THIES Ultrasonic Anemometer 2D Operating Instructions Manual
Ultrasonic Anemometer 2D
Operating Instructions 4.3801.00.000
1. Range of Application
The Ultrasonic Anemometer 2D is designed to detect
the horizontal components of wind speed and wind
direction in two dimensions as well as the virtual
temperature. Due to its very short measurement
intervals, the instrument is ideal for the inertia-free
measurement of gusts and peak values.
In certain weather situations the accuracy of the air
temperature measurement (virtual-temperature)
surpasses that one of the classic method where the
temperature transmitter is used a weather and thermal
radiation shield.
The measured data are available as analogue signals
and as a data telegram via a serial interface. The
ultrasonic transducers as well as its carrying arms are
automatically heated so that the measuring results, in
case of critical ambient temperatures, are not affected
by icing rain or snow, and the risk of operation trouble,
caused by icing, is minimized.
2. Mode of Operation
The Ultrasonic Anemometer 2D consists of 4 ultrasonic transducers, in pairs of 2 which are opposite each
other at a distance of 200 mm.
The two measurement paths thus formed are vertical to each other.
The transformers act both as acoustic transmitters and acoustic receivers.
The respective measurement paths and their measurement direction are selected via the electronic control.
When a measurement starts, a sequence of 4 individual measurements in all 4 directions of the
measurement paths is carried out at maximum possible speed.
The measurement directions (acoustic propagation directions) rotate clockwise, first from south to north, then
from west to east, from north to south and finally from east to west.
The mean values are formed from the 4 individual measurements of the path directions and used for further
calculations.
A measurement sequence takes approx. 10 msec at +20°C.
.
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3. Measurement Principle
3.1 Wind speed and direction
Wind from NNE
Y-Component
X-Component
E
N
W
S
The speed of propagation of the sound in calm air is
superposed by the speed components of an air flow in
wind direction.
A wind speed component in the direction of the
propagation of the sound supports the speed of
propagation, thus leading to an increase in the speed. A
wind speed component opposite to the direction of
propagation, on the contrary, leads to a reduction of the
speed of propagation.
The speed of propagation resulting from the
superposition leads to different propagation times of the
sound at different wind velocities and directions over a
fixed measurement path.
As the speed of sound is very dependent on the air
temperature, the propagation time of the sound is
measured on both of the measurement paths in both
directions. In this way, the influence of the temperaturedependent speed of sound on the measurement result
can be eliminated.
By combining the two measuring paths which are at right angles to each other, one obtains the
measurement results of the sum and the angle of the wind speed vector in the form of rectangular
components.
After the rectangular speed components have been measured, they are then transformed by the µ-processor
of the anemometer into polar co-ordinates and output as sum and angle of wind speed.
3.2 Acoustic-Virtual Temperature
As previously mentioned, the speed of the propagation of sound is shows a radix dependency on the
absolute air temperature, but is rather independent of air pressure, and only slightly dependent of humidity.
Thus these physical properties of gases can be used to measure air temperature at constant and known
chemical composition.
It is a measurement of gas temperature which is made without thermal coupling to a solid state sensor.
The advantages of this measured variable is, on the one hand, its inertia free reaction to the actual gas
temperature, and, on the other hand, the avoidance of measurement errors such as those which occur when
a solid state temperature sensor is heated up by radiation.
Due to the low dependency of the speed of propagation of the sound on the air humidity, the “Virtual
Temperature” refers to dry air (0% humidity) under the same pressure conditions as that one actually
measured.
The deviation of the measured “acoustic-virtual temperature”, compared with the real air temperature, is
linear-dependent from the absolute humidity content of the air.
The part of water vapour in the air increases proportionally the sonic speed, as H
2
O-molecules have approx.
only half of the mass of the remaining air-molecules (O
2
and N2).
The rise of the sonic speed leads to an apparent (virtual) rising of the measured temperature in humid air
compared with dry air of the same temperature.
The deviation of the measured virtual temperature in humid air, compared with real air temperature, can be
corrected according to the following correlation, when the value of absolute humidity is given:
Tr = Tv – Tv * 0,135 K * m3 / g * H
abs
and Tr represents the real air temperature, T
v
the measured acoustic-virtual temperature and H
abs
the
absolute humidity in grams H
2
O per m³ of air.
The virtual temperature at 100 % is too high by approx. 2 Kelvin with an air temperature of 20°C.
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4. Technical Data
Wind Speed
Measurement range 0...65 m/s
Accuracy
± 0.1 m/s , at the range 0 ... 5 m/s
resp. ± 2 % rms from measured value at > 5 m/s
Resolution 0.1 m/s
Wind Direction
Meas. range 0...360°
Accuracy
± 1.0°
Resolution 1°
Virtual Temperature
Meas. range - 40 .... + 70 °C
Accuracy
± 0.5 K
Resolution 0.1 K
Data output digital
Interface RS 485 / RS 422
Baud rate 1200, 2400, 4800, 9600, 19200 selectable
Output
Instantaneous values of speed, direction and temperature
Gliding mean values 1sec.; 10sec.; 1min.; 2min.; 10min.
Output rate Spontaneous 1 per 100 msec up to 1 per 25.5 sec,
selectable
On request, asynchronous or synchronous measurement
Status identification
Heater status, path disturbance, δT temperature path to path
General
Internal meas. rate 400 measurements per second, at 25 °C
Temp. range - 40 ... + 70 °C
Operating voltage Supply 20…28 V
rms
AC/DC, max. 70 VA
Idling voltage when heating is switched-off: max. 32 V
rms
Protection IP 65
Icing according to THIES STD 012001
Corrosion No corrosion after 3 month of salt fog and condensation
EMV EN 55022 5/95 class B; EN50082-2 2/96
Model V4A Stainless steel for housing and sensor arms
Mounting to a mast tube 1
½ ”, for ex. DIN 2441
Type of connection 8 pole plug connector in the shaft
Weight approx. 2.5 kg
Scale Drawing
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5. Plug Connection Assignment
Pin-No. Function Remark
1 (A)
Selection Instr.-ID (Low active), bit 0 Pull up 10 KΩ intern
2 (B)
Selection Instr.-ID (Low active), bit 2 Pull up 10 KΩ intern.
3 (C)
TX− / RX− (Z) RS 485 / RS 422 Serial interface
4 (D)
Selection Instr.-ID (Low active), bit 1 Pull up 10 KΩ intern.
5 (E)
TX+ / RX+ (Y) RS 485 / RS 422 Serial interface
6 (F)
GND Serial interface
7 (G)
Supply 20−28 VAC, nom. 24 VAC Idling volt. 32 VAC
8 (H)
Supply 20−28 VAC, nom. 24 VAC Idling volt. 32 VAC
5.1 Hints for supplying the instrument:
The instrument must be supplied by 24 volts DC or AC
rms
, In order to guarantee the complete heating power.
Mounting sha ft
for Mast tube 1½“
40 mm depth
Ø 70
200
275
422
8 pole
plug
In the shaft
In order to protect the heating winding the supply voltage must not succeed an absolute value of 28v ac or
dc.
The maximum permissible idling voltage with switched-off heating is effectively 32 V DC or AC
rms
.
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