The positions of the F0 and F1 keystones require special consideration since the fishing rod in F1 is not operational.
According to entries 7900 and 8135, in order to have the optic at the correct height the following relationship must hold (provided BF LVDT = 0 µm)
LVDT_F0 + LVDT_F1 = -1263 µm
In order to choose a suitable value for the positions of F0 and F1 keystones I took a look to their positions during the previous 30 days from the 13th of March. During this period there were temperature changes as large as 1.4 ºC. Additionally, the suspension was in vacuum from the 15th to the 26th of February. Maximum and minimum values are
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Temperature
- Maximum: 24.6 ºC at 03:04 hrs. UTC on 20-02-2019.
- Minimum: 23.2 ºC at 13:16 hrs. UTC on 24-02-2019.
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F1 displacement
- Maximum: -193.4 µm at 07:06 hrs. UTC on 14-02-2019.
- Minimum: -1250 µm at 02:04 hrs. UTC on 19-02-2019.
The mid-point position of F1 keystone during this period was -721 µm. Therefore, the F0 keystone position should be -542 µm.
Gas filter intended positions
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F0: -542 µm.
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F1 position: -721 µm.
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BF position: 0 µm.