Genevieve, Lance, Tyler, Robert

In August, we determined that the 52 Hz peak in DARM could be dramatically reduced or eliminated by turning off the chilled water pump CHWP-2 at EX (72331), which was running at 52 Hz. On Friday I decided to check if the water pump was lining up in frequency with a mechanical resonance that made the coupling worse. So I used the variable frequency drive to move the pump frequency around. The figure shows that I found three frequencies where the water pump did not produce an obvious peak in DARM and one where it produced a bigger peak in DARM.

After consulting with Tyler, I have left the frequency at 58 Hz (98% on the FMCS screen). Of course whatever resonance was associated with the peak in DARM at 52 Hz will still be excided by non-pump seismic motion, so the 52 Hz peak may not go away completely. I may move the pump frequency around some more this week to better understand the coupling.