Gina

Not true actually - RH = 74% for air from freezer Living room RH = 43% according to my wal thermometer and humidity meter.

OK I'll try that

Thought I'd try an experiment so I unplugged the USB lead and put the box and Arduino in the freezer for a while. Then brought it back into the living room and reconnected to the PC. Here are the results for the first 15 minutes. This shows how the dew point depends on temperature as well as humidity.

Oh yes, I think so. However, this is with just two silica gel bags and I shall put as many in as I can. If I can print the parts I can arrange to keep the bags away from the mechanism - barriers with holes in. Here's a screenshot of the serial output with another couple of bags added.

Another 20m of drying.

I've set up a drying test with the box, DHT22 T & RH sensor and Arduino. Here's a screenshot of the first few minutes of drying and a photo of the setup.

Here are a couple of screenshots from SketchUp showing the idea. Front side of box removed for clarity. Also, I haven't shown the grommets or the box details. This is just a rough sketch but it is to scale. The arcs show the path of the cover glass as its fitted onto the sensor frame. The shaft shown is a 6mm aluminium rod but I may choose a different size depending on the size of grommets - I have quite a variety. I might use silicone grease on the grommets to aid sealing. I still have to work out how the sensor assembly will be held in the right place and orientation and also the lever on the shaft and attachment to the cover glass. It will be next week (or later) before I'm ready to replace the cover glass on the working sensor, as there's plenty to do before then so I might wait until I get the 3D printer working again. Then I can print parts with just the right dimensions, angles etc.

Yes, I should think so I was thinking of mounting the lever on a smooth shaft going through grommets. With a nice close fit of course to make a seal.

I'm still thinking about the lever - I have some ideas but not decided yet. I may do a SketchUp model. Trouble is SketchUp doesn't cater for a moving model AFAIK. Also, I don't know when I'm going to get the replacement control board for my 3D printer so I may have to build it the hard way. The sort of thing I have in mind is to hold the sensor assembly with the sensor facing slightly downwards so that any dust doesn't settle on it. And the cover glass with the inside face also facing slightly downwards. Then the cover glass swung round and onto the sensor frame once the humidity has dropped sufficiently. We haven't had a fire for a few days now so I'm hoping the dust level indoors is suitably low

Thanks They look similar to the ones in my kit but I've ordered one to see. Shold be here Friday or Saturday.

I think I may have the answer to the glue problem - double sided adhesive tape. Placed around the frame of the sensor. Then the cover glass could be moved into position and gently pushed home onto the sticky tape. Likewise the cover glass can be attached to the lever with double sided adhesive sponge. With the adhesive sponge on the outside of the cover glass any residue can be easily cleaned off.

I've sorted out a clear plastic box that I can use to dry the air round the sensor and apply the cover glass. This will also contain colour changing silica gel bags - of which I have plenty I plan to have a DHT22 digital temperature and humidity sensor also in the box with the cable going through a gland and connected to an Arduino to check the dew point of the air. That way I can be sure the air is dry enough.

I'll try the the epoxy/IPA approach. I saw your post on page 74 and I've ordered those conical tools but the earlier link shows several options and I just wondered which of those you got.

Have you tried using a dry tool on an 1100D sensor? These have a much tougher CFA than earlier models. I tried dry on a 350D sensor (I think) and the CFA came off eventually. I tried dry on the 1100D and even after about 5 mins continuous buffing the sensor was polished and very hot but still a strong green colour - no CFA had come off at all and the buffing tool was still white. Maybe the tools you are using are different, harder perhaps. I have some of the pointed tools mentioned earlier, on order from ebay and I'll see how they work. I can say I was surprised how even the CFA removal was with the paint scratch polishing paste - quite different from what I achieved manually.

Still looking out the bits and pieces to make up the test rig. Can't find the Peltier TEC I was going to use - a 12v 3A one from Farnel and more efficient than the Chinese ones. However, I do have a 3.3v 2A one (TEC1-4902) about 7W I/P power and a 50mm square CPU cooler. I have that setup running now and the cold side has already collected a thick layer of ice

Yes, but then it might run over the frame where the cover glass is going to go. Anyway, time will tell

Back to the debayering... I have had a very very quick go at debayering the 1100D duff sensor with Dremel look-alike and felt buffing tool plus paint scratch repair paste. Here is a photo of the result. When I get the epoxy resin I can practice adding resin to the area around the sensor - see if I can cover the gold wires but keep below of the frame so that a cover glass could go back on when I work on the real job (a working sensor).

Yes, I was thinking of a sealed container with desiccant but the problem is to lower the cover glass onto the frame. It has to be clear of the sensor and its frame to allow dry air to get to the sensor. I'm thinking in terms of a transparent plastic box with the cover glass attached to a lever on an axle going through grommets in the sides of the box to seal. Not sure what to do about the glue though.

I agree. "Reliable" is the crux of the matter

Tried the buffing tool on dud sensor and with a bit of the ScratchX 2.0 applied to the sensor and then buffed, the CFA came off immediately and left a pretty smooth golden result. Without the scratch removal paste and dry the buffer tool wouldn't touch the CFA. I think it just removed the micro lenses as the surface turned from matt to shiny but still very green

Yes, I wondered if the epoxy disconnected a gold wire (or two) when cold and remade the contact when warm. OTOH it could have been something entirely different. I need to check the sensor for cold working at every stage. If I were to use my table vice to hold the sensor unit the glass would fall onto the carpet on the floor but I think I'll do something more sensible - hot glass falling on the carpet is not ideal! The sensor will be fitted with a cold finger first anyway so that I can check that it works before I start so I could hold it with that. Removing heat from the sensor is a good idea anyway - helps stop it heating up when removing the glass and failing from that. If the cover glass cracks/breaks I have another from another sensor anyway that I can use. Whether I reuse a cover glass depends if I can devise a way of removing moisture from the sensor either as it's replaced or afterwards. The dew point of the air between glass and sensor needs to be below -20C (or at least -10C). I would prefer to have the sensor sealed with dry air around it and a glass covering as that makes design of the other parts much easier. I have three possible ideas for dehumidifying the air around the sensor. Replace the cover glass in a very dry environment (and dust free) Drill tiny holes in the sensor frame to purge with dry air after replacing the cover glass Use the IR filter (not the colour correction blue filter) in the filter frame and drill tiny holes in this where there's a bit more room to purge with dry airMy past experience of drilling tiny holes is not good - broken drill bits etc. so I would really prefer the first option if I can devise a way to do it

I have found some more information on the PX804C potting resin. The mix ratio is 4.8:1 by volume ie. about 5:1 as opposed to 1:1 for normal epoxy resin. I'll be able to confirm this when I get the resin. So I guess I'll be getting around 200gm of resin and 50gm of hardener or very roughly translated into volume something like 200mL resin and 50mL hardener.

I need to approach this scientifically viz. arrange a test setup that I can use relatively easily. It will need to have cooling as in one case previously I found the sensor was fine at ambient temperature but failed when cooled. Warmed up again, it worked again. This surprised me as I expected debayering to either work or fail. This was one with the ordinary slow set epoxy resin so I'm hoping the potting resin won't do that (if it was the resin - no way to be sure). I have the 1100D carcass I've used in the past for astro so I can use that. I also have an almost complete camera where the back has been replaced with a cold finger and ambient temperature cooling. Whereas an uncooled camera would reach 30C with long exposures, I could reduce the sensor temperature by at least 10C producing a significant noise redustion. I could add Peltier TEC and control system to provide astro level cooling. Misting up of the sensor won't really matter as the previous sensor failed completely at low temperature and that will be what I'll be testing for. I need to produce a new control system as the previous one relied on a large manual control box that I had on the pier. Most of that has been dismantled and cannibalised long since The new control system will want to be a lot smaller and I plan to have it computer controlled. In fact I will want to control it remotely with local netbook wi-fi linked to my main desktop indoors. I'm planning to use the final debayered, cooled camera with built-in FW and OAG on my second pier for widefield DSO imaging.

Seems JTW use epoxy resin to protect the gold wires and that definitely seems to be the way to go. But it has to be the right sort of epoxy as I found out for myself! Do you use the felt tips dry? I ask because I tried that with a dry tip on the dead 1100D but even after some time it just polished the surface - I think it will need the car paint polish I used with the manual method. It's very easy to go too deep and destroy the sensor that way. Some parts cause dead pixels, some dead rows and/or columns and some complete failure - I've seen all of these! I've yet to try a blowtorch on a complete cover glass but I have hopes of success.

I tried my Bremel blowtorch on the remains of the cover glass on the 1100D sensor and yes, they dropped off. The sensor got rather hot but that may have been because most of the glass had already come off in bits. I'll try a full cover glass removal tomorrow.