Impact Test (DAQmx)

LabVIEW 2017

The Impact Test application example acquires data from one force hammer and up to 15 accelerometer channels. This application supports multiple test configurations for scenarios that require measurement sets from a roving hammer and accelerometers. The top-level VI executes three loops in parallel:

• User Interface (UI) Loop—This loop accepts front panel user input and passes it to other loops for processing.
• Data Acquisition (DAQ) Loop—This loop implements a queue-driven state machine for acquiring continuous analog input data.
• Processing (PROC) Loop—This loop verifies impact data by limit test, measures frequency response functions, saves time waveforms to a TDMS file, saves frequency response functions to a UFF58b file, updates displays, and manages internal data caches.

The follwing figure is a map of the Impact Test block diagram:

For each impact, the Impact Test example performs the following actions:

• Windows each channel and computes the frequency response
• Displays results of each frequency response as magnitude and phase
• Graphs coherence to evaluate the validity of the measured frequency response.

Running this Sample Project

1. Connect the first channel to an instrumented force (impact) hammer.
2. Connect the other channels to accelerometers mounted on the structure under test.
3. Configure an equal number of rows in the node table and the channel table in the Configure Acquisition menu. The node table is on top of the channel table.
4. Specify a unique data directory to save your session results.

   Note  You may lose data if you do not specify a unique data directory for each session.

   The following figure shows the configuration screens for the logging directory and the data acquisition hardware:

   
5. Click Start to begin an acquisition session.
6. Update the node table during acquisition or while acquisition is stopped to change the following settings:
   • impact direction
   • impact location
   • response direction
   • response location.

   Note  You cannot update the DAQmx configuration while acquiring data.

Test Configurations Supported by this Example

SISO—Single Input, Single Output

MISO—Multiple Input, Single Output—roving hammer

SIMO—Single Input, Multiple Output—roving accelerometer

MIMO—Multiple Input, Multiple Output—roving hammer with multiple response locations

Ensuring Successful Impact Testing

• The force hammer and tip should input enough force across the frequency range of interest to excite the structure without inducing non-linear behavior. Inappropriate excitation can damage even large structures.
• Do not select accelerometers that introduce excessive mass loading.
• Set the DAQmx timing sample rate at least 2.5 times higher than the maximum frequency of interest. The block duration should capture all responses until they decay to zero/noise.
• In cases of extremely low damping, use an exponential window to reduce leakage in the measured FRFs.
• Impact perpendicular to the surface.
• Avoid double hits. Strike the structure just hard enough to trigger. Ensure the hammer pulls back before the structure rebounds.
• Practice impact testing:
  • Strike the structure just hard enough to trigger.
  • Avoid double hits by retracting the hammer before the structure rebounds.

• Tune the hammer and response limits to reject overloads, double hits, and excessive ringing.

  

System Requirements

• LabVIEW Full Package
• NI-DAQmx driver software
• NI Sound and Vibration Toolkit

Developer Walkthrough

Refer to ni.com for a developer walkthrough of the sample projects.

LabVIEW Features and Concepts Used

• Case structures
• Clusters
• Control refnums
• NI-DAQmx VIs
• Enums
• Error clusters
• Event structures
• LabVIEW Schema VIs and Functions
• Notifiers
• Parallelism
• Producer/Consumer design pattern
• Project libraries
• Queues
• Stacked Sequence Structures
• State machines
• Shift registers
• Sound and Vibration Measurement Analysis VIs
• Typedefs
• User events
• Value change events
• While Loops

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