Genevieve and Sam identified the sources of many of the peaks that were vibrationally coherent with DARM in the 20 to 40 Hz region (8012 ). We suspected coupling at HAM1 and I tested this recently using local injections and the beating shaker technique.

With local injections at HAM1 using shakers and HEPI, we can produce much larger  signals at the HAM1 table top then at the PSL or HAM2. The coupling site will likely have the same ratio of locally injected peaks to distant equipment peaks in its vibration sensors as the ratio of these peaks in DARM. The figure shows that the ratio of the injected peak at 25 Hz to the Air Handler peak at 26.35 Hz is consistent with coupling at HAM1 but not HAM2 (or any place else – most other potential coupling sites don’t even detect the peak injected locally at HAM1)

The figure also shows that the beats from the beating shakers matched DARM at the HAM1 table top, but could also be consistent with coupling at HAM2, so this technique, as implemented, gave a consistency check but did not discrimate well between HAM1 and 2.