[Jason O, Stuart A]

Power spectra measurements taken earlier this week (see LHO aLOG entry 16917) suggested we should target the ITMY Oplev for our initial B&K hammer measurements.

Problems with the B&K data acquisition card yesterday prevented us from taking measurements. However, thanks to Calum, who had seen simialr occurrences at Caltech, we were able to get back up and running. Just to note that, the B&K Capabilities Wiki collates relevant documentation, and a Troubleshooting guide has now been added.

We proceeded to take B&K measurements for both the ITMY RX Leaner and TX Large Dwarf OpLev piers. A tri-axial accelerometer was clamped to a cross member near the top of each pier (see images of the set-up below). Measurements were taken using the "Simple Hammer Display 3.pls" template available in T1000697. A hammer trigger threshold of approximately 8N was found to work best. ASCII data has been exported from the B&K Pulse analysis software directly into text files (*.txt) so that it can be plotted using the "BandK_plot.m" script.

Plots are available below for the two pier types tested. The frequency of the first resonances observed (X response to X excitation) can be compared to previous measurements made on production units at Caltech, see T1100152, as well as those measured at LLO. The resonance measured at Caltech is denoted by the dashed black line in the plots and was taken when the various structures were bolted and grouted.   

Resonance Summary:

OpLev   Type   Pier Name     DCC#      Caltech   LHO 
ITMY    RX     Leaner        D1001297  34.5 Hz   21 Hz 33 Hz
ITMY    TX     Large Dwarf   D1000452  85.5 Hz   34 Hz

First structural resonances for both ITMY Leaner & Large Dwarf piers appear consistent with similar non-grouted piers measured at LLO. However, the Leaner pier exhibits an extra resonance feature around 34 Hz, which is most likely due to the bolting configuration (n.b. as well as no grout, there are also no vibration absorbers fitted). Interestingly, there is no evidence of the 3.3 Hz or 6.6 Hz features, present in the OpLev Spectra, seen in either pier.

All data and plotting scripts have been committed to the SUS svn:

/ligo/svncommon/SusSVN/sus/trunk/Common/MatlabTools/BandK_plot.m

/ligo/svncommon/SusSVN/sus/trunk/QUAD/H1/ITMY/BandK/
SimpleHammerDisplay3-ITMY-ITMY_OpLev_RX_LPier_T1a-SUSunlocked-ISIunlocked-VAnotfitted-Ximpact.txt
SimpleHammerDisplay3-ITMY-ITMY_OpLev_RX_LPier_T1a-SUSunlocked-ISIunlocked-VAnotfitted-Yimpact.txt
SimpleHammerDisplay3-ITMY-ITMY_OpLev_TX_LDPier_T1a-SUSunlocked-ISIunlocked-VAnotfitted-Ximpact.txt
SimpleHammerDisplay3-ITMY-ITMY_OpLev_TX_LDPier_T1a-SUSunlocked-ISIunlocked-VAnotfitted-Yimpact.txt

n.b. the raw B&K Pulse *.pls file for each measurement was also checked into the svn along with the exported *.txt file.