FEMtools Data Acquisition

Time Signal and Transfer Function Acquisition through National Instruments Frontends

The FEMtools Data Acquisition (DAQ) is a FEMtools add-on tool for acquiring vibration signals from a structure through data acquisition hardware. The required hardware includes response transducers like accelerometers and an optional excitation device (impact hammer or shaker) that is equipped with a piezoelectric-based force transducer.
This module can be combined with other FEMtools add-ons such as FEMtools MPE for modal parameter extraction or FEMtools RBPE for rigid body properties extraction, which can ultimately be used for applications in structural dynamics or to validate and update a finite element model.

FEMtools DAQ is installed and used as an add-on to the FEMtools Framework or any other FEMtools configuration.


The DAQ module adds the following features integrated in a easy-to-use and interactive environment:

  • Direct interfacing with data acquisition frontends from National Instruments for Dynamic Signal
    Acquisition (DSA) using NI-DAQmx drivers. The NI CompactDAQ, CompactRIO, PCI and PXI product
    lines are supported through the NIDAQmx device drivers.
  • Test model display to assist in connecting data channels to measurement degrees of freedom .
  • Reference channel selection.
  • Support for roving hammer or roving sensor impact test with optional automatic measurement point increment.
  • Trigger-based data acquisition for hammer excitation with audio and visual feedback.
  • Shaker signal generation (chirp, burst random, pure random, pseudo-random).
  • Free run data acquisition (for operational modal analysis).
  • Real-time monitoring of time series (amplitude or FFT) for selected channels.
  • Signal windowing options.
  • Linear and exponential averaging.
  • H1, H2 and Hv FRF estimators.
  • Auto and Cross-Power Spectra (XPS), FRF and  Coherence function monitoring.
  • Time histories manipulation (detrending, decimation and filtering).
  • Preview and selection of transfer functions before saving them in the FEMtools internal database.
  • Direct access of FRF and XPS functions by other FEMtools modules for modal parameter extraction, mass properties extraction and correlation with FE analysis.
  • Exporting of measured time series, FRF and XPS functions is done using the Universal File format.


FEMtools DAQ can be used as a tool for obtaining time histories and transfer functions that are then exported to other software, or used together with other FEMtools modules. The following applications are available:

  • Modal Parameter Extractor (MPE) - Modal parameters can be extracted from FRFs (input-output) or XPS (output-only). The resulting modal parameters can be used for applications like:
    • Dynamic response analysis - Dynamic analysis relies on modal superposition of mode shapes for response analysis in time or frequency domain.
    • Structural Dynamics Modification (SDM) and Modal-Based Assembly (MBA) - Simulate the dynamic response of assembled structures, using coupled modal models obtained from test.
    • FRF re-synthesis - Test FRFs can be denoised by re-synthesis from extracted modal parameters, which is recommended if these FRFs are to be used for FRF-based updating of FE models.
    • Modal-based correlation and updating - Comparing reference test modes with simulated modes provides a means to validate simulation models. Finite element models can then be updated by improving the correlation between reference test modes and predicted ones.
  • Rigid Body Properties Extractor (RBPE) - Rigid body mass properties can be extracted from FRFs if the measurements respect a number of conditions. The resulting properties can be used for lumped mass model creation or as a target for FE model updating.
  • FRF-Based Assembly (FBA) - Test FRFs obtained  from a component can be assembled with FRFs obtained from other components, either by test or simulation.
  • FRF-Based correlation and updating - Finite element modes can be updated to improve the correlation between reference test FRFs and simulated FRFs.

FEMtools DAQ can also be part of a complete vertical solution that integrates data acquisition, modal extraction and FE model updating for applications such as:

  • Material Identification - Identification of material properties using mixed numerical-experimental vibration analysis.
  • Structural Health Monitoring (SHM) - Automated monitoring of modal parameters of structures for damage assessment and residual lifetime estimation.

User Interface

All definition, editing and analysis accessible via intuitive menus and dialog boxes or using free format commands for batch processing and process automation.

  • Complete electronic documentation.
  • Dedicated graphics viewers for model inspection and results evaluation.
  • Point-and-click interactive selection.
  • Direct access to test data.
  • Unlimited customization with FEMtools Script language.


  • Easy to Use - A single control window is used for all settings and very little user-interaction is required once test setup is ready.
  • Flexible - Shaker tests, impact hammer tests or output-only tests can be run, according to the user needs and available hardware.
  • Integrated - Combined with other FEMtools modules and add-ons, multiple applications can be explored from start to finish with one software only.

Prerequisites and Licensing

The FEMtools DAQ add-on requires a separate license that is used together with a license for any FEMtools standard configuration.


MPE FRF Selection Tab

 (a) FEMtools DAQ panel.


MPE Pole Extraction Tab

(b) Signal processing tab during impact hammer test.


MPE Modes Extraction Tab

(c) Transfer functions tab during impact hammer test.


Local MPE 

(d) FRF magnitude and coherence functions.