Campbell UT10, Instruction Manual, Page: 60 / 70

UT10 Universal Tower
50
8.5.18 Wind Direction Sensor Orientation
8.5.18.1 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 USFA map, local airport, or through the National
Geophysical Data Web site at:
www.ngdc.noaa.gov/geomag . A general map
showing magnetic declination for the contiguous United States is shown in
FIGURE
8-34 .
Declination angles east of True North are considered negative, and are subtracted
from 360 degrees to get True North as shown FIGURE
8-35 (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
8-36 .
For example, the declination for Logan, Utah is 13.5° East. True North is 360° –
13.5°, or 346.5° 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 for wind direction using the *6
Mode of the datalogger, or, the Monitor Mode of
LoggerNet with an on-line
PC.
3. Loosen the band clamps or set screws that secure the base of the sensor to the
mast or crossarm. While holding the vane position, slowly rotate the sensor
base until the datalogger indicates 0 degrees. Tighten the band clamps or set
screws loosened previously.
4. Engage the orientation ring indexing pin in the notch at the instrument base
(05103, 05106, and 05305 sensors only), and tighten the band clamp on the
orientation ring.
* Other methods employ observations using the North Star or the sun, and
are discussed in the Quality Assurance Handbook for Air Pollution
Measurement Systems, Volume IV - Meteorological Measurements
4
.