Modal FRF Trigger Point Recalculating

  • Software
  • Modal FRF Trigger Point Recalculating
Ben McMahon

Posted on 21.06.2017 02:45


I am helping a client with some post processing of a Dewesoft X2 file (the file is a bit messy sorry and has some displays that are redundant). The file is is a Modal FRF with a roving impact method setup with triggering on the hammer. The impact detection appears to have working properly with the original file, however, I want to include some post processing such as an integration channel and changing no lines on display. I am finding that when I recalculate the maths channels the triggering detection of the TF's is lost and the modal test results are nulled. Should this occur?

I would like to share the files with you but the files are too large for the uploader in the forum. Is there another way to upload files to you so you can see what I mean?


Ben Mcmahon

Ben McMahon

Posted on 21.06.2017 05:36

I managed to cut down the test file to only include the first 6 Mb to get into forum uploader. The file with integration is too large to upload.

Attached files:
Anže Baš
Software Test Engineer I
Posted on 22.06.2017 13:04

Hello Ben,

unfortunately roving hammer method of the Modal FRF doesn't work in analysis (offline) mode. This is because you only have multiple excitations linked to the same input channel, but different groups and one response channel and the software doesn't know how to divide the hammer channel between all the groups. In measure mode this is achieved manually with clicking on the control channel next group. So there unfortunately isn't a way to change the line resolution of your data file.

Luckily you can integrate the FRF transfer functions, but only with formulas. In the attached demo data file you will see two formulas, which can be used to apply an integration and a double integration to your transfer functions. In the datafile there is also a comparison between integrating the response channel and applying the integration after the modal test to the transfer functions. As you can see the results are the same.

I hope this information will help solve some of your issues.

Attached files:
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