How about measuring the actual weight with a scale? There are a couple of scales on Yuta's desk.

Thanks, I was actually looking for a scale earlier but could not find it after asking a couple of people. One of the scales reads 298 g, while the other has a limit of 200g. Looks like it is indeed aluminium.

[Reuben, Radhika]

Checked out the AUX PDH locking system at the XARM. Started by locking the AUX laser using the uPDH servo box and adjusting the test masses to maximize transmission (~0.6 achieved). There were some issues where the fundamental mode would be briefly visible and then lose lock. Higher order modes were also seen which could be removed by adjusting test masses. We also noticed the laser spot moving around a lot, as if the test masses were swaying. Finally after repeated tries we managed to lock and hold the laser to the cavity long enough to measure the open loop transfer function using the Moku:Go frequency response analyzer tool. Got an idea of the finicky and temperamental nature of the locking process.

Taking the transfer function data from the Moku:Go and using a Python script, found the UGF to be around 25.6 kHz and phase margin to be around 25.5 deg. My current goal is to keep reading up on control systems and related theory (I still feel like I lack understanding of the important principles needed), and parallelly making a small script that can take the transfer functions data and calculate some useful information (halfway done).

One issue I found with the script was that the Python control library was giving me a wrong value of Gain Margin (~0.26 where ~-5 was expected) while using the control.margin function. The other parameters phase margin and crossover frequencies agree with the data visually.

Vertex SUS DAC-0 card is kaput (aka C1SUS DAC failure) ed: Koji

[Paco, Yuta]

Continuing our investigation of how a couple of coils seemed to be malfunctioning and the local damping was affected, we did the following:

• We calibrated ITMX actuation strength with ALS beat at 211.11 Hz and found 5.105 nm / count / f^2 or just 5% off from the previous values. So nothing seemed strange (e.g. 25% difference from single coil failure)
• We tried calibrating BS actuation strength and found it very hard to lock MICH. Furthermore the result was off by a factor of ~ 2 with respect to previous values!! Highly sus...
• We tried calibrating ITMX/ITMY actuation strengths and found they were also weaker by ~ 2 with respect to previous values. Extremely sus.. Attachment #1 summarizes these results.
• We decided to repeat our DW board transfer function estimates using single coil to Oplev transfer function measurements, but this also seemed harder in comparison with our last measurements. (couldn't even replicate using our dtt saved template results)

Finally we checked the analog electronics, breaking the BS AI to DW board connection of ULCOIL. We then used awggui to drive the single coil and the AI test mon output to read the commanded signal. We repeated this for a couple more coils, and also for other optics (PRM, SRM). We found that PRM had the same issue as BS that the DAC output couldn't drive positive voltages! In contrast, SRM worked fine. We then swapped the DAC adapter (see Attachment #2) units by swapping cables between SRM /MC3 and BS/PRM (D080303 -- not on DCC) and ruled out a failure from the buffered Test MON outputs on the AI board. So the problem was narrowed down to the DAC_0 card on c1sus chassis.

To try and fix this, we stopped the c1sus model, shutdown its frontend computer, and power cycled the IO chassis including the DC power at the front. This time, we tested the DAC outputs by driving the face coils separate from the side coils (running on DAC_2) using a 0.1 Hz sine excitation on ITMX, BS, ITMY and PRM from awggui and looking at the coil Vmon channels from the acromag on all suspensions. See Attachment #3-4 for a summary of all the tests (BS, PRM, ITMX, ITMY are bad, SRM, MC1-3 are good).

After verifying that this didn't fix the issue, we concluded that c1sus - DAC_0 fails to drive positive voltages.

Next steps

• Replace DAC_0 with spare (does not seem to exist in our cds supplies)
• Swap the Side coil DAC (DAC_2) with the failing DAC (DAC_0) and drive the side coils with an offset since SIDE coils are not critical.
• Adapt the AI boards to be compatible with existing spare 18-bit DAC units.

ITMY actuator calibrated with higher resolution using ALS

Today I came briefly in the lab and restarted all models because the beams were missing in the BHD camera; implying the ASS model controlling TTs has tripped into a weird state. The problem got fixed after that and I recovered the IFO alignment more or less. Thus I began another quick calibration run --

I wrote a script to put calibration line and update the LSC YARM notch filter using python-foton so as to take an ALS calibration sweep of the YARM test mass actuator responses. For a given sweep frequency array, the script loops over the frequency, updates the notchSensMat (LSC-YARM FM10), loads the coefficients, and ramps up the SENSMAT OSC gain and frequency to inject the noise. The YAUX laser is locked to the YARM and YARM is locked to PSL during this measurement. Then, the real-time demodulated BEAT_Y signals are averaged for ~ 3 seconds (just wanted a quick scan, not a very accurate or precise one) and the result is plotted in Attachment #1. Notice that I have included the phase tracker loop correction to account for the high frequency calibration line inferred response (1 + i f/2000)

I then used foton in gui mode and exported the violin filter transfer function (FM1-4 and FM6 for ITMY) magnitude and inverted its effect to get the "dc actuation strength" of ITMY.

Discussion

• The value is consistent with our recently poor actuation due to c1sus - DAC-0 failure, at ~ 3 nm /count /f^2. I look forward to another measurement after the DAC-0 has been replaced / fixed.
• No more "high frequency" lift as seen before?
• There is still some residual frequency dependence near the phase tracker BW; maybe not just a simple integrator?

The idea of having the response shape is so I can then use the 5 lines only to get the response to high accuracy.