[Evan, Kevin, Elenna]

Tonight we tested running a DAC dither. We used the Turn_on_DAC_dithers.py script (located in gitcommon/labutils) to turn on a DAC dither on ITMX. We took a reference of the LL master out channel as well as the LL noisemon channel with no dither on. Then, we turned on the 7 kHz dither, starting low with the amplitude and increasing up to 60000. We saw no change in the noisemon channel from the dither. We tried moving the dither 5500 Hz as well, ran with the same amplitude and again saw no change. First screenshot shows the 5500 Hz settings and results on ITMX only.

Then, we turned on dithers on all test masses and ran them at 7 kHz with amplitudes of 60000. The second plot shows the results. Again, no change in the noisemon channels.

For all tests in this alog, the dither script sets up a pringle drive in the lkin2osem bank. All PUM DACs were in state 3, Acq off and LP on. As an aside, the "Turn on SUS DAC dithers" guardian state is currently configured to run these settings on the PUM DACS only. I commented out all other DACs for the time being, since we have not properly tested them.

We conclude that the dithers have no effect on the DAC noise. This does not change if you change the dither frequency or amplitude. This is the same for all test masses.

We performed this test because our noise budget currently shows we are limited by PUM DAC noise from 10-20 Hz.