4 Transmissibility-based TPA

If the mere purpose of a TPA is to identify the dominant path contributions in the assembled product, the efforts to set up and conduct the entire experiment, that comes with a classical or component-based TPA, can be relatively disproportionate and costly. This is especially the case when multiple incoherent vibration sources are to be investigated.

Transmissibility-based TPA avoids the stage of explicit force determination. Instead, the path contributions are determined from so-called “transmissibilities” between sensors, possibly calculated from operational measurements. The following properties describe the method:

1. Measurements are conducted on the assembled product only, saving time to dismount the active components. The interfaces between the active and passive components are no longer of principal interest.
2. Path contributions are determined from well-chosen indicator points around the sources or connections. These indicator points function as inputs to the TPA.
3. The analysis result is highly subject to the choice for these indicator points; therefore, care should be taken to include all transmission paths.

Transmissibility-based TPA departs from the traditional source-transfer-receiver model that assumes a physically meaningful set of loads, FRFs, and responses. Although potentially less accurate, it tends to be easy to set up, versatile concerning the sensor type, and remarkably effective for ranking contributions from several sources. From a practical point of view, transmissibility-based TPA tries to outrun the physically correct methods by its ability to conduct multiple cycles in a shorter time. Nevertheless, under certain conditions, results of similar (or even equivalent) accuracy can be achieved in comparison with classical and component-based TPA methods.