NIRSPEC
Filter Wheel Mechanisms: Status, Control and Troubleshooting

Filter Wheel Status

17 November 2000

Both filter wheels are working properly after the repairs carried out at various times, concluding with the overhaul in September 2000. The information below no longer applies to normal operations. It is only for reference in the unlikely event of another wheel failure in the future.

25 April 2000
  1. Hardware
    • The filter wheel 1 (FW1) motor driver cable has been disconnected to avoid moves of any kind. This cable will need to be reconnected prior to any testing or the intentional move to the AO stop position.
    • Filter wheel 2 (FW2) should only be moved at low level by using two scripts: fil2.csh and rfil2.csh. These moves should only be initiated by CARA personnel, or the observer after being properly trained. Once the desired filter is in position, the initialization procedure must be run to define the position without moving the motors further. The initialization script will be called from one of 3 procedures accessable from the NIRSPEC Control Menu on the nirspec account main menu on HQ computers: either Start-up NIRSPEC Control, Enable Night-time Mode, or Initialize Motors.
  2. Control
    • FW2 can be inadvertantly moved by selecting a new filter from XNIRSPEC, or from the EFSgui. Users will need to take special precaution to avoid selecting new filters.
    • The wheels will not move during any normal initialization procedure. XNIRSPEC/Engineer/Motors/Init will call a script that only defines the position of FW1. The standard start-up procedure will call a new script /kroot/kss/nirspec/ui/csh/init_filters_fix, which will prompt the user to specify which filter is in position, and then set keywords to define the position without moving any motors.

Troubleshooting and failure recovery

This is the procedure for recovering use of a NIRSPEC filter wheel which refuses to home. The symptom is that when the filters are commanded to home or change positions via the NIRSPEC startup script, the XNIRSPEC/Engineer/Motors/Init menu, XNIRSPEC/Filter menu, or EFS scripts, either XNIRSPEC or the EFS returns an error message indicating that one of the filter wheels failed to home or move properly.

Introductory Information

  1. Each wheel has 12 positions with 9000 motor steps nominal between each position. Positive motor moves rotate the wheels to higher numbered positions (see the table of filter wheel positions ).
  2. The filter wheels are located in a single housing located in the collimated beam in between the image rotator and the F-converter. Filter wheel 2 is the forward wheel (first in the optical path), and filter wheel 1 is behind it (when viewed from the front). In order to observe FW1 externally, then, FW2 must be in the open position. Each filter slot has a Lyot stop with a central obscuration, except for the 2.2 mm wide AO stop in position 2 of FW1.

    One can look down the beam with a flashlight to observe wheel motion; the person visually inspecting must climb into the K2 elevation journal (careful!), and the NIRSPEC front cover must be initialized and open. The person doing the visual should talk by telephone headset or radio to the other person issuing the motor moves. When viewed from the front, the wheels move CCW positive, that is, the filters will rotate from top to bottom of the observers view into NIRSPEC's light path when positive motor moves are issued.

Recovery Procedure

  1. Attempt to initialize the stage one more time only using the XNIRSPEC/Engineer/Motors/Init menu item.
  2. Check the status of the switches using the XNIRSPEC/Engineer/Motors/Read Switches menu item.
  3. If no switches are set for the filter wheel in question, this indicates that the stage is not centered on a filter. Follow these steps to recenter:
    • Login to waimea as user nirspec.
    • Issue the command cdkw to go to the NIRSPEC keyword software directory.
    • Issue the command 
      source fil1.csh
      (if filter wheel 1 is failing, else use fil2.csh). This script will move the stage 10,125 motor steps in increments of 75 and print out the status of the switches after each move. The status will be 15 as long as the wheel is between position. Interrupt the script (using Ctrl-C) immediately if the value changes from 15 to another value. If the script completes 10125 motor steps without ever seeing a switch, then a significant number of motor steps must have been lost (or the switch is failing). In this case, repeat the script once more to attempt to find the switch. If it fails again, then it is unlikely to work at all --- the wheel is probably stuck and/or the motor is burned out.
    • Check the status of the switches using the XNIRSPEC/Engineer/Motors/Read Switches menu item. If the position switch is set, then you were able to stop the mechanism in a centered position --- proceed to the next step. If not, you must backtrack to locate the switch position by typing this command: 
      source rfil1.csh
      (or rfil2.csh as appropriate). Note that this script prints out both the status of the filter wheel switches and the status of the slit switches. Again, hit Ctrl-C if and when the fil1sw value changes. Re-check the switch settings as described above and, if needed, run fil1.csh to go back in the other direction. Repeat as needed until you are able to catch the position switch 'on'.
  4. On the Read Switches menu, check whether the Pri Init or Sec Init light is 'on':
    • If Pri Init is on, you are a lucky soul, because you found the primary initialization position for this wheel. Consult this table to determine which filter you are at. Read the corresponding motor step position, and enter this command to initialize the wheel manually: 
      m filMinitloc=N
      where M is the filter wheel number (1 or 2) and N is the number of motor steps from the table. Example: if you are on filter wheel 1 and have hit the primary init switch, then you've found M-wide at 90,000 motor steps.
    • If Sec Init is on, you are an equally lucky soul, because you found the secondary initialization position for this wheel. Consult this table to determine which filter you are at. Read the corresponding motor step position, and enter this command to initialize the wheel manually: 
      m filMinitloc=N
      where M is the filter wheel number (1 or 2) and N is the number of motor steps from the table.
    • If neither the Pri Init nor the Sec Init light is 'on', then we still can't determine our location unambiguously. In this case, continue running fil1.csh (or fil2.csh) until you hit the next position switch, then again use Read Switches to check for Pri Init or Sec Init. Continue as needed until you hit one or the other.
  5. Once you've located a primary or secondary initialization switch and used the filMinitloc keyword to define position, the XNIRSPEC window should properly reflect the current position. This means that you can use the Echelle Format Simulator window to manipulate the instrument as long as you set the requested filter to whatever is currently in the flaky wheel.
  6. If you are brave, you can try moving to an adjacent filter using the filter selector buttons on XNIRSPEC. But beware --- if the move fails, you'll need to start again looking for position switches and initialization switches!
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Last modified: Sun Mar 12 23:16:19 HST 2000