Anti dewing

Hello all ....

I am using an Arduino UNO and a MLX90614 IR sensor as a cloud detector outside of my observatory. This works brilliant until it gets wet with dew and then the sky readings go completely - not surprising looking through water.

Now I am using the 3.3v out to power the MLX90614 leaving the 5v free and was wondering whether this would be able to power some form of heating element enough to stop the sensor and its box dewing up. The sensor is mounted in a small plastic project box glued into a hole in the lid.

Any and all suggestion very welcome.

I would like to point out that I am a complete newcomer to electronics so please treat me as such. 8-))

Thanks

-- Mick

If you can add a source of 12v, you could use some car heaters. Theres small blowers like this: http://www.amazon.com/Wagan-EL9933-Visor-Mounted-Heater-Defroster/dp/B000BQOO6O/ref=sr_1_10?ie=UTF8&qid=1327788697&sr=8-10

110v Contact heaters like this: http://www.amazon.com/Kats-1153-Handi-Heat-Magnetic-Heater/dp/B000BOABS6/ref=sr_1_29?ie=UTF8&qid=1327788722&sr=8-29

And 110v heating pads like this: http://www.amazon.com/Kats-24150-Watt-Universal-Heater/dp/B000I8TQD6/ref=pd_rhf_se_shvl5

A simple transistor and relay would let you control this with the arduino if you had to. i don't know what your setup looks like, but the 12v heater would probably be the best at keeping dew off it.

I am using an Arduino UNO and a MLX90614 IR sensor as a cloud detector outside of my observatory. This works brilliant until

Can you post this part of the code?

Do you have a picture of the mounting of the sensor? Did you try a small 5V PC fan?

Have you tried spraying anti-fog compound on the sensor, or whatever cover is over the sensor? I mean the stuff used to prevent bike visors from fogging up - basically something to reduce surface tension and promote wetting, as I understand it.

How does the MLX90614 IR sensor detect cloud?

Pete

First of details of the Cloud sensor can be found here ..... http://tech.groups.yahoo.com/group/sgl_observatory_automation/

In the Files area .... I am using the info from the SGL Files area.

On a clear day the MLX90614 reads the temperature of the upper atmosphere and will return a figure of ~ -23 or so. It also reads the ambient temperature. If clouds (even extremely fine stuff - it is that sensitive) move in the sky temp will fall. As the cloud thickens the sky temp will fall further. You can just watch the sky temp but the difference between ambient and sky temp can be used to create a traffic light system of cloud/part cloud/cloudy. In astroimaging the slight falls in sky temp are really useful to know about as that can be cloud or dust which can affect the seeing.

For example ......

It works extremely well - I just need to stop the dewing. The sensor has to be open to the sky. Any covering will mean the sensor is just reading the temp of that. As for the anti fogging stuff ..... I am not sure that would be a very long term solution.

It is impractical to use a fan. The box the sensor is mounted in is tiny. I was considering using a loop of nichrome attached inside the box around but not touching the sensor. The wire only needs to be warm. I am not talking lots of heat here. The amount of wire needed against the voltage is all greek to me though so all help is very welcome. 8-((

Depending how directional your sensor is, you could shield the bulk of your device and just leave a small hole for the sensor to see through. That would reduce radiation cooling (i.e. exactly the same effect that you're trying to measure) so the device as a whole would stay warmer and keep the sensing element warmer.

If that isn't enough, it would only need a small heater to keep the sensor above the ambiant air temperature. Lamps make great self regulating low powered heaters. If you mechanically attach your sensor to a small filament bulb that would be an effective low powered heater. I don't know how what effect that might have on the accuracy of the sensor, though.

If it didn't draw so much maybe a peltier cooler would come in handy, you could then regulate the heat to stay in a certain range