As expected the stability of the lock is strongly affected by the performance of local controls. The occasional presence of spikes or excess of noise has been observed on the local controls of BS, PR and INPUT mirror.

 

In the following table I report the normal angular variation for each suspension that can be used as reference values to detect excess of noise. 

 

	open loop (urad)	closed loop (urad)
PR yaw	1-2	0.5-1
PR pitch	4-8	2-3
BS yaw	3-4	2-3
BS pitch	5-6	4-5
INPUT yaw	2-3	1-2
INPUT pitch	4-5	3-4
END yaw	2-3	1-2
END pitch	4-5	3-4

 

The value of the angular variation in micro radiant is reported on the top of each error signal plot in the labview control VIs and it is computed measuring the difference between the maximum and the minimum of the error signal over a second and multiplied it by the respective calibration. 

 

PR

We observed spikes on pitch and yaw signal on the morning of the 28th june for the first time.  Since this spikes where also present when disconnecting the signal in input to the ADC we suspecting the ADC itself or the softwere. We changed the ADC with a spare one from the labview control of the west arm without notice any improvement. ( We put back the original one.)

The spikes has disappeared the day after and I have never observed them again.

 

BS

Similar kinds of spikes are are sometimes appearing (bringing the motion up to 15-20 urad). They disappear when I disconnect the input cableto the ADC and are not present on PR signals which is using the same ADC. Maybe they are not coming from the electronics.

 

INPUT 

Excess of noise can be observed periodically. It bring the mirror motion up to 20-30 urad making impossible to keep a proper alignment. I have observed that they disappear switching on and off the  laser of the INPUT local control. I have changed the laser power supply but it didn’t solve the problem.

 

END

Nothing to report

 

My statistics is too small to extrapolate a trend for these noise occurrences but if you spend few hours working on the locking you are likely to have some noisy periods of BS and or INPUT. 

 

Investigation on the origin on the issue should be done in order to fix it. The possibility to record and store long periods of data will help this.