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Reports until 16:19, Friday 19 December 2014
H1 AOS (ISC)
eleanor.king@LIGO.ORG - posted 16:19, Friday 19 December 2014 - last comment - 14:58, Thursday 14 May 2015(15758)
PRM high bandwidth filters

Thomas, Stefan, Jeff, Kiwamu, Elli

Continuing along the same line as yesterday's work on PR3 (alog 15727), we have designed high-bandwidth (<10Hz) actuation filters for the PRM.  These filters are applied to H1ASC-PRC1P and H1ASC-PRC1Y in the central part of the ASC WFS servo.

The filters added to ASC WFS central are called 'PRM^-1' and are:
H1:ASC-PRC1_P:   zpk([0.2+i+0.9;0.2-i*0.9;0.05+i*3.41;0.05-i*3.41],
                [0;0.2+i*2.75;0.2-i*2.75;0.125+i*9.99922;0.125-i*9.99922],1,"n")
H1:ASC-PRC1_Y:     zpk([0.04+i*1.08;0.04-i*1.08;0.1+i*2.08;0.1-i*2.08;0.05+i*3.43;0.05-i*3.43],
                [0;0.15+i*1.8;0.15-i*1.8;0.05+i*3.3;0.05-i*3.3],1,"n")
Some old unused filters were also removed.


Low-pass filters called 'RLP17' were added to the PRM M3 locking filters in pitch and yaw:
H1:SUS-PRM_M3_LOCK_P:  zpk([4+i*119.933;4-i*119.933],[6.78887+i*13.9134;6.788887-i*13.9134],1,"n")
H1:SUS-PRM_M3_LOCK_y:  zpk([4+i*119.933;4-i*119.933],[6.78887+i*13.9134;6.788887-i*13.9134],1,"n")

Comments related to this report
thomas.vo@LIGO.ORG - 18:27, Friday 19 December 2014 (15760)
Link

After getting the hang of creating some of these filters and we werestrongly encouraged to write a detailed proceudre:
 
1. Create a white noise, M3 to M3 transfer function using the templates located in /ligo/svncommon/SusSVN/sus/trunk/HSTS/H1/PRM/SAGM3/Data, you can actually use any bottom stage sensor that is available, OSEMs or OptLevs but on PRM, we're only let with the OSEM option.
 
2. The idea is to use the transfer function and then add zeros and poles using the calibration feature in DTT to roughly get a filter than will give you the damped motion you're looking for with the correct phase without waiting for measurements to run everytime you're changing the Q or freq of the pole/zero:
We start by finding the frequency of the lowest resonance and then this will give us an idea of the complex portion and then we eyeball a Q depending on the original transfer function's Q.  By shifting the complex portion of the zero, we attempt to get the correct phase and dither by hand until we roughly supress the resonance with 30-35 degrees phase margin.  We move on with the same procedure for the higher frequency measurements, creating poles and zeros when necessary.  Attached is a before and after look at the transfer function.
 
3. Now that we have the right idea for the ZPK values, we can create a filter module in the ASC WFS Servo Control.  For PRM the correct filter is h1ASC-PRC1 and so we just copied the new filter values into foton and then test by first locking PRMI and then ramping the gain slowly and watching if the DAC saturates or the PRMI breaks lock.  If it doesn't break lock we can tell that our loops are unconditionally stable and then retake OL transfer functions with the new filters in place to see if we're adding any new noise.  Then you're pretty much done.​
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stefan.ballmer@LIGO.ORG - 00:44, Saturday 20 December 2014 (15764)
Link 

I had to sighly correct the filters to make them stable. Attached is what we now have running.

The filters are:
PITCH: zpk(  [0.1+i*1.02;0.1-i*1.02;0.12+i*3.35;0.12-i*3.35],  [0.12+i*2.75;0.12-i*2.75;11.1111+i*38.4258;11.1111-i*38.4258]  ,1,"n")
YAW:   zpk(  [0.015+i*1.09;0.015-i*1.09;0.03+i*2.05;0.03-i*2.05;0.02+i*3.43;0.02-i*3.43],  [0.05+i*1.75;0.05-i*1.75;0.02+i*3.25;0.02-i*3.25;11.1111+i*38.4258;11.1111-i*38.4258],1,"n")
Images attached to this comment
betsy.weaver@LIGO.ORG - 14:58, Thursday 14 May 2015 (18430)
Link

Note, commissioners (Kiwamu/Evan) report that they turned these filters off ~April 21st, 2015 since they were no longer needed.  Filters now off are PRM M3 LOCK P and Y FM9 (RLP17).  SDF has been updated.

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