The following is an update to the status of the H2 SUS ETMy L2 stage (PUM) actuation. The L2 stage has not been completely vetted with clean transfer function measurements and good coherence seen in all of the OSEMs.  The drive amplitudes needed for these measurements are approaching the DAC limit of ~131,000cts for individual OSEMs coils.  Note that this value is much higher than the actuation watchdog limit set in the SUS QUAD User model, which was initially set at 15,000cts.  The limits were increased to allow these large excitations to pass.  

The first plot is a whitenoise transfer function measurement taken on 07/02/2012 in the Longitudinal DoF on ETMy L2.   There is great coherence above 3.5Hz for one of the OSEMs (the "LR" OSEM), however, the drive is sent equally to each OSEM.  The remaining OSEMs have some coherence, but is much lower than expected for a healthy OSEM response. The DC coherence is essentially zero for all OSEM responses.  The WhiteNoise amplitude for this measurement was ~300,000cts in the "*_TEST_L_EXC" channel, corresponding to roughly a 75,000ct amplitude per OSEM coil.  The reason why one OSEM has such a high coherence is still an ongoing investigation.  Possible measurements would be to measure the impedance of the Coil Driver box or the Satellite amplifier for each of the OSEM drive signals. For the transfer function plot itself, the resonances are somewhat visible but not sharp enough to be distinguished.  

The second plot is the same measurement taken back on 06/04/2012 but with a lower excitation amplitude of 90,000cts in the "*_TEST_L_EXC" channel. There is great coherence above 6Hz for one of the OSEMs (the "LR" OSEM).  The remaining OSEMs have some coherence, but is still not quite as good enough for a clean transfer function measurement.  For the DC coherence, each of the four OSEMs do respond in equal magnitude with the "UR" OSEM having a slightly lower DC response.  The same can be seen in the transfer function at DC, where the "UR" OSEM has a slightly lower DC response.  Resonances are still not clearly visible as well.