Vaisala WAA251 User manual

• Non-freezing all weather sensor
• Lightweight cups with integral heaters
• Non-contact heating power transmission
• Low inertia and starting threshold
• Excellent linearity up to 75 m/s
• Distance constant 2.7 m
DESCRIPTION
The WAA251 is an optoelectronic heated-cup anemometer with
excellent performance even in extreme climatic conditions. High
sensitivity and linearity are achieved y a unique non-contact heating
power transmission. Foil heaters are inserted in each cup and in the
cup wheel hu ena ling low power consumption. The cup wheel is
remova le, with a 2-pin connector for heating electricity.
The transmission of heating power to the anemometer’s rotor is
contactless, with no slip rings nor rushes, hence eliminating sparks
and excessive friction and wear. The cup heaters are supplied via a
rotary transformer, with 26 kHz sine wave, providing low EMI.
A heating on/off switch circuit is included, controlled y an exter-
nal NTC resistor sensing the am ient temperature. The circuit also
controls power feed to the non-rotating heater in the anemometer’s
shaft tunnel.
Power consumption, typically 70 W, is very low considering the
protection it gives against freezing. Approximately 49 W of the
heating power is on the cup wheel, 12 W on the shaft and earings,
and 9 W on the ody.
The WAA251 can e mounted to Vaisala’s standard WAC151 Cross
Arm with a regular 6-pin connector. Besides the standard cross arm
the WAA251 also complies with the WAT12 and WAT15 Wind
Transmitters.
A single 24 VDC (4 A) power supply feeds the device, including
oth the heater and the transducer. A recommended power supply
is Vaisala's WHP25, designed for outdoor use and mounta le to the
sensor mast. The WAA251 even provides the operating and shaft
heating voltages to a WAV151 Wind Vane mounted to the same
cross arm. The wind transmitter WAT12 or WAT15 as well receives
its operating power from the WAA251. Hence a single power sup-
ply is enough for the whole sensor/transmitter system.
WAA251’s transducer has an optochopper and output interface simi-
lar to those of the WAA151. Hence, upgrading to a heated-cup sys-
tem is easy; the only alteration needed is for the wiring in the
WAC151 junction ox, see Fig. 3. Notice that the NTC resistor
shown in the figure is essential for the system temperature control.
The WAA251 is mounted to the southern end of the cross arm.
Installation is safer with the cup wheel removed. Fit the 6-pin plug
through the mounting flange of the cross arm, then carefully con-
nect it to the sensor. Mount the sensor to the flange y twisting, and
tighten the screws. Refer to Figure 1.
The WAA251 complies with the ASTM 5096-90 performance test
(refer to technical data) and several MIL-test standards.
INSTALLATION
WAA251 Heated Anemometer
Quick Reference Guide
Figure 1. Mounting of wind sensor
Figure 2. WAA251 connector
A +12 Vout (for vane and transmitter)
B +24 Vout (for vane)
C Fout (signal output)
D GND ( ommon ground)
E +24 Vin (power input)
F HCin (heating ontrol / NTC)
Figure 3. WAC151 Standard Wiring for WAA251 & WAV151

Head Office:
VAISALA Oy
PL 26, FIN-00421 Helsinki
FINLAND
Phone (int.): ([phone]
Telefax: ([phone]
Telex: 122832 vsala fi
I
SO 9001
CERTIFIED
QUALITY
SYSTEM
MAINTENANCE AND REPAIR
Ball earings must e checked once a year visually and y rotating
the sensor shaft. To do this, remove the cup wheel. The shaft should
spin smoothly and should not create any detecta le noise.
Replacement should e done only y a trained technician, as fol-
lows:
1Loosen and carefully remove the hexagon screw of the
cup wheel, not ending the connector pins on top of the
shaft.
2Loosen the hex nut of the connector (with 22 mm tool).
3Loosen the three screws at the ottom of the sensor ody
(with 7 mm tool).
4Remove the ody cover; handle carefully the O-rings.
5Release the three wires from the screw terminals on the
lower circuit oard.
6Loosen the three nuts at the ottom of the circuit oard.
7Remove the lower circuit oard.
8Loosen the spacer screws (with 6 mm tool); carefully, not
ending.
9Remove the upper circuit oard.
10 Loosen the hexagon screw of the rotating transformer
assem ly and remove it.
11 Remove the retaining ring at the shaft tunnel (using
narrow-pointed pliers).
12 Remove the upper earing after pulling out the shaft.
13 Remove the retaining ring at the shaft (using narrow-
pointed pliers).
14 Remove the lower earing.
Be careful when handling the ball bearings!
Reverse work order for assem ling the sensor.
NOTE for reassem ly! At step 10, the rotating transformer is in-
stalled ut its fixing screw is not fastened until the lower circuit
oard is installed and fixed (steps 7, 6). After that, to adjust the air
gap etween the transformer coils, first push the transformer (10)
as far up as possi le. The ferrite coils are breakable, do NOT
prise them ith any hard tool. Then place a screwdriver tip into
the slot etween part 10 and the shaft tu e, and pry until the air gap
underneath part 10 is 0.4 mm (0.016"). Finally, fasten the hexagon
fixing screw. Make sure the part 10 does not touch the trans-
former lo er part at any rotary position of the shaft.
The O-rings must be replaced by new ones before reassembling.
TECHNICAL DATA
Sensor/Transducer type Cup anemometer/ Opto-chopper
Measuring range 0.4 ... 75 m/s
Starting threshold < 0.5 m/s 1)
Distance constant 2.7 m
Transducer output 0...750 Hz square wave (for 0...75 m/s)
Characteristic Transfer Function Uf = 0.2425 + 0.09793 × R
(Uf = wind speed; R = o/p pulse rate)
Accuracy (within 0.4 ... 60 m/s)
with Characteristic Transfer Function ± 0.17 m/s 2)
with “simple transfer function” Uf = 0.1 × R –0.3/+1.0 m/s 3)
Transducer output level High state > 11 V (with Iout < +5 mA)
Low state < 1.5 V (with Iout > –5 mA)
Input power supply 24 VDC ± 10 %, max. 3.3 A
(max. 3.9 A with WAV151 added)
Power consumption 70 W elow +2 °C; 1 W a ove +5 °C
(typical, with Uin = 24 VDC)
Heating control Shaft heating on at < +5 °C (12 W)
Cup heating on at < +2 °C (49 W)
Temperature sensing With external 10 kohm NTC-resistor
included in the cross arm j- ox wiring
O/P power (for WAV151, WAT12 etc.) 13 VDC, 70 mA max.
24 VDC, 0.6 A (on at < +5 °C)
Electrical connections MIL-C-26482 type 6-pin plug;
6-wire ca le through cross arm tu ing
Operating temperature –55 ... +55 °C
Storage temperature –60 ... +70 °C
Housing material AlMgSi, grey/partially lack anodized
Cup material PC reinforced with glassfi re; lack
15 W foil heater integral in each cup
Dimensions & Weight 270 (h) × 90 (Ø) mm; weight 860 g
Swept radius of cupwheel: 91 mm
1) Measured with cup wheel in position least favored y flow direction.
Optimum position would yield < 0.35 m/s threshold.
2) Standard Deviation
3) Typical error vs. speed with the “simple transfer function” used :
Spare parts: Order number:
Cup wheel assem ly WA35066
Set of earings & gasket 16644WA
RANGE m/s 0-5 5-10 10-15 15-20 20-24 24-29 29-34 34-39 39-44 44-48 48-58
ERROR m/s -0.2 -0.1 0.0 +0.1 +0.2 +0.3 +0.4 +0.5 +0.6 +0.7 +0.85
Ref. WAA251-U186en-1.1
Figure 4. WAA251 assemb y