Campbell 03002, Instruction Manual

Page: 32 / 39

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. The preferred method to obtain the
magnetic declination for a specific site is to use a computer service offered by
NOAA at www.ngdc.noaa.gov/geomag . Magnetic declination can also be obtained
from a map or local airport. A general map showing magnetic declination for the
contiguous United States is shown in FIGURE C-1 .
Declination angles east of True North are considered negative, and are subtracted
from 360 degrees to get True North as shown FIGURE C-2 (0° and 360° are the
same point on a compass). Declination angles west of True North are considered
positive, and are added to 0 degrees to get True North as shown in FIGURE C-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 center 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 or computer.
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.