Alexa, Daniel, Sheila
Today we were able to lock COMM stably. (Thanks to some extra time from the red team and SEI people). By COMM I mean that we can lock the PSL to the green arm transmitted power, using the mode cleaner as an actuator. I don't want to call it the CARM handoff as we called it durring HIFOY, to make a distinction between this ALS handoff and when we do the handoff of the common arm degree of freedom to corner IR signals from the ALS signals.
We have 2 scripts that do the handoff in the new way, userapps/als/h1/scripts COMM_handoff and COMM_down_2
COMM_down_2 brings COMM down in a nice way that does not unlock the mode cleaner. We will work on getting this into guardian at some point. We will try simplifying the COMM handoff script in the future.
We are now using a crossover at 15 Hz, 23 degrees of phase margin (plot attached). This allows us to engage the two notches in the MC2ISCINF (at 29 and 40 Hz) that prevent us from ringing up suspension modes. We struggled to get the crossover this low, because the slow path losses phase at low frequencies much faster than we understand. We added into LSC CARM a z5p20 to get some phase back, and also lowered our compensation filter (6) zero to 6Hz. We are also no longer using the z40:p150 which is used by the mode cleaner locking in MC2M3.
The ugf is at 10s of kHz, Alexa has plots she will post. The open loop gain shows a peak at around 27kHZ. When we looked into why this was, we saw that the PLL has almost no phase margin.
Anyway, the good news is we can reliably do the handoff, and it seems to stay locked at least as long as we left it alone, which wasn't more than 10 minutes or so.
Settings after the handoff:
COMM PLL
- Polarity: OFF
- Gain: 31dB
- Common Filter 1: ON
- Common Filter 2: ON
- VCO Compensation: ON
- Low Pass filter: ON
IMC Servo Board
- Input 1 enable: ON
- Input 1 pol: POS
- Input 2 enable: ON
- Input 2 pol: POS
- Input 2 gain: 16 dB
- Input 1 gain: 10 dB
- Common Compensation: ON
- Boost 1: ON
- Generic filter: ON
- Fast Gain: -6dB
- Fast enable: ON
- Fast Pol: POS
- Bypass: ON
CM Servo Board
- Input 1 enable: ON
- Input 1 polarity: POS
- Fast polarity: POS
- Slow polarity: NEG
- Bypass: OFF
- Input 1 gain: 9dB
- Fast gain: 6dB
LSC:REFL_SERVO_SLOW Filter
- FM1 ON (antiwhitening gain)
- Gain: -1
LSC-CARM Filter
- FM8 (z6:p1k), FM1(z5:p20), FM4, FM5 ON
- Gain: 80
MC2_M3_ISCINF Filter
- FM6, FM7 (notches) ON
- Gain 1
MC2_M3_LOCK_L Filter
- FM9 (chebychev at 300Hz) ON
- Gain: -300
- FM3 On/Off as specified
MC2_M2_LOCK_L Filter
- FM3, FM4, FM10 ON
- Gain: 0.01
Note: no gains present in any of the input matrices
Measurements:
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SCRN0110.TXT, SCRN0111.TXT, SCRN0112.GIF are the magnitude, phase, and pic of the COMM PLL open loop transfer function with the above settings.
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SCRN0102.TXT, SCRN0103.TXT, SCRN0101.GIF are the magnitude, phase, and pic of the CM common path open loop transfer function with the handoff (case of MC2_M3 filter FM3 On)
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SCRN0104.TXT, SCRN0105.TXT, SCRN0106.GIF are the magnitude, phase, and pic of the IMC open loop transfer function without the handoff (i.e. above settings w/ input 2 enable: OFF)
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SCRN0108.TXT, SCRN0109.TXT, SCRN0107.GIF are the magnitude, phase, and pic of the IMC open loop transfer function with the handoff (i.e. above settings, case of MC2_M3 filter FM3 Off)
