Data Acquisition Toolbox For Use with MATLAB® Computation Visualization Programming User’s Guide Version 2 How to Contact The MathWorks: www.mathworks.com Web comp.soft-sys.matlab Newsgroup [email protected] Technical support [email protected] Product enhancement suggestions [email protected] Bug reports [email protected] Documentation error reports [email protected] Order status, license renewals, passcodes [email protected] Sales, pricing, and general information 508-647-7000 Phone 508-647-7001 Fax The MathWorks, Inc. Mail 3 Apple Hill Drive Natick, MA 01760-2098 For contact information about worldwide offices, see the MathWorks Web site. Data Acquisition Toolbox User’s Guide COPYRIGHT 1999 - 2002 by The MathWorks, Inc. The software described in this document is furnished under a license agreement. The software may be used or copied only under the terms of the license agreement. 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Printing History: May 1999 First printing New for Version 1 November 2000 Second printing Revised for Version 2 (Release 12) June 2001 Third printing Revised for Version 2.1 (Release 12.1) July 2002 Online only Revised for Version 2.2 (Release 13) Contents Preface What Is the Data Acquisition Toolbox? . xii Exploring the Toolbox . xii Related Products . xiii Using This Guide . xiv Expected Background . xiv Using the Documentation Examples . xv How This Guide Is Organized . xv Installation Information . xvii Toolbox Installation . xvii Hardware and Driver Installation . xvii Typographical Conventions . xviii Introduction to Data Acquisition 1 Anatomy of a Data Acquisition Experiment . 1-2 The Data Acquisition System . 1-3 Data Acquisition Hardware . 1-5 Sensors . 1-7 Signal Conditioning . 1-10 The Computer . 1-12 Software . 1-12 i The Analog Input Subsystem . 1-15 Sampling . 1-15 Quantization . 1-19 Channel Configuration . 1-23 Transferring Data from Hardware to System Memory . 1-26 Making Quality Measurements . 1-28 Accuracy and Precision . 1-28 Noise . 1-32 Matching the Sensor Range and A/D Converter Range . 1-33 How Fast Should a Signal Be Sampled? . 1-34 Selected Bibliography . 1-38 Getting Started with the Data Acquisition Toolbox 2 Toolbox Components . 2-2 M-File Functions . 2-3 The Data Acquisition Engine . 2-4 The Hardware Driver Adaptor . 2-7 Accessing Your Hardware . 2-8 Acquiring Data . 2-8 Outputting Data . 2-9 Reading and Writing Digital Values . 2-10 Understanding the Toolbox Capabilities . 2-12 The Contents M-File . 2-12 Documentation Examples . 2-12 The Quick Reference Guide . 2-13 Demos . 2-13 Examining Your Hardware Resources . 2-17 General Toolbox Information . 2-17 Adaptor-Specific Information . 2-18 Device Object Information . 2-19 ii Contents Getting Help . 2-20 The daqhelp Function . 2-20 The propinfo Function . 2-21 The Data Acquisition Session 3 Overview . 3-2 Creating a Device Object . 3-4 Creating an Array of Device Objects . 3-5 Where Do Device Objects Exist? . 3-6 Adding Channels or Lines . 3-8 Mapping Hardware Channel IDs to MATLAB Indices . 3-9 Configuring and Returning Properties . 3-12 Property Types . 3-12 Returning Property Names and Property Values . 3-14 Configuring Property Values . 3-18 Specifying Property Names . 3-19 Default Property Values . 3-19 The Data Acquisition Property Editor . 3-20 Acquiring and Outputting Data . 3-22 Starting the Device Object . 3-23 Logging or Sending Data . 3-23 Stopping the Device Object . 3-24 Cleaning Up . 3-25 iii Getting Started with Analog Input 4 Creating an Analog Input Object . 4-2 Adding Channels to an Analog Input Object . 4-3 Referencing Individual Hardware Channels . 4-5 Example: Adding Channels for a Sound Card . 4-6 Configuring Analog Input Properties . 4-8 The Sampling Rate . 4-8 Trigger Types . 4-10 The Samples to Acquire per Trigger . 4-11 Acquiring Data . 4-12 Starting the Analog Input Object . 4-12 Logging Data . 4-13 Stopping the Analog Input Object . 4-13 Analog Input Examples . 4-14 Acquiring Data with a Sound Card . 4-14 Acquiring Data with a National Instruments Board . 4-18 Evaluating the Analog Input Object Status . 4-21 Status Properties . 4-21 The Display Summary . 4-22 Doing More with Analog Input 5 Configuring and Sampling Input Channels . 5-2 Input Channel Configuration . 5-3 Sampling Rate . 5-5 Channel Skew . 5-6 iv Contents Managing Acquired Data . 5-8 Previewing Data . 5-8 Extracting Data from the Engine . 5-12 Returning Time Information . 5-17 Configuring Analog Input Triggers . 5-19 Defining a Trigger: Trigger Types and Conditions . 5-20 Executing the Trigger . 5-25 Trigger Delays . 5-25 Repeating Triggers . 5-29 How Many Triggers Occurred? . 5-35.