wayneharridge@xxxxxxxxxxxxxxx writes:
<<
Thanks for jogging my memory. Can you hazard a guess at whether such a
device could be attached to the CCD of a film scanner ?
>>
Wayne,
I would guess you would have trouble to get the spacing right
since the ccd is likely to be soldered down like a chip to a printed circuit
board. The peltier coolers are about 3mm thick and to make them work
effectively you need to heatsink the back side. This is because the
efficiency is quite low so you want the back to stay as close to room
temperature as possible. Otherwise the delta temperature is split between the
self heating ,heat pumping etc. rising above ambient. Adding a heatink makes
it even thicker and more difficult to fit. Typically the best delta T you can
achuieve pumping almost a zero heat load is of the order of 20-25C delta T.
Another problem is that condensation may cause leakage problems on the ccd
device as well as blurring the front window. In the typical military
applications where peltier cooling is used on detectors, they cascade two
coolers to get a bigger delta T and place the whole assembly in an evacuated
container to prevent condensation on the front window as well as reduce
conductive losses on the front. Unless the CCD device is running very hot
(seems unlikely since the dissipation is not huge usually) you don't even
gain much with a 20C increment. Typically the dark current halves
approximately every 10C reduction so 20C is a 1/4 of the noise current. Not a
huge improvement especially as the circuit may be limited by the A/D
convertor resolution or other factors not the detector.
Regards,
Tim Hughes
>>Hi100@xxxxxxx<<
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