M. Barton & S. Steplewski

On Thursday (June 14, 2012) we tried testing the L2 stage actuators. First we noticed that the binary input/output switches were not set to use Acquire/LP filters, while the switches for the corresponding ETMY L2 stage tests had been enabled. Changing the L2 stage binary IO switch to 3 enables a low pass filter that has a gain of 10 at low frequency, which sends more drive to the coils for a given excitation amount (see state machine diagram T1100507). After finding how many counts could be safely sent to the coils without saturating, we excited H2:SUS-ITMY_L2_TEST_L_EXC with one million counts of white noise to get maximum coherence in the measurement.

The attached plot shows the OSEM response with NO DAMPING at the top stage to clearly see resonances. The peaks roughly line up with the resonances we are expecting in the suspension model. The magnitude of the response is very similar for three out of four OSEMs, but the (upper right) UR OSEM is lower by nearly a factor of 5 in amplitude. The reason for this is not totally clear, but it could be that the position of the UR OSEM is different so that it doesn't apply as much force to the PUM as the other three.

The DTT session that was used to generate these results is in:

/ligo/svncommon/SusSVN/sus/trunk/QUAD/H2/ITMY/SAGL2/2012-06-14_H2SUSITMY_L2_DTT_actuation_tests_LTF.xml