TOPICS
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Implementing a VI
TOPICS
A. Designing Controls and E. Timing a VI
Indicators
F. Data Feedback in Loops
B. LabVIEW Data Types
G. Case Structure
C. While Loop
H. Disable Structures
D. For Loop
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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 PropertiesOperations 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 Flowchart Pseudo Code
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While Loop
Conditional terminal
Iteration terminal
" Defines when the loop stops.
" Returns number of times
" Has two options:
loop has executed.
- Stop if True
" Is zero-indexed.
- Continue if True.
Iteration Terminal
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 Terminal
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 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 While Loop
" Executes a set number of " Stops executing only if the
times unless a conditional value at the conditional
terminal is added. terminal meets the condition.
" Can execute zero times. " Must execute at least once.
" Tunnels automatically " Tunnels automatically output
output an array of data. 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 VI finishes Run again
Block Diagram 1st run 2nd run
Initialized
Shift
Output = 5 Output = 5
Register
Not
Initialized
Output = 4 Output = 8
Shift
Register
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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
Case Selector Label
- Lets you wire an input
value, or selector, to
determine which case
executes.
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
lð Use it to disable a section of code on the block
diagram.
lð Multiple subdiagrams are possible  one is enabled.
lð Disabled subdiagrams appear grayed out.
lð 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 with shift register and 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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