Observation of the elements of weather and climate requires meteorological tools that are sensitive, robust, simple and precise. Judging from the way the readings, meteorological equipment consists of two types, namely:
Recording is a tool that can record data continuously, since the installation until the turn of the next tool. Example: barograf and anemograf.
Non recording tool that is used when data must be read at certain times to obtain the data. Example: barometer, and anemometer ermometer.
Anemometer is a device used to measure wind speed and direction. Meteorological unit of wind speed is Knots (Beaufort Scale). While the meteorological unit of wind direction is 0o - 360o and direction of the wind. Anemometer should be placed in open areas.
At the time of the wind, baling-baling/mangkok contained on the anemometer will be moving in the direction of the wind. The greater the wind speed blowing bowls are, the faster the speed of rotation of the disc bowls. Of the number of revolutions in one second it can be seen the wind speed. Anemometer at the counter there is a tool that will calculate the wind speed. The results obtained enumerator recorded instrument, then matched with Beaufort.c Scale Figure Anemometer is:
Anemometer itself there are two general types. Types are as follows:
a. Anemometer with three or four bowls
The sensor consists of three or four fruit bowl mounted on a radius centered on a vertical axis or all of the bowl is mounted on a vertical axis. The whole bowl is facing a circumferential direction so that when the wind blows the rotor rotates in the direction fixed. Rotational speed of the rotor depends on wind speed. Through a mechanical system of gears, rotor rotation rate of accumulation systems regulate the distance the wind pointer. Anemometer type "cup counter" can only measure the average wind speed over a period of observation. With this tool, the addition of value that can be read from one observation to the next observation, stating the accumulated mileage of wind during the time of the second observation, so that the wind speed is equal to the accumulated distance traveled divided by time interval of the observations.
b. Thermal Anemometer
This anemometer is a sensor used to measure the velocity of a fluid (air) shortly. The workings of this sensor is based on the amount of the convective heat loss from the sensor to the environment around the sensor. The amount of heat transferred from the sensor is directly related to the fluid velocity passing through the sensor. If only the fluid velocity is changed, then the heat loss can be interpreted as the fluid velocity. Anemometer work follows the principle of pitot tube, which is calculated from the static pressure and velocity pressure.
Anemometer Measurement Process
The following example of a simple calculation of the wind velocity measured by three cup anemometer. Long circular arrangement of bowls is 3 m, and the composition at a time rotating it 20 times in 10 seconds, then the wind speed can be calculated: [(20x3) / 10 m = 6 m / s]
To facilitate the counting rotation of the disc then one cup anemometer was given another color.
Because of differences with respect to wind speed from a variety of different heights, then the installation of the anemometer height is usually adapted to the purpose or usefulness. For fields with a height sensor mounted agroklimatologi (bowl) 2 meters above ground level. To collect supporting data for the Class A pan evaporation measurements, anemometer mounted as high as 0.5 m. In general, the airfield installation height of 10 m. Listed open area at stake that is strong enough. For the purposes of navigation tools should be installed at a distance of 10 x height barrier factors such as a building or tree. Most of the Anemometer is generally not able to record wind speeds below 1-2 miles / hour because there is friction factor of what the early rounds.
Anemometer calibration process
Anemometer calibration process is done periodically in order perfomansi and recording the results remained stable and good. The following sequence on the anemometer calibration process.
For wind direction calibration, the method can yield Following an accuracy of ± 5 ° or better if carefully done. Begin by connecting the instrument to a signal conditioning circuit the which indicates wind direction value. This may be an indicator of the which displays wind direction values in angular degrees or simply a voltmeter monitoring the output. Hold or mount the instrument so the vane center of rotation is over the center of a sheet of paper the which has 30 ° or 45 ° crossmarkings. Position the mounting theinstrument so crossarm is oriented north-south with the vane on the north and the anemometer on the south. With the counterweight pointing directly at the anemometer the wind direction signal should correspond to 180 ° or due south. Looking from above, visually align the vane with each of the crossmarkings and Observe the indicator display. It should correspond to vane position within 5 °. If not, it may be Necessary to adjust the relative position of the vane skirt and shaft. See step 3 in the MAINTENANCE section under potentiometer replacement.
It is Important to note That while the sensor mechanically rotates through 360 °, the full scale wind direction signal from the signal conditioning Occurs at 352 °. For example, in a circuit where 0 to 1:00 VDC represents 0 ° to 360 °, the output must be adjusted for 0978 VDC when the instrument is at 352 ° full scale. (352 ° / 360 ° 1:00 X volts = 0978 volts).
Wind speed calibration is determined by the cup wheel turning factor and the output characteristics of the transducer. Calibration Formulas showing cup wheel rpm and output frequency vs. wind speed are included below.
Calibration Formulas for Model 03 102 Wind Sentry Anemometer
WIND SPEED RPM vs CUP WHEEL
m / s = (0.01250 x rpm) + 0.2
knots = (0.02427 x rpm) + 0.4
mph = (rpm x 0.02795) + 0.4
km / hr = (0.04499 x rpm) + 0.7
WIND SPEED vs OUTPUT FREQUENCY - Hz
m / s = (0.7500 x Hz) + 0.2
knots = (1.4562 x Hz) + 0.4
mph = (1.6770 x Hz) + 0.4
km / hr = (2.6994 x Hz) + 0.7