According to the pre-test of proving shocks to the PR3 suspension in 16373, the ~1 mrad jump seems within a certain allowable amount; am I correct, hopefully??

With Hirata-san.

Summary: We aligned the mirror such that the oplev beam was again at the centre of the tilt QPD. However, V1 OSEM went out of range with 300 counts.  A measurement of IM-Y transfer function suggests that the OSEM flags are not touching their bodies.

• We moved the BF with the fishing rod from 3670 um to the setpoint 3350 um in order to set the vertical OSEM flags in nominal conditions.
• OSEM V3 came closer to be in range with  3200 counts.
• As an initial assessment we measured transfer functions IM-V, IM-P and IM-Y: it seemed the OSEMs flags were not touching the OSEM bodies.
• Before moving the IM to recover the oplev readout, we moved SF close to its setpoint. The vertical positions of GAS filters tend to affect the yaw of the mirror via the cables.
• Inside of the clean room we saw that the oplev beam was above the QPD so, we moved the IM in negative pitch ("REV" in medm screen) until the oplev came in range and close to the vertical center of the QPD.
• Unfortunately, OSEM V1 went out of range with about 300 counts.
• We recovered the yaw alignment of the mirror by setting the oplev beam at the horizontal centre of the QPD (IM-Y changed from 1200 urad to 650 urad).
• We measured IM-Y transfer function again and the result suggests the OSEMs flags are not touching their bodies.

In the afternoon we should move IM-V OSEM to bring it into range.

>Inside of the clean room we saw that the oplev beam was above the QPD

I attached picture of Oplev beam.

With Hirata-san.

Summary: We fixed the cable connection in pins 1 and 6 in the BF picomotor cable.

According to the meeting this morning, it was agreed that the strategy to follow to bring the V1 OSEM into range is to use a combination of BF-RM tilt and BF keystone height adjustments. In order to do this we needed to fix  the cable of the picomotors that produce the tilt of the BF.

The problem was the flip adapter. We changed it and now we measure the capacitance that we expected. The before and after measurements are:

• Flange and connector: P1-7.
• Pins 1-6: 40.0 pF ⇒ 179.26 nF
• Pins 2-7: 189.17 nF ⇒ 189.11 nF
• All the other cable threads are healthy.

Summary: Last week it was agreed that the strategy to follow to bring the V1 OSEM into range is to use a combination of BF-RM tilt and BF keystone height adjustments. Today I tried to do this, but realized the BF pitch picomotor doesn't seem to be working yet. Nevertheless, I was still able to move the BF keystone down and do an assessment.  

I measured transfer functions having the system close to the nominal position of the BF at 8um (error function value). In this configuration, the readout of the OSEMs in number of counts is:

• V1: 390
• V2: 9310
• V3: 8310
• H1: 5546
• H2: 8020
• H3: 6460

Surprisingly, IM-V doesn't look so bad despite IM-V1 having a low readout. However IM-P does look bad. IM-Y looks relatively healthy. See screenshots.

Before moving the BF-P picomotor, I tried moving the BF keystone down to bring V1 OSEM into range at the expense of V2 and V3. Namely, I moved it to -565 um and -767 um. In both cases, the transfer fucntions IM-V becomes bad and and IM-Y suggest the OSEM flags must be touching the bodies. 

Then I proceeded to move the BF pitch picomtor but it didn't work. We must go to the tunnel and check.

With Hirata-san.

We found that the cable adapter from D-sub 9 to RJ connector (that plugs into the picomotor driver) might have not been working. We borrowed the one from PRM and then the picomotor worked. We'll give it back once we have a replacement.

Now both BF picomotors are working.

PR3 BF cable confirmed.
As you can see in the picture, there was a solder burr on it, and I suspect this may have been a bad thing because I want to be able to remove it easily by touch.
I think it would be better to remove and rejoin everything.
I will repair it and give it to you.

With Hirata-san.

Summary: the moved the BF pitch picomotor. The readout of V1 OSEM changes from 280 counts to 500 counts. This is still not enough and we need to move it more. There was an improvement of the IM-P transfer function.

After fixing the picomotor cable this afternoon we proceeded to tilting the BF in pitch.

The initial conditions were

• BF damper readout:
  • L:  -779 um
  • T: 41 um
  • V: 1,317 um
  • R: 854 urad
  • P: -1,144 urad
  • Y: 5,543 urad
• IM OSEMs in counts:
  • V1: 280
  • V2: 9,320
  • V3: 8,290
  • H1: 5,500 cnt
  • H2: 8,060
  • H3: 6,440 cnt
• The BF was at 12 um from the setpoint.

After we moved the BF pitch picomotor,  some of the the changes measured by the OSEMs and BF damper are

• H1: -334 um, 4511 cnt
• V1: 213 counts, -15 um (out of range).
• V2: 32 um, 432 counts,
• V3: 61 um, -907 counts
• BF-P: -1,377 urad

One of the relevant quantities is the ratio of (H1 displacement ) / (V1 displacement): H1/V1=-1.57 um/cnt. Although V1 is not in its linear range, it's possible to calculate an upper limit of how much we need to change H1 readout flag in order to bring V1 into range. Currently V1 is at about 500 counts. If we want to move it to 1500 counts more, we would need to move H1 2,355 um more. It might be possible. We will continue tomorrow.

We measure IM-Y and IM-P transfer functions. The IM-Y one suggests no flag it's touching its OSEM and the IM-P one shows improvement compared to the one we measured in the morning.

Acording to Fabian's suggestion, I checked the LVDT signal at BF stage of PR3 wht the earthquake happens (fig1).
As you can see, no signifinant jump can be observed: that means only below IM stage was jumped.
Basically, IM inclination and TM inclination should be almost the same while differential pitch motion between IM and IRM is much smaler than TM inclination in this time.
What happens?

I continued the adjustment of PR3 by adjusting the pitch of the BF.

As usual, the suitability of this method depends on the compromises we can or are willing to tolerate. In general, the compromises that would be expected, and the measurements to assess them, are the following:

1. OSEM H1 going out of linear range, IM-L transfer function.
2. OSEM flags H2 and H3 touching their respective OSEM bodies, IM-Y transfer function.
3. OSEMs V2 and V3 going out of linear range, IM-R transfer function.

Of course, we can in principle know whether an OSEM is within range by looking at its output. However, when we're in doubt we should measure the transfer function.

From the tests I've carried out so far, it seems that the most important compromise is item 1, the range of H1 OSEM. So far, I've tested two configurations described by the V1 OSEM readout: 500 count and 790 counts. The screenshots show transfer functions measurements groups by pair of the same kind.

The case of V1 having 500 counts

• H1 readout is 9560 counts, which is converted into -102 um.
• Displacement measured by H1 from the position in which V1 was not usable: 300 um.
• In the transfer function IM-P, at low frequencies the amplitude decreases about 8 dB (2.5 times) with respect to the reference.
• In the transfer function IM-L, at low frequencies the amplitude decreases by more than 5 dB (1.8 times)  with respect to the reference.
• Additionally, in IM-L the frequency at which the noise becomes dominant decreases from ~35 Hz to  ~26 Hz.
• The transfer fiunctions for R, Y and V look fine.

The case of V1 having 790 counts

• H1 readout is 10,160 counts, which is converted into -147 um.
• Displacement measured by H1 from the position in which V1 was not usable: 345 um.
• In the transfer function IM-P, at low frequencies the amplitude decreases about 5 dB (1.9 times) with respect to the reference, an improvement of 3 dB from the previous case.
• However, amplitude of the IM-L the transfer function decreases by 20 dB (10 times)  with respect to the reference.
• In IM-L, the frequency at which the noise becomes dominant decreases to almost 10 Hz.
• The transfer fiunctions for R, Y and V look fine.

Using the information from both configurations, the displacement of H1 per displacement of V1 is 45 um / 290 cnt = 0.155 um/cnt.

Additional observations

The position of H1 when V1 was not usable was 200 um (5500 cnt). This means that we could move H1 OSEM to a smaller number of counts in order to increase the amount of correction we can achive using this method.

Right after the earthquake, the readout of V1 OSEM was 6772 cnt, V2 3280 cnt and V3 1931 cnt. This suggests that we could move V1 such that its readout increases by 2000 counts and it could still be usable in both configurations.

Summary: I calculated the pitch of the mirror after the earthquake using geometrical considerations: 13.4 mrad. In an analogous way, I did the same using data from OSEMs V2 and V3: 9.5 mrad and 8.8 mrad respectively. The values are different, but to a certain extent consistent.

Using Hirata-san's picture posted in the klog 18330, and Kamiizumi-san's CAD drawing of the PCB board, it was determined that the position of the oplev beam spot with respect to the centre of the QPD was:

• Horizontal: 1.5 mm
• Vertical: 17.3 mm

From Yokozawa-san's drawings we also know that the distance from the mirror to the tilt QPD is 1050 mm, with the angle of incidence on the mirror 52 degrees.  This means that the effective lever arm length is 0.646 m. In turn, this implies that the pitch of the mirror is ( 17.3 mm / 0.646m ) / 2 = 13.4 mrad.

The pitch of the mirror was 13.4 mrad from the direction defined by the centre of the QPD

Using OSEMs V2 and V3, we can estimate by how much we moved the IM when we recovered the pitch alignment. This should be similar to the pitch displacement just calculated.  OSEM V1 ended up in out of range after recovery, so I didn't use it for this calculation. Along the longitudinal direction, OSEMs V2 and V3 are 48 mm from the suspension rod. The measured displacement of each OSEM and the pitch associated to such displacement are

• V2: -456 um, 9.5 mrad.
• V3: -423 um, 8.8 mrad.

Although the values calculated using the oplev are all different, they are consistent in the sense that they indicate a very large displacement.

From the information written in klog 18391, it is possible to calculate how much V1 OSEM flag moved  when we corrected the orientation of the mirror.

• The average displacement of the mirror due to the earthquake, calculated from the oplev, V2 and V3 OSEMs is 10.6 mrad.
• The distance of V1 OSEM from the suspension rod (along the longitudinal direction) is 96 mm.

This means that the V1 OSEM flag moved 10.6e-3 * 96 mm = 1.01 mm. Coping with an OSEM flag displacement of this magnitude is very challenging, if possible. The usual measuring range of OSEMs is ~0.9 mm.

Another piece of useful information is the change in pitch of the IM during the earthquake. All the vertical OSEMs were either within or close to functional range. The only OSEM in a questionable position after the earthquake was V3 with 1935 counts. Examples of calibration curves can be found in klog 5914.  The plots show that the limit is around 2000 counts. For the sake of consistency check, I calculated the pitch change from the readings of the individual OSEMs and geometrical considerations:

• IM-P: 1053 urad.
• Pitch suggested by V1: 1.7 mrad.
• Pitch suggested by V2: 2 mrad.
• Pitch suggested by V3: 1.1 mrad.
• IM-R: 102 urad.

There was also a small change in roll, which the calculation using the individual OSEMs V2 and V3 did not consider. The values show consistency considering that the change in roll is relatively small.

A pitch displacement of 1053 urad would move V1 OSEM flag by 1.053e-3 * 96 mm = 0.101 mm.

With Hirata-san

Summary: We moved V1 OSEM into linear range. We measured IM transfer functions. They look fine although the coherence is not as good at low frequencies.

• We noticed the temperature is relatively high: 23.9 °C whereas O3GK temperature is  23.2 °C.
• We moved the BF to the setpoint using the fishing rod.
• The readout of H1 OSEM was 10,146 counts.
• The readout of V1 OSEM was 772 counts.
• There was a problem with the adapter from D-sub 9 to the RJ connector in the BF picomotor cable. It went away by disconnecting and connecting the adapter, but we need to check the reason.
• We tilted the BF until the readout of V1 was 280 counts and H1 5,500 counts.
• We adjusted the pitch of the mirror finely such that the oplev beam was at the QPD centre.
• We measured TF: IM-R, IM-Y and IM-L. They all look fine.
• Hirata-san moved the OSEM from  280 to 3380 counts. My aim was 2000 counts but it's hard to aim when the OSEM is initially out of linear range.
• We measured transfer functions. The coherence is relatively low at low frequiencies, nevertheless, the system looks healthy.

Hi Fabian,

Could you show the graph of measured transfer function?

Here I show transfer functions measurements from yesterday and today.

Apparently, the microseismic motion was higher yesterday and that migt be reason the coherence at low frequencies was low. Today, it's better.