LabVIEW DAQ Hands On Manual

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Hands-on Introduction to Data Acquisition with LabVIEW 1

1

Introduction to LabVIEW and Computer-Based Measurements Hands-On Seminar

2

Company Profile

• Leaders in Computer-Based

Measurement and Automation

• Long-term Track Record of Growth and Profitability • $660M Revenue in 2006 • $184.4M in Q3 2007 (12% YOY) • More than 4,300+ employees;

operations in 40+ countries • Fortune’s 100 Best Companies to

Work For 8th Consecutive Year • FT 50 Best Workplaces UK 2006 &

2007

3

National Instruments Vision

“To do for test and measurement what the spreadsheet did for financial analysis.”

Virtual Instrumentation The software is the instrument

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4 The NI Approach – An Integrated Platform

High-Speed Digitizers

Dynamic Signal Acquisition Digital I/O Instrument

Control

Counter/ Timers MachineVision Motion Control

Distributed I/O and Embedded Control Laptop PC PDA Desktop PC

PXI Modular Instrumentation

Keypad LCD Sound Acoustics RF Signal Battery

Body & Chassis Audio Engine Durability

Tire & Brake Safety Emissions Electronics Temperature

Monitoring

Waste Monitoring

Process Control Motor and Valve Control High-Resolution Digitizers and DMMs Multifunction Data Acquisition 5 Agenda • Introduction to LabVIEW

 Exercise 1: Create a simple LabVIEW VI

• Data Acquisition with LabVIEW

 Exercise 2a – 2c: Introduction to Data Acquisition with LabVIEW

• Decision making in LabVIEW

 Exercise 3: Controlling program execution

• Analogue Output and Digital Control

 Multiple operations with Analogue IO

6

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7

LabVIEW Graphical Programming

• Compiled graphical development environment • Development time reduction of four to ten times • Tools to acquire, analyze, and present your data

8

The LabVIEW Environment

Front Panel – User Interface Block Diagram – Compiled Code

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Graphical Programming – Dataflow

1 Start of _{Data Flow}

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• LabVIEW automatically divides each application into multiple execution threads

• LabVIEW introduced multithreading in 1998

Automatic Multithreading in LabVIEW

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• LabVIEW automatically divides each application into multiple execution threads

• LabVIEW introduced multithreading in 1998

Automatic Multithreading in LabVIEW

thread thread thread

13 Exercise 1: Create a Simple LabVIEW VI

What you will learn:

– Working in the LabVIEW environment

Create an application that:

– Simulates data collection – Performs RMS Calculation

– Turns on an a front panel indicator when threshold is reached

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14

PC-Based Data Acquisition with LabVIEW

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PC-Based Data Acquisition (DAQ)

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Measuring Analogue Input Signals

• Architecture Multiplexed Simultaneous sampling • Sampling rate • Resolution • Signal conditioning Analogue Input To PC …

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Analogue Input – Architectures

Channel 0 Channel 1 ADC Channel 0 Channel 1 Simultaneous sampling MUX Multiplexed AMP ADC Channel 0 Channel 1 ADC Channel 0 Channel 1 AMP AMP Interchannel delay No interchannel delay 18

Analogue Input – Sampling Rates

• Undersampling may result in the misrepresentation of the measured signal (aliasing).

• After a signal is aliased, it is impossible to reconstruct the original signal.

• For accurate frequency representation:

Sample at least 2x the highest frequency signal being measured.

• For accurate shape representation

Sample 5–10x the highest frequency signal being measured.

19 Time (ms)100 150 200 50 0 0 1.25 5.00 2.50 3.75 6.25 7.50 8.75 10.00 Amplitude (Volts)

16-Bit versus 3-Bit Resolution (5 kHz Sine Wave) 16-bit 3-bit 000 001 010 011 100 101 110 111 | | | | |

Analogue Input – Resolution

• Number of bits analogue-to-digital converter (ADC) uses to represent a signal

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20

Sensors/Signals

Amplification, Linearisation, and Cold-Junction Compensation, Filtering

Isolation Thermocouples

RTDs

Strain Gauges Common Mode or High

Voltages

Signal Conditioning

DAQ Device

Analogue Input – Signal Conditioning

High voltage signals and most sensors require signal conditioning to properly read the signal

Current Excitation, Linearisation, Filtering Voltage Excitation, Bridge Configuration, Linearisation, Filtering

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NI CompactDAQ

Hi-Speed USB 2.0

Mix and match over 30 hot-swappable modules Built-in signal conditioning Synchronized I/O 22 C Series Modules Thermocouples 4 to 20mA High Voltage (60V) RTD Accelerometer Strain Gauge Load Cells Digital I/O

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23 Data Acquisition with LabVIEW

•Triggering

• Sample rates • Clocking

NI-DAQmx driver software provides connectivity between LabVIEW and your hardware

Programmatic Interface

NI-DAQmx driver configures • Buffering • Signal routing • etc… Configuration Based 24 Exercises 2a –2c:

Introduction to Data Acquisition with LabVIEW

• Taking measurements from scratch using NI CompactDAQ and NI LabVIEW

• Create an application that

Measures from a thermocouple Logs data to a file

25 DAQ Solution for Your Application

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26

Analysis in LabVIEW

27 Choose Your Analysis Approach

Configuration Oriented

Textual Math

Standard VIs

Express VIs LabVIEW MathScript

LabVIEW has over 600 built-in analysis functions

28 LabVIEW Analysis

Built-in functions available for signal processing, analysis and math

• Signal synthesis

• Curve fitting and interpolation • FFT-based frequency analysis • Mathematics

• Probability and statistics

• Time- and frequency-domain analysis • Digital signal processing

• Waveform alignment and resampling • Much more…

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29 LabVIEW Toolkits

• Sound & Vibration • RF and Communications • Digital Filter Design • Database Connectivity • Reporting Interface to MS Office • And many more…

Productivity enhancing functionality found in several toolkits, including…

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Presenting Data in LabVIEW

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Presenting Data

• Graphs and strip charts • Buttons and checkboxes • Knobs and sliders • Text and combo boxes • Tree controls • Tables • ActiveX objects • etc...

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32 Options for Professional UIs

LabVIEW is optimised for creating technical user interfaces Displaying data, visualising processes and controlling machines

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LabVIEW File I/O

• ASCII • Binary

Functions for saving your data to files and databases

NI TDM file format provides an easy way to make test data searchable

• Excel • Databases

ni.com/tdm

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LabVIEW Report Generation

Functions for creating reports and documenting test results

• HTML • XML

• MS Office • DIAdem

The Report Generation toolkit provides connectivity to MS Office

NI DIAdem provides a WYSIWYG report editor

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35

Controlling Program Execution

• Looping (For and While) • Case structure

• Sequence structure • State machines • Event structure • State diagram editor • Timed loop Is Limit Met? Turn On Output Yes Reset Output No Start 36

LabVIEW Looping Basics

While Loop For Loop Run until stop

condition met Run N times

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LabVIEW Case Structure

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Exercise 3: Controlling Program Execution

– How to incorporate logic into your LabVIEW application

Create an application that:

– Charts a sine or triangle wave depending on toggle switch position – Turns on/off digital outputs based on

user selections

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Analogue Output – Considerations

• Accuracy: digital-to-analog converter (DAC) resolution • Update Rate: settling time and waveform frequency • Range: fixed or adjustable output voltage/current

DAC Channel 0 Channel 1 DAC Channel 0 Channel 1 • 16-bit • 100 kS/sec •±10 VDC, 0–20 mA 40 Exercise 4:

Multiple Operations with Analogue I/O

What You Will Learn

• Creating parallel operation in LabVIEW • Create an application that

 Outputs an analogue signal

 Uses analogue input channel to acquire

and display on front panel

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41 Analogue Output Functions – PID Control

1 Read Sensor 2 Calculate_{PID value} 3 Output to _Actuator

Analogue IO can be used in combination for control applications

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Additional Measurement Platforms

43 NI LabVIEW™Everywhere PC Networked I/O PC Boards Handheld Micro-processors PXI Wireless Tektronix open Windows

oscilloscopes FPGA Platforms: • Desktop • Mobile • Industrial • Embedded

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44 Modular Instrumentation

Data Acquisition

Sensors, voltage and current

I/O

Measurements: DC to 10 MHz

Resolution: ~18 to 24 bits

Modular Instruments

– DMMs, Switches, Oscilloscopes, High-speed digital, Power supplies, RF

– Measurements: DC to 6 GHz – Resolution: Up to 26 bits

45 Interfacing with Benchtop Instruments

Processor RAM ROM Display Power Supply Hard Disk

LabVIEW uses drivers for PC connectivity

• Benchtop instruments involve:

– Fixed functionality – Vendor defined interface

46 Instrument Control with LabVIEW

GPIB - USB - Ethernet RS 232 - RS 485 - LXI

Over 5,000 Instrument drivers online, from over 250 vendors

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47

Using NI CompactDAQ to Crash Test Safety Helmets

Application: Designing a highly accurate and portable high-level impact test application for the certification of safety helmets.

NI Products Used: NI CompactDAQ

Solution: CompactDAQ is used to control the height from which the helmet under test is dropped, as well as acquiring data related to what a person's head would be subjected to upon impact. The system was chosen as it had sufficient throughput to ensure that each helmet test is thoroughly and accurately documented.

“A system upgrade such as the one we required is a major budget consideration, and for this reason we were very deliberate in our

search for a new hardware package”

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NI Customer Solutions Microsoft Uses NI LabVIEW and PXI Modular Instruments to Develop Production Test System for Xbox 360 Controllers

Application: Creating an updated versatile test system to test and validate new Xbox 360 controllers. NI Products Used: LabVIEW, Modular Instruments and PXI/CompactPCI

Reasons for Choosing NI Products: “Using the LabVIEW graphical development environment, we created more than 100 tests, implemented Ethernet communication, and incorporated a data storage interface to our Microsoft SQL Server database…we implemented a test strategy that resulted in a 50 percent increase in our test throughput per test station.”

Microsoft Uses NI LabVIEW and PXI Modular Instruments to Develop Production Test System for Xbox 360 Controllers

49 Your Next Steps

• Visit ni.com/labview

 Try LabVIEW Online for FREE

 Read technical white papers

 View webcasts on-demand

 Find other seminars in your area

• Schedule a visit with your local field engineer to discuss your application

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Hands-on Introduction to Data Acquisition with LabVIEW 17 50 Useful Resources Measurement Fundamentals www.ni.com/measurementfundamentals 51 LabVIEW Skill Development Plan

ni.com/training Certifications LabVIEW Basics I LabVIEW Basics II LabVIEW Intermediate I Certified LabVIEW Developer Exam LabVIEW Advanced I Certified LabVIEW Architect Exam LabVIEW Intermediate II Courses

New User Experienced User Advanced User

Core Courses Begin

Here

Certified LabVIEW Associate Developer Exam

• Save development time and cost • Differentiate skills with professional credentials

• Multiple training formats – Classroom, Onsite, Online, Self-Paced

52 Questions or Comments?

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Hands-on Introduction to Data Acquisition with LabVIEW 18

Exercise 1: Create a Simple LabVIEW VI

In this exercise, you will create a simple LabVIEW VI that simulates an analog signal and plots it on a waveform graph. The VI will test the input values against a user-specified limit and light an LED if the input value exceeds that limit.

Below are pictures identifying each of the palettes found in LabVIEW to assist you as you complete these exercises.

Note: LabVIEW has a built-in Automatic Tool Selection feature that changes the behavior of the

cursor depending on what type of object you are currently pointing to.

Controls Palette

Functions Palette

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Hands-on Introduction to Data Acquisition with LabVIEW 19 Once you launch LabVIEW, a splash screen like the following appears.

2. Click More…

3. Expand From Template. Notice the different categories on the left of the window that correspond to the types of tasks from which you can choose. You can select Blank VI to start from scratch. There are also Template VIs to use as a starting point for building your application. Projects and Other Files are more advanced components and will not be described in detail. To get more information on any of the listings in the New Dialog Box, click the Help button in the lower right corner of the window.

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Hands-on Introduction to Data Acquisition with LabVIEW 20 4. Select VI»From Template»Tutorial (Getting Started) »Generate and Display and click OK.

Two windows appear. The gray window is the front panel, and the white one is the block diagram. The front panel contains the parts of your VI used for presenting information, whereas the block diagram contains the code that controls the functionality of the VI. You can toggle between the two windows by selecting Window»Show Block Diagram or

Window»Show Front Panel. You can also switch between the windows by pressing <Ctrl-E>

on the keyboard.

5. Examine the front panel and block diagram of this template VI. The front panel contains a Waveform Chart and a STOP button as shown in the following figure.

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Hands-on Introduction to Data Acquisition with LabVIEW 21 The block diagram contains a Simulate Signal VI, which is currently configured to simulate a sine wave and plot it to the chart.

6. Switch back to the front panel by pressing <Ctrl-E>. Since the Run button (the white arrow in the top left corner) is solid, you can run this VI as it is. Click the Run button and examine the operation of the VI. When you are finished, click the STOP button on the front panel to stop running the VI.

Note: As you will see later in the exercise, when the Run button in the upper left corner of

both the front panel and the block diagram changes from a solid white arrow, to a broken gray arrow, this new icon indicates that the VI is currently not executable.

7. Now we can add some functionality to this basic VI. We will modify the VI to flash an alarm whenever the signal value is above a certain level. Open the Controls palette (if it is not open already) by right-clicking the front panel window. A small pushpin icon in the upper left corner of this palette appears. Click this pushpin to force the palette to remain on your screen.

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Hands-on Introduction to Data Acquisition with LabVIEW 22 8. Click the Numeric Controls palette, and select a Vertical Pointer Slide to be placed on the

front panel. To do this, click the Vertical Pointer Slide and drag it to the front panel. Click once to place it.

9. Click the Express menu item on the Controls palette to return to the Express Controls palette.

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Hands-on Introduction to Data Acquisition with LabVIEW 23 11. Right-click the Vertical Pointer Slide and select Properties. A property page will appear.

Examine the different properties that you can modify. Make the following changes on the

Appearance tab and click OK to apply the changes. Label: Limit

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Hands-on Introduction to Data Acquisition with LabVIEW 24 12. Right-click the Round LED labeled Boolean, and select Properties. Examine the different

properties that can be modified. On the Appearance tab, change the label from Boolean to

Alarm. Click OK to apply your change. Move the objects on the front panel so it resembles

the following.

13. Switch to the block diagram by pressing <Ctrl-E>. Double-click the Simulate Signal Express VI to bring up its properties window. Examine the different properties you can modify. Change the Amplitude of the signal to 10. Click OK to apply this change and to close the properties window.

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Hands-on Introduction to Data Acquisition with LabVIEW 25 14. Bring up the Functions palette by right-clicking the block diagram. Select Express & Signal

Analysis and place the Amp & Level Express VI on the diagram.

15. When you place the Comparison Express VI on the block diagram, a dialog box appears. Select RMS as shown below.

16. As shown below, wire the output of the Simulate Signal VI to Signals input on the

Amplitude and Level Measurements VI. Then right-click on RMS output and select Create»Numeric Indicator from the context menu.

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Hands-on Introduction to Data Acquisition with LabVIEW 26 17. Bring up the functions palette by right-clicking the block diagram. Select Arithmetic &

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Hands-on Introduction to Data Acquisition with LabVIEW 27 When you place the Comparison Express VI on the block diagram, a dialog box appears that lets you configure what type of comparison you will be doing. Make the following

selections, then click OK to apply these changes and to close the dialog box.

Compare Condition: Greater

Comparison Inputs: Compare to second input

18. You can connect Controls, Functions, and Indicators on the block diagram by pointing to an object and clicking it when the cursor changes to a spool of wire. You can then move the cursor to the object you want to connect it to and click again. Connect the Limit control to the Alarm indicator.

Note: The Run button in the upper left corner of both the front panel and the block diagram

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Hands-on Introduction to Data Acquisition with LabVIEW 28 the VI is currently not executable. If you click the Run button when it is solid and white, it runs the VI. Clicking it when it is broken and gray brings up a dialog box that will help you debug the VI.

19. Click the Run button now. The resulting dialog box shows that, in this case, the error results from connecting terminals of two different types. Since the Limit control is a Numeric type and the Alarm indicator is a Boolean type, we cannot wire these two terminals together. Highlight the error by clicking it, and then click Show Error. LabVIEW will highlight the location of the error.

20. Notice that the wire between Limit and Alarm is dashed and a red  is displayed on it.

To delete this broken wire, press <Ctrl-B>. This keyboard shortcut removes all broken wires from the block diagram.

21. Make your block diagram resemble the following image by completing the following steps.

a. Wire the Limit control to the Operand 2 input of the Comparison function.

b. Connect the wire between the Simulate Signals block and the Waveform Graph to the

Operand 1 input of the Comparison block.

c. Wire the Result output of the Comparison block to the Alarm indicator.

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Hands-on Introduction to Data Acquisition with LabVIEW 29 22. Switch to the front panel by pressing <Ctrl-E>.

23. Save the VI in the Desktop\CustomerWork folder by using the File menu and name it

Exercise1.vi.

Note: Be sure to save this VI, as you will be using it later in the seminar.

24. Run the VI. While running the VI, you can change the Limit value. Also notice that when a data point received from the Simulate Signal VI is greater than the Limit value, the Alarm indicator lights up.

While the VI is still running, switch to the block diagram by pressing <Ctrl-E>. Enable

highlight execution by clicking the light bulb on the tool bar. This will allow you to see the

flow of data through your program.

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Optional Exercise 1: The LabVIEW Help System

The LabVIEW help system is a great place to learn about LabVIEW and to go when you have questions. This exercise will introduce you to the rich source of information that is available for you to take advantage of.

1. Go back to the VI you just created, and press <F1> on the keyboard to start the help system

2. Expand Fundamentals»LabVIEW Environment and explore the information available here, click around and get a feel for how it is organized.

3. Take a few minutes to explore other topics in the help system.

4. Click on the Search tab try searching on analysis functions for features you might need in your work applications.

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Optional Exercise 2: LabVIEW Example Finder

As you learned in Optional Exercise 1, LabVIEW has a comprehensive help system. LabVIEW also includes an extensive set of examples that in many cases are the building blocks for your

applications. This exercise will introduce you to what examples are available. 1. Go back to the VI you created, and from the Help menu select Find Examples.

2. Expand New Examples for LabVIEW 8.5»Express and double-click on Select Signals.vi. 3. Run the VI and explore the block diagram.

4. Take a few minutes to look around at the other example programs available, search on terms that you are familiar with, i.e., “analysis”, and try out as many as there is time for.

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Exercise 2a: Data Acquisition with NI LabVIEW

Exercise Overview

Objective

Learn about data acquisition in LabVIEW

Goals

When you have completed this exercise, you will:

 Know how to configure a data acquisition device

 Know how to use the DAQ Assistant and take measurements with NI LabVIEW

Exercise Instructions

Set up hardware

1. Make sure that the NI CompactDAQ chassis (cDAQ-9172) is powered on. 2. Connect the chassis to the PC using the USB cable.

3. NI-DAQmx driver installed on the PC automatically detects the chassis and brings up the following window.

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4. Click on Configure and Test This Device to open Measurement & Automation Explorer (MAX).

Note: NI Measurement & Automation Explorer is a configuration utility for all National Instruments

hardware.

Configure Hardware

5. Devices and Interfaces section under My System shows all the National Instruments

devices installed and configured on your PC. The DAQmx Devices folder shows all the NI-DAQmx compatible devices. By default, the NI CompactDAQ chassis NI cDAQ-9172 shows up with the name “cDAQ1”.

6. This section of MAX also shows the installed modules as well as empty slots in the CompactDAQ chassis.

7. Right-click on NI cDAQ-9172 and click on Self-Test.

8. The device passes the self test, which means it is configured properly and ready to be used in your LabVIEW application.

LabVIEW

9. Open NI LabVIEW 8.5 and press <Ctrl-N> to open a blank VI. 10. Press <Ctrl-T> to tile front panel and block diagram windows.

11. Pull up the Functions Palette by right-clicking on the white space on the LabVIEW block diagram window.

12. Move your mouse over the Express»Input palette, and click the DAQ Assist Express VI. Click again on the white space of the LabVIEW block diagram to place the DAQ Assistant VI.

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13. The Create New Express Task… window appears:

14. To configure a temperature measurement application with a thermocouple, click on Analog

Input»Temperature»Thermocouple. Click the + sign next to the cDAQ1Mod1 (NI 9211),

highlight channel ai0, and click Finish. This adds a physical channel to your measurement task.

15. Change the CJC source to Built In and Acquisition Mode to Continuous. Click the Run

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Hands-on Introduction to Data Acquisition with LabVIEW 35 16. Click OK to close the Express block configuration window to return to the LabVIEW block

diagram.

17. Notice that LabVIEW automatically creates the code for you for this measurement task. Click Yes to automatically create a While Loop.

18. Right-click the data terminal output of the DAQ Assistant Express VI (the blue output arrow on the right side) and select Create»Graph Indicator.

19. Notice that a graph indicator is placed on the front panel.

20. Your block diagram should now look like the figure below. The while loop automatically adds a stop button to your front panel that allows you to stop the execution of the loop.

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Hands-on Introduction to Data Acquisition with LabVIEW 36 21. Rather than displaying our data in a graph indicator, we want to display our temperature

readings in a thermometer indicator. To do this, go to the front panel by pressing <Ctrl-E>. Right-click the graph indicator and select Replace. The Controls palette will appear. Select

Modern»Numeric»Thermometer. The thermometer indicator should now appear instead

of the graph indicator.

22. Also, right-click on the stop (F) button and select Replace. The Controls palette will appear. Select Boolean»Stop Button.

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Hands-on Introduction to Data Acquisition with LabVIEW 37 23. Modify the thermometer indicator by right-clicking it and selecting Properties. On the

Appearance Tab, change the Label to Temperature.

On the Scale tab, change the Minimum to 20 and the Maximum to 30.

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24. Switch to the block diagram. Expand the While Loop. Your block diagram should now

resemble the following illustration.

25. To perform analysis on your data, select the Express»Signal Analysis»Statistics Express VI and place it on your block diagram.

26. A properties window will appear. Make the following selections and click OK.

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Extreme Values: Maximum, Minimum

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Hands-on Introduction to Data Acquisition with LabVIEW 40 28. Right-click the Arithmetic Mean output of the Statistics VI and select Create»Numeric

Indicator. This will create a numeric indicator on the front panel that will display the mean.

Repeat this step for both the Maximum and Minimum outputs of the Statistics VI. Your block diagram should resemble the following.

29. Switch to the front panel and rearrange your controls and indicators to resemble the following.

30. Save the VI in the Desktop\CustomerWorkfolder by using the File menu and name it

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Hands-on Introduction to Data Acquisition with LabVIEW 41 31. Run the VI. Hold the thermocouple between your fingers to raise the temperature. Notice

the change in temperature on the thermometer. If you are not seeing enough of a temperature fluctuation, stop the VI and decrease the range on your thermometer indicator.

32. Click the STOP button on the front panel when you are finished. 33. Close the VI.

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Exercise 2b: File I/O in LabVIEW

Exercise Overview

Objective

How to log data to a file using LabVIEW.

Goals

 Know how to use Write to Measurement File express VI and how to log data to a file using

LabVIEW.

Exercise Instructions

1. Open the VI from exercise 2a.

2. Right-click on the block diagram and select Express» Output» Write to Measurement File and place it inside the While Loop on the block diagram.

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Hands-on Introduction to Data Acquisition with LabVIEW 43 3. A configuration window will appear. Enter the following parameters and click OK.

4. Wire the output of the DAQ Assistant Express VI to the input of the Write to Measurement

File Express VI.

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6. Save the VI in the Desktop\CustomerWorkfolder by using the File menu and name it

Exercise2b.vi.

7. Run the VI momentarily and press STOP to stop the VI. 8. Your file will be created in the folder specified.

9. Open the file using Microsoft Office Excel or Notepad. Review the header and temperature data saved in the file.

10. Close the data file and the LabVIEW VI.

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Exercise 2c (Optional): Automatic Code

Generation in LabVIEW

Exercise Overview

Objective

Create DAQmx code from the DAQ Assistant.

Goals

 Know how to generate code automatically from the DAQ Assistant.

 Have experience using some of the NI-DAQmx VIs.

Exercise Instructions

1. Open the VI from Exercise 2a.

2. Delete all the functions and terminals from the block diagram except the DAQ Assistant. Delete all the wires as well.

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Hands-on Introduction to Data Acquisition with LabVIEW 46 4. NI-DAQmx will now generate LabVIEW code using the NI-DAQmx API. Your block diagram

should now resemble this:

5. Double-click on the configuration VI (shown below) that NI-DAQmx generated for you on your block diagram

6. The block diagram of the configuration VI should appear as shown below. This is an example of how you can use the DAQmx VIs if you need to create customized DAQ code that includes features beyond those offered by the DAQ Assistant.

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Hands-on Introduction to Data Acquisition with LabVIEW 47 In this block diagram, you will see 3 SubVIs:

DAQmx Create Task.vi

DAQmx Create Channel.vi

DAQmx Timing.vi

To learn about each VI, hover your mouse over each one and press <Ctrl-H>. This will bring up the Context Help which explains the parameters and functionalities of each VI.

7. Close the VI and do not save any changes.

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Exercise 3: Controlling Program Execution

If you are up for challenge, try to build the following LabVIEW application without using the instructions; if you feel you need more guidance skip down to the section step-by-step for a complete set of instructions.

Challenge Application

Using a While Loop, case structure, toggle switch and the Simulate Signal VI, create a simple application that charts a sine or triangle wave depending on toggle switch position.

When you are done, save your VI as Exercise3-Decisions.vi. You will use it in the next

exercise.

If you are really up for a challenge add logic to the VI so it will stop either when you press the stop button or when the loop iterations have exceeded 10,000.

Step By Step Instructions

In this exercise, you will create a LabVIEW VI that will output a triangle or sine wave to a front panel graph depending on the state of a toggle switch. You will use a case structure to handle the logic of which signal is output and a While Loop to keep the application running until a Stop button is pressed.

1. Let’s start by placing a While Loop on the block diagram. Draw it large enough to

accommodate the other code you will be placing inside it. You can locate the While Loop on the Express»

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Hands-on Introduction to Data Acquisition with LabVIEW 49 2. Next select the Case Structure from the Execution Control palette and place it inside the

While Loop as shown below.

3. Next we will add the simulate signal VIs two the case statement. Remember one will output a triangle wave, the other a sine wave. From the Express»Input palette, select

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Hands-on Introduction to Data Acquisition with LabVIEW 50 4. Configure the first Simulate Sig to produce a triangle wave by selecting the Signal type

as shown below.

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Hands-on Introduction to Data Acquisition with LabVIEW 51 6. Next, switch the case statement from True to False, as shown below.

7. Repeat steps 3 and 4, except this time leave the default settings for the Simulate Sig VI so it will generate a sine wave.

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Hands-on Introduction to Data Acquisition with LabVIEW 52 9. Also add a vertical toggle switch from the Boolean palette to the front panel as shown

below.

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Hands-on Introduction to Data Acquisition with LabVIEW 53 11. Switch back to the block diagram and wire the toggle switch to the input of the case

statement as shown below.

12. Next, wire the outputs from both of the Simulate Signals to the waveform graph. Note that you will have to wire through the wall of case statement. Don’t forget wire both the cases, True and False.

13. You are ready to test your VI by switching the toggle switch back and forth. You should see the graph switch between a sine and triangle wave.

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Adding Digital Output to Your Project

Often when you are creating control applications, controlling digital lines is necessary to interface with pumps, valves, lamps, etc. In the next part of this exercise we will extend our application to include control of the digital output lines.

8. Right-click on your front panel and select an empty array container as shown below.

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Hands-on Introduction to Data Acquisition with LabVIEW 55 14. You can create an array of controls by simply inserting them into the array. Right-click

on the front panel and select a push button from the Boolean palette and drop it into the empty array.

15. It should look like the following.

16. Next we will increase the size of the array of Booleans so it contains eight elements. To do this, click on the right side of the array container and drag it to the right until eight push-buttons are visible.

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Hands-on Introduction to Data Acquisition with LabVIEW 56 17. VERY IMPORTANT STEP- Click on the eighth switch to initialize the array size:

18. Next configure the hardware to recognize these switches and control one digital output per switch. Start by switching to the block diagram using <Ctrl-E>.

19. Next select the DAQ Assistant from the Express»Output palette

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Hands-on Introduction to Data Acquisition with LabVIEW 57 21. Select all the digital output lines by clicking on the first then holding the shift key down

before clicking on the last out, then click Finish.

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Hands-on Introduction to Data Acquisition with LabVIEW 58 23. Finally wire the output of the array to the data input on the DAQ Assistant, as shown

below.

24. Switch to the front panel and Run the VI. Use the push buttons to activate the digital outputs on the NI 9472 module and watch the LEDs change as you select different push buttons.

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Optional Steps

1. Add logic to the VI so it will stop either when you press the STOP button or when the loop iterations have exceeded 10,000.

2. Do this by inserting an Or gate from the Boolean palette before the STOP button, as shown below.

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Hands-on Introduction to Data Acquisition with LabVIEW 60 3. Next select the greater than function from the Comparisons palette.

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Hands-on Introduction to Data Acquisition with LabVIEW 61 5. Right-click on the open terminal of the greater than block and select Create»Contant.

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Hands-on Introduction to Data Acquisition with LabVIEW 62 7. Finally, open and examine the State Diagram template that ships with LabVIEW. Select

File»New and select Standard State Machine from the list box as shown below.

Examine the comments included on the template. There are several templates such as this one to help you get started with your LabVIEW applications. Take a few minutes to familiarize yourself with what is available.

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Exercise 4: Multiple Operations with

Analogue I/O

Exercise Overview

Objective

In this exercise, you will use the DAQ Assistant to build a LabVIEW VI that generates and outputs an analogue waveform. You will then add a second loop that measures the waveform using an analogue input channel.

Goals

 Know how to generate signals in LabVIEW with NI CompactDAQ

 Run loops in parallel for multiple analogue operations

Exercise Instructions

1. If you closed LabVIEW after the last exercise, launch it. Open a new VI. 2. Press <Ctrl-E> to switch to the LabVIEW block diagram.

3. Browse to the Input subpalette on the Functions»Express palette and click the Simulate Sig Express VI as shown below. Place the VI on the block diagram.

4. In the Signal section of the window, set Amplitude to 5.

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Hands-on Introduction to Data Acquisition with LabVIEW 64 6. Bring up the Functions»Express palette again, and browse to the DAQmx Assist VI on

the Output subpalette of the Functions palette. Place the VI on the block diagram.

7. In the Create New window, select Analogue Output as the Measurement Type and then select Voltage.

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Hands-on Introduction to Data Acquisition with LabVIEW 65 8. In the next window, click the + sign next to cDAQ1Mod3 (NI 9263), select ao0, and click

the Finish button.

9. In the DAQ Assistant configuration window, select Generate Continuously from the Task

Timing tab in the lower part of the window. Uncheck Use timing from waveform data,

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Hands-on Introduction to Data Acquisition with LabVIEW 66 10. On the block diagram, move the DAQ Assistant Express VI to the right side of the

Simulate Signal Express VI. Wire the Sine output of the Simulate Signal VI to the data input of the DAQ Assistant VI. To create a wire, move your cursor over the blue arrow on the Sine output terminal of the Simulate Signal VI and left-click to start the wire. Move your cursor to the data input terminal of the DAQ Assistant VI and left-click again to attach the wire. Your block diagram should resemble the following figure.

11. To make the VI run continuously, create a While Loop. A While Loop causes all parts of the program inside the loop to run continuously until a Stop button is clicked. To create the While Loop, browse to the Exec Ctrl subpalette of the Functions palette and select a While Loop.

12. Draw the While Loop around your entire block diagram. Your block diagram should resemble the following figure.

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Hands-on Introduction to Data Acquisition with LabVIEW 67 13. To create a slide control for varying the frequency of the sine wave, press <Ctrl-E> to

switch to the LabVIEW front panel. Right-click on the empty gray space to pull up the

Controls palette. Select Vertical Pointer Slide from the Numeric Controls subpalette of

the Controls palette. Place the vertical pointer slide on the front panel.

14. Right-click the slide control and select Properties. On the Appearance tab, change the

label to Frequency. On the Scale tab, change the Scale Range so Minimum equals 0.00

and Maximum equals 1000.00. Click OK to close the Properties window.

15. Press <Ctrl-E> to switch to the block diagram. Notice the orange Frequency slide control terminal. Move the control inside the While Loop to the left side of the Simulate Signal Express VI. Wire the knob control to the Frequency input terminal of the Simulate Signal Express VI (the second orange arrow on the left side of the Simulate Signal Express VI).

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Note: Make sure that you wire the knob control to the correct input terminal of the

Simulate Signal Express VI. If you make a bad wire connection, double-click the wire to select it and press <Delete>.

Your block diagram should resemble the following figure.

16. This VI will now use the frequency knob on the LabVIEW front panel to generate a sine wave at the specified frequency. This sine wave is then generated on analogue output channel 0 of the NI 9263 C Series module by the DAQ Assistant Express VI.

17. Save the VI as Analogue output.vi in the Desktop\CustomerWork folder.

18. Increase the size of the block diagram window to make space for another While Loop to go below the existing Analogue Output code.

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Hands-on Introduction to Data Acquisition with LabVIEW 69 19. Place a DAQ Assistant Express VI from the Input subpalette of the Functions»Express

palette. Select Analogue Input as the Measurement Type and select Voltage. In the next window, expand channels of the cDAQ1Mod2 (NI 9215) by selecting the + sign, and select ai0. Click the Finish button.

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Hands-on Introduction to Data Acquisition with LabVIEW 70 20. In the DAQ Assistant window, select Acquire Continuously from the Task Timing tab in

the lower part of the window. Set the Rate (Hz) to 10,000 and click OK.

21. Once you click OK, a dialog window will appear asking if you would like to create a While Loop around the DAQ Assistant. Select Yes to automatically create a While Loop for this continuous acquisition.

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Hands-on Introduction to Data Acquisition with LabVIEW 71 22. The block diagram should resemble the figure above. Next, create a graph indicator to

display the analogue input data. To create a graph indicator, right-click the data output terminal of the DAQ Assistant Express VI, and select Create Graph Indicator.

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Hands-on Introduction to Data Acquisition with LabVIEW 72 23. Below is a picture of the completed block diagram.

24. Press <Ctrl-E> to switch to the LabVIEW front panel.

25. Locate the stop (F) Push Button control and right-click to replace it with a Stop Button control, as shown on the diagram below. (Replace»Boolean»Stop Button)

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Hands-on Introduction to Data Acquisition with LabVIEW 73 26. Rearrange the front panel controls and indicators to resemble the figure below.

27. Save the VI as Analogue Input and Output.vi in the Desktop\CustomerWork

folder. 28. Run the VI

29. The analogue output loop is generating a sine wave on analogue output channel 0, which is wired directly to channel 0 of the analogue input module. Use the slider control on the front panel to control the sine wave frequency, and look at the graph on the front panel to monitor the sine wave.

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Beyond the Exercise

For Loops can be used to generate arrays using a feature called automatic indexing, as shown in the following figure.

Try building the following block diagram to further manipulate the waveform being generated.