NMEA data output refers to standardized text sentences used to transmit data between marine electronic devices, such as ADCPs. Nortek ADCPs can be configured to output NMEA data for integration with external systems.
For legacy AWACs both current and processed wave data can be output as NMEA strings, depending on the instrument firmware (see Firmware). The process for configuring NMEA output also differs depending on the firmware.
Legacy AWACs with wave processing firmware (WPC)
First generation AWACs with ProLog and Wave Processing firmware can output both average current data and processed wave data as NMEA. This can be configured directly in the Deployment Planning window in the instrument software as shown in the screenshot below:
Both average current and wave data messages are output via the serial port after the wave burst is completed. Raw binary data, as well as binary processed wave data, will simultaneously be stored to the instrument's internal recorder.
Legacy AWACs without wave processing firmware
If your AWAC does not have the wave processing firmware, it can only output average current data as NMEA messages. This must be configured by starting the measurements using the NM or NS command. These commands are described in the Integrators Guide. Note that it is not possible to store data to the internal recorder while outputting NMEA data.
When the instrument receives the NM or NS command, it responds with the number of seconds until the first NMEA message is output. This number equals the configured average interval. If the instrument responds with 0000 (which is NMEA's NackNack) it may indicate that the baud rate is too low to transmit NMEA messages, or that the configuration is incompatible with NMEA output. Also note that a continuous deployment plan cannot be used when enabling NMEA.
If you are unable to start the measurements:
- Ensure that there is enough time between the end of one measurement and the start of the next for the instrument to send the message.
- Reduce the number of cells to decrease the number of messages to be sent.
Note that to start data collection with NMEA output of the average current data using the NM or NS commands, the instrument must be running the non-AST firmware and use a configuration with wave measurements disabled. The AST firmware is required for wave measurements with the AWAC. If you downgrade from the AST firmware and remove this option, you will need a license key in order to reinstall the AST firmware to resume wave measurements.
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