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3. Graphical programming
language
& Data flow
◦ LabVIEW relies on graphical symbols rather than textual language to
describe programming actions
◦ The principle of dataflow, in which functions execute only after
receiving the necessary data, governs execution in a straightforward
manner
4. How does LabVIEW work?
◦ LabVIEW programs are called:
◦ Virtual Instruments (VIs)
◦ because their appearance and
operation imitate actual instruments.
◦ However, they are analogous to main programs, functions and subroutines from
popular language like C, Fortran, Pascal, …
5. Front Panel
• Controls = Inputs
• Indicators = Outputs
Block Diagram
• Accompanying “program”
for front panel
• Components “wired”
together
LabVIEW Programs Are Called
Virtual Instruments (VIs)
6. LabVIEW Introduction
◦ Two “sets” for development
◦ Front Panel
◦ Block Diagram
◦ Wiring connections
◦ LabVIEW Conventions
◦ Running LabVIEW programs
7. LabVIEW Front Panel
◦ All user interface goes here!
◦ Used to display Controls or
Indicators
◦ Highly customizable
8. LabVIEW Block Diagram
◦ Actual program
◦ Invisible to user
◦ Read left to right, like a book
◦ Where the MAGIC happens!
9. Terminals
When you place a control
(or indicator) on the
FRONT PANEL
LabVIEW automatically
creates a
corresponding
control (or indicator)
terminal on the BLOCK
DIAGRAM
11. Manipulating Controls and Indicators
◦ Right click on an indicator to
◦ Change to control
◦ Change format or precision
◦ Right click on a control to
◦ Change to indicator
◦ Change mechanical action (whether to latch open or
closed, and what to use as default…)
12. Wiring Connections
◦ Wires transport data
through the block
diagram
◦ Wire color indicates
variable type
◦ A red “X” means
something is wrong!
13. Wires
A LabVIEW VI is held together by wires connecting nodes
and terminals; they deliver data from one source terminal to
one or more destination terminals.
14. Broken wires
If you connect more
than
one source or no source
at all to a wire,
LabVIEW
DISAGREES with what
you’re doing, and the
wire will appear broken
15. Messy vs. Clean Wiring
CLEAN: Easy to troubleshoot
MESSY: What is going on?
16. Basic wires used in block diagrams
and corresponding types
Each wire has different style or color, depending on
the data
type that flows through the wire:
Scalar 1D array 2D array Color
Floating-point
number
orange
Integer number blue
Boolean green
String pink
17. LabVIEW Conventions
◦ Front panel items
◦ Controls and indicators
◦ Block diagram items
◦ Program structures (loops, case structures, math, etc.)
◦ Controls vs. Indicators
◦ Wires attach to controls on the right (give values)
◦ Wires attach to indicators on the left (receive values)
◦ Wiring colors
◦ Wires are color coded to correspond to data types
18. Running LabVIEW Programs
◦ ALMOST ALWAYS put your program in some
sort of loop that can be stopped with a
control
◦ AVOID using the red “x” to stop your
program
19. Lab. Equipment
◦ Oscilloscope
◦ Function Generator
◦ Digital Voltmeter (DVM)
Universal Measuring
Instruments
Signal Generator
20. Add/edit text
Wire features together to
control flow of data
Select a feature to
edit or move
Operate a control
Probe Data
(troubleshoot)
22. Add a structure such as for,
while, and case statements
Add a numeric
operator (+,-,…)
File I/O
Add a boolean
operator (and, or…)
Data Acquisition
Signal analysis
Comparison
Mathematical
Functions
Timing/dialog
25. The Run Button
◦ The Run button, which looks
like an arrow, starts VI
execution when you click on
it
◦ It changes appearance
when a VI is actually running.
◦ When a VI won’t compile,
the run button is broken
27. Example 1:
Craps
◦ From the functions – numeric
panel insert a pair of dice
◦ From the Controls panel
insert a numeric digital
indicator (on the front panel)
◦ Use the wiring tool to
connect the two (in the
wiring diagram) and click
the “run” button repeatedly.
◦ Numbers from 0.00 to 1.00
should be displayed in the
front panel
28. Example 1: Craps
(continued)
◦ Delete the wire
◦ Add a multiplication node and
a numeric constant to allow
multiplication by 5
◦ Add an addition node and
numeric constant to allow
addition of 1
◦ Add a mathematical “Round
to Nearest” node.
◦ Make a second copy of this
structure to represent a second
die and wire them together
through an addition node with
an output to a numeric
constant
This wiring diagram simulates the rolling
of 2 dice and their addition to form a number
from 2 through 12.
29. Example 2: Analog & Digital
Voltmeter (simulated signal)
◦ Uniform noise used as simulated
signal – Functions – Signal Processing
– Signal Generation menu
◦ Absolute value function from
functions – numeric menu
◦ Mean value of data series from the
functions – mathematics – Probability
and Statistics menu
◦ The 250 ms wait implemented from
the time and dialog menu slows the
“flutter” of the meter.
30. Example 3: Reading an analog input
signal
Requires A/D board to implement
◦ From the functions menu
select data acquisition and
then analog input. Then
select either “Sample
Channel” or Sample
Channels”
◦ This places the sampling
icon in your wiring diagram
◦ You then need to configure
the channel(s) and wire the
output to other parts of your
program.
32. Example 5: Creating Sub-VIs
◦ In wiring diagram use
selection tool (mouse box)
to select all items to be in
the SubVI.
◦ From Edit menu select
“Create SubVI”
◦ Double click on new icon
and save it as a separate
VI.
◦ Cut-and-paste it at will or
insert it using “Functions –
Select VI menu”
Editor's Notes
LabVIEW programs are called virtual instruments (VIs).
Stress that controls equal inputs, indicators equal outputs.
Each VI contains three main parts:
Front Panel – How the user interacts with the VI.
Block Diagram – The code that controls the program.
Icon/Connector – Means of connecting a VI to other VIs.
The Front Panel is used to interact with the user when the program is running. Users can control the program, change inputs, and see data updated in real time. Stress that controls are used for inputs- adjusting a slide control to set an alarm value, turning a switch on or off, or stopping a program. Indicators are used as outputs. Thermometers, lights, and other indicators indicate values from the program. These may include data, program states, and other information.
Every front panel control or indicator has a corresponding terminal on the block diagram. When a VI is run, values from controls flow through the block diagram, where they are used in the functions on the diagram, and the results are passed into other functions or indicators.
When you create an object on the Front Panel, a terminal will be created on the Block Diagram. These terminals give you access to the Front Panel objects from the Block Diagram code.
Each terminal contains useful information about the Front Panel object it corresponds to. For example, the color and symbols provide the data type. Double-precision, floating point numbers are represented with orange terminals and the letters DBL. Boolean terminals are green with TF lettering.
In general, orange terminals should wire to orange terminals, green to green, and so on. This is not a hard-and-fast rule; LabVIEW will allow a user to connect a blue terminal (integer value) to an orange terminal (fractional value), for example. But in most cases, look for a match in colors.
Controls have an arrow on the right side and have a thick border. Indicators have an arrow on the left and a thin border. Logic rules apply to wiring in LabVIEW: Each wire must have one (but only one) source (or control), and each wire may have multiple destinations (or indicators).
The program in this slide takes data from A and B and passes the values to both an Add function and a subtract function. The results are displayed on the appropriate indicators.
