Lesson 9 Data Acquisition and Waveforms

1
Lesson 9Data Acquisition and Waveforms

• TOPICS
• Plug-in DAQ devices
• Data Acquisition in LabVIEW
• Analog Input
• Data Logging
• Analog Output
• Counters
• Digital I/O

2
Overview and Configuration

• Fundamental task of a DAQ system is to measure or
  generate real-world physical signals
• DAQ system consists of
• Transducers
• Signal Conditioning
• Plug-in DAQ device
• Driver
• Software

3
Measurement Software Framework

• NI-DAQ contains
• Traditional NI-DAQ
• NI-DAQmx

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DAQ Hardware Configuration
Measurement Automation Explorer (MAX)
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Channels and Tasks
Channel names
Sine Wave 1
ai 0
Signals
Sine Wave 2
ai 1
ai 2
Sine Wave 3
Tasks
Timing and Triggering
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The DAQ Signal Accessory
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NI-DAQmx versus Traditional NI-DAQ
Feature NI-DAQmx Traditional NI-DAQ
Test Panels ? ?
DAQ Assistant with code generation ? no
On-line diagnostics ? ?
Scaling to voltage and physical units ? ?
50 kS/s with single point I/O ? ?
Measurement multithreading ? ?
Instant calibration ? ?
Automatic selection of optimal gains ? ?
Guaranteed lossless data ? ?
650 Alliance members ? ?
Integration with LabVIEW ? ?
Developer Exchange discussion forum ? ?
Compatible with Legacy ISA Boards no ?
Productivity
Performance
Accuracy
Quality
Compatibility

• ? Best
• Good
• ? Fair

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Data Acquisition in LabVIEW

• NI-DAQmx
• Next generation driver
• VIs for performing a task
• One set of VIs for all measurement types

• Traditional NI-DAQ
• Specific VIs for performing
• Analog Input
• Analog Output
• Digital I/O
• Counter operations

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NI-DAQmx Data Acquisition
Single set of VIs used to perform analog I/O,
digital I/O, and counter operations

• DAQ Assistant Express VI
• Quickly and easily program the DAQ device
• Creates a local task
• Most applications can use the DAQ Assistant
  Express VI

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NI-DAQmx Data Acquisition Task Types

• Measurement type can be
• Analog Input
• Analog Output
• Counter Input
• Counter Output
• Digital I/O

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Analog Input
Analog Input task is specific to the measurement
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Analog Input Task Timing and Triggering
Configures the number of samples and sample rate
for the task
Configures the start and reference triggers for
the task
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Data Logging

• It is often necessary to permanently store data
  that is acquired from the DAQ device
• LabVIEW includes the ability to read and write a
  LabVIEW Measurement File
• LabVIEW Measurement File is an ASCII text file

14
Analog Output
Analog Output task is specific to the generation
type
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Analog Output Task Timing and Triggering
Configures the number of samples and sample rate
for the task
Configures the start and reference triggers for
the task
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Counters

• A counter is a digital timing device
• Typical uses of a counter
• Event counting
• Frequency measurement
• Period measurement
• Position measurement
• Pulse generation

Gate
Output
Count Register
Source
Count register Stores the current count of the
counter Source Input that causes the counter to
increment each time it toggles Gate Input that
is used to enable or disable the function of the
counter Output Signal that generates pulses or
a series of pulses
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Digital Input and Output

• Digital I/O can read from or write to a line or
  an entire digital port
• A digital port is a collection of digital lines

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Summary

• MAX is the primary configuration and testing
  utility that is available for the DAQ device.
• The DAQ Assistant is used to configure the DAQ
  device and perform data acquisition.
• Most application can use the DAQ Assistant. For
  applications that require advanced timing and
  synchronization use the VIs that come with
  NI-DAQmx.
• The DAQ Assistant can perform Analog Input,
  Analog Output, Digital I/O, and Counter
  operations.

19
Lesson 10Instrument Control

• TOPICS
• Instrument Control Overview
• GPIB Communication and Configuration
• Instrument I/O Assistant
• Virtual Instrument Software Architecture (VISA)
• Instrument Drivers
• Serial Port Communication
• Waveform Transfers

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Instrument Control Overview

• Control any instrument if you know the following
• Type of connector on the instrument - Type of
  cables needed
• Electrical properties involved - Communication
  protocols used
• Software drivers available

Instruments
Computer
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GPIB Communication
GPIB Interface
GPIB Instruments
GPIB Cable
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Standards Introduction
1965
HP designs HP-IB (Hewlett Packard Interface Bus)
HP-IB becomes IEEE 488
1975
1987
IEEE 488.2 adopted IEEE 488 becomes IEEE 488.1
1990
SCPI (Standard Commands for Programmable
Instruments) added to IEEE 488.2
1992
IEEE 488.2 revised
HS488 proposed
1993
HS488 approved
1999
23
GPIB Hardware Specifications

• Max cable length between devices 4 m (2 m
  average)
• Max cable length 20 m
• Max number of devices 15 (2/3 powered on)

24
GPIB Software Architecture Windows
Diagnostics Tools GPIB Diagnostic Tool NI-Spy
Instrument Driver VIs
Driver Software (.DLL)
NI-VISA
Interface Board (GPIB, PXI, VXI, computer based,
etc.)
LabVIEW
Configuration Tools Measurement Automation
Explorer
25
Configuring GPIB Board and Instruments

• Measurement Automation Explorer (MAX)

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What is the Instrument I/O Assistant?

• Accessed through a LabVIEW Express VI
• Sets up device communication and data parsing
  step by step through a configuration interface

27
Communicating with an Instrument
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Virtual Instrument Software Architecture
VISA
GPIB
VXI
Serial
PXI

• Platform independent
• VISA is the backbone of the IVI and Plug Play
  Instrument Drivers

• Interface independent
• Must know SCPI command set to program directly
  with VISA

29
VISA Terminology

• ResourceInstrument, Serial Port, or Parallel
  Port
• SessionConnection to a Resource
• Instrument DescriptorResource location
• Format Interface TypeAddressINSTR
• Examples

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Instrument Descriptor Syntax

• Resource Name contains interface info
• VISA Aliases also work

Interface Resource Name Grammar Serial ASRLboard
INSTR GPIB GPIBboardprimary
addressINSTR VXI VXIboardVXI logical
addressINSTR GPIB-VXI GPIB-VXIboardGPIB-
VXI primary addressVXI logical
addressINSTR
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VISA Resource Name

• Exact name and location of the instrument
• Use the VISA Resource Name control
• You can specify the full resource name of the
  VISA Alias

32
Instrument Drivers

• More than 1200 LabVIEW Instrument drivers
• Programming simplified to high-level API

33
Installing and Finding Instrument Drivers

• Drivers available at ni.com/idnet
• Install the instrument driver VI Library into
  LabVIEW 7.0\instr.lib directory
• Access drivers from FunctionsInputInstrument
  Drivers subpalette

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IDNET - Instrument Driver Network

• Learn about drivers
• Get help with developing drivers
• Submit your driver to the network
• Download drivers

35
Instrument Driver Model
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Instrument Driver VIs

• Initialize
• Configure
• Action/Status
• Data
  
• Utility
  
• Close
  

37
Instrument Driver Inputs and Outputs
HP34401A Initialize.vi

• Instrument Descriptor
• VISA Sessions
• A connection or link to a specific instrument
• Created after instrument is initialized
• Used throughout VI whenever you communicate with
  that specific instrument
• Error cluster

38
Putting It All Together

• Initialize instrument
• Do operation(s)
• Close instrument
• Check error status

39
Serial Communication

• Popular means of communication between computer
  and peripheral device
• Data sent one bit at a time across the cable
• Used for low transfer rates or long distances
• Only a cable is needed since most computers have
  at least one available serial port

PC Serial Port
RS-232 Cable
RS-232 Instrument
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Serial Hardware Connection

• RS-232
• DCE or DTE configurations
• 9-pin or 25-pin
• RS-422
• DCE or DTE
• 8-pin
• RS-485
• Multidrop

Pin DTE DCE 1 DCD Input Output 2 RxD I O 3
TxD O I 4 DTR O I 5 Com - - 6 DSR I O 7
RTS O I 8 CTS I O 9 RI I O
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Serial Communication

• Terminology
• Baud rate bits per second
• Data bits inverted logic and LSB first
• Parity optional error-checking bit
• Stop bits 1, 1.5, or 2 inverted bits at data
  end
• Flow control hardware and software handshaking
  options

42
Using the Instrument I/O Assistant with Serial

• Select COMX as the instrument address
• Use the I/O Assistant as done with GPIB

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Summary

• LabVIEW can communicate with any instrument that
  connects to your computer if you know the
  interface type
• Use the Measurement Automation Explorer (MAX)
  to detect, configure, and test your GPIB
  interface and instruments
• Use the Instrument I/O Assistant for easy and
  fast GPIB and serial programming.
• An instrument driver eliminates the need for your
  to have detailed knowledge of the specific
  strings used by an instrument
• Instrument Library more than 2000 instruments
  supported
• Instrument driver VIs share a common hierarchy
  and come with an example to help you get started

44
Lesson 11VI Customization

• TOPICS
• Configuring Appearance of Front Panel
• SubVI Front Panels
• Keyboard Shortcuts
• VI Properties
• Customizing Palettes

45
Customizing VI Properties

• Access VI Properties by right-clicking the icon
  pane or selecting it from the File menu
• Affects every instance of that VI in all
  applications

46
Window Appearance

• Only affects VI panel while VI is running

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Window Size

• Set minimum and current panel size
• Adjust size of panel relative to the monitor
• Scale objects on panel as window resizes

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Creating Pop-Up Panels Every Instance

• Use Top-Level Application Window or Dialog
  appearance types
• Create custom window appearance

49
Creating Pop-Up Panels Single Instance

• Access SubVI Node Setup by right-clicking on
  subVI icon on calling VIs diagram

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Key Navigation

• Assigns keyboard strokes to front panel controls

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Preventing Editing of a VI

• Opens, runs, and closes LabVIEW without user
  intervention
• Remove menus, Abort button, etc
• Save with Options

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Summary

• Use VI Properties to set VI execution, window,
  and documentation options
• Use SubVI Node Setup to set execution options for
  a single instance of a subVI
• Use the Key Navigation option to assign front
  panel controls to a keyboard key combination
• Use the Save with Options from the file menu to
  make backups of your VIs
• You can often edit VIs by aborting them from the
  diagram of another VI

53
Technical Support Resources

• Award-Winning Website www.ni.com/support
• Drivers Updates
• Product Manuals
• KnowledgeBases
• Example Code
• Tutorials
• Application Notes
• Discussion Forums

54
Info-LabVIEW Listserve

• User-sponsored Internet mailing list
• Send subscription messages to the Info-LabVIEW
  list processor
• listmanager_at_pica.army.mil
• Send other administrative messages to the
  Info-LabVIEW list maintainer at
• info-labview-REQUEST_at_pica.army.mil
• Post a message to subscribers at
• info-labview_at_pica.army.mil

55
LabVIEW Publications

• LabVIEW Technical Resource quarterly newsletter
  by LTR Publishing
• LabVIEW Graphical Programming and LabVIEW Power
  Programming by Gary W. Johnson, McGraw-Hill
• LabVIEW for Everyone by Lisa K. Wells and Jeffrey
  Travis, Prentice-Hall
• LabVIEW Signal Processing by Mahesh Chugani,
  Abhay Samant, and Michael Cerna, Prentice-Hall
• LabVIEW Applications and Solutions by Rahman
  Jamal and Herbert Pichlik, Prentice-Hall