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Reports until 10:58, Tuesday 23 September 2014
betsy.weaver@LIGO.ORG - posted 10:58, Tuesday 23 September 2014 - last comment - 19:32, Tuesday 30 September 2014(14095)
3IFO QUAD 06 Phase 1B testing

QUAD 06 (Q6) Phase 1B transfer function plots are attached.   We had a hard time obtaining good coherence in the Transverse TF, so it is a bit hashy.  Will try again.  


Most notably is that, like Q8, the second pitch mode frequency is unexpectedly pushed upward on the main chain.  Recall, we never found the mechanism to fix it on Q8.  Interestingly, both the Q8 and Q6 assemblies are of the same batch of wires and are fresh builds, but by 2 different assembly teams, and on 2 different solid stack/test stand units.  Q8 is an ETM type of QUAD while Q6 is an ITM QUAD, but both main chains have the same pendulum parameters - both are detailed in the 'wireloop' model.


The Q6 data is plotted as QUADTST.

Non-image files attached to this report
Comments related to this report
betsy.weaver@LIGO.ORG - 15:14, Tuesday 23 September 2014 (14100)

We've checked that all wire diameters are as per the specs and that the wire segment clamps are seated properly on the masses.  We've also checked that the wire segments have been assembled with the proper assymetry as per specs (looking for something obvious).


Attached are pix of this unit, in case someone wants to look at them.  To me, they look just like the last few QUADs we've built, including Q8.

Images attached to this comment
brett.shapiro@LIGO.ORG - 17:20, Tuesday 23 September 2014 (14112)

Maybe this is a long shot, but we've exhausted all the simple causes...could the top wire be the wrong material? If the modulus of elasticity was higher, within a factor of 2 from where it is supposed to be, that would explain this strange pitch mode.

One way to test this is to measure the violin modes of the topmost wire in situ and see if it is right. Or maybe more simply, cut some wire from this wire stock, hang some wieght off of it, and measure its violin mode.

The correct 1.1 mm diameter wire should have a violin mode of 

frequency in Hz = sqrt(tension/0.0067)/(2*L)

where 0.0067 is the mass per unit length.


For example tungsten has a modulus about 2 times higher than what we are supposed to have. If for whatever reason we ended up with a tungsten wire, it would have an in-situ violin mode in the low 200s of Hz, rather than the 332 Hz spec (much denser than the usual piano wire).

brett.shapiro@LIGO.ORG - 17:52, Tuesday 23 September 2014 (14113)

Or even more simply, you could weigh some length of wire. The piano wire should be something close to 7 g/m. If you get different value from that, then the wire is the wrong material.

betsy.weaver@LIGO.ORG - 15:52, Wednesday 24 September 2014 (14129)

To confirm Brett's latest suggest regarding the wrong wire:  We have 2 rolls of 1.1mm diameter top wire here at LHO which could have possibly been used for QUAD builds.  Both are labeled as the correct stuff.  We weighed a 1m segment from each spool.  One measures 7.1g, the other measures 7.3g.


To be continued...

betsy.weaver@LIGO.ORG - 15:59, Wednesday 24 September 2014 (14131)

Another sanity check:

The Top Mass blade sets used for these 3 pitch-problematic QUADs are as follows:

Q6 - SET 10

Q8 - SET 8 - although I can't find the actual records

Q9 - SET 2


Q7 - SET 7 - still to be tested, unknown pitch frequency TFs


The SETs go from SET 1 being the most STIFF to SET 16 being the most SOFT.  So, the sets we are using for the 3IFO QUADs are somewhat scattered or in the middle of the pack.  They are not all clustered at the soft end, nor all at the stiff end...

betsy.weaver@LIGO.ORG - 14:43, Thursday 25 September 2014 (14151)

And here's the spectra of this Q6.  Note, the lowest stage (L2) does not have flags during the all-metal Phase 1 assembly, so the spectra plots of L2 are junk.

Non-image files attached to this comment
betsy.weaver@LIGO.ORG - 16:16, Thursday 25 September 2014 (14155)

And now attached are a damped TF from each R0 and M0.  As we all have noted in SUS - damped TFs on Phase 1 test stands are not useful since the damping is a function of the code on the out-dated test stands and the loops are not tuned very well.  Long story short, there is a little bit of damping evident, given whatever filters and gains are loaded, and we can see healthy excitations run through the suspension so all seems well with damping capabilities of Q6.

Non-image files attached to this comment
brett.shapiro@LIGO.ORG - 19:32, Tuesday 30 September 2014 (14235)
I ran the matlab model fitting code on the wireloop model for QUAD06. I used the measured top mass resonance frequencies, as well as the long-pitch frequencies from the triple hang data that Betsy collected. The latter was extremely helpful in refining the results beyond what top mass TFs provide on their own.
* The top mass and UIM inertias converged to the same values obtained from the fiber H1ETMY fitting results (lho log 10089), within the error bars. This includes +12% on the UIM pitch inertia from what is given in the final quad design doc T1000286. Note, this means the same large shift has been found on two different configurations of different quads. So it is likely that the fitted value is correct. But great news for consistency on the suspensions.
* Some of the d's moved significantly. However, the move is noticebly less if you start from the previous fit to H1ETMY rather than the base model.
    -dn (top blade tip) increased by 1.25 mm relative to the H1ETMY fit. It is +2 mm relative to the base model. Note, one could alternatively shift dm instead.
    -d1 (uim blade tip) did not move significantly relative to the H1ETMY fit. However, it is +3 mm from the base model. Note, one could alternatively shift d0 instead.
    -d2 (PUM round prism, not part of fiber model) decreases by 1.25 mm.  This actuall could be due to errors in my previous estimate of what this value should be. In fact, this shift puts it about where it is supposed to be for the fiber quad.          Not sure if that is the intent with this prism.
* Still not clear what caused the shift in dn (or dm) relative to previous suspensions, like H1ETMY. The model fitting wouldn't say that though. All it can do is say that either dn or dm is off.
Plots of comparisons of the before/after models against the meadured data are attached. The first 6 pages show the top mass TFs. The 7th and final page merely shows the triple hang long-pitch frequencies since this data was pulled from an amplitude spectrum. In these plots, there are notable shifts in just 2 modes. The 2nd pitch mode (1.5ish Hz) on the top mass TF, and the first mode of the triple hang (0.4ish Hz), which is also pitch. The updated model shows pretty good agreement all around.
The parameter shifts required to make the match were originally rather large, for both the d's and the pitch moments of inertia. Interstingly, the moments of inertia for all the top two masses (didn't need to float the lower ones) consistently converged to the model fitting results from the fiber ETMY quad. Thus, I updated the wireloop model (update not committed to the svn yet) with the fitting results from H1ETMY for all the parameters of the top two masses (springs, inertias, d's). I then used this updated wireloop model as the staring point for the model fit.
The shifts in the parameters are below. The d's moved noticeably. The spring stiffnesses did not move a great deal, but were useful in fine-tuning the fit. The inertias did not need any further refinement from H1ETMY. I find this last point extremely exciting.
* mm shifts in the d's from H1ETMY fitting results
dn: 1.2438 +- 0.069243 mm   -> top mass blade spring tip
d1: 0.38916 +- 0.16088 mm   -> UIM blade spring tip
d2: -1.2815 +- 0.10267 mm    -> round PUM prism
* % shifts in the blade spring stiffnesses from H1ETMY fitting results
kcn: 2.1235 +- 1.8491 %         -> top-most blade stiffness
kc1: 0.56079 +- 0.45919 %     -> top-mass blade stiffness
kc2: -1.493 +- 0.58382 %        -> UIM blade stiffness
Non-image files attached to this comment
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