Lesson 9

Data Acquisition and Waveforms

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

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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

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Measurement
Software
Framework

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

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DAQ Hardware Configuration

Measurement & Automation Explorer (MAX)

4
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

5
The DAQ Signal Accessory
NI-DAQmx versus Traditional NI-DAQ
Feature NI-DAQmx Traditional NI-DAQ
Test Panels  
DAQ Assistant with code generation  no
Productivity
On-line diagnostics  
Scaling to voltage and physical units  
50 kS/s with single point I/O  
Performance
Measurement multithreading  
Instant calibration  
Accuracy Automatic selection of optimal gains  
Guaranteed lossless data  
650 Alliance members  
Quality Integration with LabVIEW  
Developer Exchange discussion forum    Best
Good
Compatibility Compatible with Legacy ISA Boards no  Fair

7
Data Acquisition in LabVIEW

Traditional NI-DAQ NI-DAQmx

Specific VIs for Next generation driver:
performing: • VIs for performing a
• Analog Input task
• Analog Output • One set of VIs for all
• Digital I/O measurement types
• 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

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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

15
Counters
A counter is a digital timing device
Typical uses of a counter:
• Event counting Gate Output
• Frequency measurement
Count Register
• Period measurement
• Position measurement Source
• Pulse generation
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

17
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.

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Lesson 10
Instrument 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

20
GPIB Communication
GPIB Interface

GPIB Instruments

GPIB
Cable
 Standards Introduction
1965 HP designs HP-IB (Hewlett Packard Interface Bus)
1975 HP-IB becomes IEEE 488

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
1993 HS488 proposed

1999 HS488 approved

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GPIB Hardware Specifications
• Max cable length between
devices = 4 m (2 m average)
• Max cable length = 20 m
DIO1 DIO5 • Max number of devices =
DIO2
DIO3
1 13 DIO6
DIO7 15 (2/3 powered on)
DIO4 DIO8
EOI REN
DAV GND (TW PAIR W/DAV)
NRFD GND (TW PAIR W/NRFD)
NDAC GND (TW PAIR W/NDAC)
IFC GND (TW PAIR W/IFC)
SRQ GND (TW PAIR W/SRQ)
ATN 12 24 GND (TW PAIR W/ATN)
SHIELD SIGNAL GROUND

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GPIB Software Architecture — Windows
Diagnostics Tools:
GPIB Diagnostic Tool
NI-Spy

Driver
Instrument
Software NI-VISA
Interface Board Driver VIs
(*.DLL)
(GPIB, PXI, LabVIEW
VXI, computer
based, etc.)

Configuration Tools:
Measurement &
Automation Explorer
Configuring GPIB Board and Instruments

Measurement & Automation Explorer (MAX)

25
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

26
Communicating with an Instrument

27
Virtual Instrument Software Architecture

VISA

Serial GPIB VXI PXI

• Platform independent • Interface independent

• VISA is the backbone of the • Must know SCPI command
IVI and Plug & Play set to program directly with
Instrument Drivers VISA

28
VISA Terminology
• Resource—Instrument, Serial Port, or Parallel Port
• Session—Connection to a Resource
• Instrument Descriptor—Resource location
– Format: Interface Type::Address::INSTR
– Examples:

29
Instrument Descriptor Syntax
• Resource Name contains interface info
• VISA Aliases also work

Interface Resource Name Grammar

Serial ASRL[board][::INSTR]

GPIB GPIB[board]::primary address[::INSTR]

VXI VXI[board]::VXI logical address[::INSTR]

GPIB-VXI GPIB-VXI[board][::GPIB-VXI primary

address]::VXI logical address[::INSTR]

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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

31
Instrument Drivers
• More than 1200 LabVIEW Instrument drivers
• Programming simplified to high-level API

32
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 Functions»Input»Instrument Drivers
subpalette

33
IDNET - Instrument Driver Network
• Learn about drivers
• Get help with developing drivers
• Submit your driver to the network
• Download drivers

34
Instrument Driver Model

35
Instrument Driver VIs
• Initialize • • •

• Configure • • • • • • • •

• Action/Status • • • • • • • • • • • •

• Data • • • • • • • • • • • • • • • • • • • • • • • • • •

• Utility • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

• Close • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
•

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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

37
Putting It All Together

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

38
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

39
Serial Hardware Connection
• RS-232
– DCE or DTE
configurations
– 9-pin or 25-pin Pin DTE DCE
• RS-422 1 DCD Input Output
2 RxD I O
– DCE or DTE 3 TxD O I
– 8-pin 4 DTR O I
5 Com - -
• RS-485 6 DSR I O
7 RTS O I
– Multidrop 8 CTS I O
9 RI I O

40
 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

41
Using the Instrument I/O Assistant with Serial

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

42
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

43
Lesson 11
VI Customization

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

44
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

45
Window Appearance
Only affects VI panel while VI is running

46
Window Size
• Set minimum and current panel size
• Adjust size of panel relative to the monitor
• Scale objects on
panel as window
resizes

47
Creating Pop-Up Panels – Every Instance
• Use Top-Level Application Window or Dialog appearance types
• Create custom window appearance

48
Creating Pop-Up Panels – Single Instance
Access SubVI Node Setup by right-clicking on subVI icon on
calling VI’s diagram

49
 Key Navigation
Assigns keyboard strokes to
front panel controls

50
Preventing Editing of a VI
• Opens, runs, and closes LabVIEW without
user intervention
• Remove menus, Abort button, etc…
• Save with Options

51
 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

52
Technical Support Resources
Award-Winning Website www.ni.com/support
• Drivers & Updates
• Product Manuals
• KnowledgeBases
• Example Code
• Tutorials
• Application Notes
• Discussion Forums

53
Info-LabVIEW Listserve
User-sponsored Internet mailing list
• Send subscription messages to the Info-LabVIEW list processor
listmanager@pica.army.mil
• Send other administrative messages to the Info-LabVIEW list
maintainer at
info-labview-REQUEST@pica.army.mil
• Post a message to subscribers at
info-labview@pica.army.mil

54
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

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