NI-DAQmx Basic Course NITS John Shannon

Transcription

1 NI-DAQmx Basic Course NITS 2005 John Shannon

2 Agenda Intro to DAQMX Difference between traditional / DaqMX MAX and DAQ Assistance Analog Input / Output Property Nodes Buffered / Continuous Acquisition Analog Output Triggering Counter / Timers Counter Timer Concepts

3 What is NI-DAQmx? Driver level software DLL that makes direct calls to your DAQ device NI-DAQ does not support 3rd party Data Acquisition devices Supports the following National Instruments software: LabVIEW Measurement Studio Also supports the following 3rd party languages: ANSI C Borland C++ Microsoft C/C++ Borland Delphi Visual Basic Subset of NI-DAQmx can run under other Operating Systems MAC OS X Linux

4 Measurement Services: More than just a driver Streamlined API Polymorphic functions Automatic code generation Simple and intuitive API Improved Driver Architecture Multithreaded measurements Easy, Instant calibration 20x faster for single-point operations Code generation Configuration Manager (MAX) LabVIEW DAQ Assistant API Driver Engine Hardware NI-DAQmx Measurement Services Software

5 Measurement and Automation Explorer (MAX) Task and channel creation Built-in test panel windows Device configuration and connection management Signal connection diagrams 5 April 2002

6 DAQ Assistant A step-by-step guide that helps you configure DAQ tasks, virtual channels, and scales with zero programming. Can be launched by right clicking on DAQmx controls. DAQ Assistant Express VI (local to application, not in MAX) MAX, right click Data Neighborhood and select Create New.

7 Physical & Global Channels in MAX Physical Channels Terminal of pin at which you can measure or generate an analog or digital signal. Hardware level Global Channels Global channels configured in MAX or application through DAQ Assistant. Can be used in any application or added to any task. If you modify a global channel, it will affect all tasks in which it is used.

8 NI-DAQmx Task A collection of one or more local or global virtual channels with timing, triggering, and other properties included.

9 KF2 Example 1 Explore MAX Run Test Panels Configure a Global Channel, Scale, and Task

10 Slide 9 KF2 need to add B & C portions to this exercise that show calibration, import/export wizard Kristi Fairchild, 11/23/2004

11 Programming with NI-DAQmx and LabVIEW Flexible programming options: DAQ Assistant Creating Tasks and Channels in MAX DAQ Assistant Express VI DAQmx Task Name Constant Automatic code generation NI-DAQmx API DAQmx VIs DAQmx Property Nodes

12 KF3 Example 2 Measuring Voltage in LabVIEW Using the DAQ Assistant Express VI

13 Slide 11 KF3 need to add B & C portions to this exercise that show calibration, import/export wizard Kristi Fairchild, 11/23/2004

14 NI-DAQmx - VI s & Property Nodes in LabVIEW Core Polymorphic VIs NI-DAQmx Task and Channel Constants DAQ Assistant Property Nodes Advanced Utility Functions 12 April 2002

15 DAQmx Property Nodes NI-DAQmx uses these LabVIEW constructs to provide complete programmatic control for all properties supported by the NI- DAQmx API. NI-DAQmx also provides a set of VIs that you can use to write your application, they are equivalent but easier and more convenient to use. The two examples are functionally equivalent.

16 Read VI & Read Property Node Read VI Used for analog, digital, counter, and raw data Single or multiple channels and samples Properties include Offset Channels to Read Waveform Attributes Status Current Sample # Advanced Raw Data Width And many more!

17 Write VI & Write Property Node Write VI Used for analog, digital, and unscaled data Single or multiple channels and samples Properties include Position Offset Regeneration Mode Status Space Available in Buffer Advanced Raw Data Width And many more!

18 Data Transfer for an Input Operation Onboard FIFO Memory DATA Input Rate PCI Bus Transfer Rate ASIC PC Buffer ADE (Application) Memory RAM LabVIEW

19 Finite Buffered Acquisition Perform a hardware-timed, finite buffered acquisition Set the buffer size, sampling mode, sampling rate, and number of samples to read per channel Number of samples per channel equals the buffer size or configure with Configure Input Buffer VI. Configure buffer, sampling mode, and rate NSamp = Multiple Samples

20 Continuous Buffered Acquisition If Num of samples per channel is unwired or set to -1, DAQmx automatically determines how many samples to read, based on task configuration. Set buffer size Select continuous samples for sample mode Available samples per channel = # available to read While loop around DAQmx Read

21 DAQmx Analog Output Set the buffer size, sampling mode, sampling rate, and number of samples to read per channel. Number of samples per channel equals the buffer size. Can be set with either the DAQmx Timing VI or with Configure Input Buffer VI.

22 Example 2 Analog Input

23 Trigger VI & Trigger Property Node Trigger VI Configures the task to start or stop on a rising or falling digital edge, analog edge, or analog windows Properties include Start Trigger Type Start Digital Edge Source Start Analog Window Top Reference Pre-Trigger Samples per Channel Reference Analog Edge Slope And many more!

24 Triggering Digital Triggering Acquired Signal Input Signal Trigger Signal

25 Triggering Analog Triggering Acquired Signal Input Signal Trigger Signal Trigger Threshold

26 Counter Applications Edge Counting Simple Edge Counting Time Measurement Pulse Generation Single Pulse Generation Pulse Train Generation Pulse Measurement Period Measurement Pulse Width Measurement Frequency Measurement Position Measurement Gate Source Count Register Out

27 DAQmx Source and Gate Selectors Source and gate selection is seamless The terminology morphs depending on the specific application You only need to specify the input terminal for your measurement and DAQmx will connect it to the appropriate source or gate depending on the application Counter signals can be input on any PFI pins DAQ Assistant will give you the default PFI pin for the application

28 DAQmx Simple Edge Counting Use the Counter instance of the DAQmx Read VI Start Task Count Edges Stop Task

29 DAQmx Pause Trigger Edge Counting Pause trigger is set with DAQmx Trigger property node Create Virtual Channel Start Task Count Edges Stop Task

30 Example 4 Simple Event Counting

31 The Latest and Greatest Features of NI-DAQmx USB Support (7.5) Simulated Devices (7.4) Virtual Channel Calibration (7.4) Ability to Programmatically Save Tasks/Channels/Scales to MAX (7.4) Connection Diagram Report Generation (7.4) Continual Addition of Example Programs

32 Questions?

33 Virtual Channels Virtual Channels Are a collection of settings that can include a name, a physical channel, input terminal connections, type of measurement / generation and scaling info. Can be configured with DAQ Assistant (MAX or Application) Can also be configured through the DAQmx API in your application (DAQmx Create Virtual Channel VI). Virtual channels created inside a task are local channels. Virtual channels defined outside a task are global channels.

34 NI-DAQmx Simulated Devices Run NI-DAQmx programs and Assistant without the hardware! Assistant and programs run just like on a real device with some exceptions: Timing and triggering are instantaneous Reads return fake data (for AI, data is a sine wave with some noise) Works for any supported DAQmx Device (DAQmx Plug-in Devices, SCXI, SCC s, etc.)

35 Virtual Channel Calibration Complete end-to-end calibration Analog Input only Multi-channel if all same type All done in software Can be combined with all other scaling types: measurement, devicecal, TEDS, custom scales, etc.

36 Create Virtual Channel VI & Channel Property Node Create Virtual Channel VI Programmatic creation of virtual channel(s) Adds the created channel(s) to a specified task Properties include Channel Type Physical Channel Name Description Analog I/O Custom Scale Name Digital I/O Number of lines Counter I/O Pulse Duty Cycle And many more!

37 DAQmx Analog Output DAQmx allows single-point, buffered, continuous, or triggered generation. The Use Waveform instance of the DAQmx Timing VI allows you to generate a waveform data type Output waveform frequency depends on update rate and the number of cycles of the waveform in the buffer

38 DAQmx Virtual Channel Counter Options Frequency Instance Time Instance Ticks Instance

39 DAQmx Read Function 1. Select Settings Signal Type Single or Multiple Channels? 2. Verify Settings Single or Multiple Samples? Return data as waveform or double (array) type? Analog 1 Channel 1 Sample Waveform

40 Reference Triggering Acquisition starts as soon as software is started Data in the buffer keeps getting overwritten (first in first out) until the stop trigger is received Typically only for finite input operations Start acquire Post-trigger Data = Size of Buffer Pre-trigger Data Pre-trigger data Post-trigger data Reference Trigger

41 Advanced Trigger Method: Pause Triggering Allows you to pause an acquisition/generation Operation stops when trigger signal is low and resumes when trigger signal is high Analog Pause Trigger: Digital Pause Trigger: