Slow or Inadequate Cooling
The LAS3000 camera should be able to achieve a cooling of -35C (typical normal operation is set to -30C, but setting the temperature to -35C is a good test of the health of the camera). From first being switched on it should take around 3 minutes to cool from ambient to -35C followed by around 1 minute further for the temperature to stabilise (it will initially overshoot by 1C or 2C). If the peltier cooling device has become damaged either by a natural component failure, or more likely due to the introduction of moisture into the counting chamber, then gradually the cooling capability of this peltier device is reduced. Initially the user will see that it takes much longer to arrive at the working temperature and then progressively the user must operate the camera at warmer temperatures. -25C is the warmest the camera can be operated at, but a repair as soon as a fault is detected is recommended.
Frosted CCD or Window
As air is drawn into the counting chamber moisture in the air can form frost on the CCD or even the window at the front of the counting chamber. This will manifest itself as blurred images and greatly reduced sensitivity. If the camera is allowed to warm this frosting may evaporate the camera may be cooled again and the frosting not necessarily re-appear. Of course with time this frosting will become more frequent.
Condensation on the CCD or Window
As air is drawn into the counting chamber moisture in the air can condense on the CCD and drop onto the CCD window. Images acquired may show areas affected by droplets of water, some being quite large covering up to one third of the image. Of course condensation also forms at other places in the chamber which can cause damage to the CCD, peltier cooler or internal electronics. As soon as this fault is detected the camera should be repaired.
Oxide Deposits on the CCD or Window
Moisture in the air drawn into the chamber can cause oxidation of the aluminium and steel components which become airbourne and are deposited on the CCD or window when condensation of moisture occurs. This manifests itself as blurring of acquired images.
Erratic Temperature Monitoring
A common problem is the CCD temperature being displayed with erratic values. The CCD may operate correctly for a while and then suddenly show very high or very low values. This is invariably due to the thermistor by the CCD being affected by condensation or frosting.
Cracked Chamber Window
A rare effect is a cracked CCD window. Well, believe it or not it looks like a crack but is in fact just an obscure effect caused by the condensation of moisture on the window. This is easily cleaned during the refurbishment process. |