This
cloud sensor is based on the H&R TM92HVC2178 Peltier cooler
module
run as a generator. I used an aluminum plate designed as a hand
plate
for a door push painted black. Plastic screws were used to clamp the
junction
because the instructions said to not short the top and bottom
plates.
The surface seems to be ceramic so I don't know why they said that.
28
Oct 2004 A better cloud sensor may be a common IR
Thermometer. The ZyTemp
TN105 from Metric
Instruments
($20) has the following readings:
| Clouds |
Temp F |
| total
overcast & rain |
43 |
| daytime
clear blue sky |
-11 |
| patchy
clouds & clear sky |
depends on
where pointed |
This sensor works around 10 nm wavelength and so detects heat.
If you stand up from a chair and point the sensor at the chair it reads
80 deg F but a table top reads 72 deg F. The box says the range
is -33 to +220 C (-27 to +428 F) so the above sky temperatures are
within it's range. I believe that these units are individually
trimmed at the factory and that the on board micro controller
compensate for manufacturing variations allowing this non cooled sensor
to perform much better than raw sensors.
The TN9 IR thermometer could be combined with a small PIC microcontroller and packaged in a weatherproof way and could send the sky temperature back to your PC using RS-232. A plot of sky temp vs. time would give a good picture of the cloud cover.
The view angle of the TN105 & TN9 IR sensors is what they call 1
to 1, meaning that at 1 foot from the sensor a 1 foot diameter circle
is being sensed. This is much too wide to see clouds
moving. By aiming the sensor down onto a parabolic mirror that
angle could be reduced and as clouds drifted by the variation in
temperature would give a feel for what was going on. The trick is
finding a parabolic mirror good ar near IR (a slightly lesser
requirement than for optical use, but not by much) and has a useable
f/D
ratio.
Edmund Optics does
have Off-Axis
Parabolic Metal Mirrors that I think would work
but they cost hundreds of dollars.
Fixed Mount
versions of the TN105 that are already interfaced for RS-232 (ZF-5283)
are in development.
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