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Telescope Tracking

Using the SDSS Fiber Throughput Tester

Sloan Digital Sky Survey Telescope Technical Note 19970415-05

Russell Owen

Contents

Initial Setup

At least one hour before you plan to use the tester, power it up as follows (please do not leave the lamp or stepper motor driver on for days at a time because that wastes bulbs and electricity).

  • Turn on power to the Newport Stabilized Light Source, Keithley picoammeter and Anorad Linear Stage Controller. The lamp and picoammeter take approximately one hour to stabilize.
  • Start the "FiberTester" application by double clicking it.

Measuring A Harness

Tools required: 3/32" hex wrench.

To measure the throughput of a fiber optic harness, first set up the fiber harness as follows:

  • Arrange the harness so that the v-groove block is near the linear stage, the ferrules are near the Source, and there are no sharp bends in the fibers. Pay particular attention to the fibers where they come out of the anchor block! I suggest placing the 10-fiber tubing (leading to the v-groove block) under the red jacketing (leading to the ferrules), so that changing ferrules in the source doesn't disturb the fibers in the 10-fiber tubing.
  • Mount the v-groove block in the block holder, with 1-2 mm of the v-groove block sticking out beyond the end of the holder, and the end of the v-groove block roughly parallel to the end of the holder. Make sure the foam holding down v-groove block down does not block any light. Lock the cover down using the two cam screws, but don't over-tighten!

Mounting the v-groove block

Mounting the V-Groove Block on the Linear Stage

  • Mount the block holder (with v-groove block) on the linear stage. The end of the v-groove block should be butted up against the knife edge at the front of the linear stage. Hold the spring plunger up to let the holder under, and make sure the plunger has plenty of holding force (if it's weak, remove the block holder from under the plunger and screw down the plunger a turn or two).

Once the harness is set up, run the throughput tester software as follows:

  • If the linear stage and/or Macintosh have been powered down since last use (or if in doubt), you must initialize the linear stage. Please see "Initializing the Linear Stage" above for instructions. Otherwise, simply run the software by clicking the run button (the "right arrow" button in the upper left corner of the window), or selecting Run from the Operate menu, or typing -R.
  • Type in the serial number of the harness when requested. (For test runs and other non-production work you may also use letters, but be sure the string is no longer than 20 characters, else writing the data to a file may fail.)
  • You will then be asked to set up the input intensity measurement. To do this loosen the Detector's rail holding screw, gently mate the Detector to the Source, and tighten the rail holding screw again.

Input measurement setup

Measuring Input Intensity

  • After measuring input intensity, you will be asked to set up the first fiber measurement. To do this, gently position the Detector against the Stop. It is very important to not move the Stop, so don't bump it. A good technique is to set the Detector on the rail, then carefully squeeze the Stop and Detector together, trying not to bump. Once they touch, squeeze them together firmly while tightening the Detector's rail holding screw.

Throughput measurement setup

Measuring Throughput

  • For each fiber requested, plug the fiber into the hole at the end of the Source. Examine the fiber by looking in the microscope eyepiece. Any visible dirt should be dealt with. Visible damage probably indicates a fiber that does not meet surface quality specifications. If there is lighting overhead, be sure to replace the light cover on the microscope eyepiece.
  • When all 20 fibers have been measured, you will be asked to set up another input intensity measurement. Set that up as described above.
  • After the final input intensity measurement, the final data is computed, displayed and automatically written to a file in the "FiberData" folder.
  • The specifications are: 87% minimum throughput for any one fiber, 90% minimum average throughput for all 20 fibers. If the harness meets specifications you will see a green "Good". If something is not right, you will see a red "Bad". Figure out what went wrong. If the input intensity changed by significantly more than the amount of the problem, you may wish to study the intensity change (see the "Troubleshooting" section) and then measure the harness again.
  • To test another harness, click on the main window (which will be visible behind the results window) to bring it to the front. Then run by repeating the steps above.
  • When you are finished you may leave the software running. To shut down the computer see "Shutting Down", below.

Shutting Down

Rules and suggestions for shutting down the system:

  • Please do not leave the equipment on for days at a time because it wastes power and light bulbs. On the other hand, once you turn on the system for the day, I suggest not turning it off until you are sure you are finished measuring fibers, due to the need for a one hour warm up time. (You may leave the computer sleeping when not in use.)

Aborting a Run

You may abort a run at any time. However, you will have to start from the beginning next time you wish to measure that harness. To abort a run click the Cancel button.

Troubleshooting

The Program Fails to Start

If you see an error message when you start the program then it is probably having trouble talking to the Keithley picoammeter. Unfortunately this is quite common if anyone has fiddled with the meter (e.g. putting it into local mode after the software has been talking to it).

The safest way to get out of this is as follows:

  • Power cycle the Keithley picoammeter.
  • Quit the fiber tester program.
  • Unplug the Keyspan USB/RS-232 adapter from the USB port.
  • Wait 5 seconds.
  • Plug the Keyspan USB/RS-232 adapter back into the USB port.
  • Wait 30 seconds (for the adapter to be recognized).
  • Launch the fiber tester program, enter a harness number and press Start.
  • If it still fails, quit and relaunch the program one more time.
  • If that does not work then log out and log back in again.

The Measured Input Intensity Varies by 0.5% or More

(triggering a warning message on the line of data showing input intensity). The first thing to check is whether or not the lamp source is actually varying in intensity (there are other possible causes, discussed below). To measure lamp stability, run the program "FT Test Lamp Stability", by double-clicking the appropriate icon on the desktop. I suggest a run of 1/2 hour or more, measuring approximately once a minute. Enter the desired parameters, then run the program by pushing the Run button. To change the x or y scale of the graph, type in new values for the extreme left, right, top and/or bottom numbers shown on the scale. If the lamp is varying in intensity, this may be caused by one of several factors:

  • Insufficient warm-up time for the lamp and/or picoammeter.
  • Drafts on the lamp (or possibly the controller), or severe temperature changes.
  • The source fiber is getting jarred.
  • Severe variations in A/C power. If this is a common problem you may have to buy a power conditioner,. Some good quality Uninterruptible Power Supply (including models made by Best) regulate output voltage. I suggest plugging both the lamp controller and the picoammeter into the power conditioner, since fluctuations in power can presumably affect both of these devices.
  • The screws holding the lamp into its socket may have loosened. (This is very likely if the "regulator" light on the lamp controller flickers when the lamp housing is bumped or vibrated.)
  • The lamp is burning out. Try replacing the bulb. Be sure to burn in the new bulb for at least 1/2 hour before measuring fiber throughput.
  • If the lamp is not varying in intensity (according to your measurements), then the next suspicion is operator error, i.e. not setting up the input intensity measurement sufficiently carefully. The Detector must be accurately mated to the Source, and the rail holding screw should then be tightened appropriately. This source of problem can also be measured using the "FT Test Lamp Stability" program. Simply set the time interval to 0. Then the program will ask you to push an OK button before each measurement. This gives you a chance to move the Detector away and put it back again, measuring the intensity after each transition.

The Stop Is Out of Position

If you suspect the Stop is out of position, compare its position (as read using its vernier scale) to the recorded value, or compare the position of the Detector to the recorded value. For a more thorough check, contact me for adjustment instructions.

Technical Support

If you have any questions about use of this fiber tester, please contact:

Russell Owen
206-543-2859
rowen@u.washington.edu.

Document History

  • 5: Added link to new section Replacing the Bulb in technical note 19970416. 2009-06-10.
  • 4: Added troubleshooting entry "The Program Fails to Start". 2009-01-22 R. Owen.
  • 3: Modified for double-clickable application. 2008-06-26 R. Owen.
  • 2: Modified for SDSS III fiber tester (software rewritten in Python) version 1.1. Made compliant with HTML 4.01 Transitional. 2008-06-02 R. Owen
  • 1: First release, for SDSS (software written in LabVIEW). 1997-04-15 R. Owen