Instructions for Third Party Front Ends

Three different capabilities are supported by the VES-700 Multi-channel Acquisition Option.  However, not all capabilities are supported by each third party front end.

1. ODS & OMA Acquisition

During ODS or OMA Acquisition, Operating Deflection Shape (ODS) or Operational Modal Analysis (OMA) data is acquired from an operating machine, or from a structure that is excited by ambient or unmeasured excitation forces.  ODS or OMA data can consist of broad band, narrow band, or cyclic responses.  Output-only responses can be acquired in two ways,

  1. All channels of data are simultaneously acquired

  2. Some channels are simultaneously acquired together with a (fixed) reference response in multiple Measurement Sets.

ODS or OMA data can be post-processed  to yield,

  1. single channel time or frequency domain measurements

  2. cross channel frequency domain (Cross spectrum, ODSFRF) measurements

FRF-based curve fitting is used to extract operational modal parameters from a set of FRFs, Cross spectra, or ODS FRFs.

2. Impact Testing

Impact testing is done by providing an impact force using an impact hammer. The impact force channel is typically designated as the trigger channel on the Trigger channels spreadsheet. Data is acquired when user-specified trigger conditions are met on the trigger channel.  Trigger conditions include +/- trigger level and pre-trigger delay. Overload detection and double hit detection can also be enabled using commands in the Acquire menu

If the impact force is acquired on the trigger channel, and responses to the force are simultaneously acquired on other channels, an FRF between the impact force and each response can be calculated. FRF-based curve fitting can also be used to extract modal parameters from a set of FRFs. Coherence as well as Auto & Cross spectra can also be calculated from simultaneously acquired data.

3. Shaker Testing (using the VES-7620 Option)

Source signals can be output through some brands of supported third party acquisition hardware to as many as six shakers.  Two different kinds of broad band signals can be output.  Periodic random or Burst random, and fast sine sweep (chirp) or Burst chirp signals are available.

Burst chirp and Burst chirp are ideal excitation signals for acquiring linear, alias-free measurements. These measurements are ideal for extracting either experimental modal parameters or operational modal parameters using FRF-based curve fitting.

Front End Software

The software required for each supported third-party front end must also be installed on the same computer with ME'scope. When the Acquire | Connect to Front End command is executed in an Acquisition window, an error will occur if the front end software cannot be found on your system.