Introduction to LabVIEW For Scientists and Engineers

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Introduction to LabVIEWFor Scientists and
Engineers

• UTSI Short Course
• Tullahoma, TN
• September 10 - 12, 2001
• Brad Winkleman, Ph. D.

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Data Acquisition

• Difficult because of the number of error sources
• VI
• LabVIEW installation
• Hardware installation
• Hardware configuration
• Sensor or experimental setup
• Operator error
• Bugs

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Overview of Data Acquisition

• Hardware requirements
• DAQ cards
• Signal conditioners
• Sensors
• Communication link
• Software
• LabVIEW (usually all you need)
• Specific drivers (for unique hardware)

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Installed Data Acquisition Hardware

• National instruments PCI - 6023
• PCI bus
• 200 kHz sample rate
• 8/16 AI channels
• 8 digital outputs
• 2 timers
• Also cable and termination board

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The Data Acquisition Process

• Configure hardware
• Start acquisition
• Read data
• Once
• Specified amount
• Continuously
• Process acquired data
• Terminate the data acquisition process

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Multiple Levels of Programming

• Easy
• Single VI does everything
• Low Performance
• Easy
• Intermediate
• A few VIs needed
• High Performance
• Moderate Difficulty
• Advanced

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Exercise - Simple Voltmeter

• Must specify
• Device
• Channel
• Output
• Single data value
• Waveform

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Waveforms

• Special datatype
• New with 6.0
• Measured data
• Temporal data
• Many useful routines
• Simplify many operations
• Now the default output from data acq
• Many utility operations

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A Signal to Measure

• Thermocouple
• Low level signal - millivolts
• Requires gain for accurate measurements
• Connected via terminal block

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Exercise A Better Voltmeter

• Data Acq hardware
• Adjustable gain
• Different ranges
• Unipolar/Bipolar
• Parameters set by setting signal range
• High
• Low
• Given High and Low values LabVIEW determines the
  best way to set hardware parameters

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Exercise Simple Thermometer

• Use simple voltmeter
• Add thermocouple calculation
• Range setting necessary

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MAX

• Tedious keeping track of all the gains,
  conversion factors, channel assignments
• MAX can help keep keep all this straight
• I/O controls allow automatic scaling
• Demo of MAX

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Exercise Thermometer using I/O

• Much simpler
• No need to specify channel or device
• Output is scaled (engineering units)
• Drawback
• Actual hardware output not available
• Performance issues

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Signal Processing

• Thermocouple signal is noisy
• Normal
• Low level signal
• Filtering reduces noise
• Simple averaging
• Digital filters
• Analog filters

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Exercise Filtered Thermometer
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Exercise - A Signal Generator

• Simple Idea
• Use Pulse Train VI
• Set Freq and Duty inside loop
• Must make connections on termination board
• Bad News This doesnt work

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Debug Signal Generator

• Open Pulse Train VI
• Open its diagram
• See what it is doing each loop

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Exercise A Better Signal Generator

• Separate generator from voltmeter
• Use shift registers to remember last values of
  Frequency and Duty Cycle
• Execute Pulse Train VI only when Frequency and
  Duty Cycle change

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A Solution - A Better Signal Generator

• Pulse Train only executes when parameters are
  changed
• Delay slows the loop
• Saves CPU cycles

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Debugging Tools and Techniques

• Execution Highlighting
• Breakpoints
• Probes
• Interactive
• Open Front Panels
• Examine Controls
• Open Block Diagrams
• And so on

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Types of Data Acquisition

• Single Channel - Single Measurement
• Multiple Channel Single Measurement
• Single Channel Multiple Measurement
• Multiple Channel Multiple Measurement
• High Performance
• Continuous
• Buffered

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Single Channel - Single Measurement

• What weve been doing

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Multiple Channel Single Measurement

• Similar to Single Single Data Acq
• Use multiple channel VI
• Must specify multiple channels
• Will also work with I/O inputs

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Single Channel Multiple Measurement

• Similar to Single Single Data Acq
• Use multiple point VI
• Must specify
• Number of points or samples
• Sampling frequency
• Will also work with I/O inputs

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Multiple Channel Multiple Measurement

• Similar to Single Multiple Data Acq
• Use multiple point multiple channel VI
• Must specify
• List of channels
• Number of points or samples
• Sampling frequency
• Will also work with I/O inputs

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Exercise Better Voltmeters

• Single Channel Multiple Measurement
• Multiple Channel Single Measurement
• Multiple Channel Multiple Measurement

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High Performance Data Acquisition

• Previous Data Acq collects data in bursts
• Data is lost in between the bursts
• Useful for slow systems
• Continuous Data Acq
• No missing data
• Requires buffers
• More complex VI structure

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Continuous Buffered Data Acq

• Continuous buffered process
• Configure hardware and process
• Start Data Acq process
• Read data
• Process data
• Stop Data Acq
• Data always being acquired
• Reading and processing must not get behind
• Buffer overflows
• Process errors and terminates

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Configure

• Identifies channels
• Buffer size
• Important parameter
• Good rule 5 seconds of data
• Generates a task ID

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Start

• Starts a configured data acq task
• Uses task ID
• Can set total amount of data acquired

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Read

• Gets data from buffer
• Uses task ID to identify buffer
• Must specify the amount of data desired
• Delays until data ready
• User response affected
• Read frequently for best user experience

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Stop

• Stops the acquisition task
• Clears the hardware

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Putting The Process Together

• Create a VI
• Add the required VIs
• Intermediate
• Connect VIs
• Wire in controls
• Set values
• Or use LabVIEW examples

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High Performance Data Acq
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High Performance Data Acq
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Spectrum Analyzer

• Add a Power Spectrum VI in High Performance Data
  Acq VI
• Insert between Read and the display terminal
• Difficulty
• Read Output is an array of Waveform
• Power Spectrum input is Waveform
• Use Array Indexing or Loop structure

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Saving Data

• Use File I/O Routines as with Adder with save
• For full performance
• Open before loop begins
• Write during loop (only Write VI inside loop)
• Close after loop completion

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Summary of Data Acq

• Low Level
• Burst data
• Generally low performance
• Intermediate
• Buffered
• Continuous
• High performance

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Working With Charts and Graphs

• Modify components
• Operate components

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Modifying Charts and Graphs

• Change most attributes
• Labels
• Scaling modes
• Grid
• Mapping
• Precision
• Update modes
• Number styles
• Marker styles
• Marker spacing
• Line styles, colors, types
• Graph styles
• And more

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Operating Charts and Graphs

• Set autoscaling
• Zoom display area
• Set precision
• Select and move cursors
• Read values
• Copy and paste data
• Use as control

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Overall Summary

• The basics of LabVIEW programming have been
  detailed
• Data acquisition principles presented
• High performance data acquisition techniques
  provided
• LabVIEW proficiency requires
• Familiarity with VI library
• Practice and use