Thies CLIMA Ultrasonic Anemometer 2D Operating Instructions Manual

Ultrasonic Anemometer 2D

Operating Instructions 4.3800.00.940

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 in 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.

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

The speed of propagation of the sound in calm air is
superposed by the speed components of an air flow in
wind direction.

N

Wind from NNE

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

Y - component

wind speed component opposite to the direction of
propagation, on the contrary, leads to a reduction of the
speed of propagation.

W

E

The speed of propagation resulting from the
superposition leads to different propagation times of the
sound at different wind velocities and directions over a

X - component

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 temperature-

S

dependent 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 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
only half of the mass of the remaining air-molecules (O

and N2).

2

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
absolute humidity in grams H

O per m³ of air.

2

the measured acoustic-virtual temperature and H

v

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O-molecules have approx.

2

the

abs

4. Technical Data

Wind Speed

Meas. range 0...65 m/s, the analogue outputs are scaled to 60 m/s !
Accuracy

± 0.1 m/s , at the range 0 ... 5 m/s
resp. ± 2 % rms from meas. value , at > 5 m/s

Wind Direction

Virtual Temperature

Data output digital

Resolution 0.1 m/s
Meas. range 0...360°

Accuracy

± 1.0°

Resolution 1°

Meas. range - 40 .... + 70 °C

Accuracy

± 0.5 K

Resolution 0.1 K
Interface RS 485 / RS 422

Baud rate 1200, 2400, 4800, 9600, 19200 selectable
Output

Instantaneous values of speed, direction and temperat.

Gliding mean values 1sec.; 10sec.; 1min.; 2min.; 10min.
Output rate 1 per 100 msec up to 1 per 25.5 sec, selectable
Status identification Heater status, Path disturbance, temperature deviation

path to path > 8 Kelvin

analogue

Output 0 ... 20 mA / 0 ... 10 V or 4 ... 20 mA / 2 ... 10 V

Only wind velocity and wind direction

General

Output

Load at current output max. 400 Ω

Load at voltage output min. 4000 Ω

Instantaneous values of wind speed and direction

Gliding mean values 1sec.; 10sec.; 1min.; 2min.; 10min.
Update rate 1 per 100 msec
Resolution 12 bit

Internal meas. rate 400 measurements per second, at 25 °C
Temp. range - 40 ... + 70 °C
Supply voltage electronics, 12 ... 24 V AC/DC ± 10%, max. 3 VA
heater , 24 V AC/DC ± 10%, max. 70 VA
Protection IP 65
Icing acc. 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 16 pole plug connection in the shaft
Weight approx. 2.5 kg

5. Plug Connection Assignment Scale Drawing

Pin-No. Function Remark
1 (A)
2 (B)
3 (C)
4 (D)
5 (E)
6 (F)
7 (G)
8 (H)
9 (I)
10 (K)
11 (L)
12 (M)
13 (N)
14 (O)
15 (P)
16 (R)

Analogue output current WV 0 / 4 – 20 mA
Analogue output current WD 0 / 4 – 20 mA
Analogue Ground AGND
Analogue output voltage WV 0 / 2 – 10 V
Analogue output voltage WD 0 / 2 – 10 V
TX+ serial interface
RX+ serial interface
GND serial interface
RX- serial interface
TX- serial interface
Power electronics 12 ... 24V AC/DC
Power electronics 12 ... 24V AC/DC
Power heater 24 V AC/DC bridged with PIN 14
Power heater 24 V AC/DC bridged with PIN 13
Power heater 24 V AC/DC bridged with PIN 16
Power heater 24 V AC/DC bridged with PIN 15

Mounting shaft
for mast tu be 1½“
40 mm dept h

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Ø 70

275
200

16 pol.
plug
in the shaft

422

5.1 Remarks concerning Power Supply of Instrument:

The connecting cables for the heating (13 u. 14; 15 u. 16) must be bridged on the supply side in order to
guarantee the complete heating power!
The electronics is additionally supplied uncoupled via diodes through the heating connections 13,14, and 15,

16.
If the heating voltage exceeds the supply voltage the heating voltage takes on the supply of the electronics.

6. Interface Description

6.1 Telegram forms

6.1.1 Telegram VD (STX)xx.x xxx*xx(CR)(ETX)

Z. NR. FUNCTION
1 STX (HEX 02)
2 101 Wind speed
3 100 Wind speed
4 “.” Decimal point
5 10-1 Wind speed
6 space (HEX 20)
7 102 Wind direction
8 101 Wind direction
9 100 Wind direction
10 * (HEX 2A) Check sum identifier
11 High Byte check sum in HEX
12 Low Byte check sum in HEX
13 CR (HEX 0D) Carriage return
14 ETX (HEX 03)

6.1.2 Telegram VDT (STX)xx.x xxx xxx.x x*xx(CR)(ETX)

Z. NR. FUNCTION
1 STX (HEX 02)
2 101 Wind speed
3 100 Wind speed
4 “.” (HEX 2E) Decimal point
5 10-1 Wind speed
6 Space (HEX 20)
7 102 Wind direction
8 101 Wind direction
9 100 Wind direction
10 Space (HEX 20)
11 + or - sign
12 101 Temperature
13 100 Temperature
14 “.” (HEX 2E) Decimal point
15 10-1 Temperature
16 Space (HEX 20)
17 High Byte status byte
18 Low Byte status byte
19 * (HEX 2A) Check sum identifier
20 High Byte Check sum in HEX
21 Low Byte Check sum in HEX
22 CR (HEX 0D) Carriage return
23 ETX (HEX 03)

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