17 Benefits of Using a Portable Coordinate Measurement Machine to Measure a Modal Test Geometry 133 Fig. 17.13 An example showing how the on-screen visualization of the probe tip can be used to locate measurement points on the test article comparison included 41 nodes and was on a test article with multiple shape types (e.g., cylinders and cuboids). It has been the Authors experience that 30–40 node test geometries (on moderately complex structures) can be generated in ~1–3 h with the new method vs. 8–12 h with hand measurements. Note that the speed estimates are based on a single back-to-back comparison and the Authors experience over a variety of tests. One reason for the increase in speed is because it is much easier to measure locations with the PCMM when compared to hand tools. This is because the practitioner no longer needs to focus on the measurement values, since they are automatically recorded by the PCMM software. Rather, the operator shifts their focus to collecting the correct data type (i.e., plane or circle data), on the correct surface, for the correct transducer. The PCMM is also much easier to use because it is a 3D measurement device that combines multiple hand measurements (for angle and position) into a single operation. Another reason for the increased speed is because the process to generate the geometry from the measurement data is completely automated in the GGS. This is compared to the hand measurement method where manual data entry is required after the measurements are complete, which can be a lengthy and error prone process. With the new method, the operator just needs to export probe data, generate the accelerometer dimension file, and run the GGS. This step in the process can be done in a manner of minutes. The resulting test geometry from the new method is also very reliable. The primary reasons for the reliability are: • The accuracy of the probe data • The data validation features in the PCMM software and GGS • The level of automation in the process It has been the Authors experience that issues with mode shape visualizations (such as nodes moving in the wrong direction) or comparisons to the FE model are rarely due to issues with the test geometry when the new method is used. Instead, the issues are almost always related to the test set-up (e.g., the cables were plugged in wrong) or mistakes in the test documentation (i.e., mislabeling the node IDs). This makes it much faster and easier to troubleshoot visualization issues, because the practitioner rarely has to perform new hand measurements to validate the test geometry.
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