Introduction to LabVIEW for Scientists and Engineers

1
Introduction to LabVIEWfor Scientistsand
Engineers

• UTSI Short Course
• Tullahoma, TN
• November 18 - 20, 2002
• Brad Winkleman, Ph.D.

2
Course Goals

• Be able to construct simple LabVIEW programs
• Acquire data with a LabVIEW program
• Know how to continue after the course.

3
Not Course Goals

• To become an expert LabVIEW programmer
• To become a large project programmer
• Computer science fundamentals

4
What is LabVIEW?

• National Instruments Software Product
• Software or Program Development Environment
• Differences
• Graphical or Icon Based
• Dataflow

5
Why LabVIEW?

• Things are easier
• Development time is shorter (4 - 10)
• Modifications are easier
• Debugging done interactively
• Things are better
• Professional attributes
• High performance functions
• Lower Costs
• A Standard

6
LabVIEW History

• LabVIEW 1 - 1985 Macintosh only
• LabVIEW 2 - Compiled still Macintosh only
• LabVIEW 3 - The Leap - forward and backward
• LabVIEW 4 - Undoable
• LabVIEW 5 Network
• LabVIEW 6i Internet and Events

7
LabVIEW Uses

• Data Acquisition
• Experiment Control
• Process Control
• Data Reduction
• Data Presentation
• Modeling
• Calculation
• Simulation
• Internet and Intranet Communications
• General Tasks (file manipulations, data
  translation, plotting, etc)

8
Examples
9
Crucial LabVIEW Philosophy

• LabVIEW is the tool to solve your problems (not a
  LabVIEW standalone application).

10
Some Preliminaries

• A LabVIEW Program is called a Virtual Instrument
  or VI
• A VI is composed of two main parts
• The Front Panel
• The Block Diagram
• Viewing, Editing, and Running from same
  environment
• Final VI can be separated from LabVIEW, if
  necessary.

11
The Beginning - The Front Panel

• The Front Panel is the User Interface to
  operating the LabVIEW Virtual Instrument
• The Front Panel contains Control and Indicator
  icons
• Program Inputs are via the Controls on the Front
  Panel
• Results appear in Front Panel Indicators
• VI is controlled from the Toolbar

12
A Simple Front Panel
13
Exercise - Create A Simple Front Panel

• Open LabVIEW
• New VI
• Controls Palette
• Add Digital Control
• Save as Simple Front Panel.vi

14
Exercise - More Complex Front Panel

• Experiment with Controls Palette
• Add more controls
• Save as Complex Front Panel.vi

15
A Simple Block Diagram

• Example of the G Language

Control Survey Continued
16
Terminals

• Terminals come in many different types
• Shape, Color, Text tell type of terminal, I/O
• Common types
• Numeric - SGL, DBL, EXT
• Text
• Boolean
• Type determined by Front Panel Object

17
Wires

• Wires also come in many different types
• Shape, Color, Text tell type of terminal
• Common types
• Numeric - SGL, DBL, EXT
• Text
• Boolean
• Type determined by connections

18
Making Connections

• Wires go from output to input
• No Loops
• Bad Wire shows as dotted
• Wires can follow any path that is convenient

19
Exercise Create A Simple Block Diagram

• First must have an appropriate Front Panel

20
Exercise Create A Simple Block Diagram

• Open Diagram
• Use Function Palette - Add Node
• Connect with Wiring Tool
• Save as Adder.vi

21
Exercise - Running the Adder

• Change input values with Operate tool
• Click Run Arrow
• Result Indicator is Updated
• Continuous Run
• Generally not used
• Useful for special situations

22
Dataflow in Action
23
Data Dependencies Determine Execution Order

• No Dependency - No Defined Execution Order
• Light Bulb in Tool Bar of Block Diagram Shows the
  Data Flow

24
Dependency Determined by Connections

• Path of wire irrelevant
• Can take many complicated routes

25
Editing in LabVIEW
Text
Operate
Scroll Window
Position/Size/Select
Shortcut
Wire
Get Color
Breakpoint
Probe
Set Color
26
Exercise - Editing

• Change Position, Size, etc. of Front Panel
  Objects
• Change Position of Block Diagram Objects

27
Relation Between Front Panel and Block Diagram

• Front - User Interface
• Block Diagram - Relationships
• Essentially Independent With Following Exceptions
• All Controls/Indicators on Front Panel are on
  Block Diagram as Terminals
• Only Controls/Indicators on Front Panel are on
  Block Diagram as Terminals
• Initial Placement of Terminals is related to
  location of Front Panel Object

28
Review of Survey

• Virtual Instruments
• Front Panels
• Block Diagrams

29
Modifying Front Panel Objects

• Easy
• No Change required in Block Diagram
• Enhances Interface
• Requires LabVIEW not Application

30
Exercise - Modifying Front Panel Objects

• Replace controls and indicator as desired
• Block diagram unchanged
• Program has more functionality

31
Control Survey

• Controls Indicators
• Numeric
• Important category
• Numerical Information
• Digital Displays, Thermometers, Sliders, Meters,
  Etc.
• Boolean
• True / False data
• Toggles, Pushbuttons, LED, On/Off Indicators

32
Control Survey Continued

• String Path
• Text controls
• Filename controls
• Array Cluster
• Not really controls but modifiers
• Array - identical controls
• Clusters - disparate collections

33
Control Survey Continued

• List Table
• Fairly Specialized
• Allow selection or displays lists
• Graph
• Very important
• Charts - accumulate like strip charts
• Graphs - waveform data
• Specialized Graphs

34
Control Survey Continued

• Ring Enum
• Special Category
• Useful for selecting Options
• I/O
• New Category
• Used to identify I/O channels by logical name
• RefNum
• Rarely Needed
• Intra - VI communication control

35
Control Survey Continued

• Dialog
• Dialog Boxes
• Classic
• LabVIEW 5.0 Controls
• Similar Functionality
• Different Appearance
• ActiveX
• Stuff for ActiveX Components

36
Control Survey Continued

• Decorations
• Aesthetics
• Boxes, Arrows, Lines
• No Functionality
• Select a Control and User Control
• Customized Control Interface
• Browse the disk
• Include on the controls palette

37
Exercise - Familiarization With Controls Palette
38
How to Use Controls

• Most controls are not necessary
• Controls are used to make Front Panel intuitive

39
Intuitive Front Panel
40
Non-Intuitive Front Panel
41
LabVIEW Conventional

• At the User / Program level LabVIEW is a high
  level graphical language with dataflow
  programming
• Underneath LabVIEW is built conventionally as the
  previous panel highlights
• C, C are its underpinnings
• LabVIEW does use various techniques such as
  multithreading to improve performance

42
Block Diagram Control Structures

• Continuous Run of Adder
• Gave live updates
• Controlled by Toolbar
• Clumsy
• Like other languages G has Control Structures
  to simplify programming
• While
• For - Next
• Case
• Sequence (Special Control Structure)

43
While Loops

• Diagram inside repetitively executed
• Loop Index terminal begins at zero and increments
  once each execution
• By default Loop terminates when control terminal
  receives a False
• If needed loop can be made to stop on True

44
Exercise - Looping AdderFront Panel

• Add Toggle Switch to Front Panel

45
Exercise - Looping AdderBlock Diagram

• Surround everything with a Loop structure
• Connect Run switch to loop terminal
• Run from Front Panel by flipping toggle switch
  and clicking the Run arrow.
• No need for Continuous Run arrow

46
Waveform Charts

• Chart Display in Looping Adder acts oddly
• Display updates very fast
• Control changes not easily seen
• Display is updating asynchronously
• Not all results displayed
• Default mode of displays
• Display attributes can be modified to force
  synchronous update

47
For Loops

• Diagram inside repetitively executed
• Loop Index terminal begins at zero and increments
  once each execution
• Executes the number of times wired to the Count
  terminal

48
Exercise - For Loop AdderFront Panel

• Add Digital Control to Front Panel

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Exercise - For Loop AdderBlock Diagram

• Replace While with a For structure
• Connect Digital Control to Count terminal
• Run from Front Panel by setting iterations and
  clicking the Run arrow.

50
The Nature of Loops

• Terminals can be inside or outside loop
• Only terminals inside loop are dynamic
• Outside terminals read once or written once
• Loop has no memory of intermediate results
• Inputs are the same each time through loop
• Output is the last value calculated

51
Case Structure

• Standard Case Structure found in C
• Case Structure has multiple subdiagrams
• The selector terminal determines which subdiagram
  is executed

52
Exercise - CalculatorBlock Diagram

• Add Case Structure around Add Node
• Create multiple cases and subdiagrams

53
Exercise - CalculatorFront Panel

• Create a selector for the operation
• Ring and Enumerated Controls are excellent for
  this
• Save as Looping Calculator.vi

54
Sequence Structure - A Special Need

• Control structure unique to LabVIEW dataflow
  programming
• In dataflow programs data dependencies determine
  execution order
• Some operations have no data dependency but
  require a defined order
• Sequence structures provide a forced order to a
  series of operations

55
Sequence Structure

• Has multiple subdiagrams
• Subdiagrams are executed in sequence - first to
  last
• Structure has no operational controls

56
Sequence Structure Uses

• File I/O
• Data Acquisition
• Initialization
• Termination

57
Exercise - Calculator with Save

• Create Sequence
• Add File I/O operations
• Create Local Variables
• Connect Frames
• Connect Data to write

58
Exercise - Calculator with Save - Name
59
Exercise - Calculator with Save - Create
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Exercise - Calculator with Save - Write
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Exercise - Calculator with Save - Close
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Sequences are BAD

• Hide program elements
• Prevent optimal scheduling
• Can lower performance
• Prevent Parallelism
• Sequence local variables difficult to use
• Dont Use Sequences

63
Exercise - Calc with Save (No-Sequence)

• Use data dependencies to determine order
• Create dependencies if they do not exist
• Single frame Sequence structure is useful

64
Exercise - Calc with Save (No-Sequence - Another
Way)

• Use data dependencies to determine order
• Create dependencies if they do not exist

65
Event Programming

• Similar to Case structure
• Event Structure has multiple subdiagrams
• Execution determined by events
• Waits for an event to occur
• Event programming is different than dataflow
  programming

66
Events

• Front Panel Activity
• Key Down
• Key Up
• Key Repeat
• Mouse Down
• Mouse Up
• Value Changed
• Timeout event
• Application and VI
• Menu Selection
• Exiting
• Panel Closing
• Events must be configured

67
Event Cautions

• Programmatic actions do not generate events
• More than one Event structure in a loop can cause
  problems
• Latched Boolean controls are delayed
• Event structure waits for an event (possibly
  forever)

68
Exercise Looping Calculator with Event
Controlled Save

• Previous Calculator only saved the last result
• Need a Calculator that saves intermediate results
• Add Save Control
• Add Event Structure
• Configure Events

69
Exercise Looping Calculator with Controlled
Save without Events
?

• Events are not necessary for previous example
• How else can a controlled save be implemented?

70
Tunnels

• Tunnels are the nodes at the border of control
  structures
• Data passes into and out of a structure through
  the Tunnel
• A white Tunnel on a case structure means not all
  cases are wired to tunnel

71
Recycling Data in Loops

• Cannot connect a loop output to a loop input
• Violation of no cycle
• Frequently needed
• Averaging
• Accumulation
• Finite Differencing
• Control
• Creating Series

72
Shift Registers

• Shift Registers allow recycling of data in loops
• Created by popping - up on the border
• Single or Multi-element
• Uninitialized or initialized

73
Exercise - Differencing Calculator
74
LabVIEW Arrays

• Basically the same as in other languages
• Normally LabVIEW and Arrays mix well
• Complicated indexing schemes can be tedious

75
Front Panel Creation of Arrays

• Front panel array control is like a container
• Putting a control in an array control creates an
  array of controls
• Pop-menu adds dimensions
• Array index order - row, column, and so forth

76
Exercise - Array Creation

• Digital Inputs
• Change to Outputs
• Expand View
• Add Dimension
• Expand View
• Other Arrays
• Try to make an array of arrays

77
Polymorphism

• LabVIEW VIs are generally polymorphic - they
  accept various types of inputs
• Very powerful for array manipulation
• Also handle different numeric types (integer,
  single, double)
• Concept extendable to non-numeric data types

78
Autoindexing

• Loop structures can autoindex at a tunnel
• Input
• New element is used for each execution of loop
• Array size sets Count terminal on For Loop
• Output
• Elements are collected into an array
• Arrays become one higher dimension
• Autoindexing can be disabled
• Very useful feature

79
Exercise - Autoindexing

• Create Front Panel
• Array Inputs
• Array Output

80
Exercise - Autoindexing

• Place Add Node
• Surround with For Loop
• Connect terminals
• No need to wire Count terminal

81
Formula Node

• Not a Control Structure
• Easy formula calculations
• C-like syntax

82
Exercise Calc with Formula Node

• Create a calculating VI that uses the Formula Node

83
Clusters

• Agglomerations of data
• Minimize wiring
• Useful for connections to SubVIs
• Polymorphism adds to functionality
• Like structures in C
• LabVIEW has some predefined Clusters

84
Global and Local Variables

• Dataflow constructs can be a nuisance at times
• Data must flow for point to point
• Wires must be connected to define the flow
• Unwieldy and complicated diagrams can result
• Global and Local Variables allow the
  communication of data between points without
  wires.
• Overall it is best to avoid their use.

85
SubVI

• Any VI can be come a SubVI in another VI
• VIs and SubVIs are essentially the same
• Any collection of VIs in a diagram can be grouped
  into a SubVI
• Use SubVIs to
• Make diagrams more readable
• Produce modular code
• Simplify programming chores

86
Exercise - Creating a SubVI

• Open Looping Calculator
• Edit VI options
• Set Connection Pane
• Create Icon
• Embed SubVI in a main VI

87
Survey of Functions Palette

• VIs are found on the Function Palette
• VIs are grouped logically (more or less)
• The Function Palette changes
• Installed Options
• New versions (way too often)
• Due to the numerous functions a complete review
  is not possible in this course but should be
  undertaken by the student.

88
Function Survey Using Help Utilities

• Contextual Help
• LabVIEW Help
• VI and Function Reference
• LabVIEW VIs and Functions

89
The End

• Basic Concepts have been presented
• Controls and Functions have been reviewed
• Rest of LabVIEW is
• Gaining familiarity with VIs
• Developing dataflow skill (NI offers courses)
• Details, Details, Details