Jeppesen Nobeltec Solid State Heading Sensor, Owner'S Manual

Page: 17 / 48

CALIBRATION
Jeppesen Marine
11
VARIATION
Variation is the angular difference between the
True Meridian
(great circle connecting the
geographic poles) and the
Magnetic Meridian
(direction of the lines of magnetic flux). Variation
has different values at different locations on the earth, with most areas undergoing change to
the variation over time.
Normally, heading information is displayed as either a “true” heading (a direction relative to the
geographic poles) or it is displayed as a “magnetic” heading (a direction relative to the lines of
magnetic flux). North-seeking gyrocompasses are capable of measuring direction relative to
the geographic poles (“true”) whereas magnetic compasses measure direction relative to the
earth’s local magnetic flux (“magnetic”).
The SSHS is a magnetic compass; therefore, it requires an external source for variation if you
wish to view your heading in “true” format.
The SSHS is capable of receiving variation in one of three ways:
1. Via the NMEA 0183 interface
2. Via the NMEA 2000 interface
3. Through manual variation entry
Normally, the SSHS will automatically use variation from either the NMEA 0183 or NMEA
2000 interface. However, you can force the SSHS to use variation from only the NMEA 0183,
only the NMEA 2000 interface, or only use manually entered variation.
Warning:
Multiple variation sources that are received by the SSHS (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, the SSHS
needs to be programmed to use the appropriate source for reporting subsequent true heading
information. See
Page 16
for details on choosing a specific variation source when more than
one variation source is available
.
Note:
Jeppesen Marine does not provide technical support for the NMEA 2000
interface as of this printing.
Variation Input via NMEA 0183 Interface
As shipped from the factory, the SSHS automatically looks for variation data coming from the
NMEA 0183 interface. The SSHS accepts variation data from the Recommended Minimum
Specific GNSS Data (RMC) sentence, or the SSHS computes variation from the Course Over
Ground and Ground Speed (VTG) sentence.