Changes between Version 5 and Version 6 of Sensors

Timestamp:

Jul 29, 2008, 3:10:04 PM (17 years ago)

Author:

mggr

Comment:

--

Sensors

@@ -7 +7 @@
 You 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
 
+== Hawk ==
+
+Some details on Hawk's detector from Jukka @ Specim (email 25/July/2008):
+{{{
+The detector type on Hawk is MCT (Mercury-Cadmium-Telluride),
+which means that it's not a CCD that is typically used for VNIR
+spectral range.
+
+The manufacturer's specification for that MCT detector bad pixel
+is the following; if the pixel peak responsivity differs more
+than +/- 30% from average responsivity, it is considered to be
+bad. According to specification less than 2% of pixels should
+be bad. In practice that is from 0.3 to 1.0 %.
+
+The detector is sealed in a vacuum housing. This vacuum "leaks" 
+very very slowly. As a result of this new bad pixels may appear.
+Eventually the vacuum has to be recovered using a special method. 
+According to manufacturer it may take from 6 months to several 
+years before this must be done. So far we've done this only for
+a single sensor, which had been used already for several years
+before that.
+
+By they way, there are no similar bad pixels on CCD used on Eagle.
+
+... response to query from Ben re: frequency of maintenance:
+
+There is no particular way or time to say when that operation 
+is due. You will get a hint from additional bad pixels. Also
+if the detector temperature is no longer as low as it used
+to be that could be an indication of impurity in the vacuum.
+
+You don't want to try that operation periodically. It requires
+sending the system here and disassembly of some parts. After 
+that that the system must be reassembled and calibrated.
+
+I'm not expecting your system do be due for that operation yet.
+And I understand you are recalibrating the system at the moment.
+This means that new calibration file will "recover" most of the
+partially appearing bad pixels if any.
+}}}
+
 == Notes of interest ==