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計測機器 Decagon Devices DS-2のPDF 取扱説明書をオンラインで閲覧またはダウンロードできます。Decagon Devices DS-2 20 ページ。 Sonic anemometer

DS-2

This is the basic equation for the anemometer. ∆n is proportional to

the phase diﬀerence between the forward and reverse sound pulses.

The sound comes from a 40 kHz ultrasonic transducer in the head of

the anemometer. It is transmitted diagonally across the anemometer,

bouncing oﬀ of a stainless steel disk in the center, and is received by

another transducer in the anemometer head that is opposite the ﬁrst.

Once the sound pulse is received, the receiver becomes the transmit-

ter and the process is repeated. Two more sensors, mounted at 90

degrees from the ﬁrst two give the other horizontal component of

the wind. The sound travels a total distance of about 72 mm from

transmitter to receiver, but d in the equations is just the horizontal

distance, which is 40 mm.

If we take u as the magnitude of the wind vector in the east-west di-

rection (east +) and v as the magnitude in the north-south direction

(north +), then compute wind speed with equation 6.

Where the overbar indicates an average of the values sampled every

ten seconds. Compute wind direction with equation 7.

The wind measurement requires 42 ms to complete. An additional

60 ms are required for the computations to determine phase diﬀer-

ences. The anemometer samples every 10 seconds (or more often

if requested). The gust speed reported is the highest instantaneous

wind speed measured during the selected averaging interval. Cup

anemometers average over a much longer interval than 42 ms, so the

gusts measured with a sonic anemometer will have a larger peak to

mean ratio than one would see with a cup anemometer.

S =

+ v

θ = tan

(v/u)

2 THEORY

(6)

(7)