Changes between Version 5 and Version 6 of Sensors


Ignore:
Timestamp:
Jul 29, 2008 3:10:04 PM (11 years ago)
Author:
mggr
Comment:

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  • Sensors

    v5 v6  
    77You can find a thesis covering the underlying principles of the Specim instruments (Eagle & Hawk) at http://www.vtt.fi/inf/pdf/publications/2001/P435.pdf
    88
     9== Hawk ==
     10
     11Some details on Hawk's detector from Jukka @ Specim (email 25/July/2008):
     12{{{
     13The detector type on Hawk is MCT (Mercury-Cadmium-Telluride),
     14which means that it's not a CCD that is typically used for VNIR
     15spectral range.
     16
     17The manufacturer's specification for that MCT detector bad pixel
     18is the following; if the pixel peak responsivity differs more
     19than +/- 30% from average responsivity, it is considered to be
     20bad. According to specification less than 2% of pixels should
     21be bad. In practice that is from 0.3 to 1.0 %.
     22
     23The detector is sealed in a vacuum housing. This vacuum "leaks"
     24very very slowly. As a result of this new bad pixels may appear.
     25Eventually the vacuum has to be recovered using a special method.
     26According to manufacturer it may take from 6 months to several
     27years before this must be done. So far we've done this only for
     28a single sensor, which had been used already for several years
     29before that.
     30
     31By they way, there are no similar bad pixels on CCD used on Eagle.
     32
     33... response to query from Ben re: frequency of maintenance:
     34
     35There is no particular way or time to say when that operation
     36is due. You will get a hint from additional bad pixels. Also
     37if the detector temperature is no longer as low as it used
     38to be that could be an indication of impurity in the vacuum.
     39
     40You don't want to try that operation periodically. It requires
     41sending the system here and disassembly of some parts. After
     42that that the system must be reassembled and calibrated.
     43
     44I'm not expecting your system do be due for that operation yet.
     45And I understand you are recalibrating the system at the moment.
     46This means that new calibration file will "recover" most of the
     47partially appearing bad pixels if any.
     48}}}
     49
    950== Notes of interest ==
    1051