Southern African Large Telescope

Prime Focus Imaging Spectrograph

Procedure: Focus Control

SALT-3174AM0002

Jeffrey W Percival

Modification Record
Version Date Comment
1.0 19-Nov-2004 Initial Release

Prerequisites:

  1. Open "My Documents" from the desktop icon
  2. Navigate to jwp/labview/PCS/
  3. Open 08-Focus/focus-global.vi to see focus telemetry
  4. Open 00-System/enviro-global.vi to see focus position sensor (LVDT voltage).
    You can alos look at 00-System/pfis-charts.vi to see a voltage chart.
    The LVDT measures about 4 volts per mm of movement of the optic.
  5. Open 08-focus/focus.vi
  6. In "Desired Focus State" select "S1 - Focus Home"
  7. Click the Run Once arrow.
    Right now, this may time out because of focus motor velocity issues.
    If it does, dismiss the timeout error popup and click the Run Once arrow again.
    This second time, it should finish cleanly.
    Indications: Home & Killed in focus-global.vi display. Ignore "Homed" (past tense).
  8. Select the desired focus position in microns.
    The position is absolute, not relative, measured with respect to the home switch
    The position specifies the movement of the motor shaft, not the optic.
    There is about a factor of 10 "gear reduction" between the motor shaft and the optic.
    Asking for 1000 microns of the motor gets you about 100 microns of the optic.
    The LVDT measures about 4 volts per mm of movement of the optic.
  9. In "Desired Focus State" select "S2 - Focus Station"
  10. Click the Run Once arrow. Wait for the move to complete.

Example: