Measuring Concentricities

Updated on June 15, 2021, 7:44 am

The measurement of concentricities has to be made off telescope probably at the Coude Room. The minimal setup required to measure the concentricities includes, besides Hydra, a video monitor, an ICCD controller, a video cursor, a light source and the Hydra Laptop (or the Hydra PC). The video monitor plus the ICCD controller display the video signal from the gripper camera. The light source is used to illuminate the fibers from behind. And the Laptop controls the instrument. When illuminating the fibers environmental light has shown to be sufficient for the small and large fibers. To illuminate the FOPS it's not necessary to remove the FOPS camera. Removing the filter in front of the camera will allow you to introduce enough light through the space left by the filter.

If you are using the Hydra Laptop to control the instrument during this procedure you better be sure that the "CurrentLocations" and "statusFile" are not different from the ones in ctioa6 (Hydra PC). Copying this files from ctioa6 to the laptop will ensures that the software knows exactly where the fibers are. For example if the Ethernet connection is available, typing the following commands in a shell window will do it for you. Don't forget to login as "hydra".

% cd Hydra/data/status
% rcp ctioa6:/home/hercules/Hydra/data/status/CurrentLocations .
% rcp ctioa6:/home/hercules/Hydra/data/statuc/statusFile .

Now you can start "hydractio" or "hydractio-comm" if you don't want to communicate with the TCS and FOPS Guider systems (this will be often the case).

1. Taking Concentricities Data

The canonical procedure is first to put the fibers in a circle. There is a script that can do this job for you. For example, if you are measuring the concentricities for the small fibers type at the CLI/Script Tool command line:

Fiborg3.2.0> execfile configsmallcircle

After it finishes you can execute the script to actually measure the offset between the button position and the fiber position for every fiber. Don't forget to check that your light source is illuminating the fibers evenly before executing the script. What the script does is to go fiber after fiber grabbing its current position, allowing you to correct the position by offsetting the gripper and grabbing the new position. The idea is to use a video reference (video cursor) to center, by moving the gripper, the light beam coming from the fiber and use the offset between the original (button position) and final position (fiber position) to calculate the concentricity correction for that particular fiber. You should repeat the process a minimum of three times (five is a good number of repetitions), that is parking all the fibers, putting them back in a circle and grabbing the corrections. Make sure you also do FOPS concentricities measurements interleaved with the small or large concentricities measurements. The FOPS serve as the zero point correction. It is recommended to do all the fibers (small, large and FOPS) with the same TV setup just to ensure that they are all on the same zero point. All the recorded positions are kept in the log file of the current session.

For example, if you want to record concentricity data for the small fibers you should type at the CLI prompt:

Fiborg3.2.0> execfile meassmall

The gripper will move to the first small fiber and will wait for you to move the gripper. You can use the arrow buttons in the "Field Display Tool" window or the keyboard by typing "h, j, k, l" (make sure the mouse cursor is on top of the "Field Display Tool" window) to offset the gripper. You can change the size of the step by moving the red slider in the field display or by pressing a key from 1 to 9. After you finish with the first fiber type "q" or press the "Enabled" green button. At this moment the "Enabled" button will go red, the gripper will move to the second small fiber and the "Enabled" button will go green again. Repeat the process above until you finish all the small fibers.

 

2. Creating New Concentricities Files

After you finish logging the concentricities raw data you can use the "concenctio" program to generate a new concentricities file. This program lives in /home/hydra/src/concenct. First you'll have to copy the old concentricities files to that directory plus the log file(s) containing the raw data. The old concentricities file will be used as a template to produce the new file. If the name of your current concentricities file is different than "concentricities" you will have to rename it as "concentricities". Then run the program to generate the new concentricities file. The name of the new file will be "nconcentricities". For example, to generate a new concentricities file from the current "concentricities" file plus the "hydra.currentLog" log file you should do:

% cd /home/hydra/src/concenct
% cp /home/hydra/Hydra/data/inits/concentricities .
% cp /home/hydra/fiblogs/hydra.currentLog .
% concen

Enter the name of the log file: hydra.currentLog
Small Concentricities
Group 1 Average is X= 0.000000 Y= 0.000000 for 135 measurements

Another file to read? (y or n): n
ave x = 0.000000, ave y = 0.000000, sdev x = 0.000000, sdev y = 0.000000
ave r = 0.000000, sdev r = 0.000000
var = 0.000000
var = 0.000000
var = 0.000000
ave x = 0.000000, ave y = 0.000000, sdev x = 0.000000, sdev y = 0.000000
ave r = 0.000000, sdev r = 0.000000
var = 0.000000
var = 0.000000
var = 0.000000
.
.
.

ave x = 0.000000, ave y = 0.000000, sdev x = 0.000000, sdev y = 0.000000
ave r = 0.000000, sdev r = 0.000000
var = 0.000000
var = 0.000000
var = 0.000000
%

If the data is contained in more than one log file, then copy all the log files to the concenct directory and answer yes to the question "Another file to read? (y or n):". The program will prompt you for the name of the second file, third file, etc.
When you run the program, make sure you also enter the large fiber and FOPS concentricity measurements (either a new set or old data took previously) to make sure that the zero point correction is handled appropriately.

Besides the nconcentricities file there are four other output files: raw.dat, ave.dat, con.dat and plot.macro. "plot.macro" is a supermongo script to generate individual plots for the concentricity measurement for each fiber. It uses the "ave.dat" and "raw.dat" files. File "con.dat" is for diagnostic value in case something looks strange. For example, to print the concentricity measurement plots:

% sm (sm is available in solaris and sunos workstations)
Hello hydra, please give me a command
: macro read plot.macro
: device postlandfile plotset1.ps
: plotset1
: device postlandfile plotset2.ps
: plotset2
: device postlandfile plotset3.ps
: plotset3
: device postlandfile plotset4.ps
: plotset4
: device postlandfile plotset5.ps
: plotset5
: device postlandfile plotset6.ps
: plotset6

Remember to place a comment in the header of the new concentricities file and to increment its version number. Then copy the new concentricities files to its final location at the Hydra PC and test at the telescope by configuring a standard field.

 

Last Modified: April 27, 2000
rcantarutti