The weather station at the cabin consists of a number of sensors
being
polled by a computer. These sensors include:
Temperature sensors. There are several temperature sensors
scattered
around the cabin - in and out of doors.
Wind speed and direction.
Humidity
Barometric Pressure
All of these sensors are connected via a "1 Wire Network" (trademark
of Dallas Semiconductor.)
The weather data is polled via the serial port on the computer (with a
converter) and the data from each of these sensors is read, organized,
and presented by the Weather
Station
software.
The basic "1 wire weather
station" was originally created by the folks at Dallas
Semiconductor
as a promotional product: A clever way to demonstrate the
flexibility
of various electronic devices that needed only 1 wire (plus ground) to
communicate. Because each of these devices has its own unique
serial
number (that no other device ever made - or will be made - has) it can
be identified on a network of these devices. When the program is
set up, the calibration of the device "tells" the computer where each
device
is located - and in that way one can keep track of things.
This original weather station only had the capability of determining
temperature, wind direction, and wind speed, but in the recent years
more
sensors have been developed that allow humidity, barometric pressure,
rainfall,
and even lightning to be detected and measured.
Dallas Semiconductor no longer makes the weather station, but it is
still available from AAG
Electronica - plus a number of the accessories mentioned
above.
The software used at WA7X was written by Arne
Henriksen and is available for either free, or for a nominal fee
(depending
on which hardware you have, and what sensors you need to have
supported.)
The current version (the one that you pay for) is significantly more
stable
and full-featured than the earlier (free) version and is well worth the
money.
A few details about the weather station
The weather station is frequently being upgraded and modified and
new
sensors being added. Here are a few points of interest:
The "Anemometer Temperature" sensor is located in the wind
speed/direction
indicator. In the original hardware (that made by Dallas
Semiconductor)
even on bright, sunny days, the temperature reported was elevated by
only
a degree or two at most due to heating by the sun. The current
outdoor
sensor (the one made by AAG Electronica) is mechanically superior (that
is, the bugs have been worked out and it provides better weather
protection
to the electronics) but although it appears to be the same
color,
it seems to absorb a bit more infrared than the old one and thus the
reported
temperature on a bright, sunny day may be 4-5 degrees higher than
actual.
Because this sensor is in the wind direction/speed indicator, it is
also
fairly high off the ground and in the clear. (Note: As
of
12/20/03, this was renamed from "Outside Temperature" to "Anemometer
Temperature.")
The "Outdoor Temperature" temperature is not affected by
solar
radiation
as it is under an eve on the cabin. It is, however, somewhat
"buffered"
by the building's surroundings and tends not to respond quite as
quickly
to temperature swings. This sensor is actually insulated from the
building by foam insulation - which reduces this effect considerably -
but it is still slightly affected. In other words: During a
sunny day, this sensor's reported temperature may be more accurate,
while
at other times the "Anemometer Temperature" reading will respond more
quickly.
Being mounted against the building, this sensor is not as far off the
ground
as the "Anemometer Temperature" sensor in the wind instrument and thus
it's temperature may also be affected because of that. (Note:
As
of
12/20/03, this was renamed from "Humidity Temperature Sensor" to
"Outdoor Temperature.")
The humidity sensor (as mentioned above) is based on a good
quality
Honeywell
electronic humidity sensor. This sensor seems to do a very good
job
in reporting the relative humidity over an extremely wide temperature
range.
To improve accuracy, this sensor also has a built-in thermometer that
is
used by the program to correct for the known effects of temperature on
the humidity calibration. Knowing both humidity and
temperature
allows one to calculate the Dew Point - that is, the
temperature
at which the current air mass can no longer retain its moisture without
letting go of it. In other words, if the dew point is equal to
the
temperature, chances are that it's foggy!
The barometer is actually located inside - in the water
room.
Being
a sensitive instrument, it was located in a room in the basement that
has
a constant temperature. Being inside the house doesn't affect the
barometric pressure reading, however. The barometer also has its
own built-in thermometer and that is used to report the temperature of
the water room. At the moment, this temperature is slightly
elevated
due to its proximity to other electronic devices (by 2 degrees or so)
but
one of these days we'll sort that out. The barometric pressure is
believed
to be accurate, but that hasn't been officially verified. It will
indicate trending properly, though.
There are a few other temperature sensors scattered around - and
maybe
more will be added...
Note: As of January 3, 2004, the "glitching" in the
Barometric
Pressure
data seems to be fixed!
What can the weather station tell you?
Aside from a few of the obvious things, the weather station can tell
you a bit more details of present and past weather than might first
appear:
The humidity is a very good judge of what the weather
is/has
been
doing. If it shows over 95%, it was probably raining or snowing
at
that time - or in the clouds/fog.
In looking at the dew point, if it equals the current
temperature, the
cabin was in clouds (or fog) at that time.
A sudden drop of barometric pressure (not to be confused by the
"glitches")
is usually accompanied by wind - and a storm.
Occasionally, after a heavy snow, the wind speed/direction will
get
"stuck".
This is indicated by the graph showing zero wind and an absolutely
constant
wind direction (a straight line.) On the other hand, there are
occasional
periods when there is no detectable wind at all - but this is pretty
rare.
In other words, if you see no apparent wind speed/direction but there
is
a lot of new snow, the sensor's probably stuck. The "stuck
sensor"
will usually resolve itself after a few hours - when the snow either
gets
too heavy and falls off, or the wind picks up and blows it off the
sensors.
What about other weather station hardware/software?
Other than having a Davis Weather station at home, I don't have much
experience with other hardware. As for software, Arne's software
seems to be good enough and flexible enough that there has been no need
to change/update it.
How's the weather at the Glen's
Cabin?
You can look at the picture, below and/or look at his weather
station. The weather info is updated at 0, 15, 30, and 45
minutes past the hour.
Last page update: 20040107
For comments and feedback on this page, you may contact Glen via
Email.
Since June 2011, this page has had this many visitors:
