FT Technologies FT742, Manual

Page: 10 / 28

Section 2
– Functional Description
10 FT742-DM (4-20mA)
– Sensors
- User Manual
Wind Speed Scaling
References (m/s)
Value @
4mA
Value @ 20mA
Scaling Factor
(mA per m/s)
30 0m/s 30m/s 0.5333
35 0m/s 35m/s 0.4571
40 0m/s 40m/s 0.4000
45 0m/s 45m/s 0.3556
50 0m/s 50m/s 0.3200
55 0m/s 55m/s 0.2909
60 0m/s 60m/s 0.2666
65 0m/s 65m/s 0.2462
70 0m/s 70m/s 0.2286
75 0m/s 75m/s 0.2133
80 0m/s 80m/s 0.2000
85 0m/s 85m/s 0.1882
90 0m/s 90m/s 0.1778
95 0m/s 95m/s 0.1684
100 0m/s 100m/s 0.1600
Figure 3: Wind Speed Scaling Factors
On models where the full scale current has been configured above the maximum speed of the sensor, the
maximum output current will be limited to an amount equivalent to the maximum speed.
The wind speed loop can also be calibrated with non-linear scaling functions. For further information on this
advanced feature contact FT Technologies.
If a wind sensor is replaced care must be taken to ensure that the replacement sensor has
the same scaling. Otherwise the data will have reduced quality.
2.2.4 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 sensor measures the wind direction relative to the 0° datum. The 0° datum location for the sensor is shown
in Figure 4.
The default current loop output when the wind is blowing towards the 0° 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 5.