Campbell 05103, User Manual

Page: 35 / 43

C-1
Appendix C. Wind Direction Sensor
Orientation
C.1 Determining True North and Sensor Orientation
Orientation of the wind direction sensor is done after the datalogger has been
programmed, and the location of True North has been determined. True North is
usually found by reading a magnetic compass and applying the correction for
magnetic declination; where magnetic declination is the number of degrees between
True North and Magnetic North. Magnetic declination for a specific site can be
obtained from a USGS map, local airport, or through a computer service offered by
the USGS at www.ngdc.noaa.gov/geomag. A general map showing magnetic
declination for the contiguous United States is shown in Figure A-1.
Declination angles east of True North are considered negative, and are subtracted
from 0 degrees to get True North as shown in Figure A-2. Declination angles west of
True North are considered positive, and are added to 0 degrees to get True North as
shown in Figure A-3. For example, the declination for Logan, Utah is 14

East. True
North is 360

- 14

, or 346

as read on a compass.
Orientation is most easily done with two people, one to aim and adjust the sensor,
while the other observes the wind direction displayed by the datalogger.
1. Establish a reference point on the horizon for True North.
2. Sighting down the instrument centre line, aim the nose cone, or counterweight at
True North. Display the input location or variable for wind direction using a
hand-held keyboard display, PC, or palm.
3. Loosen the U-bolt on the CM220 or the set screws on the Nu-Rail that secure the
base of the sensor to the crossarm. While holding the vane position, slowly
rotate the sensor base until the datalogger indicates 0 degrees. Tighten the set
screws.