Section 2
Functional Description
12
FT702LT/D Flat Front Wind Sensor Manual
2.2.3
Wind Direction Loop
The wind direction scaling is such that a change from 4 to 20mA represents 360 degrees (with no dead band)
which corresponds to a scaling factor of 0.0444mA per degree.
The FT702LT/D measures the wind direction relative to the 0 degree datum. The 0 degrees datum location for
the FT702LT/D is shown in Figure 7.
The default setting for the current loop output when the wind is blowing towards the datum direction is 12mA. If
required, the direction loop can be set to give an output of 4mA at the datum direction. The output options are
shown in Figure 8.
Figure 7: Visualisation of direction with 4mA and 12mA current offsets
Figure 8: Comparison of wind direction current offsets
When operating in the 4mA datum current mode there is a 16mA transition each time the wind direction crosses
the datum. In the 12mA datum current mode the output current varies linearly about the 12mA value as the wind
direction moves around the datum.
2.2.4
Changing the wind datum direction
The datum direction can be electronically rotated (either clockwise or counter clockwise) in 1 deg increments
using the FT702LT/D Set Up and Test Program (see section 5) to apply this adjustment. Once the datum offset
has been set it will be retained in the FT702LT/D Flash memory.
180
225
270
315
0
45
90
135
180
