YuhangZhao - 04:50, Saturday 19 September 2020 (2217)
Trying to close the AA loop
Aritomi and Yuhang
All the loop used integrator with gain of 0.1. The pitch loop has both 10Hz low pass filter as well. These filters were chosen a bit randomly. They will be improved later.
With these filters, the loop was closed. And the alignment of filter cavity was kept as shown in the attached figure. We could see that the green power goes to maximum after the loop is closed and stays stable. Besides, all the error singal goes to zero and oscillates around.
However, there is still problem. Everytime when the loop is closed, there is a very large motion of mirror. We need to solve this problem. Apart from this, the loop works well.
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Comments related to this report
Great result!
Can you plot the oplev signals for input and end mirror at the same time of the plot you attached in the entry?
Can you plot the oplev signals for input and end mirror at the same time of the plot you attached in the entry?
The large motion of mirror after closing AA loop is due to the large gain. This large gain was causing an over shoot. By adding a ramp time of 10min, the lock becomes better. As shown in the figure 2, there is still over shoot, but mirror comes back to the good position within two minutes due to the small increase of servo output.
You can see the ramp time is 600 seconds in the figure 1.