Troxler EGauge 4590, Руководство по эксплуатации и инструкции

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G-2
G
G
P
P
S
S
A
A
c
c
c
c
u
u
r
r
a
a
c
c
y
y
As described earlier, the Model 4590 gauge can be equipped
with an optional GPS receiver that determines the location
(latitude and longitude) of the gauge. This information is stored
with each gauge measurement. The GPS receiver used in the
Model 4590 has
Wide Area Augmentation System
(
WAAS
)
capabilities, which provides accuracy to within 3 m (10 ft.).
However, the accuracy is dependent upon the user’s location
and other factors as described below.
The global positioning system is a satellite-based navigation
system that consists of 24 satellites and a network of ground
stations that monitor and control those satellites. The satellites
orbit the earth at an altitude of approximately 11,000 miles and
constantly transmit signal information back to earth. A GPS
receiver uses this information to determine its location.
To determine its latitude and longitude, a GPS receiver must
receive the signals from at least three satellites.
On average, the receiver used in the gauge is accurate to within
15 m (approximately 50 ft.) when receiving GPS data alone.
However, the WAAS capabilities can increase the accuracy to
within 3 m (10 ft.), as shown in Table 5.
The accuracy of GPS information can be affected by a number of
atmospheric forces and other conditions. The Wide Area
Augmentation System (WAAS) corrects for these factors by
placing GPS receivers at 25 known, precisely surveyed locations,
called
reference stations
, across the United States. The reference
stations determined a
measured
distance to each satellite using
the signals received from the satellites. For each satellite, the
stations compare the
measured
distance to the
actual
range (as
calculated from its known position) to determine a
differential
correction
for each satellite
Two
master stations
, located on either coast, collect data from
the reference stations to create a
GPS correction message
. This
message is then broadcast through two geostationary satellites
that are in a fixed position over the equator. The GPS receiver
applies the correction factors contained in the correction
message to increase the accuracy of its measurements.