40
REL value with the value from the airport. IN our example, the REL
display was 1022.9 where we expected 1019.1. This then tells us that
our displayed REL pressure is 1022.9 – 1019.1 = 3.8 hPa different from
the reference source.
9.
Since we assumed the absolute pressure measured was correct, and we
presumably calculated the elevation related offset correctly, we must
conclude that the absolute pressure was not correct after all. It appears
to be 3.8 too high, so we’ll now enter a correction of -3.8 in the settings
for “ABS Barometer” until it reads a value 3.8 hPa lower than before.
This kind of correction is entirely normal as during manufacturing
small shifts in the pressure sensor readings can be introduced.
10.
For a more precise procedure, locate a very precise barometer that you
can place right next to the gateway, you would adjust “ABS
Barometer” until the ABS pressure reads identical. You would then still
adjust “REL barometer” until it displays the value from the reference
airport. This procedure would also produce the correct relative pressure,
but due to a precise calibration of the absolute pressure, it too is correct.
The first procedure above generally works quite well, but for stations at
fairly high altitudes (e.g. 5,000 ft. or higher) it may be more incorrect than at
lower altitudes. In such cases comparisons with other known correct, and
nearby at similar altitude, stations may help.
Now that calibration is complete, feel free to change the pressure units to
whatever you like.
Note:
Airport METAR data is often only updated every 10, 15 or even 30
minutes. If you use the information in the procedure above, you may be
looking at pressure data that is out of date by as much as the update interval.
To get best results observe several times and figure out the update interval
and then use two values for the procedure: one taken immediately after an
update, another taken about halfway through the interval.
Note:
It is also a good idea to observe some more after the calibration procedure
is complete to make sure the numbers are correct.
Summary of Contents for GW1003
Page 33: ...33 Dashboard Graph display ...
Page 34: ...34 List display Weather Map ...
