As I’ve explained to some of my clients in the past, you can’t just
mix together two datasets recorded
by two different dataloggers and
sensors under different conditions
and expect valid results. In the case
described above, there’s a delay
between the time of a position report
and the time the flight computer
collected the environmental data. In
some cases, this probably isn’t much
of a problem, but it’s hard to know
for certain.
I can simplify and shorten the
work I do after recovery if the same
datalogger records both the
environmental data and the GPS
position data at the same time. This
has the added benefit of increasing
the precision of my environmental
data. Sounds like a winner of an idea
all around.
I next realized that a datalogger
that records altitude can also record
the speed and direction of the
balloon. Since the balloon is a
captive of the wind, this datalogger
would be recording wind speed and
direction as a function of altitude.
Therefore, by adding a temperature,
pressure, and relative humidity sensor
to the datalogger, I could turn the
datalogger into a complete near
space weather station. As you’ll see
later, it can expand its functionality to
include ground weather stations, a
hiking data computer, and a UAV
weather station.
An Introduction to the
Sensors
The first sensor is the LM335: a
three-pin temperature sensor that
produces a voltage in proportion to
its temperature. The LM335 is a TO-
92 device that only requires two of
its pins be connected (the third is an
adjustment lead for output
calibration, but can be compensated
for in a spreadsheet). The LM335 is
essentially a temperature-controlled
zener diode with a linear output.
Ideally, it produces zero volts at
a temperature of Absolute Zero
(don’t we all?) and five volts at a
temperature of 500 Kelvins. So, if one
multiplies the output voltage of the
LM335 by a factor of 100, the result
would equal the temperature in
Kelvins. It’s also easy to convert the
temperature into Celsius by
subtracting 273. For those who are
metrically challenged, the
temperature can be converted into
units of Fahrenheit following one of
two popular methods.
The second sensor is the HIH-
4000: a three-pin relative humidity
sensor. This Honeywell produced
device generates a voltage
proportional to the relative humidity.
My near space missions are tracked using
amateur radio. After recovery, the position
reports from the balloon are saved into a
file and then imported into a spreadsheet
where I can make charts of the data. That
data is not very useful unless I link the
data with the balloon’s altitude. The
process is not particularly onerous, but it
does take some time and does lack some
accuracy since the time the data was
collected doesn’t correspond exactly with
the time the balloon’s position data was
transmitted. So, I decided to create a weather station that records position
and environmental data at the same time. The result is the recording
weather station I’m describing this month. You’ll see that with minor
modifications, it can turn into other things like a weather station for ground
use, for UAV (unmanned aerial vehicle) use, and hikers.
■ BY L. PAUL VERHAGE NEAR SPACE
A Recording Weather Station for
Near Space and Beyond
54 June 2017
paul@nearsys.com