It is more difficult to cool down rather big sensors in the G3
cameras compared to smaller detectors used in the G2 series. Big
sensors require greater CCD cold chamber with larger area front
optical window, which naturally leads to higher thermal leaks and the
necessity to use much higher cooling power to achieve similar
temperature drop. To cool down sensors in the G4 cameras is even more
difficult, as the G4 cold chamber is even bigger and the optical front
window has even greater area.
Still, the G3 cameras can reach up to 48°C below the ambient temperature and the G4 camera are
able to cool down the sensor up to 45°C
below the ambient.
SIPS Imager tool showing actual temperature drop of the
standard G3 (left) and G4 (right) cameras at room temperature
25°C
However, these maximal values provide very little room for
regulation and it is not recommended to use such high delta T for
regular observations, as the camera may not be able to maintain the
absolute CCD temperature if the environment temperature rises. Also
please keep on mind that the maximum temperature drop may vary among
individual cameras, as the Peltier coolers are also manufactured with
some variations in their parameters.
As the thermal leaks cannot be easily lowered (the CCD cold chamber
dimensions, the front optical window area and also the sensor size are
fixed parameters), the only way how to achieve lower absolute
temperatures is to enhance cooling power. However, one of the design
goals of the EC cameras was keeping the total power consumption within
the 60W range of the standard power adapter. Higher power consumption
would require not only using of different power supply, but also a
different (less common) power plug connector capable to carry higher
currents. Also power cable is typically shorter, which bring another
problems with power adapter mounting close to the camera etc.
New variants of both G3 and G4 cameras with the EC suffix
are similar to the standard versions, but the camera head back shell
is thicker to accommodate larger heat sink.
Front and back outlines of EC cameras are identical to
standard models
Side view reveals bigger heat sink of the EC
variant
The thicker camera head back shell is not the only difference, EC
variant cameras also use more powerful fans. This is why EC cameras
are also a bit louder than the standard models, but this is the price
for increased amount of heat removed from the Peltier coolers hot
side.
Camera plugs on the bottom side are identical (left), top
side reveals bigger heat sink of EC cameras (right)
SIPS Imager tool showing actual temperature drop of the
Enhanced Cooling variants of the G3 (left) and G4 (right) cameras at
room temperature 25°C
Otherwise EC variants are identical to standard cameras, they have
the same BFD and use the same telescope adapters, software and drivers
etc. The absolute sensor temperature of the EC variant can achieve up
to 5°C lower temperature compared to
standard models. This may not look like big difference, but as
previously explained, the dark current depends exponentially on the
temperature, so 5°C temperature drop can
result into close to halved dark current, depending on the particular
sensor.
|
G3 standard |
G3 Enhanced Cooling |
G4 standard |
G4 Enhanced Cooling |
Maximum cooling |
48°C |
53°C |
45°C |
50°C |
Typical cooling |
45°C |
50°C |
42°C |
47°C |
CCD sensor temperature drop below ambient temperature for
standard and EC variants of the G3 and G4 cameras
|