The FT702LT is a solid-state ultrasonic wind sensor designed for accurate measurement of wind speed and direction, particularly in harsh environments such as offshore and ice-prone areas. It utilizes a patented Acoustic Resonance airflow sensing technique and is engineered for high reliability with no moving parts, aiming to reduce costly downtime and unscheduled maintenance.
Function Description:
The FT702LT measures wind speed and direction using acoustic resonance. Its design incorporates a mounting flat on the sensor body that defines the 0° wind datum, allowing for automatic alignment to a reference point. For operation in cold or icy conditions, the sensor is equipped with a highly effective, thermostatically controlled "all-body" heating system. This system uses a three-element heater (one in the top, two in the bottom) to ensure even heat distribution across the entire surface area. The sensor provides digital output via an RS485 serial link, using an ASCII-based communication protocol with checksum validation for data integrity. It can also output data in the common NMEA 0183 MWV (Wind Speed and Angle) sentence format.
The sensor includes internal filtering capabilities for wind speed and direction, which can be configured to average a fixed number of previous readings. This digital finite impulse response (FIR) filter helps to smooth out data. The electronic rotation of the datum direction allows for adjustment of the sensor's wind direction measurements relative to its physical mounting. Error detection mechanisms are in place to identify invalid readings or issues, with an error flag character indicating problems. The heater system is programmable, allowing users to set the temperature, start delay time, current limit, and undervoltage limit.
Important Technical Specifications:
- Measurement Principle: Acoustic Resonance (compensated against variations in temperature, pressure, and humidity).
- Wind Speed Measurement:
- Range: 0-50m/s
- Accuracy: ±0.5m/s (0-15m/s), ±4% (>15m/s)
- Resolution: 0.1m/s
- Wind Direction Measurement:
- Range: 0 to 360°
- Accuracy: ±2° (within ±10° of 0° datum), ±4° (beyond ±10° of 0° datum)
- Resolution: 1°
- Environment:
- Temperature Range: -40°C to +85°C (operating), -40°C to +85°C (storage)
- Humidity: 0-100%
- Data I/O:
- RS485 Option Interface: Digital RS485, galvanically isolated from power supply lines and case.
- Format: ASCII data, polled or continuous output modes.
- Data Update Rate: 5 measurements per second.
- Power Requirements:
- Supply Voltage: 20V to 30V DC (24V DC nominal)
- Supply Current (Heater off): 30mA
- Supply Current (Heater on): 6A (max) – The heater is thermostatically controlled. Heater power consumption depends on the heater energy required to keep the sensor's temperature at a user-determined set point. The heater and sensor power consumption is limited by default to 40W. (4A max)
- Physical:
- Weight: 320g (max)
- Material: Aluminium alloy, hard anodised
- I/O Connector: 5 way (RS485 option)
- Mounting Method: Self aligning, single screw fixing
- Maximum Sensor Dimensions:
- Before build version 22: h (mm) 167, w (mm) 50
- Build versions 22 and after: h (mm) 161, w (mm) 55
- Communication Settings:
- Baud Rate: 1200, 2400, 4800, 9600 (factory default), 19200, 38400
- Data Bits: 8
- Start Bits: 1
- Stop Bits: 1
- Parity: None
- User Calibration Table (available from build version 22 and above): Up to 64 user programmable records for wind speed correction, with a minimum allowable difference of 0.5m/s between consecutive records. Includes provision for a user-defined text string of up to 32 characters.
Usage Features:
- Easy Installation and Alignment: The sensor's mounting flat simplifies alignment, automatically orienting the sensor to a reference point.
- Configurable Parameters: Users can configure various settings including baud rate, datum offset, continuous update interval, wind velocity data format (Polar or NMEA), command delay interval, filter lengths for wind speed and direction, heater settings (temperature, delay, current/undervoltage limits), and listener/talker identifiers.
- Filtering: Moving average filtering for wind speed and direction can be enabled or disabled, with configurable filter lengths up to 64 previous readings (12.8 seconds).
- Electronic Datum Offset: The wind datum direction can be electronically rotated in a counter-clockwise direction (when viewed from above) to compensate for physical misalignments during mounting.
- Heater Control: The thermostatically controlled heater system can be programmed to maintain a set temperature, with adjustable start delay, current limit, and undervoltage limit to optimize power consumption and performance in icy conditions.
- User Calibration: From build version 22 onwards, a user calibration table allows for custom wind speed corrections using linear interpolation. This table can be cleared, individual records set and verified, and a label assigned.
- Run-Time Counter: From build version 22 onwards, the sensor tracks its operational hours, providing a record of its lifetime usage.
- Parameter Management: User-defined parameters can be saved to non-volatile memory, ensuring settings are retained after power cycles. There are three copies of parameters: User Parameters (active), Factory Parameters (default), and Saved Parameters (user-saved backup).
- Evaluation Pack: An optional Evaluation Pack, including Acu-Vis software and an FT054 cable, facilitates test bench assessment, allowing users to check communication, configure heater settings, and view real-time wind data.
Maintenance Features:
- Annual Inspection: Regular checks are recommended to identify signs of corrosion or damage that could affect performance.
- Cleaning: The measurement cavity has a special coating to prevent water buildup and facilitate cleaning. Dust and debris can be removed by gently rinsing with distilled water. It is crucial not to scrape or scratch the internal surfaces or insert objects into the cavity to avoid irreparable damage.
- Corrosion Management: Inspection of the mounting flat and bar for corrosion is advised. If present, corrosion should be removed with an abrasive cloth, and electrical joint compound applied before reinstallation.
- Cable and Connector Inspection: The interconnection cable and protective sleeve should be inspected for fraying or damage and replaced if necessary to prevent data errors.
- Fault Finding & Troubleshooting: A systematic approach to fault finding includes checking for physical damage, verifying communication with an Evaluation Pack, ensuring the latest software version, checking heater set points, confirming internal filtering is enabled, and processing wind data and status flag errors correctly.
- Returns Procedure: In case of a faulty sensor, FT Technologies requires a Returns Materials Authorisation (RMA) form to be completed before accepting returns for analysis.
- Lightning Protection and EMC: The manual provides detailed guidance on installing the sensor with appropriate protection against lightning and electromagnetic interference. This includes creating a protection zone using lightning interceptors, employing shielded signal cables, and using Surge Protection Devices (SPDs) for all connections to computer equipment and power supplies. SPDs should be UL 1449 listed and installed close to the point where signals enter the cabinet.
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