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Sensing and Control for hobbyists and schools: Sensing Temperature
In programming, it is usual to abbreviate various things. If there is any chance I will someday be looking at your sourcecode, a plea: Please use "Tture" as your abbreviation for "Temperature". When I see "Temp", my mind always interprets that as "Temporary".
A great source of delighted discussion are the various pagoda designs poeple ahve put forward. A pagoda is something that keeps your temperature sensor out of the sun, but in the ambient air. The Stevenson Screen is the traditional answer.
I think some of the ideas on the net are either over the top. None-the-less, make SOME provision, and don't be too complacent. I thought I had a solution... but it was reading up to 5 Celsius degrees too high.
Other people's pagoda ideas for you....
... and you can certainly find others with Google.... but have a look at my idea, below?
Do you share my love of simple ideas? Someone suggested fitting any thermo sensor shelter with a small fan... powered by a solar battery. Brilliant! No running costs, and the fan only runs when the sun is out, possibly heating the interior of the shelter. One possible hassle to consider: If you live in a climate where dew is common, will that be a problem for your fan?
It is natural to think of a Stevenson Screen, but I wonder if that is really the best design for housing a small electronic sensor. The Screen was good when humans had to access a bulky instrument. I built the following. It seems to work quite well and was easy to make.
I took a 3' length of 5" plastic pipe, to be mounted with the long axis vertical. At the top, 4" long slots were cut out, leaving three 5/8" wide, 4" long, "prongs", 120 degrees apart. Upside down, resting on the prongs, was attached a plastic flower pot.... big enough to allow good air flow up the pipe. The pot is there as a "hat" to keep rain out of the pipe.
If I what mean by the slots/ prongs is hard to visualize, start from the question "How could the flower pot be attached to the top of the pipe, but in a way that allows air to get out of the pot?"
A flower pot saucer was glued on top of the upside-down flower pot to finish sealing the top. (Bits of wire passed through holes drilled in the top of the prongs and holes in the flower pot were used to secure pot to prong.)
The temperature sensor is in the center of the pipe, near the bottom, mounted in a way that lets as much air as possible flow up the pipe.
The lower part of the pipe is insulated from the sun. There are many good ways to do this, but I did it by mounting a 18" long larger pipe clad in aluminum foil to the north side of my sensors mast. The 5" pipe described above was then mounted inside the larger pipe. While mounting it centrally is "tidy", it seemed better, and it was certainly easier, to bolt the inner pipe directly to the north wall of the outer pipe. This gives maximum airflow/ thermal gap where solar warming of pipe is worst.
I'm tempted to paint the flower pot and the top 10" of the small pipe black, hoping to warm the air up there and cause a draft to circulate fresh air over the sensor.
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