• 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 by a unique non-contact heating
power transmission. Foil heaters are inserted in each cup and in the
cup wheel hub enabling low power consumption. The cup wheel is
removable, 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 brushes, 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 by an exter-
nal NTC resistor sensing the ambient 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 bearings,
and 9 W on the body.
The WAA251 can be 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
both the heater and the transducer. A recommended power supply
is Vaisala's WHP25, designed for outdoor use and mountable 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 box, 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 by 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 (common ground)
E +24 Vin (power input)
F HCin (heating control / NTC)
Figure 3. WAC151 Standard Wiring for WAA251 & WAV151
