AHMET OZMEN

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Virtual Instruments (VIs)

•LabVIEW programs are called virtual instruments, or VIs•Appearance and operation imitate physical instruments, such as oscilloscopes and digital multimeters

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Parts of a VI

LabVIEW VIs contain three main components:1. Front Panel 2. Block Diagram 3. Icon/Connector Pane

The LabVIEW Environment“VI” = program or function

“Front Panel” = user interface “Block Diagram” = code

Front Panel-Controls & Indicators• Knobs/Dials• Graphs/Charts• Buttons• Digital Displays• Sliders• Thermometers• Customize and

create your own

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Front Panel – Controls Palette• Contains the controls and indicators you

use to create the front panel• Access from the front panel by selecting

View»Controls Palette

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Front Panel – Front Panel Toolbar

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Block Diagram

Block diagram objects include the following:

–Terminals–SubVIs–Functions–Constants–Structures–Wires

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Block Diagram – Functions Palette• Contains the VIs, functions, and

constants you use to create the block diagram

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Block Diagram – Block Diagram Toolbar

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Block Diagram Terminals

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Searching for Controls, VIs & Functions

• Find controls, function, and VIs using the Search button on the Controls and Functions palette

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DataflowLabVIEW follows a dataflow model for running

VIs• A node executes only when data are available

at all of its input terminals• A node supplies data to the output terminals

only when the node finishes execution

Dataflow Programming

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Comparison waits until all inputs are present, then executesOnce executed, output from comparison continues through code

Both Simulate Signal Express VIs execute simultaneously

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Block

Diagram

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Building a Simple VI

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Building a Simple VI – Acquire

Acquire Express VIs:

• DAQ Assistant Express VI

• Instrument I/O Assistant Express VI

• Simulate Signal Express VI

• Read from Measurement File Express VI

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Building a Simple VI – Analyze Analyze Express VIs:

• Amplitude and Level Measurements Express VI

• Statistics Express VI

• Spectral Measurements Express VI

• Tone Measurements Express VI

• Filter Express VI

Built-in Programming Assistance

Highlight Execution

Block Diagram Cleanup

Context Help

PC-Based Data Acquisition (DAQ)

DAQ Demo

While Loops

LabVIEW While Loop Flowchart Pseudo Code

Repeat (code);Until Condition met;End;

While Loops• Iteration terminal: returns number of times

loop has executed; zero indexed• Conditional terminal: defines when the loop

stops

Iteration Terminal Conditional Terminal

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

While Loops - Error Checking and Error Handling

• Use an error cluster in a While Loop to stop the While Loop if an error occurs

For Loops

LabVIEW For Loop Flowchart Pseudo Code

N=100;i=0;Until i=N:Repeat (code;i=i+1);

End;

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

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

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

Timing Methods– Wait VI – Constant time of execution– Execute A, Execute B, sleep 10 ms

– Wait Until Next Multiple VI – Variable time of execution

– Execute A, Execute B, sleep until OS timer reaches next multiple of 20 ms

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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

Iterative Data Transfer – Shift Registers

• Right-click the border and select Add Shift Register from the shortcut menu

• Right shift register stores data on completion of an iteration• Left shift register provides stored data at beginning of the next

iteration

Case Structures• Have two or more subdiagrams or cases• Execute and displays only one case at a time• An input value determines which subdiagram to execute• Similar to case statements or if...then...else

statements in text-based programming languages

Case Structures

• Case Selector Label: contains the name of the current case and decrement and increment buttons on each side

• Selector Terminal: Wire an input value, or selector, to determine which case executes

Case Structures – Default Case• You can specify a default

case for the Case structure– If you specified cases for 1, 2,

and 3, but you get an input of 4, the Case structure executes the default case

• Right-click the Case structure border to add, duplicate, remove, or rearrange cases and to select a default case

State Programming

Although Sequence structures or sequentially wired subVIs accomplish the purpose, it is not always the best choice:– What if you need to change the order of the sequence? – What if you need to repeat one item in the sequence

more often than the other items? – What if some items in the sequence execute only when

certain conditions are met? – What if you need to stop the program immediately,

rather than waiting until the end of the sequence?

State Machines

– The state machine design pattern implements a state diagram or flow chart

– When to use state machines?• Commonly used to create user interfaces, where

different user actions send the user interface into different states • Commonly used for process tests, where a state

represents each segment of the process

State Machines – Infrastructure

– A state machine consists of a set of states and a transition function that maps to the next state

– Each state can lead to one or multiple states or end the process flow

While Loop

Case StructureShift Register

State Machines – Default Transition

Parallelism

– Often, you need to program multiple tasks so that they execute at the same time

– In LabVIEW, tasks can run in parallel if they do not have a data dependency between them, and if they do not use the same shared resource• An example of a shared resource is a file, or an

instrument

• LabVIEW automatically divides each application into multiple execution threads (introduced in 1998 with LabVIEW 5.0)

• Parallel code paths will execute in unique threads

Automatic Multithreading in LabVIEW

thread

thread

thread

Multiple Loop Architectures

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Triggered Acquisition Demo

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