LWS Upgrade Project News

updated 08 August 98

The LWS upgrade project was scheduled for a "readiness review" on 18Aug98. The most recent goal was to install LWS on the Keck I telescope and begin commissioning on the night sky in early September.  However, the science grade device turned out to have a major problem, an instability of the bias voltage caused by a breakdown of the guard ring.  The review and commissioning are being postponed until the detector can be replaced. The new date for the review is not known at this time. Boeing, the detector manufacturer has been very responsive and cooperative  in diagnosing the problem. They have agreed to replace the device with one thoroughly tested and proven not to have this problem.  It is hoped that the schedule setback will not be too severe and LWS commissioning will proceed in the fall of 1998.
Timeline
  • scheduled for 19Aug98
    • Detector installation complete, cool down cycle and testing to begin
  • scheduled for 16Aug98
    • Replacement science grade detector scheduled to arrive in Hawaii
  • 04Aug98
    • Telecon occurs with members of LWS team and Boeing personnel.
    Determined that most likely cause of problem is breakdown of detector guard ring leading to a drop in bias voltage.
    Boeing to replace with a device that is shown to not have the guard ring breakdown problem.
  • 03Aug98
    • Detector tests continue with detector in good state.
    System noise shown to be much better but not quite background limited
    System noise shown to be a function of chop frequency, or 1/f noise.
    Detector proves to be very good when not experiencing repsonsivity problem.
  • 29Jul98
    • First Cold Tests of science grade device.
    Problem discovered: instability in signal level, evident on image and on oscope
    Most evident with flux on chip and temperature controlled to greater 8degK
    Problem corrects itself when power is cycled to
  •  26Jul98  Science grade device ,Boeing 128^2 As:Si BIB Moderate Flux, arrives in Hawaii
  • Jun 97
    • System testing with Engineering array
    System Noise problem improved significantly to around 0.7 adu
    Stray radiation problem significantly improved, now negligible for typical integration times
  •  May 98
    • First cold tests () of the engineering grade chip were successful!
    One dead channel on engineering array.
    Sensitive for all filters, sensitivity not yet quantified.
    Problem discovered: system/detector noise being higher than background noise (~3adu).
    Stray radiation in dewar detected, limiting ability to test and quantify system characteristics
    Temperature control of detector worked very well in range 6 to 11 deg K
  • Project review and summit commissioning anticipated for late summer 98

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    LWS Image of Test Aperture at 11.7 microns, 30May98