Maretron SSC300, Руководство пользователя

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SSC300 User’s Manual
Page 14 Revision 1.0
Normally, the SSC300 will automatically use variation from either the NMEA 0183 interface or
the NMEA 2000
®
interface, however, you can force the SSC300 to use variation from only the
NMEA 0183 interface or you can force the SSC300 to use variation from only the NMEA 2000
®
interface or you can force SSC300 to only use manually entered variation.
WARNING: Multiple variation sources that are received by the SSC300 (i.e., NMEA 0183
and NMEA 2000
®
interfaces) will cause confusion as to the correct source to be used for
true heading indications. If more than one variation source is available, then the SSC300
needs to be programmed to use the appropriate source for reporting subsequent true
heading information. See Section 4.4 for details on choosing a specific variation source
when more than one variation source is available.
4.1 Variation Input via NMEA 0183 Interface
As shipped from the factory, the SSC300 automatically looks for variation data coming from the
NMEA 0183 interface. The SSC300 accepts variation data from the Recommended Minimum
Specific GNSS Data (RMC) sentence or the SSC300 computes variation from the Course Over
Ground and Ground Speed (VTG) sentence. If the SSC300 does indeed receive variation
information from the NMEA 0183 interface, then it will do the following:
1. Transmit the Heading, Deviation & Variation (HDG) sentence including the variation field
as seen from the RMC or VTG sentence over the NMEA 0183 interface if HDG is enabled
(see Appendix A for enabling or disabling NMEA 0183 sentences).
2. Transmit the Heading True (HDT) sentence using variation data from the RMC or VTG
sentence over the NMEA 0183 interface if HDT is enabled (see Appendix A for enabling
or disabling NMEA 0183 sentences).
3. Transmit over the NMEA 2000
®
interface the Magnetic Variation PGN (127258) with the
Variation Source field value corresponding to the received NMEA 0183 variation data
from the RMC or VTG sentence. The PGN’s Variation Source field will be transmitted with
the lowest possible quality indicator, which is “Manual Entry”.
4.2 Variation Input via the NMEA 2000
®
Interface
As shipped from the factory, the SSC300 automatically looks for variation data coming from the
NMEA 2000
®
interface. The SSC300 accepts variation data from the Magnetic Variation PGN
(127258). If the SSC300 does indeed receive variation information from the NMEA 2000
®
interface, then it will do the following:
1. Transmit the Heading, Deviation & Variation (HDG) sentence including the variation field
as seen from the Magnetic Variation PGN (127258) from the NMEA 2000 interface if HDG
is enabled (see Appendix A for enabling or disabling NMEA 0183 sentences).
2. Transmit the Heading True (HDT) sentence using variation data from the Magnetic
Variation PGN (127258) from the NMEA 2000 interface if HDT is enabled (see Appendix
A for enabling or disabling NMEA 0183 sentences).
Some NMEA 2000
®
networks may have multiple nodes transmitting the 127258 Magnetic
Variation PGN, which can cause problems with true heading output on the NMEA 0183 interface
if any of the nodes are transmitting incorrect magnetic variation values. If you notice heading