SEPTENTRIO PolaRx5TR, Справочное руководство

Страница: 60 / 512

2 Operation Details
0 0.5 1 1.5 2 2.5 3 3.5 4
−0.5
0
0.5
Up Time [hours]
RxClkBias = t
Rx
−t
GNSS
[ms]
Figure 2-1:
Example of the evolution of the receiver time offset with respect to the
GNSS time in free-running mode.
Note that the clock bias is computed with respect to a particular GNSS time system (GPS,
Galileo, BeiDou, ...) as set with the
setTimingSystem
command. The time offset between
those systems is at the level of a few tens of nanoseconds only, and is ignored when applying
the X-millisecond threshold.
When a receiver clock jump occurs, all measurements jump simultaneously. For example,
a clock jump of 1ms will cause all the pseudoranges to jump by 0.001s * velocity_of_light =
299792.458m. The jump is applied on both the pseudoranges and the carrier phase mea-
surements, and hence will not be seen on a code-minus-phase plot.
The cumulated clock jumps since the last reset of the receiver is reported in the
CumClkJumps
field of the
MeasEpoch
SBF block.
As can be seen in Figure 2-1, the initial clock bias is not necessarily zero, but it can take any
value within -0.5ms and +0.5ms. This is the default configuration. You can use the second
argument of the
setClockSyncThreshold
command to force the clock bias to be close
to zero (typically <100ns) at startup. When this feature is enabled, a jump of a non-integer
number of milliseconds is applied right after the first position fix, followed by a short loss of
signal tracking.
2.3.2 Clock Steering
In steered mode, the receiver time is continuously steered to a GNSS time. The particular time
realization (GPS, Galileo, BeiDou, ...) is generally irrelevant as the difference is very small. It
can be selected with the
setTimingSystem
command if needed.
In the example of Figure 2-1, if the user would have enabled clock steering one hour after
start up of the receiver, the clock bias would have been like in Figure 2-2 below.
60