stefan.ballmer@LIGO.ORG - posted 01:09, Saturday 08 February 2014 - last comment - 20:10, Saturday 08 February 2014(9930)
Lisa is disappointed
Evan, Lisa, Kiwamu,Stefan Tonight we fixed our PRC oscillation problem: it was due to a demod phase that was 11deg off. Combines with the fact that MICH is only acting on the BS, this messed up our loop shape. We carefully phased REFL_45 to 144.6deg, and lowered the MICH gain to 50 and PRCL GAIN TO -0.6. (All these gains are in guardian now.) Next we went on to 3f locking. We phased the 27MHz by simply maximizing the signal in I (we needed 90deg). Switching PRCL to 27_I was straight forward. For MICH we wanted to user the 135MHz signals, but the signal seemed dead. Thus we tired 27_I. The transition worked fine, but we are still saturating the BS around 30-40Hz, and typically loose lock after 20sec or so. As a result Lisa was disappointed: despite cooking dinner for us, be didn't quite achieve a stable lock on 3f tonight. But we promised her that we'll increase the modulation depth and the light of the 3f diode.
Also, we implemented a new state in the PRMI guardian for the 3f locking. It transitions the sensor from the 1f signals to the 3f signals by ramping the sensing matrix elements. This works fine although the way it does currently is a rough discrete gain step.
Another thing we would have to mention is that we could not bring HAM3 ISI back to its level 3 isolation. We tripped the ISI when we accidentally tripped PR2. We tried the isolation script from the medm screen but it seems that it tries to enable a couple of blank filters and stops at some point before ramping up the isolation gains. This needs to be revisited. Currently it is only damping.
Lisa, Kiwamu
Today, we looked at free swinging wave form of the 3f signals. The signals in REFLAIR_B_RF135 was visible and we confirmed that the signal size made sense by comparing it with the RF27 signals.
Here are our back of envelope calcuation:
Therefore the RF27 and RF135 should be almost the same signal level. Indeed, we see almost the same size (i.e. peak-to-peak) of the signals in both RF27_I and RF135_I which showed 700 counts p-p and 800 counts p-p respectively without any whitening gains or whitening stages. We didn't check the absolute value at this point.