On Tue, 29 May 2012 11:36:59 -0400, "Johnny Appleseed"
wrote:
I have a digital thermometer like the one he
http://www.walmart.com/ip/Acurite-Wi...meter/16888921
The temperature the outdoor sensor reads is at least 3 degrees off from what
it should be.
Move the thermometer into the shade, away from sources of heat
(vents), and away from anything that will reflect or accumulate heat
(black meal objects). You want to measure the air temperature, not
the temperature of the reflected sun.
Also, how do you know what it "should be"? Your "reference"
thermometer might be just as far off. Incidentally, 3 degrees
variation isn't all that bad.
Such accuracy issues are constant source of entertainment among those
that weather stations that appear on the internet. Some really good
hints:
http://www.wxqa.com/aprswxnetqc.html
Here's one that I help maintain:
http://weather.gladstonefamily.net/site/AR779
Oops. I forgot to calibrate the barometer to altitude the last time
the power died and the backup battery lasted about 2 hours. Anyway,
this is my version of what it takes to get decent temperature
readings:
http://802.11junk.com/jeffl/pics/wx/slides/radiation-shield-01.html
It's called a "radiation shield" or "pagoda". The idea is to keep the
sensor out of direct (or indirect) sunlight, while still allowing for
air flow. However, there's still a problem. The building is a remote
radio site with lots of warm transmitters inside. The slit near the
roof allows hot air from inside the building to dribble out of the
slit. It was close enough to affect the sensor to have had an effect.
None of the cheapo wireless weather sensors have a proper radiation
shield including yours.
Is there any way to adjust the temperature reading in these
units? The instructions don't say anything about this issue.
Not on the cheap wireless sensors. The basic thermistor accuracy is
about +/-0.2% of full scale, which is less than 1 degree. Calibration
isn't really an issue. What is an issue is whether you're measuring
air temp, ground temp, wall temp, reflected sky temp, vent temp, etc.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558