Cup Anemometer Basics
Wind speed and direction are
basic parameters typically collected at weather / meteorological
data collection sites. One of the most common methods for
measuring wind speed is with a wind driven spinning device
called a cup anemometer. The spinning cup anemometer consists
of three (typically) conical shaped cups that turn when
moving air impinges on the cups from any direction. As the
cups spin on a central low-torque bearing suspended shaft,
they move one or more magnets past a magnetic reed switch.
Each time the magnet passes by the reed switch the switch
contacts close, resulting in a frequency of contact closures
which correlates to wind speed.
Spinning cup anemometers are available
in many variations and may be configured for horizontal
as well as vertical (shear) wind detection.
Data Logger Interface
Interface to a spinning cup anemometer
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,
process and store wind speed readings from the spinning
cup anemometer signal, 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 2 seconds, the Frequency icon
(which represents the hardware input channel connected
to the anemometer) is sampled. This frequency is fed to
a Math icon where the frequency is converted algebraically
to MPH. The data then fans out and is passed to three
other icons that perform an Average, Minimum and Maximum
calculation every 5 minutes. The Avg, Min and Max data
is then passed to Memory channel icons... indicating storage
to the data loggers internal memory.
Additionally, a Probe Point icon (looks
like a meter probe) which is attached to the output from
the Math icon is included in the Program Net. This icon
allows remote access to a logger at any time from a PC
via a serial link (modem, RS-232, Ethernet, etc) and the
real-time wind speed can be displayed. Display can be
done on the PC screen from within the HyperWare software,
graphically, numerically and/or right from the data logger's
local display... if so equipped.