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Previously…

We created a simulated temperature reader which alerts if too

hot or too cold…

Download the solved practice to keep in sync:

Thermostat.vi

15.10.2013

Gruppo di Misure Meccaniche e Termiche

UNIBS - DIMI

D. While Loops

LabVIEW While Loop Flowchart Pseudo Code

Repeat (code);

Until Condition met;

End;

15.10.2013

Gruppo di Misure Meccaniche e Termiche

UNIBS - DIMI

D. While Loops

• Iteration terminal: returns number of times loop has

executed; zero indexed

• Conditional terminal: defines when the loop stops

Iteration Terminal Conditional Terminal

15.10.2013

Gruppo di Misure Meccaniche e Termiche

UNIBS - DIMI

Practice

Add a STOP button to the previous practice, then include everything in a while loop in order to stop the program when the user hit STOP.

Add a CHART and display the current iteration number on it.

Please note: from now on the RUN CONTINOUSLY button won’t be used, use the RUN button instead.

AVOID HITTING THE ABORT BUTTON AT ALL COSTS!!

15.10.2013

Gruppo di Misure Meccaniche e Termiche

UNIBS - DIMI

D. While Loops – Tunnels

• Tunnels transfer data into and out of structures

• The tunnel adopts the color of the data type wired to the tunnel

• Data pass out of a loop after the loop terminates

• When a tunnel passes data into a loop, the loop executes only after data arrive at the tunnel

15.10.2013

Gruppo di Misure Meccaniche e Termiche

UNIBS - DIMI

Practice

Please open again the previous vi.

Using an input tunnel display the time the vi has been active

(in seconds) and stop it when such time is MORE THAN 20s

or if the user hits the STOP button.

Think about this: what are the differences between a simple

wire and a tunnel? Can a wire HOLD data? Can a tunnel?

15.10.2013

Gruppo di Misure Meccaniche e Termiche

UNIBS - DIMI

F. Timing a VI

Why do you need timing in a VI?

• Control the frequency at which a loop executes

• Provide the processor with time to complete other tasks,

such as processing the user interface

Gruppo di Misure Meccaniche e Termiche

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F. Timing a VI – 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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F. Timing a VI – Elapsed Time Express VI

• Determines how much time elapses after some point in your

VI

• Keep track of time while the VI continues to execute

• Does not provide the processor with

time to complete other tasks

Gruppo di Misure Meccaniche e Termiche

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Practice

Open task manager and run the previous vi.

Add to the previous practice the proper wait function in order

to force the loop time to 200ms

Open task manager and run the vi again.

Add to the previous practice the proper function in order to

display a string version of time elapsed

Gruppo di Misure Meccaniche e Termiche

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E. For Loops

LabVIEW For Loop Flowchart Pseudo Code

N=100;

i=0;

Until i=N:

Repeat (code;i=i+1);

End;

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E. For Loops

• Create a For Loop the same way you create a While Loop

• If you need to replace an existing While Loop with a For

Loop, right-click the border of the While Loop, and select

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

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Gruppo di Misure Meccaniche e Termiche

UNIBS - DIMI

E. For Loops – Conditional Terminal

You can add a conditional terminal to configure a For Loop to

stop when a Boolean condition or an error occurs

Gruppo di Misure Meccaniche e Termiche

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E. For Loops – Numeric Conversion

• The number of iterations a For Loop executes must be specified in

nonnegative integers

• If you wire a double-precision, floating-point numeric value to the

count terminal, LabVIEW converts the larger numeric value to a 32-bit

signed integer

Gruppo di Misure Meccaniche e Termiche

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• Normally, when you wire different representation types to the

inputs of a function, the function returns an output in the larger

or wider format

• LabVIEW chooses the

representation that

uses more bits

• However, the For Loop

count terminal always

coerces to a 32-bit signed

integer

E. For Loops – Numeric Conversion

Coercion Dot

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E. For Loops – Numeric Conversion

• Avoid coercion for better performance

− Choose matching data type

− Programmatically convert to the matching data type

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Practice

Reproduce the following block diagram

What will be the result displayed in A? in B? in C? When?

What will be the content of D?

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E. For Loops – Conditional Terminal

For Loops configured for a conditional exit have:

• Red glyph next to the count terminal

• Conditional terminal in the lower right corner

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E. 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

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

28.10.2012

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A. Arrays

• An array consists of elements and dimensions

− Elements: data that make up the array

− Dimension: the length, height, or depth of an array

− An array can have one or more dimensions

and as many as (231)–1 elements per

dimension, memory permitting

• Consider using arrays when you work with

a collection of similar data and when you

perform repetitive computations

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A. Arrays

• The first element shown in the array (3.00) is at index 1 and

the second element (1.00) is at index 2

• The element at index 0 is not shown in this image, because

element 1 is selected in the index display

• The element selected in the index display always refers to

the element shown in the upper left corner of the element

display

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A. Arrays – Creating

1. Place an array shell on the front panel

2. Drag a data object or element into the array shell

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A. Arrays – 2D Array

• Stores elements in a grid

• Requires a column index and a row index to locate an

element, both of which are zero-based

• To create a multidimensional array on the front panel, right-

click the index display and select Add Dimension from the

shortcut menu

• You also can resize the index display until you have as

many dimensions as you want

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A. Arrays – Initializing

• You can initialize an array, or leave it uninitialized

• For initialized arrays, you define the number of elements in

each dimension, and the contents of each element

• Uninitialized arrays have dimension but no elements

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A. Arrays – Creating Constants

• To create an array constant:

− Select an array constant on the

Functions palette

− Place the array shell on the block diagram

− Place a constant in the array shell

• You can use an array constant to store

constant data or as a basis for comparison

with another array

• Array constants also are useful for passing data into a subVI

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A. Arrays – Auto-indexing

• If you wire an array to or from a For Loop or While Loop, you

can link each iteration of the loop to an element in that array

by enabling auto-indexing on tunnel

• The tunnel changes from a solid square to the image shown

above to indicate auto-indexing

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A. Arrays – Auto-indexing Input

For Loop executes

a number of times

equal to the number

of elements in the

array

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A. Arrays – Auto-indexing Input

If the iteration count terminal is wired and arrays of different

sizes are wired to auto-indexed tunnels, the actual number of

iterations becomes the smallest of the choices.

28 15.10.2013

Gruppo di Misure Meccaniche e Termiche

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Practice

Create a new VI having the following block diagram

Which values will be displayed by A,B and C?

15.10.2013

Gruppo di Misure Meccaniche e Termiche

UNIBS - DIMI

A. Arrays – Auto-indexing Output

• When you auto-index an array output tunnel, the output

array receives a new element from every iteration of the

loop

• Auto-indexed output arrays are always equal in size to the

number of iterations

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A. Arrays – Creating 2D Arrays

You can use two For Loops, one inside the other, to create a

2D array

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Practice @HOME

Open the thermostat practice VI,

Instead of generating a single temperature value per cycle,

create a set of 100 samples, put them in an array.

Display all the 100 samples on both the CHART and the

GRAPH, while controlling the boolean indicators only on the

AVERAGE of the array

Please try to keep you block diagram as tidy as possible

15.10.2013