A good diagram on the timing of a hardware injection through the DARM path:
LLO aLOG 22361

We made a test with the CER unit by changing its output termination. Nominally, it runs into 50 Ohms. In the attached plot just before 70s the terminator was removed briefly and put back again. This resulted in a up-down glitch. Then, this was repeated around 80s. Between 200s and 210s the terminator was removed and replaced by a cable with clips attached to the end. The clips were then shorted repeatedly resulting in pairs of down-up glitches. Looking at alog 21789 and its second attachment we can see two up-down glitches—albeit at a much smaller scale.

Keita went out during a lockloss and started tapping at different points in the RF distribution chain of the 45.5MHz RF signal.

No effect:

• Tap at the outputs of the distribution amp
• Wiggling the large diameter cable that goes between racks

Effect similar to what we see:

• Wiggling the BNC cable connected to the unit in the CER (plot 1)
• Tapping the balun of the cable going to the PSL unit at the field rack (plot 2)

Effect much larger than what we see:

• Removing a terminator from an unused port of the distribution amp (plot 3)
• Tapping the N elbow in the cable run to the PSL unit at the field rack (plot 4)

Only the removal of the terminator was seen in both units. The other glitches were only seen by the unit which is fed by the tapped cable or connector.

The most sensitive point was the tapping of the elbow indicating a possible connector, cable or adapter problem nearby. We should probably redo the extension cable which was inserted to account for the phase delay.

Here's some plots.

The script finished right before an EQ knocked us out of lock.  Attached are results, we can decide if we are keeping these decouplings durring the maintence window.

The three changes made by the script which I would like to keep are ETMX pit, ETMY yaw, and ITMY pit.  These three gains are accepted in SDF.  Since we aren't going to do the other work described in the WP, this is now finished. 

All the results from the script are:

ETMX pit changed from 1.263 to 1.069 (1st attachment, keep)

ETMX yaw reverted (script changed it from 0.749 to 1.1723 based on the fit shown in the second attachment)

ETMY pit reverted (script changed it from 0.26 to 0.14 based on the 3rd attachement)

ETMY yaw changed from -0.42  to -0.509, based on fit shown in 4th attachment

ITMX no changes were made by the script, 5th +6th attchments

ITMY pit (from 1.37 to 1.13 based on 7th attachment, keep)

ITMY yaw reverted (changed from -2.174 to -1.7, based on the 8th attachment which does not seem like a good fit)

By the way, the script that I ran to find the decoupling gains is in userapps/isc/common/decoup/run_a2l_vII.sh  Perhaps next time we use this we should try a higher drive amplitude, to try to get better fits.

I ran Hang's script that uses the A2L gains to determine a spot position (alog 19904), here are the values after running the script today. 

I also re-ran this script for the old gains, 

So the changes amount to +0.4 mm in the horizontal direction on ETMY, -0.9 mm in the vertical direction on ETMX, and -1.1mm in the vertical direction on ITMY.  

Please be aware that in my code estimating beam's position, I neglected the L2 angle -> L3 length coupling, which would induce

an error of l_ex / theta_L3, 

where l_ex is the length induced by L2a->L3l coupling when we dither L2, and theta_L3 is the angle L3 tilts through L2a->L3a.

Sorry about that...

Adding SEI tag, so people see it.

Is the STS signal calibrated correctly above 30 Hz or are you just assuming its a flat velocity sensor?

If its really close, you should be able to add the seismic data streams with the right signs and then take the coherence between this pseudo-channel and DARM and see something more than we expect by just the seismic model estimates.

Hmmm, good point Rana.  I should have thought of that - it looks like the STS calibration doesn't compensate for the roll-off, so I'll put that in, and redo the traces. 

Jenne, The estimate you're getting in the 15-20 Hz region is an order of magnitude or more higher than the estimate made by Jan Harms for L1, found in T1500284.

Can you post the ground noise spectra you are using so we can compare with what Jan used for L1?

The originally posted NN estimate spectra is totally wrong.  I forgot to take the sqrt of the seismic spectra after pwelching, before calibrating to meters. 

This corrected plot is much more consistent with Jan's estimates from T1500284. 

EDIT, 3:15pm:  Calibration was missing a factor of 2*pi.  Plot has been updated.

Great. I like consistent results. Another remark; seismic displacement measured at a test mass has vanishing correlation with its NN. This is true at least for seismic surface fields. So if you want to proceed with correlation measurements, then the pseudo-channel needs to be constructed from an array of seismometers, with non of these seismometers being located at the test mass.

Here I include a version of the Newtonian noise estimate plot, with the GWINC estimate of aLIGO's sensitivity, in addition to the current LHO sensitivity. 

The trace "GWINC with NN term" is just the regular output of Gwinc, assuming no Newtonian noise cancellation.  The trace "GWINC no NN term" is all terms in gwinc except for the Newtonian noise. In particular, recall that the Gwinc NN term is not identical to the NN estimate I plot here.

The point here is to show that, although at our current sensitivity we are not limited by Newtonian noise, if we can eliminate the LSC and ASC control noise terms from our latest noise budget (aLog 21162), we likely will be.

EDIT: a further version of this plot now includes the GWINC NN curve.

The 109s delay is a little higher than expected, but not to strange.  I'm not sure where DMT marks the time, as the start/mid/end of the minute it outputs.

The 30s sample rate of the DMT to EPICS IOC is configurable, but was chosen as a good sample rate for a data source that produces data every 60 seconds.

It should also be noted that at least at LHO we do not make an effort to coordinate the sampling time (as far as which seconds in the minute) that happen with the DMT.  So the actual delay time may change if the IOC gets restarted.

EDITED TO ADD:

Also, for this channel we record the GPS time that DMT asserts is associated with each sample.  That way you should be able to get the offset.

The value is available in H1:CDS-SENSMON_CAL_SNSW_EFFECTIVE_RANGE_MPC_GPS

Hang, Evan

We measured the input-referred voltage noise of the summing node and common-mode boards.

• We terminated the input of the SNB that receives REFL9Q (INA2). INA1 was disabled. On the CMB, IN1 was enabled with -22 dB, and IN2 was disabled. The 40 Hz / 4 kHz boost was engaged. The fast gain was 7 dB.
• We measured the noise at the output of the CMB fast output.
• We then took the TF from SNB INA2 to CMB fast out. This is sufficient to get the input referred noise.

According to this estimate, the CARM loop is not shot noise limited; rather, at 1 kHz the noise is about a factor of 3 in ASD above shot noise.

I looked back at the CARM sensing noise data I took (on 12 Aug) using the new gain distribution: 0 dB SNB gain, −13 dB CMB common gain, 0 dB CMB fast gain, and 107 ct/ct digital MCL gain.

[For comparison, the old CARM gain distribution was 0 dB SNB gain, −20 dB CMB common gain, 7 dB CMB fast gain, and 240 ct/ct digital MCL gain.]

☞ For those looking for a message in this alog: something about the current frequency noise budgeting doesn't hang together. The projection based on the CARM sensing noise and the measured CARM-to-DARM coupling TF suggests a CARM-induced DCPD sum noise which is higher than what can be supported by coherence measurements.

☞ Second attachment: As expected, the noise (referred to the input of the SNB) is lower; at 40 Hz, it is about 350 nV/Hz^1/2. However, we are not really shot-noise (or dark-noise) limited anywhere.

☞ Third attachment: I am also including the CARM-to-DARM coupling TF from a few weeks ago. This TF was taken by injecting into the CARM excitation point and measuring the response in OMC DCPD sum, using the old CARM gain distribution. Then I referred this TF to the SNB input by multiplying by the SNB gain (0 dB), the CMB common gain (−20 dB), and the CMB common boost (40 Hz pole, 4 kHz zero, ac gain of 1).

This gives a coupling which is flat at 1.0×10⁻² mA/V, transitioning to 1/f² around 250 Hz. Or, to say it in some more meaningful units:

• Assuming a REFL9Q demodulation coefficient of 2900 V/W, this implies a flat power coupling of 3.4×10⁻⁶ mA/W above 250 Hz, rising like 1/f² below that.
• Assuming a CARM optical gain of 13 W/Hz and an optical pole of 0.48 Hz, this implies a 1/f frequency coupling above 250 Hz, a 1/f³ coupling below 250 Hz, and an overall magnitude of 6.2×10⁻⁵ mA/Hz at 1 kHz.
• Stated in terms of phase coupling (Stefan's favorite), the magnitude of the CARM optical plant is 6.2 W/rad above the cavity pole, which implies a flat phase coupling of 6.2×10⁻² mA/rad above 250 Hz, rising like 1/f² below that.

☞ Synthesis of the above: based on the measurements described above, at 40 Hz we expect a coupling into the DCPD sum of 350 nV/Hz^1/2 × 0.4 mA/V = 1.4×10⁻⁷ mA/Hz^1/2, which is very close to the overall DCPD sum noise of 3.2×10⁻⁷ mA/Hz^1/2.

But what is wrong with this picture? If 1.4/3.2 = 44 % of the DCPD sum noise comes from CARM sensing noise, we should expect a coherence of 0.44² = 0.19 between the DCPD sum and the CARM error point.

☞ First attachment: The coherence between the CARM error point and the DCPD sum is <0.01 around 40 Hz. Now, it is almost certainly the case that not all of the CARM error point noise is captured by LSC-REFL_SERVO_ERR, since this channel is picked off in the middle of the CMB rather than the end. Conservatively, if we suppose that LSC-REFL_SERVO_ERR contains only dark noise and shot noise, this amounts to 180 nV/Hz^1/2 of noise at 40 Hz referred to the SNB error point, or 0.72×10⁻⁷ mA/Hz^1/2 referred to the DCPD sum. This would imply a coherence of 0.05 or so.

☞ What is going on here?: Four possibilities I can think of are:

• I've overestimated the sensing noise.
• I've overestimated the CARM-to-DARM coupling TF.
• I've made an algebra mistake somewhere.
• LSC-REFL_SERVO_ERR is corrupted by noise that is not in the CARM loop.

☞ A word about noise budgeting: In my noise budget, there was a bug in my interpolating code for the CARM-to-DARM TF, making the projection too low below 100 Hz. With the corrected TF, the projected CARM noise is much higher and begins to explain the mystery noise from 30 to 150 Hz. However, given that the above measurements don't really hang together, this is highly speculative.

According to the CMB schematic and the vertex cable layout, the CARM error point monitor goes through some unity-gain op-amps and then directly into the ADC. So I don't think we have much chance of seeing the 180 nV/Hz^1/2 of shot/dark noise above the 4 µV/Hz^1/2 of the ADC.

According to the CMB schematic and the vertex cable layout, the CARM error point monitor goes a gain of 200 V/V and then directly into the ADC. So the 180 nV/Hz^1/2 of shot/dark noise appears as 36 µV/Hz^1/2 at the ADC. But as Daniel pointed out, this should be heavily suppressed by the loop. For comparison, the ADC's voltage noise is 4 µV/Hz^1/2.

For the sake of curiosity, I'm attaching the latest noise budget with the corrected CARM-to-DARM coupling TF. However, I note again that this level of frequency noise coupling is not supported by the required amount of coherence in any of our digitally acquired channels. Additionally, this level of frequency noise coupling is not seen at Livingston, although they've done a better job of TCS tuning than we have. I would not be surprised to find out that this coupling is somehow an overestimate.