This evening, I was not able to successfully transition CARM from ALS to 1/sqrt(trans) signals.  The TRY time series looked odd, so I took a spectra, and we have huge 60Hz noise in TRY. 

I found a lock stretch from around 6:30pm that did not show the 60Hz noise, and then there was a lock stretch around 8pm that did have the noise.  So, something happened at the Yend between 6:30 and 8pm tonight.

Asking around, this was the time frame in which Manasa was down at the Yend to realign the green beam, and to check cabling for the PZT_OUT and ERR_MON signals to the ADC.

Looking at the spectra, Rana noted that we have even as well as odd harmonics of the 60Hz line, which is unusual.

To try to diagnose the problem, Rana and I tried to make sure no cables' connectors were touching, and that no equipment was plugged in that shouldn't be.  We noticed that none of: the shutter, the Thorlabs TRY PD, or the QPD TRY are isolated from the table.  To see if perhaps the shutter was the problem, I turned off the power to the Yend green shutter, and unplugged the cable.  The cable is laying on the table, with the connector sitting on a piece of plastic to isolate it.  Removing the shutter from the system did not change anything. 

We don't see the 60Hz noise in the Xarm, so it's not on the laser light itself.  Also, we don't see the 60Hz lines in the Yarm feedback signal, so we're not putting the lines onto the mirror, and thus onto the Yarm's light. 

Manasa, can you please take a look, and see if you can figure out what is going on?  We need TRY so that we can transition to 1/sqrt(trans) signals for CARM.  Thanks!!