A brief overview of labview data acquisition daq
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A Brief Overview of LabVIEW Data Acquisition (DAQ). J. Carroll 10/14/03. Overview of LabVIEW DAQ. Two characteristics help classify the type of DAQ operation performed Whether you use a buffer Whether you use an external trigger to start, stop, or synchronize an operation . Buffers.

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Overview of labview daq
Overview of LabVIEW DAQ

  • Two characteristics help classify the type of DAQ operation performed

    • Whether you use a buffer

    • Whether you use an external trigger to start, stop, or synchronize an operation


  • A buffer is an area of PC memory reserved for data, DMA allows data to be acquired directly into computer memory

    • Not using a buffer means you must handle each data point one at a time, as it is acquired

  • Use buffered I/O when:

    • Many samples are acquired at a rate faster than is practical to display, store, or analyze in real-time

    • Data is acquired/displayed continuously on the fly

    • The sampling period must be precise and uniform throughout the data samples


  • Use nonbuffered I/O when:

    • The data set is small and short (e.g., acquiring one data point every 100ms)

    • Reduced memory overhead is required (since a buffer takes up memory)

  • There are separate LabVIEW VIs for both buffered and nonbuffered I/O


  • Triggering is any method which initiates, terminates, or synchronizes a DAQ event

  • A trigger is usually an analog or digital signal whose condition is analyzed to determine a course of action

    • Software triggering is the easiest and most intuitive

    • Hardware triggering lets the circuitry of the DAQ board take control, adding more precision and control


  • Use software triggering when:

    • The user needs to have explicit control over all DAQ operations

    • The timing of an event does not need to be precise

  • Use hardware triggering when:

    • Timing a DAQ event needs to be precise

    • You want to reduce software overhead, i.e., to reduce the need for a While Loop)

    • DAQ events need to be synchronized to external events

Analog i o definitions
Analog I/O Definitions

  • A device is the “number” that NI-DAQ assigns to an I/O board

  • A sample is one A/D conversion (one data point)

  • Channels specify the physical source of the data

  • A scan is a sample taken from each channel

    • represents data versus channel number

  • A waveform is a set of samples from one channel, collected over a period of time

    • represents data versus time

The daq palette
The DAQ Palette

  • The DAQ palette has three VI “tiers”

  • Top tier VIs are easiest to use but least flexible

    • these VIs are synchronous with the DAQ data, meaning that they do not finish executing until all of the data is read/written from the board

    • one fundamental limitation with these VIs is that every time the VI is called the hardware is “setup” for the sampling operating (adding excessive overhead)

    • multiple sample points acquired using a While Loop, which adds additional overhead

    • see class web site for more examples

Top tier examples
Top Tier Examples

Nonbuffered, software triggered ADC

Buffered, hardware triggered ADC

The middle bottom vi tiers
The Middle/Bottom VI Tiers

  • Middle tier VIs offer more functionality, flexibility and efficiency

    • allows buffered acquisition that is hardware controlled (see web for more examples)

    • allows continuous or real-time acquisition using “circular” buffers

    • returns data from an acquisition in progress without interrupting the acquisition

  • Bottom tier VIs offer the most functionality, flexibility and efficiency, at the cost of complexity (see web examples)

Middle tier example
Middle Tier Example

Buffered DAQ


Continuous, Circular Buffered DAQ