Dew Point
Dew Point is the temperature to which air must be cooled at
constant pressure for water vapor to condense. Dew Point is
reported as a temperature in °C or °F. The sensor calculates
Dew Point (in °C) with the formula:
In this formula, RH is the Relative Humidity (as a percentage),
T is Temperature in °C, and SatVP is the saturation water vapor
pressure, given by:
Wind Chill
Wind Chill (or Wind Chill Index) indicates a combined effect of
temperature and wind speed. It is reported as an apparent
temperature in °F or °C. The sensor calculates Wind Chill (in °F)
using the formula:
where T is air temperature (in °F) and v is wind speed (in mph).
Wind Chill is defined for temperatures at or below 50 °F and
wind speed above 3 miles per hour; outside of those limits, the
sensor reports a value equal to Temperature.
Heat Stress Index (Humidex)
Heat Stress Index (or Humidex) indicates a combined effect of
temperature and humidity. It is reported as an apparent
temperature in °F or °C. The sensor calculates Humidex (in °C)
using the formula:
where T is the ambient air temperature in °C and e is the water
vapor pressure in kPa.
Sea-level corrected pressure
A typical weather station does not report the actual measured
barometric pressure. Rather, it reports a "sea-level corrected"
value. The sea-level corrected pressure is not calculated
automatically but can be found using this equation:
where h is the sensor’s elevation in meters and BP is the
Barometric Pressure in mbar. To have this calculation done
automatically, type this equation into the Calculator tool in
PASCO Capstone or SPARKvue.
Wireless GPS Sensor
The Wireless GPS Sensor uses signals received from the Global
Positioning System (GPS) to determine its latitude, longitude,
altitude, and horizontal velocity anywhere on Earth. This sensor
can be used alone or in conjunction with other sensors for
outdoor experiments in environmental science, physics, and
other subjects. Data from the Wireless GPS Sensor can be
relayed via Bluetooth or micro USB cable to PASCO Capstone
or SPARKvue.
Theory of operation
The Wireless GPS Sensor must
receive data from at least three
GPS satellites to determine its
position. When the sensor is first
powered on, it searches the sky
for available satellites. This
process typically takes between
30 seconds and 2 minutes. Once
satellites have been identified,
the sensor actively tracks them
and acquires new satellites as
they come into view.
The Wireless GPS Sensor
performs best outdoors, with a
clear view of the sky.
Sensor set-up
Orientation and positioning
It is important to orient the sensor properly to receive signals
from satellites overhead, especially during initial search mode
(when the GPS Status LED is blinking red). The antenna detects
signals through the top side of the sensor. The antenna is
located above the rectangular window which houses the
temperature, pressure, and humidity sensing elements. Hold the
sensor with the top side up and approximately horizontal, facing
the sky. Do not cover the antenna area.
Modes
The color of the GPS Status LED indicates whether or not the
sensor is ready to make measurements. At initial power on, the
sensor enters "search mode", in which it searches the sky for
available satellites. During "search mode", the LED blinks red.
When the sensor is actively tracking three or more satellites, the
LED blinks green.
If the sensor cannot track at least three satellites, it enters "lost
mode". In this mode, the sensor continues to report its most
recent position measurements. Use this "stale" data with
caution, as it is incorrect if the sensor has moved since its last
valid measurement. In lost mode, the GPS Status LED blinks
red and the sensor searches for available satellites again.
If the Wireless GPS Sensor is turned off in the data collection
software, or if there is a hardware problem, the GPS Status LED
does not shine.
Wireless Weather Sensor with GPS | PS-3209
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