Units and signals in the AOC

Telemetry files

The AOC saves many kinds of telemetry files. These are used to monitor the system state. These can be accessed directly by using a dumpdata command to the AOC (see AOC ICD). The files are stored in dated directories on the AOC computer. They are not necessarily saved in a format that is amenable to easy analysis.

There is a est of IDL wrappers that you can you can use to easily command telemetry dumps and conveniently load them into IDL in the proper format. use these whenever possible.

For most tasks, you will use a single function, called as

IDL> res = rtc_retrieve_dumpdata(telem1=data1, telem2=data2, /many_options)

This will format everything into the correct dimension.


Though most of the code has a clunky calling convention where the data variables are assigned first before calling, the latest version of the code does not require this.

Units and signal sizes

The following units are used

Signal Unit
Slopes milliarcseconds (mas)
Phase microns
Voltages volts

The following signal dimensions are standard

Signal Unit
Slopes 96 x 48 (x at left, y at right)
Phase (tweeter) 48 x 48
Phase (woofer) 9 x 9

Given these basic signal types, there are some handy procedures for displaying them. These show the signals and relevant AO system feature, e.g. the location of dead actuators when you examine a phase signal.

Abbreviations and other conventions

Abbreviation Explanation
DM Deformable mirror
Wfr Woofer - Cilas DM
Twt Tweeter - 4K BMC MEMS (MicroElectroMechanical System)=
TT Tip/Tilt stage on which the Wfr is mounted
WFS WaveFront Sensor unit
FTR Fourier-Transform wavefront reconstruction. This is the filtering algorithm that is used to reconstruct the wavefront phase from the measured slopes.
PNC Pointing and Centering pair in the AO relay (another PNC pair exists in the CAL-IFS relay and is usually referred to as the CAL PNC)
SF Spatial Filter in the WFS