In the tunnel application, airflow can be presented with one mA output channel, because airflow goes along the tunnel. Typically, a relatively long average time (time constant) for wind speed parameter is applied.
The sensor must be installed in a tunnel so that the sensor’s North is aligned with the tunnel. The Aout1 channel (x component) provides the airflow in the tunnel. The following figure shows a typical WMT700 installation in a tunnel.
The following figure shows the 4…20 mA output as a function of airflow. The zero value is in the middle of the output scale (12 mA). When airflow increases from 0 m/s towards North, mA output reduces from 12 mA linearly resulting in 4 mA with 20 m/s wind. Similarly, when airflow increases from 0 m/s towards South, mA output increases from 12 mA linearly resulting in 20 mA with 20 m/s wind.
The parameter aout_map with setting 1 is used to get the North-South component of wind.
s aout_map,1
The North-South component to Aout1, the current output, -20 ... 20m/s to 4 … 20mA, Aout2 disabled:
s aout1_g,0.0004
s aout1_o,0.012 s
aout1maxv,0.020
s aout1minv,0.004
s aout1mode,0
s aout1err ,0.002 s
aout2mode,7