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Tipping
Bucket Rain Gauge Basics
A basic parameter to be
collected for most weather / meteorological site
studies is rainfall data. A simple low-cost rain
fall measuring device that can be used in many
applications and locations is a tipping bucket
rain gauge. Many variations of tipping bucket
rain gauges exist from different manufacturers
however most operate on a simple principle.
At the top of the gauge
is a funnel of standard diameter that collects
rainfall over a known area. The funnel is typically
covered with a screen to prevent leaves and other
debris from clogging the opening at the bottom
of the funnel. The funnel feeds the collected
rain into a rocking pair of small buckets... precisely
balanced on a center fulcrum... much like a child's
"teeter-totter". As the rain fills one bucket,
it's weight causes it to rock downward and lift
the opposing empty bucket. The rain then spills
out of the bucket and the cycle starts again.
Each time the buckets
tip, they cause a switch of some type (typically
a reed switch) to close momentarily. This contact
closure can then be counted by an attached data
logger. Rain gauges are manufactured so that each
tip (switch closure) corresponds to a particular
amount of rainfall... eg 0.01".
Data Logger Interface
Interface to a tipping bucket
rain gauge is simply done with the Logic Beach
data logging instruments. The switch contacts
are directly wired to an Counter type input channel
(which already has an internal power supply for
powering the rain-gauge switch. The logger can
then be configured through the HyperWare software
to sample periodically read the Counter channel's
value, process it and eventually store it to logger
memory.
Data Logger Program Example
To program the data logger
to sample and process the rain-gauge input, the
above Program Net can be used. The program is
developed graphically in HyperWare (running on
a PC) then downloaded into the data logger's memory
where it executes. The program functions as follows...
Every minute, the Counter
icon (which represents the hardware input channel
connected to the tipping bucket rain-gauge) is
sampled. This count is fed to a Math icon where
the counts are converted algebraically to inches,
then passed along to an hourly total Summation
icon. The hourly rainfall total is then passed
to a daily (24 Hr total) Summation function and
every day the 24 hour total is stored to memory.
Additionally, the hourly total is also fed to
a non-clearing Summation icon that keeps an accumulating
year to date rainfall total, which also is stored
to logger memory every day.
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