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The tapping test has shown that structures around 30,42,44,52 Hz normally already present in the spectrum of all top stage LVDT and geophones are largely enhanced when the B1 mini-link is excited. The displacement recorded by the LVDTs was up to few micrometers RMS which is huge but
it doesn't explain why the suspension control unlocks.
Instead, a check of the raw signals from the 3 geophones used for the IP control clearly shows that all of them clip during the tapping. This
indeed will cause the suspension control to unlock. The plot shows the geophone raw signal in normal conditions vs during the tapping.
All three geophones were clipping, GEO_H0 at 52Hz, GEO_H1 at 44Hz, GEO_H2 at 52Hz. The reason why the geophones are so sensitive to these modes is that, since these are tilt modes, they couple unfiltered to the IP platform.