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The Camera
Our CCD camera was designed and built in-house. The CCD device is a SITe
(Scientific Imaging Technologies, Inc.) 512 x 512, 24 micron pixel, thinned,
backside illuminated, anti-reflection coated device. With our telescope,
this produced a 7 X 7 arc/min field and the pixel scale is .97 arc/sec. This CCD
is mounted inside the camera vacuum chamber which is nominally maintained at 20
microns. The frames are in 16-bit FITS format and take 6 seconds to read out.
Each FITS frame is automatically time stamped at the middle of its exposure from
a WWV time standard receiver clock. The stated accuracy is only +/- a few
milliseconds from the atomic clock in Boulder, Colorado where the radio signal
originates.
The camera is machined out of solid aluminum and separates into three
pieces, essentially the top, the main body and bottom. The top incorporates
a rotating mounting plate and the UniBlitz 32mm diameter electric shutter.
The bottom has the Melcor three stage thermoelectric cooler (Model 3CP 085
065-71-31-17), the heat sink for the liquid coolant, and the necessary
electrical connectors to run the CCD.
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The CCD mounting arrangement
The Melcor is epoxied with special non-outgassing cement into a
shallow milled area centered on the inside of this bottom piece. On its
top (third stage) is epoxied an aluminum block. The CCD is fastened to
this block with an Indium wafer sandwiched in between for thermal conductivity
and held in place by thin and narrow bronze clips. In this way, the CCD can be
replaced if necessary. The Melcor device has a Delta T-max of 97C. O-ring
sealed DB connectors are mounted onto this bottom plate for the electrical
connections to operate the Melcor and the CCD. Along side the CCD is mounted a
"getter" device (SAES Getters, USA, Inc., Model St-172) to help in maintaining
the chamber vacuum in the closed camera by absorbing molecules.
The CCD is operated with two 16 bit (analog and digital) 4 layer PC
boards (mounted near the camera on the telescope), and an AT-bus control
board. These boards are patterned after those used by the US Naval
Observatory here in Flagstaff and designed by FHH Engineering. The AT-bus
control board was wire-wrapped at Braeside and, in conjunction with the
analog and digital camera boards, control all aspects of the CCD camera.
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