Applanix POS MV V5 Installation And Operation Manual page 192

POS MV V5 Installation and Operation Guide
Fault
Identification
GAMS
9-18
Occasional failures of ambiguity resolution, for example at intervals of
10 to 20 minutes, are quite common and may be the result of changes
to the satellite constellation.
Repeated or continuous failures in ambiguity resolution may be the
result of a poor GAMS calibration or excessive vibration at the
antennas. These failures may also indicate weak signal reception
from the satellites, requiring changes to the installation.
Use the following steps to further diagnose the problem:
1. Select V iew, GNSS D ata and examine the L1 Signal-To-Noise
Ratios (SNR) for the available satellites, see Figure 55 on page 8-
2. If the L1 SNR is below 38 dB for more than one satellite, the
GNSS antenna cables are introducing too much signal
attenuation. To correct this fault, shorten the cables or substitute
them with new low-loss cables.
2. Examine the antenna mountings; they must be rigid with respect
to each other and with respect to the IMU. Make any necessary
modifications to secure the antenna mounting positions so that
they experience no significant twisting or movement relative to the
IMU.
3. Repeat the GAMS calibration and ensure that:
• The Positional Dilution of Precision (PDOP) is below 2.5
(preferable below 2.0)
• The GAMS Solution window shows at least six Space
Vehicles (SVs) in the solution
Prior to the calibration, perform a series of calibration manoeuvres
and ensure the heading accuracy is better than 2.0°. Refer to the
Initial GNSS Configuration description on page 4-21 for the
instructions to complete this calibration procedure. Try to achieve
a heading accuracy better than 1.0°.
Within the first ten minutes after calibration, GAMS uses dynamic
inputs to verify the calibration. Therefore, once the calibration is
completed, perform a series of dynamic and vigorous
manoeuvres with the vessel for ten minutes to support this
process.