What is the purpose of the silver screw in the side of the TEC camera and the silver tube (desiccant cartridge)?

A: Unlike other cameras, the Hypercam TEC sensor chamber is sealed and assembled in a protective atmosphere.

The silver side-screw provides access to the hermetically sealed sensor chamber. The desiccant cartridge provides a fallback solution in case moisture is allowed into the sensor chamber. It attaches to the chamber by means of the side-port, which is sealed by the screw.

NOTE: Do not remove this screw unless absolutely necessary. We strongly recommend contacting Altair Astro for confirmation before you remove this screw. 

Desiccant Chamber Sealing Screw

Desiccant Chamber Sealing Screw

The silver desiccant cartridge can be attached to the side of the camera to purge moisture, if your sensor does get frost forming on it. A frosted sensor is very unlikely with an Altair camera, and we recommend that before removing the screw or trying to use the cartridge, you get in touch with Altair or your dealer with a picture to confirm that your sensor really is frosting on the INSIDE of the sensor chamber and does not just have moisture on the OUTSIDE, i.e. on the front of the optical window (moisture on the outside of the optical window is a different problem easily solved).

If moisture REALLY has gotten into the chamber, your sensor will show ice crystals forming on it when the TEC system is running at below zero degrees, and these crystals are unmistakable, usually sharply in-focus, hairlike formations, similar to frost forming on a window.

Frost on glass surface

Frost on glass surface

Instructions to use desiccant cartridge – to purge your sensor chamber:

Desiccant Cartridge

Desiccant Cartridge sealed in bag, with spare O-Ring

  1. Switch off the TEC cooling, but keep the camera running in loop mode say exposures of a few seconds. This will evaporate any moisture and clear the sensor as the CMOS sensor gently warms up.
  2. Remove the side-screw, remove the silver cartridge from it’s sealed bag, and screw the cartridge into the hole. Keep the screw in a clean bag or container and ensure the little O-Ring on the screw is as dust-free as possible.
  3. The cartridge contains a desiccant to remove moisture from the sensor chamber. We recommend leaving the camera looping for at least 24hrs in a warm dry area so that the moisture can be captured by the desiccant cartridge.
  4. Remove the cartridge from the camera, and IMMEDIATELY replace the silver screw making sure that the small O-Ring on the screw is not dirty or has things like hair sticking to it (dust or fibres on the O-Ring will impair the sealing). Do not remove the cartridge from the bag unless you really need it because the bag is sealed with another desiccant bag to stop the cartridge losing it’s charge.
  5. When you have discharged your desiccant cartridge, remove the O-ring from the front and place the cartridge in a fan oven at 120C for 2 hours. This will drive the moisture out of the desiccant, and it will be ready for another use.
  6. When this operation is complete, replace the O-Ring on the front of the cartridge (be sure to keep it clean), and place the cartridge in a sealed plastic bag or small airtight container with extra desiccant, so that it’s ready for re-use.