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Message ID: 2124     Entry time: Wed Aug 8 14:57:48 2018
Author: aaron 
Type: Update 
Category: Cryo Q 
Subject: Update to SiQ model and MEDMs 

I made a major revision to the SiQ model in the last two days, and began to make the skeleton of the MEDM screens to match. The main change is that now the model contains four moderingers. There are still many changes that need to be implemented.

Summary of Structure

There is a master model, which contains three main subsystems:

  1. Optics
    1. This contains filtering of the QPD signals, and may eventually include some steering mirror controls. Right now this system is pretty bare bones.
  2. Disk
    1. Contains readout and control for the disk as an oscillator.
    2. In the model, the DISK block contains four moderingers, whose outputs are summed and sent to the ESD's DAC channel.
    3. The DISK MEDM screen contains four blocks that link to the moderinger. I'd like this screen to display the following (incomplete list):
      1. Real time Q of each mode
      2. Passband of each mode (if not the frequency itself, but we'd have to add that to moderinger)
      3. Maybe the setpoint or UGF?
      4. Probably would be good to display some of the information about the temperature of the disk from eigenfrequency tracking in this screen.
  3. Temperature
    1. The TCTRL model block demodulates the signal at some high mode frequency and the rate of change of the mixing phase is related to the frequency by 2\pi*f=d/dt(atan(Q/I)).
    2. The temperature control PID loop is still controlled by a python script.
    3. The MEDM screen should contain
      1. settings for the PID script
      2. Readouts of all temperature probes
      3. some indicators that say whether the temperature control loop is running and whether it is stabilized by frequency and/or RTDs
      4. Heater level and a heater control that can override the PID loop
  4. master page
    1. Contains a diagram of the experiment and some top-level information like
      1. Vacuum pressure
      2. One indicator for disk temperature (as opposed to 4-5 on the temperature screen)
      3. Top level OPTICs information, like the dynamic QPD diagram
      4. GDS-TP

What we need

  1. Optimal use of pitch/yaw information
    1. I think a good improvement to the moderinger would be to take as an input both pitch and yaw (right now it takes a single signal), then rotate these two into each other at some angle \phi, the idea being that the disk oscillating in a pure mode with no other sources of beam motion would cause the beam to move back and forth on the QPD in a straight line along some arbitrary axis on the QPD.
    2. We could add another control loop to the moderinger that sets \phi to minimize the out-of-phase component of the two QPD degrees of freedom after rotating pitch and yaw into each other. The in-phase component would then be sent to the existing loop to stabilize the amplitude.
    3. This would ensure that we are using as much of our signal as possible, and would avoid calibration issues. I'm not sure how this was dealt with before, but if this optimal \phi is time dependent then the existing moderinger reading only pitch OR yaw would see the signal amplitude change over time even with a constant excitation, corresponding to a changing Q value despite the system itself not changing. I think moderinger has only been used for cantilevers before, where the system itself is always oscillating in a well defined direction, but since the disk can rotate on the lens after loading and is not in the same orientation after each loading, I think this would be a problem.
  2. Need to calibrate the moderinger for the disk--not sure on this process, I'll need to peruse Nic's paper.
  3. The screens are all hideous, they need to be more organized to be really functional.
  4. Automatically populate the LO frequency for the temperature control when we start the moderingers
  5. I definitely have more, I'll continue adding as they reenter my mind.
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