K. Venkateswara

This week, I will be installing and testing the "damping turn-table" to actively damp the beam-balance in the BRS whenever it gets driven to large amplitudes.

BRS had stopped working a few days back, so I took a look at the BRS-DAQ laptop today. Just as before 13817 the CCD had temporarily stopped working causing the program to freeze up. Still not clear on why this happens but it looks like the crashes are irregular.

After restarting the program on the laptop, I noticed that the main-mirror pattern had barely drifted off the CCD (it was missing one peak out of 38). To correct this I adjusted the left-right center of mass (COM) of the balance using the small flexible adjuster located in the front face of BRS. The correction was an iterative process and took about 30-45 mins. For future reference, moving the moveable rod (located on the balance) towards the right (or south) shifts the center of the pattern to the right and vice versa.

After damping the balance and turning on the program, I noticed that there was some excess noise visible in the output going to the CDS which seemed to be due to the lack of an anti-aliasing low pass filter in the code. I had bypassed the low-pass filter to save computation cost, but apparently there is more high-frequency noise in the CCD output than before. After enabling the anti-aliasing filter, the output going to CDS looked clean again.

Over the next few days Jeff and I'll also try to resume where he left off here: 14047. I've attached a pdf showing the BRS, GND_STS and ST1_T240 measurements for comparison. This data set was measured this afternoon starting at: 1096665586. ST1 motion is smaller now in 10-100 mHz band after improvements to the configurations over the last several weeks, but there is still a lot of coherence with the GND sensor.