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NRG_34m_TallTower_Installation_Manual_and_Specifications_Rev_1.05.docx
19 April 2011
Figure 5
Using Data Analysis Software to Correct for Magnetic Declination
If you orient your wind vanes toward magnetic north but want the direction data reported relative to true north, enter
the magnetic declination for the site into the offset or magnetic declination field in your wind data analysis software.
NRG‟s BaseStation Software, for example, has a field called
Mag Declin.
BaseStaion applies the declination to all
wind direction data for the site if the Mag Declin field is set to anything but zero.
Declination is not needed if you
orient your wind vanes to true north.
Note:
Wind direction vanes have a small range centered around the sensor‟s north reading that is called the dead
band and produces a zero reading. Although NRG Loggers have an algorithm that interprets north readings
correctly, when the prevailing wind is from the north, it may make sense to orient the vane to a direction other than
north. If you do this, compensate for the orientation by entering a value in the wind vane „offset‟ field of your data
analysis software. For example, if you orient your wind vane to the south (180 degrees), enter an offset of 180 for
the vane.
Note:
If you orient your wind vane to a magnetic bearing other than magnetic north, you need to enter values for
both magnetic declination and offset in your data analysis softw
are. Enter the site‟s magnetic declination so that your
software can compensate for the declination; enter an offset to compensate for the orientation of the vane. If just one
offset field is available in your software, such as NRG‟s Symphonie Data Retriever software, you will need to
combine the magnetic declination value with the offset value (if wind vanes are not oriented to true north) and enter
the net value. For example, if your wind vanes are oriented to the south instead of north, and your site has a
magnetic declination of 15 degrees west, you would enter 165 (or -195) in the offset field. Declinations to the west of
true north are subtracted from the magnetic reading, and declinations to the east of true north are added to the
magnetic reading.
