Summary: Ran test of SPI TIA chassis noise - TIA chassis noise seems fine, QPD B electronics in chamber have elevated noise.

Following on from yesterday's alog today I went to the floor and unplugged the input cables from TIA variant 1 in the SUS-R2 rack (SPI_HAM2_009) and TIA variant 2 in the SUS-R3 rack (SPI_HAM3_015).

Then I remeasured the dark noise in CDS after resetting the offsets in QPDA and B to 15050 counts and 16750 counts, respectively, as they were yesterday.

In the attached ASDs you can see that I compare my dark noise measurement from yesterday when the laser was shuttered ( and the JAC/IMC was unlocked to avoid scatter in HAM2/3) and one done today with the QPDs unplugged from the TIA chassis.

 I have done two comparison plots for each quadrant with QPD A on the top plot and QPD B on the bottom, segments 1, segments 2, segments 3, segment 4.

For QPDA the overall noise magnitude is unchanged between each measurement. For QPD B all four segments are different when the QPD is unplugged.

Segment 4 is by far the worst. This implies to me that the TIA is ok but there is something wrong with the QPD B electronics in chamber.