Section 2
– Functional Description
8
FT742-DM (4-20mA)
– Sensors
- User Manual
2 FUNCTIONAL DESCRIPTION
2.1 Technical Performance
Sensor Performance
1 & 2
Measurement Principle
Acoustic Resonance, compensated against variations in temperature,
pressure and humidity.
Wind speed Measurement
Range
0-75m/s
Resolution
0.1m/s
Accuracy
±0.3m/s (0-16m/s)
±2% (16m/s-40m/s)
±4% (40m/s-75m/s)
Wind Direction Measurement
Range
0 to 360
Accuracy
4
RMS
Resolution
1
Environment
Temperature Range
-40 to +85
C (operating & storage)
Humidity
0 - 100%
Altitude
0 - 4000m
Data I/O
Analogue Option
4-20mA, galvanically isolated from power supply lines and case
Format
1x 4-20mA current loop for wind speed (see Section 2.2 for scaling factors)
1x 4-20mA current loop for wind direction (4-20mA = 0 to 360°) (see
Figure 5 for offset options)
Reading Update Rate
10Hz
Configuration Port
3
RS485 half-duplex, non-isolated relative to power ground
Power Requirements
4
Supply Voltage
24VDC nominal (12-30VDC range)
Supply Current (Heater off)
31mA typical for the 2x current loops (4-20mA)
Supply Current (Heater on)
6A (max)
5
– The heater is thermostatically controlled. Heater power
consumption will depend on the heater energy required to keep the sensor’s
temperature at a user determined set point. The sensor is limited to 4A and
99W
5
by the default software settings (the current limit can be modified, see
Section 4 or contact FT for details).
Physical
Weight
380g (without size adaptors)
Material
Aluminium alloy (hard-anodised)
I/O Connector
8 way
Mounting Method
Pipe-Mount screw-fix (33.7mm external diameter EN10255 pipe).
Various size adaptors and pipe-inserts available.
Notes:
1. All specifications subject to change without notice.
2. Specifications calculated with default settings.
3. The Configuration Port is provided to allow the user to change the internal settings of the sensor
and to
perform diagnostic testing. This interface should only be used for configuration and test purposes. This
interface is not intended for permanent connection to the computer.
4. The heater set point and current limit can be pre-configured in the factory or adjusted using the FT Acu-Test
Analogue kit.
5. See safety instruction requirements (pages 4 and 5).
