DR + GPS
STARTER KIT REFERENCE MANUAL
Lassen DR + GPS Reference Manual 121
DPP recovery, solution snapped to GPS.
Condition cause: Incorrect DPP at start-up, or substantial drift of DR+GPS DPP
estimate.
Effect before Action: Large speed offset between GPS and DR outputs for a
number of seconds.
Soft Event Detected: Compute average of “window” of recent DPP estimates,
derived directly from the raw GPS speed and number of
pulses. Soft event occurs if this window average passes
a series of criteria (see DR+GPS KF algorithm document
45172-XX-SP) and the offset relative to the DR DPP is
large enough.
Action: The DPP estimate is snapped to the window average.
GPS receiver fixes not reasonable; try to recover.
Condition cause: pseudorange error or ephemeris error.
Effect before Action: GPS positions incorrect.
Soft Event Detected: Fix altitude is above 18000 m or below –1000 m and fix
speed is above 515 m/s.
Soft Event Cleared: Cleared at reset.
Action (ROM15): Erase BBRAM and RTC, re-start unit.
Gyro readings do not stay within specification
Condition cause: Hardware failure.
Effect before Action: Position goes in circles.
Soft Event Detected: Average gyro reading over ten seconds at standstill is
not between 2.0 V and 3.0 V.
Soft Event Cleared: Cleared at reset.
Action: Gyro labeled “bad”. DR suspended. Speed measurement
continues and tacho continues to be calibrated.