Dry Air Purge System

      The first three images are examples of moisture condensing on the 'outside' of the chip's window, the last image is Frosting on the 'inside' of the chip window due to moisture inside the chip chamber. Condensation occurs when moisture gets inside the STL Filterwheel area, as the chip is cools eventually the chip window will be come cold enogh that moisture will condense on the outside of the chip windlow like a glass of iced tea.

      SBIG installed an additional, the third, window heater on my camera. SBIG now installs three chip window heaters on their STL series cameras. But due to Florida's high humidity I still ocassionally experience condensation issues.

      To address this problem I made a Dry Air Purge system. I bought a DrieRite Labratory Gas Drying Unit, stock# 26800 @ $49.23. Fittings cost about $5 at my local ACE Hardware store.

      I believe DrieRite uses Anhydrous Calcium Sulfate as a desiccant. Following DrieRite's recharging instructions to the exact letter still resulted in dusting after about five recharges. The 3/8" filter pads contained inside the DrieRite canister keeps this dust from entering the optical path, but I didn't like the dust.

      I changed over to Blue Indicating SilicaGel which doesn't dust if you do not overheat when recharging. After using the 'bead' style Silica Gel for a few years I switched over to "crystals". The reason I stress "Crystals" is crystal granules have more surface area than the 'beads' varity. More surface area results in more moisture abbsorption.

      I have been using these SilicaGel crystals for over three years now, recharging apx. one pound at 250F requires 4hrs. SilicaGel does not dusted at all if you do not over-cook. Heating Silica Gel, 300F or higher will cause Silica Gel to start to dust and loose its drying properties. (you can find a lot of information about SilicaGel properties at www.silicagel.net. This web site only sells in large lots)

      Initially I bought a couple 1lb bags of Blue Indicating SilicaGel 'beads' from VertiTemp or you can find SilicaGel at McMaster-Carr. One pound is more than enough to fill the DrieRite canister. Sometimes you can find bulk SilicaGel 'Crystals' at hobby or flower drying shops.

      McMaster-Carr pg-624, or search on part# 2189K47, $9.80 p/pound.

      Presently I use Silica Gel 'crystals', which, IMHO, are the best. Grainger Searching on "Dayton Silica Gel". 1.7lbs so for $19.63 years ago, now selling for ~$31.00 This used to be all 1/8" blue crystals but now reported to be a mixture of bead Silica Gel. Your chioce though.

      I use a 'Single' Stage Aquarium Air Pump from Wal-Mart. Dual Stage pumps push too much air through the Desiccant using it up quicker. Depending upon your application you may only need run the Dry Air Purge 5-10mins at the beginning of the night. One recharge lasts me a full 2-3 months in Central Florida humidity.

      To keep the air hose as limber as possible I use RC Model Airplane "Silicone" Fuel Line from AeroTrend $20 for 30ft. Better still is the 3/16" ID Silicone Aquarium Airline, 10FT for $10.25, or 250ft for $29.95 from Strictly Pet Supplies. Silicone hose is also great for chilled water systems as this hose doesn't stiffen when it gets cold. Remember though to only use small lengths ~3ft because the small ID restricts fluid flow.

      I have a STL11K which requires an AP Field Flattener (FF) for my AP155EDFS. To attach the FF to the STL11K I used Precise Parts to make all my custom adapters. I drilled and taped in a 1/8" nipple, 3/8" NPT Brass Hose Barb into the FF to STL11K Adapter.