jeffrey.garcia@LIGO.ORG - posted 16:44, Tuesday 06 September 2011 - last comment - 10:43, Thursday 08 September 2011(1345)
H2 ITMY Quad Vibration Absorber ON/OFF hammer tests
On Friday, Impulse response measurements were conducted using a Bruel and Kjaer (B&K) impact hammer and tri-axial accelerometer (also B&K) on the Quad structure. The purpose of these investigations is to assess the effectiveness of the newly-installed Vibration Absorbers on the Sleeve of the QUAD structure. The Vibration Absorbers are arranged in a "spiral" arrangement around the frame of the sleeve structure of the Quad. One VA is on each corner of the sleeve with the position heights incremented upwards around each corner - giving a "spiral" arrangement around the sleeve. The accelerometer was positioned on the M0 chain side of the Quad on the cross brace of the Lower structure just above the Test Mass. It's X-axis was oriented along the beam path, the Y-axis crossing the beam path in the same horizontal plane, and the Z-axis vertically up through the Quad. The accelerometer's position did not change throughout each test. Tap tests were conducted for three sub-structures of the Quad, with multiple spots selected within each sub-structure. The three sub-structures are the Upper Structure (cage around M0/R0), the Lower Structure (cage surrounding everything below M0/R0), and the stiffening Sleeve Structure (structure surrounding the whole build) installed on August 19th. The Upper Structure had three tap test locations, the Lower Structure had four, and the Sleeve had five. The configuration for the BSC-ISI/QUAD system was: BSC8 ISI - locked H2 ITMY QUAD - unlocked, suspended with damping loops closed for both M0 and R0 chains. Watchdogs did not trip during any of the tap tests. Data was processed in real-time using the PULSE software provided with the B&K instruments. The PULSE software monitored for "double-hits" and for impact Force range. Data was then extracted after each measurement into .txt files that were imported and processed in Matlab. The VA OFF tests were conducted first. Three spots on the Upper Structure, four on the Lower, and five on the Sleeve were selected. The VAs were then replaced to their previous locations, and the tap tests were repeated at the same locations for the VA ON tests. The attached plots are Frequency response comparison plots of the Accelerometers in each degree of freedom (DoF) at each tap test location. The magnitude ((m/s^2)/N) of the accelerometer response is plotted against the frequency range (0.5-800Hz). Each plot has a trace in dashed-red displaying the data from the tests with the VAs OFF and a trace in solid blue of the data from the tests with the VAs ON. Each plot is of the same tap test location for ON and OFF. The pdf files are grouped by sub-structure (upper, lower, sleeve) and display the responses for all locations (in separate plots) on that sub-structure for a specific DoF. I have only attached the X and Y DoFs, but the Z DoF plots will be in the SVN. Data collection parameters were: 0-800Hz response with a 0.5Hz resolution. ---------------------- Tap Test Locations *for location reference, when facing the Quad from the M0 chain, the "Beam Tube side" is on the right and the "Clean Room side" is on the left.* Upper Structure: location 1 - M0 side tapping from the Beam Tube Side across to the Clean Room side. location 2 - R0 side tapping from Clean Room side across to the Beam Tube side. location 3 - Beam Tube side - diagonal cross-brace in a downward direction. Lower Structure: location 1 - M0 bottom - from Beam Tube side across to the Clean Room side. location 2 - R0 bottom - from Clean Room side across to the Beam Tube side. location 3 - R0 side tapping on cross-brace just above the PUM from Clean Room to Beam Tube side location 4 - M0 side tapping on cross-brace just above the PUM from Beam Tube to the Clean room side Sleeve Structure: location 1 - M0 bottom right corner of sleeve on the Beam Tube side location 2 - R0 bottom right corner of sleeve on the Clean Room side location 3 - M0 top left corner of sleeve on Clean room side location 4 - R0 top right corner of sleeve on Clean room side location 5 - diagonal cross brace on the Beam Tube side
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2 Supplemental Items: -------- 1.) Attached is a picture of the location of the accelerometer used for the tests. The aLog automatically rotated the photo 90 deg counter-clockwise, but one can see the accelerometer on the cross-brace just above the test mass and slightly off center. 2.) The SUS SVN has been updated with the data and plots of these measurements as follows: Data Location: '~/sus/trunk/QUAD/H2/ITMY/Common/Vibration_Absorber_tap_tests/Data/' where the file names denote the Vibration Absorber ON/OFF configuration, which sub-structure on the Quad, and the location of the measurement. "VA_tap_test_data_VA_*OFF/ON*_*sub-struct*_*location*_110902.txt" Plots are located in: '~/sus/trunk/QUAD/H2/ITMY/Common/Vibration_Absorber_tap_tests/Plots/'
Also, it should be noted that these tests were performed with the H2 ISI ITMY (BSC-ISI) *locked* for these measurements. The suspicion is that the resonant modes seen between ~10 and 50 Hz are modes of the support structure coupling through the locked BSC-ISI. We'll need further B&K transfer function + ST2 ISI transfer function measurements with the BSC-ISI unlocked in order to confirm; the hope is to obtain these after H2 SUS ITMY (QUAD)'s lower half is returned.