TOPICS
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Quiz
Which types of folders are available
in a LabVIEW Project?
a)
b)
c)
d)
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Virtual folder
Logical folder
Auto-updating folder
Auto-populating folder
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Quiz Answer
Which types of folders are available
in a LabVIEW Project?
a)
b)
c)
d)
2
Virtual folder
Logical folder
Auto-updating folder
Auto-populating folder
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Quiz
Match the data types with wires that represent
them on the block diagram.
a)
b)
c)
d)
3
String
Boolean
Integer Numeric
Floating-Point Numeric
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Quiz Answer
Match the data types with wires that represent
them on the block diagram.
a)
b)
c)
d)
4
String
Boolean
Integer Numeric
Floating-Point
Numeric
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Quiz
What is the value in XOR Result after the
following code has executed?
a)
b)
c)
d)
0
1
True
False
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Quiz Answer
What is the value in XOR Result after the
following code has executed?
a)
b)
c)
d)
0
1
True
False
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Quiz
In the following VI, what is the execution order of
functions?
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Quiz Answer
In the following VI, what is the execution order of
functions?
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Implementing a VI
TOPICS
A. Designing Controls and
Indicators
B. LabVIEW Data Types
C. While Loop
D. For Loop
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E.
F.
G.
H.
Timing a VI
Data Feedback in Loops
Case Structure
Disable Structures
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A. Designing Controls
and Indicators
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Labels & Options
Make sure to label controls and indicators clearly
and set a default value if necessary.
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B. LabVIEW Data Types
Shortcut Menu and Properties Dialog Box
Numeric Types
Boolean Types
String Types
Enums and Other Types
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LabVIEW Data Types
Terminals visually communicate information about
the data type represented.
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Shortcut Menus
• All LabVIEW objects
have associated
shortcut menus.
• Use shortcut menu
items to change the
look or behavior of
objects.
• To access the shortcut
menu, right-click the
object.
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Properties Dialog Box
• All LabVIEW objects
have properties.
• To access properties,
right-click the object
and select Properties.
• Property options are
similar to shortcut
menu options.
• Select multiple objects
to simultaneously
configure their
common properties.
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Numerics
Various data type
representations:
• Floating-point
• Unsigned integers
• Signed integers
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Numeric Conversion
Coercion Dot
• Coercion dots indicate that
LabVIEW converted the value
passed into a node to a different
representation.
− Occurs when a node expects an input
with a different representation.
• LabVIEW chooses the
representation that uses more bits.
• Avoid coercion by
programmatically converting
to a matching data type.
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Booleans
• Behavior of Boolean
controls is specified by
the mechanical action.
• Boolean have only
TRUE/FALSE values.
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Mechanical Action of Booleans
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Mechanical Action of Booleans
Use the Properties»Operations tab of a Boolean
control to learn about the different switch and latch
actions.
DEMONSTRATION
Strings
• A string is a sequence of
ASCII characters.
• Strings have various
display styles.
− Backslash codes
− Password
− Hex
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Enums
• Enums give users
a list of items from
which to select.
• Each item represents
a pair of values.
− String
− Unsigned integer
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Other Data Types
Refer to LabVIEW Help for complete list of terminal
symbols for different types of controls and indicators.
• Dynamic
− Stores the information generated or acquired by an
Express VI.
• Path
− Stores the location of a file or directory using the
standard syntax for the platform you are using.
• Waveform
− Carries the samples, start time, and dt of a waveform.
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Searching Help for Data Types
Use LabVIEW Help to learn about LabVIEW data
types.
DEMONSTRATION
C. While Loop
Iteration and Conditional Terminals
Tunnels
Error Checking
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While Loop
Repeat (code);
Until Condition met;
End;
LabVIEW While Loop
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Flowchart
Pseudo Code
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While Loop
Iteration terminal
Conditional terminal
• Returns number of times
loop has executed.
• Is zero-indexed.
• Defines when the loop stops.
• Has two options:
− Stop if True
− Continue if True.
Iteration Terminal
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Conditional Terminal
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While Loop – Tunnels
• Tunnels transfer data into and out of structures.
• When a tunnel passes data into a loop, the loop
executes only after data arrive at the tunnel
(at all tunnels,
if there is more
than one).
• Data pass out of
a loop after the
loop terminates.
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While Loop – Error Checking and Error
Handling
Use an error cluster in a While Loop to stop the
While Loop if an error occurs.
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Auto Match VI
Use a While Loop and the iteration terminal and
pass data through a tunnel.
DEMONSTRATION
Auto Match VI
How many times is the Number of Iterations
indicator updated? Why?
DISCUSSION
D. For Loop
Conditional Terminals
Comparison with While Loop
Numeric Conversion for Count Terminal
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For Loop
N=100;
i=0;
Until i=N:
Repeat (code;i=i+1);
End;
LabVIEW For Loop
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Flowchart
Pseudo Code
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For Loop
• Create a For Loop the same way you create
a While Loop.
• You can replace a While Loop with a For Loop
by right-clicking the border of the While Loop
and selecting Replace with For Loop from the
shortcut menu.
• The value in the count terminal (an input
terminal) indicates how many times to repeat
the subdiagram in the For Loop.
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For Loop – Conditional Terminal
You can add a conditional terminal to configure a For
Loop to stop when a Boolean condition is true or an
error occurs.
This is similar
to a ‘break’
statement in
text-based
programming
languages.
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For Loop – Conditional Terminal
For Loops configured with a conditional terminal have:
• A red glyph next to the count terminal
• A conditional terminal in the lower right corner.
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For Loop / While Loop Comparison
For Loop
• Executes a set number of
times unless a conditional
terminal is added.
• Can execute zero times.
• Tunnels automatically
output an array of data.
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While Loop
• Stops executing only if the
value at the conditional
terminal meets the condition.
• Must execute at least once.
• Tunnels automatically output
the last value.
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For Loop – Numeric Conversion
• The number of iterations a For Loop executes must be
specified in non-negative integers.
• If you wire a double-precision, floating-point numeric
value to the count terminal, LabVIEW converts the
numeric value to a 32-bit signed integer.
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Group Exercise
Concept: While Loops versus For Loops
When to use a While Loop and when to use a For
Loop?
DISCUSSION
E. Timing a VI
Reasons To Use Timing
Wait Functions and Express VIs
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Timing a VI
Why do you need timing in a VI?
• To control the frequency at
which a loop executes.
• To provide the processor with
time to complete other tasks,
such as processing the user
interface or running other
applications.
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Wait Functions
A wait function inside a loop:
• Allows the VI to sleep for a set amount of time.
• Allows the processor to address other tasks
during the wait time.
• Uses the operating system millisecond clock.
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Elapsed Time Express VI
• Determines how much time elapses after some
point in your VI.
• Keeps track of time while
the VI continues to execute.
• Does not provide the processor
with time to complete other tasks.
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Wait Chart VI
Compare and contrast using a Wait function and
the Elapsed Time Express VI for software timing.
DEMONSTRATION
F. Data Feedback in Loops
Shift Registers
Initializing Shift Registers
Default for Unwired Values
Compound Shift Registers
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Data Feedback in Loops
• When programming with loops, you often need to
know the values of data from previous iterations of
the loop.
• Shift registers transfer values from one loop iteration
to the next.
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Shift Registers
• Right-click the border and select Add Shift
Register from the shortcut menu.
• Right part of shift register stores data on
completion of an iteration.
• Left part of shift
register provides
stored data at
the beginning
of the next
iteration.
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Initializing Shift Registers
Run once
Block Diagram
VI finishes
Run again
1st run
2nd run
Initialized
Shift
Register
Output = 5
Output = 5
Not
Initialized
Shift
Register
Output = 4
Output = 8
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Default Value if Unwired
Default values vary by data type:
Data Type
Default Value
Numeric
0
Boolean
FALSE
String
Empty
Uninitialized shift registers use default values for
the first run. At the beginning of next runs, they
remember the last value they stored.
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Multiple Previous Iterations
• Stacked shift registers remember values from
multiple previous iterations and carry those
values to the next iterations.
• Right-click the left shift register and select Add
Element from the shortcut menu to stack a shift
register.
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G. Case Structures
Parts of a Case Structure
Enum Case Structures
Error Case Structures
Input and Output Tunnels
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Case Structures
• Have two or more subdiagrams (cases).
• Use an input value to determine which case to
execute.
• Execute and display only one case at a time.
• Are similar to case statements or if...then...else
statements in text-based programming languages.
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Case Structures
• Case Selector Label
− Contains the name of the current case.
− Has decrement and increment arrows.
• Selector Terminal
− Lets you wire an input
value, or selector, to
determine which case
executes.
Case Selector Label
Selector Terminal
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Case Structures
Selector terminal data
types:
• Boolean
− True case and False case
• Error Cluster
− Error case and No Error
case
• Integer, string or enum
− Structure can have any
number of cases
− Include a Default diagram
to avoid listing every
possible input value
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Shortcut Menu
Use the shortcut
menu of a Case
Structure to:
− Customize the structure
and diagrams.
− Remove or replace the
structure.
− Add, duplicate, remove
or rearrange cases.
− Specify the Default case.
− Switch cases.
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Enum Case Structure
• Gives users a list of items from which to select.
• The case selector displays a case for each item
in the enumerated type control.
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Error Case Structure
Use Case structures inside VIs to execute the
code if there is no error and skip the code if there
is an error.
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Input and Output Tunnels
You can create multiple input and output tunnels.
• Inputs tunnels are available to all cases if needed.
• You must define each output tunnel for each case.
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Case Structures
• Create case structures using different data type
selectors.
• Add, remove and duplicate cases.
• Create different types of output tunnels.
DEMONSTRATION
H. Disable Structures
Diagram Disable Structure
Conditional Disable Structure
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Diagram Disable Structure


Use it to disable a section of code on the block
diagram.
Multiple subdiagrams are possible – one is enabled.


Disabled subdiagrams appear grayed out.
Great tool for troubleshooting – no need to re-write
code.
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Conditional Disable Structure
•
Use it to define conditions that indicate which code
on the block diagram executes.
•
Examples:
–
–
If running as an executable,
then programmatically close
LabVIEW when VI finishes.
If running on Windows, look
for file here; if running on
Mac OSX, then look here.
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Homework:
Blinking LED
Use a While Loop a timing function to blink an LED.
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Homework: Average Temperature VI
Use a While Loop and stacked shift registers to
average data.
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Homework: Temperature Limits VI
Use a Case
Structure to output
a string indicating
if the temperature
is OK or outside
the limits.
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