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NMEA 2000 data instance (3) may be used when multiple Devices are installed. For example,
“Inside Humidity” with data instance 0, 1, 2 may mean humidity in saloon and in the bow and aft
cabins. Chart plotters with factory settings are usually able to show only one value with data instance 0,
but manufacturers may supply dealers and professional installers by internal instruments to customize
chart plotter screens. Please refer to your chart plotter manual before changing this setting.
Inside / outside (4) setting switches the transmitting type of measured data between inside (cabin, saloon)
air temperature and humidity to outside (the boat) and vice versa. Actually, it changes only the type
of transmitted data. The calculated dew point temperature is not affected by this setting because
NMEA 2000 only has the “Dew Point Temperature” data type. This can cause a conflict if two Devices
are installed. In theory, this conflict can be solved by assigning different data instances (3) to the Devices
or selecting a data source in the chart plotter or instrument display. But in practice many of modern chart
plotters and instrumental displays have no such capabilities. In this case, you can leave only one source
of dew point temperature in your network with the next setting.
Table 2. Data types in periodically transmitted messages
NMEA 2000 Message
Humidity
Air temperature Dew point
PGN 130311 Environmental Parameters
Yes
Yes
No
PGN 130312 Temperature
No
Yes
Yes (1)
PGN 130313 Humidity
Yes
No
No
PGN 130316 Temperature, Extended Range
No
Yes
Yes (1)
Note 1:
Dew point sent in separate message from air temperature
Settings (5) allows you to turn off a specific data type in the transmitted messages. For example, when
humidity is turned off, a message with PGN 130313 is transmitted with a “no data available” value.
And the same for air temperature. The only exception is for the dew point temperature. The Device will stop
sending messages with dew point temperature if this data type is turned off.
