Campbell Met One 034A-L Manuale dell'Operatore Scaricare il pdf (Pagina 26)

Installation, Operation and Maintainance of Automatic Meteorological Stations

Sensors

Wind speed is measured by the anemometer, which consists of three cups in a horizontal plane that rotate on

a vertical shaft. This rotation activates a sealed reed switch. Each open-closure event of this switch generates an

electric pulse, which is recorded by the datalogger. The rate of pulses is proportional to the wind speed.

Wind direction is also sensed electronically. The wind vane drives a 10-kilo ohm potentiometer connected to the

logger. The recorded voltage is a function of the declination of the vane, and thus of the wind direction.

For detailed technical specifications, the reader is referred to the corresponding Campbell Scientific Instruction

Manual for the Met One 034A-L Wind Set.

3.2.2 Installation

The wind sensors should be located away from wind obstructing obstacles like trees and buildings. As a general

rule, the horizontal distance between wind set and obstruction should measure at least ten times the height of the

obstruction.

Follow the below instructions to install the Wind Set. Figure 8 presents a graphic explanation of some of the ter-

minology used.

• Attachthe019ALUcrossarmtothetopofthetripod;

• Orientthiscrossarmintheeast-westdirection,with¾”x1”Nu-railfacingWestontheSouthernhemi-

sphere, and East on the Northern hemisphere, and tighten the set screws;

• Removethealignmentscrewatthebaseofthe034A-L(windset)andinsert034A-Lintothealuminumbush-

ing (black) provided with the sensor;

• Aligntheholeinthebushingwiththatinthe034A-Lbaseandreplacethescrew

• PlacetheWindSetwithbushinginto¾”x1”NU-railandtightenthealignmentscrewfirmly;

• AlignthesensorssothatthecounterweightpointstothetruesouthandtightenthesetscrewsontheNU-

rail;

• Removetheshoulderscrewtoallowthevanetorotate;

• Attachthesensorcable,properlykeyed,tothesixpinmaleconnectorontheWindSet;

• Fingertightentheknurledring;

• RoutethesensorcablealongtheundersideofthecrossarmtothetripodanddowntotheENC12/14protec-

tive enclosure;

• Leadthecablethroughthebottomoftheenclosuretothedatalogger;donotcutanyexcesscablesincethis

may be useful at other occasions, instead tie it up carefully;

• Connectthecabletothewiringpanelaccordingtotable1inparagraph2.2,andAnnex2,asfollows:

- green wire to terminal H3:

- blue wire to terminal E1;

- white wire to the AG terminal next to E1;

- clear wire to the last G terminal of the connector block;

- red wire to terminal P1:

- black wire to the G terminal next to P1;

Box 5: Determining the Geographic North

A compass is the appropriate instrument for locating the North. However, a compass determines the mag-

netic north, which differs from the geographic one. Though the location of the magnetic north is subject to

constant change, it can be considered stable for time spans in the order of magnitude of 100 years.

The magnetic declination is defined as the angle between magnetic and geographic north. It has been deter-

mined for each spot on earth and is exactly THREE DEGREES and ZERO MINUTES West in the Lake Victoria

region.

To determine the geographic north, measure the magnetic north with a compass and adjust for the existing

magnetic declination by adding THREE DEGREES and ZERO MINUTES in a clock- wise direction.

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Campbell Met One 034A-L Manuale dell'Operatore Pagina 26

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