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C H A P T E R T W E L V E
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M e r i d i a n I I U s e r M a n u a l
F R O N T - P A N E L K E Y P A D A N D D I S P L A Y
FLASH and will be restored after a power outage. After position has been determined, the instrument
can achieve time lock with only one satellite.
In some situations, visibility of the sky is limited and the unit may not be able to determine its posi-
tion. In this case you must determine an accurate WGS-84 position by other means and input it either
through the serial interface or via the front panel. In addition to loading a new accurate reference
position, you can also invalidate an existing one by setting the position source to unknown. This will
force the instrument to re-establish a new reference position using the GPS satellite constellation.
Push the EDIT key to start the process. First, select the reference position source:
Unknown: Selecting “unknown” will cause the CALCULATE NEW POSITION AVERAGE
confirmation display to appear. Select YES. The front panel will return to the GPS
Reference Position display. This action will force the unit to re-establish a new reference
position. Once the receiver has computed a new accurate reference position the position
source will change from “unknown” to “average”.
User:
Selecting “user” will allow you to enter a position. It is very important that the new
reference position be accurate. Refer to
Appendix E - Installing the GPS Antenna,
GPS Reference Position
for detailed instructions on how to obtain an accurate reference
position for your location.
Receiver: Last Fix Position (Last_Fix)
This display provides the last computed GPS position. When tracking four or more satellites, the
GPS Receiver provides a 3D-position fix. The last-fix position is normally less accurate than the ref-
erence position, but it does provide a good indication that the receiver is working properly. Position
is provided in latitude, longitude and height. By scrolling down, the PDOP, HDOP, VDOP and TDOP
along with the Out-of-Range count are shown.
Receiver: UTC Information (UTC_Info)
This display shows the UTC Information which includes leap seconds (LS) and future leap seconds
(LSF) for the week number (WN_lsf) and day number (DN) displayed. It also shows the IS-GPS-
200 almanac parameters which are used to calculate the offset between UTC and GPS time. These
include parameters for determining leap seconds and the parameters for calculating the small residual
offset between the GPS master clock ensemble and UTC(USNO). This latter value is typically less
than 10 nanoseconds. Press HELP to read more detailed information on the fields shown in this
display.
Receiver: Dynamic Mode (Dyn_Mode)
The GPS dynamic mode setting affects the position value used by the system to derive accurate time
synchronization. In dynamic mode, the average position is displayed as the current position, in other
words - there is no position averaging. Dynamic mode is suitable for shipboard applications only.
It is important to set the mode to “OFF (static installation)” when the instrument is in a static instal-
lation. This is the factory-default setting. Set the mode to “ON (dynamic installation)” ONLY if the
instrument is installed on a moving platform such as a ship.
Summary of Contents for Meridian II
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