The serial wind transmitter WAC155 provides a 2-wire half-duplex RS-485 serial bus for data interchange. Wind data is provided in standard NMEA 0183 messages. A service connection is available for configuration and status information.
Several transmitters can share the same RS-485 bus. If there are several transmitters in the same bus, auto-transmission cannot be enabled, and data must be polled from one sensor at a time using NMEA query. If you use only one transmitter, you can configure it to automatically transmit data at selectable intervals.
Each device in the bus has a unique, configurable ID, containing 1 to 5 characters. Alphabetical characters a - z, A - Z (case-sensitive), and numbers 0 - 9 are accepted.
Typically, only a 4-wire shielded cable is required for the line between WAC155 and the host. Two of the four wires provide the operating power for the system. The other two wires are for the RS-485 serial line. Vaisala recommends twisted pair wires for both the power line and the data line.
The recommended maximum length of the RS-485 line is 1200 m (4000 ft). In practice, the achievable line length is affected by the electrical noise and the number of transmitters in the bus. Very long lines may also gather overvoltage transients and surge currents caused by nearby lightning strikes.
WAC155 has on-board surge protection on the RS-485 line, accomplished with discharge tubes and transient zener diodes.