A-1Appendix A. Wind DirectionSensor OrientationA.1 Determining True North and Sensor OrientationOrientation of the wind direction sensor is done after the datalogger has beenprogrammed, and the location of True North has been determined. True North isusually found by reading a magnetic compass and applying the correction formagnetic declination; where magnetic declination is the number of degreesbetween True North and Magnetic North. Magnetic declination for a specific sitecan be obtained from a USGS map, local airport, or through a computer serviceoffered by the USGS at www.ngdc.noaa.gov/geomag. A general map showingmagnetic declination is shown in Figure A-1.Declination angles east of True North are considered negative, and are subtractedfrom 0 degrees to get True North as shown Figure A-2. Declination angles west ofTrue North are considered positive, and are added to 0 degrees to get True North asshown 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 thesensor, 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 counterweightat True North. Display the input location or variable for wind direction using ahand-held keyboard display, PC, or palm.3. Loosen the u-bolt on the CM220 or the set screws on the Nu-Rail that securethe base of the sensor to the crossarm. While holding the vane position, slowlyrotate the sensor base until the datalogger indicates 0 degrees. Tighten the setscrews.
