It was reported in entry 9797 that the SR3 TM-L transfer function had a wrong slope above the resonant frequency.
After some investigation I realized the problem is solved by turning off the anti-whitening filters (AntiWTN) in the OPLEV INPUT FILTERS block. They are 8 filters in total, one for each QPD segment. The attached picture shows the transfer function measured with the filters off.
Directory: /kagra/Dropbox/Subsystems/VIS/TypeBData/SR3/TF/Measurements/20190806/
File: SR3_TML_exc.xml
This suggests the configuration of the hardware whitening filter is not correct. It doesn't seem to be doing anything because it does not require software filters on.
I went to the tunnel and checked the configuration of the 32 bit dip switch boards inserted onto the whitening chassis for the different suspensions.
The switch configuration is the same for SRM and SR2. For BS and SR3 the configurations are different. Additionally, the configuration of the two boards used for the BS oplev are different from each other.
The diagram of the whitening filter board describes what each switch is for: JGW-D1302081.
SRM
- Oplev tilt QPD: S1809027, board number 53,
- Oplev length QPD: S1809025, board number 51,
- The following switches are on in both boards: 1, 4, 9, 12, 17, 20, 25, 28. A letter B preceeds these numbers.
- The rest are on.
SR2
- Oplev tilt QPD: S1605442, No 21,
- Oplev length QPD: S1605428, board number 007,
- The following switches are on: the same as SRM.
- The rest are on.
SR3
- Oplev tilt QPD: S1809024, No 50,
- Oplev length QPD: S1809021, No 47,
- The following switches are on in both boards: 0, 3, 4, 8, 11, 12, 16, 19, 20, 24, 27, 28. A letter B preceeds these numbers.
- The rest are on.
BS
- Oplev tilt QPD: S1605438 , No 17,
- Oplev length QPD: S1807678, No 33,
- The following switches are on in tilt QPD: 0, 4, 8, 12, 16, 20, 24, 28. A letter B preceeds these numbers.
- The following switches are on in length QPD: 0, 3, 4, 8, 11, 12, 16, 19, 20, 24, 27, 28. A letter B preceeds these numbers.
- The rest are on.
