1. LabView Physics 3 - IT skills
Miles Padgett

2. Objectives
To acquire familiarity with the LabView Programming language
To be able to write LabView programmes incorporating pre written and new VI’s
To use LabView in the study of 2-D diffraction patterns
You get exercise marks for completion of each milestone.

3. LabView - the basics
All LabView programmes comprise of two screen types
The “front panel” (grey) which acts as the user interface
The “diagram” (white) which contains the “programme”

4. LabView - getting going
Like most programs, LabView can be launched by double clicking on the LabView icon
Programs themselves are called “vi” (virtual instruments)
To start a new “vi”, select “new vi” from the LabView start up screen
The LabView icon
The LabView start up screen

5. LabView - front Panel
Controls (data input) and indicators (data output) can be selected from the “controls” window and placed on the front panel.
To find controls
select “show panel” from “window” menu
select “show controls palette” from “window” menu
The controls palette

6. LabView - diagram
Functions (program operations) can be selected from the “functions” window and placed on the diagram.
To find functions
select “show diagram” from “window” menu
select “show functions palette” from “window” menu
The functions palette

7. LabView - tools
Tools (cursor/mouse functions) can be selected from the “tool” window
To find tools
select “show tools palette” from “window” menu
The tools palette

8. Using LabView to add two numbers
Create new program
Select “new VI” from the file menu
Select a digital control from the controls palette and place it on the front panel (grey)
Do the same again
Select a digital indicator from the controls palette and place it on the front panel
Selecting a digital control
Selecting a digital indicator

9. Adding two numbers - front panel
Controls and indicator placed on front panel
N.B. software automatically numbers controls of the same type in sequence
The front panel

10. Adding two numbers - diagram
Data terminals automatically appear on diagram
The diagram

11. Adding two numbers - placing the function
Select and drag the “addition function onto the diagram
To find addition
Show function panel
Click on numeric
Select and drag addition onto diagram
Selecting a numeric function
Dragging onto the diagram

12. Adding two numbers - wiring the function
Select “wiring tool” from tools palette
Cursor now changes function
“click” on wire start point “drag” to end point then “release”
Use wiring tool to connect
Digital controls to function inputs
Function output to digital indicator

13. Adding two numbers - running the program
Select “arrow” from tools palette
Cursor now changes function
Running the program
Use arrow tool to “click” single arrow on front panel to run once
Or “click” looped arrow on front panel to run continuously
Stopping the program
Use arrow tool to “click” red stop button
Run continuously
Stop the program
Run once

14. Adding two numbers - operating the program1
Select “finger hand” or “text tool” from tools palette
Cursor now changes function
Changing the input
Use “finger” on up/down arrows of numeric controls
Or use “text tool” to highlight and edit number field (white) within numeric control
If running continuously then program is interactive
Text field
Up/down arrows

15. Adding two numbers - saving the program
Select “save” from within the file menu
When prompted enter filename
Note in windows LabView files have a ***.vi file extension
Vi - stands for virtual instrument
DO IT NOW AND KEEP DOING IT!

16. Customising the program (text)
Select “text tool” from tools palette
Cursor now changes function
Changing the name of the input
Use “text tool” to highlight and edit the names (grey) numeric control
Use “text tool” to highlight and edit the name (grey) numeric indicator
Indicator text field
Control text field

17. Customising the program (data)
Selecting data range
Select “arrow tool” from tools palette
Cursor now changes function
Changing the allowed range and up/down increment of the controls
Right click (windows) on the numeric control to generate menu then select “Data range…”
Within data range can set upper limit/lower limit and increment
Now run the program again
Max/Min/Increment

18. Customising the program (display) -1
Select the front panel
Show “controls panel from window menu”
Use “arrow tool” to select numeric control
Use “arrow tool” to select “meter” and “drag” it onto front panel
Use “text tool” to optionally edit name of meter
Use “text tool” to optionally highlight and edit the range of the meter
Selecting a digital meter
Name of meter
Range of meter

19. Customising the program (display) -2
Select the diagram
Select “wiring tool” from tool palette
Use wiring tool to connect meter terminal to existing output wire of the “addition” function or equivalently to the existing numeric indicator terminal
I.e. click on start, drag to end then release
Run the program again, note meter display matches indicator

20. Accessing LabView’s help
To get help on a function
Select the diagram
Select “arrow tool” from tool palette
Use arrow tool to right click (windows) on function
Select help from pop up menu
Function help appears in sub-window
More general help can be obtained through the “help menu”
“Content and index” is good for specific questions
LabView comes with a “learn by activities package”
Also a great set of example programs

21. Useful tips - indicators, controls and terminal
Every indicator on the front panel has a terminal on the diagram
Every control on the front panel has a terminal on the diagram
Right clicking(windows) on any terminal, control /indicator gives the option of highlighting the corresponding control /indicator or terminal

22. Useful tips - switching between tools
Rather than picking your tool from the “tools palette” pressing the “tab” key toggles the tool between
On the diagram
Arrow (allows selection and/or movement of terminals and functions around diagram
Text (allow text edit of terminal and addition of extra text comments)
Wiring (allows wiring connection of functions and terminals)
Finger (allows selection of terminals)
On the panel
Arrow (allows movement of controls around panel
Text (allows text edit of control/indicator and addition of extra text comments)
Paint (allows colour change of control or indicator)
Finger (allows adjustment of controls)

23. Useful tips - showing various windows
Any window or tool panel can be made active by selecting it from the window menu
Alternatively “clicking” on a window will make it active
This is a quick way of switching between the diagram and the front panel

24. Useful tips - finding errors
If the current LabView programme is non executable the “run” arrow on the front panel appears broken
Activating the arrow results in an error list contain the faults
Selecting any fault highlight the offending part of the diagram
Broken “run” arrow
error list

25. Looping programs
Computers become power when you make them do something many times!
LabView loops are examples of structures and placed on the diagram
Show diagram
Shows functions palette
Select structure
Selecting the structure sub palette from the functions palette

26. Incorporating a “while loop”
Select a “while loop” from the structure palette
Place while loop on diagram to surround program
Click top left drag to bottom right and release
While loop will run whilst condition is true
“While loop”
Condition

27. Setting the condition of a “while loop”
Need Boolean (true/false) control to set state of while loop
Show front panel
Show controls palette
Select “boolean”
Select “push button” and drag and place (release) on front panel
Optionally use “text tool” to highlight and edit name (grey) of new control

28. Wiring the condition of a “while loop”
Need to wire the Boolean terminal to the condition of the while loop
Use arrow tool to move (if necessary) the terminal of the Boolean control to the inside of the while loop
Use the wiring tool to connect the boolean terminal to the condition terminal

29. Running a “while loop” 3
Running/stopping the program within a while loop
Use finger tool to toggle Boolean control to true (dull green arrow becomes bright green)
Use finger or arrow tool to “run” program (NB not continuously run)
Program will now run continuously
Use finger or text tool to change/edit numeric controls
Use finger tool to toggle boolean control to stop program

30. Using LabView to draw a sine curve
Objective
To plot a sine curve in the range 0- 10p
Start a new program
Select “new VI” from the file menu
Save it now
Select “save” from the file menu and when prompted provide name

31. Using a “for loop” Show the diagram
Select a “for loop” from the structure palette
Place the “for loop” on the diagram
“click” “drag” “release”
A “for-loop” will run N times then stop
i increments from 0 to N-1
For loop
Terminal for N
Terminal for i

32. Wiring N on a “for loop” Show the front panel Show diagram
Select digital control from the controls palette
Place control on front panel
Show diagram
(If necessary) move terminal of digital control to outside of loop
Wire digital control terminal to N terminal of for loop
NB one terminal is blue the other orange!

33. Understanding data types
Computers store number in different forms, e.g.
Integers, 8 bit, 16bit, 32 bit - BLUE in LabView
Floats single precision, double precision - Orange in LabView

34. Converting Data type Show either diagram or front panel
Right click (window) on control or terminal and select “representation”
“click” on data type of choice to convert numeric
Do this to change numeric control to I32 integer
Edit numeric value to 100

35. Drawing a sine curve - defining the range (1)
Selecting a constant
To define the 0-10p range
Show diagram
Select and place constant outside loop - edit to 10
Select and place p outside loop
Select and place multiple function outside loop
Wire “10” and “p”””””“ into “x” function
Selecting p

36. Drawing a sine curve - defining the range (2)
Select and place divide function inside loop
Wire “i “into quotient of divide
Wire numeric input through wall into denominator of divide
Select and place multiple function
Wire output of divide into multiply
Wire “10 x p””“ product through loop wall into multiply

37. Drawing a sine curve - calculating the value
To calculate the sine value
Select and place sine function inside loop
Wire output of multiply to input of sine
Wire output of sine to loop wall
Selecting sine

38. Drawing a sine curve - displaying the curve
Show front panel
Select and place “waveform graph” on front panel
Show diagram
(if necessary) move waveform graph terminal outside loop
Wire wall of loop to waveform graph terminal
Selecting waveform graph

39. Drawing a sine curve - displaying the curve (2)
Show diagram
(if necessary) move waveform graph terminal outside loop
Wire wall of loop to waveform graph terminal
NB orange wire on outside of loop is thicker than inside
Indicates wire carries an array of numbers

40. Drawing a sine curve - running the program4
Use arrow tool to “run continuously the program
Adjust numeric control to change number of points calculated
Use arrow tool to “stop” program when finished
Use text edit tool to rename x-axis of graph (angle), name of numeric control (number of data points) and name of waveform graph

41. Drawing a sine curve - modifying the program
To make 10p range variable
Select and place digital control on front panel
Show diagram
Delete 10p product structure and wire from outside loop to leave unwired loop entry
Move new numeric terminal to similar position
Wire in terminal to loop entry
Run continuously and experiment with changing the range

42. Drawing a sine curve - extending the program FFT (1)
To obtain an FFT of the sine wave
Select and place FFT function on diagram near existing waveform graph terminal - the route to FFT is
Functions
Analyse
Signal processing
Frequency domain
Wire waveform graph (or neighbouring wire to Input of FFT function
Selecting FFT function

43. Drawing a sine curve - extending the program FFT (2)
Wire waveform graph (or neighbouring wire to Input of FFT function
On front panel place additional waveform graph
On diagram wire output of FFT function to terminal of waveform graph
Use text tool to edit name of waveform graph and x axis of graph on front panel

44. Drawing a sine curve - seeing the FFT5
Run program continuously
Update range control
Examine FFT of sine wave
Note the FFT has two peaks
Note FFT peaks have +ve and -ve values

45. Drawing a sine curve - seeing the power spectrum (1)
More usual to consider the power spectrum
Need to take modulus squared of each FFT component
Delete wire between FFT and waveform graph terminal
(if necessary) move terminal of waveform graph away from FFT
Select and place modulus function after FFT
Select and place multiply function after modulus
Wire FFT to modulus
Wire modulus to both inputs of multiply
Wire multiply to waveform graph terminal

46. Drawing a sine curve - seeing the power spectrum (2)6
Power spectrum is +ve
Still twin peaked
Run program
Note that a higher “frequencies” of sine wave power spectrum peaks move towards centre
Double peaks can be through to represent +ve and -ve frequency

47. Using LabView to draw a 2D function
Objective
To plot an “egg box” type pattern
Start a new program
Select “new VI” from the file menu
Save it now
Select “save” from the file menu and when prompted provide name

48. Double nested “for loop”
A single for loop will create a vector of N elements
To create an array use a for loop within a for loop

49. Useful tips - copying and moving items on the diagram
To move a selection of functions and wires on a diagram
Use arrow tool to define rectangle of interest, i.e. click upper left and drag to lower right
Use cursor keys to move selected region
To copy a selected section of the program
Use arrow tool to define rectangle of interest, I.e. click upper left and drag to lower right
Use standard copy and paste functions to replicate program

50. Calculating the “egg box”
Assume an egg box is generated by taking the product of two sine functions (one in the x-direction and one in the y)
Use double nested loop and repeat logic of previous program, note
Both N terminals of loop wired to control
i indices of loops wired to form x and y axis
Out wired through inner loop to form output from outer loop

51. Visualising the “egg box” (1)
Show front panel
Select and place intensity graph on front panel
Use text tool to rename x-axis, y-axis and name of graph
Selecting an intensity graph

52. Visualising the “egg box” (2)
Show diagram
(if necessary) move terminal of intensity graph to outside of nested loop
Wire output from outer loop to terminal of intensity graph
NB note orange wire becomes “double wire” which indicates it is an array

53. Useful tips - Polymorphic
In LabView, most functions are polymorphic.
e.g.. the same addition function will add two numbers or two vectors or two arrays (vectors or arrays must have the same dimensions
Adding numbers
Adding vectors
Adding arrays

54. Running the “egg box” 7 Show front panel
Use finger or text tool to set numeric controls to ≈100 loop iterations and a plot range of ≈30
Run or run continuously the program
Need to set z-axis of graph to autoscale
“right click” (window) on graph, select z-scale and select autoscale z
Auto-scaling the z-axis of an intensity graph

55. Useful tips - changing the number format
Previously we have seen how to change the range over which a numeric control can be varied
To change the way it is displayed
Show front panel
“rick click” (windows) on control
Select “format and precision”
Edit forma and precision window as desired
NB this only affects the display NOT the precision of the calculations

56. The challenge - diffraction patterns
To calculate and display the far field diffraction pattern of a circular aperture
The far field diffraction pattern of a circular aperture is the same form as the Fourier-transform (but in 2D)
In the first instance “forget” about the wavelength (which sets the scaling between the aperture and the diffraction pattern) - just concentrate on the “shape”!

57. Useful functions for challenge (1)
“Comparison” functions allow logic decisions
NB wire carrying logic, i.e. Boolean (0..1) date are green
When defining the aperture, you may need
“select”
“less” or “greater”
Use LabView’s help to understand these functions

58. Useful functions for challenge (2)
“array” functions allow manipulations of array and vectors
Wire containing array data appear a two parallel wires. These may be blue (for integer)or orange (for floats)
When doing the FFT, you may need
“transpose”
“rotate 1D array”
Use LabView’s help to understand these functions

59. Useful functions for challenge (3)
If the N terminal is left unwired, “for loops” will self-index
When a vector is wired into a “for loop” the loop will split the array and run it on each element
When an array is wired into a “for loop” the loop will split the array and run it on each row
To switch off “self-indexing” right click (windows) on wire entry to loop and select “disable indexing” (not needed in challenge)
vector to element
array to vector

60. Useful functions for challenge (4)
Standard LabView does not have a function for 2D FFT
Given a 2D array, a 2D FFT can be completed by doing 1D FFT’s on each row and each column
You may need this when calculating the diffraction pattern - note use of “self-indexing”
A component of a “diagram” for completing a 2D FFT

61. Diffraction pattern 8 Run your programme
Do you get a diffraction pattern centred in the four corners?
This is a issue with most FFT algorithms - where should the zero “frequency” be located? At the centre or the edges?
We need to centre our zero in the middle of the image

62. 2D FFT with zero at centre
Can use “1D rotate function to move zero to centre (NB need to rotate by N/2)
Note also modulus squared added to output of FT to give power spectrum (i.e. light intensity)

63. Calculating a diffraction pattern9
One program that works!
Autoscale-z switched off and z-scale set to reveal structure

64. Calculating a diffraction pattern
One program that works