to be kidding!
• Maybe within a manufacturer.
• Almost non-existent otherwise

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RTUs vs PLCs
High-end PLC
RTU

• Programmable Logic
• I/O (Inputs/Outputs)
• Serial Communications
• Network Communications
• Integrated Radios/Modems
• Alarm Dialer
• Data Logger
• Internet Services
• Extended Temperature

• Programmable Logic
• I/O (Inputs/Outputs)
• Serial Communications (limited)
• Network Communications

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RTUs
Sixnet VersaTRAK
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RTU or PLC

• RTU Remote Terminal Unit
• PLC Programmable Logic Controller

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PLCs
Modicon - Momentum
Siemens S7 series
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Programming Languages

• Basic
• Ladder-logic type
• Most are not portable between hardware
  manufactures
• Industry Standard

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International Standard IEC 61131

• The International Standard IEC 61131 applies to
  programmable controllers (PLC) and their
  associated peripherals such as programming and
  debugging tools (PADTs), Human-machine interfaces
  (HMIs), etc. which have as their intended use the
  control and command of machines and industrial
  processes.
• PLCOpen.org

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IEC61131 Concept

• IEC 61131-3, the only global standard for
  industrial control programming. It harmonizes the
  way people design and operate industrial controls
  by standardizing the programming interface.
• A standard programming interface allows people
  with different backgrounds and skills to create
  different elements of a program during different
  stages of the software lifecycle specification,
  design, implementation, testing, installation and
  maintenance. Yet all pieces adhere to a common
  structure and work together harmoniously.

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IEC61131 Concept continued

• The standard includes the definition of the
  Sequential Function Chart (SFC) language, used to
  structure the internal organization of a program,
  and four inter-operable programming languages
  Instruction List (IL), Ladder Diagram (LD),
  Function Block Diagram (FBD) and Structured Text
  (ST). Via decomposition into logical elements,
  modularization and modern software techniques,
  each program is structured, increasing its
  re-usability, reducing errors and increasing
  programming and user efficiency.

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IEC Programming Environments

• Many of them offer
• graphical programming screens
• support for multiple windows
• mouse operation
• pull-down menus
• built-in hypertext help function
• software verification during design

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icstriplex - ISaGRAF

• Sequential Function Chart
• Function Block Diagram
• Ladder Diagram
• Structured Text
• Instruction List
• Flow Chart not included in all implementations
  of the IEC61131 standard

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The IEC 61131-3 Programming Languages
Instruction List Structured Text
Function Block Diagram Ladder Diagram
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Language Selection Guidelines

• Where are you starting your programming?
• From flow charts
• Who needs to understand the program?
• What languages can they at least somewhat
  understand?
• Who would make changes to the program?
• Who will be doing quality control and what
  languages are they familiar with?

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DU 6.77(KP(FE1-FE2)(KIFE1)) /
GW(ZP/ZG)SQRT(Ydif) (feet)
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Upstream Control Flow Chart
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Software Development Cycle

• Design
• /
• Development
• /
• Installation
• /
• Maintenance..

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software development cycle...

• enhancements..
• .. new requirements ...
• . new functionality .
• . new wishes ...
• the never ending story of software

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Quality Control

• How can you determine if the program follows the
  flow chart?
• If the program does not work correctly, is the
  problem the control logic (algorithm) or the
  programming?

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Software Development/Quality Control

• Testing in the office
• Software Simulator mode
• Model Simulator