Applanix POS MV V5, Инструкция по установке и эксплуатации

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POS MV V5 Installation and Operation Guide
POS-GPS
Timing
Copyright © Applanix Corporation, 2017
H-4
Internal POS Timing
POS uses its internal clock to keep track of
POS time
, which starts from 0 when the system is powered up
and continually increases. POS time never resets the way GPS and UTC seconds of the week do. POS
uses the 1PPS pulse and the corresponding time message from the Primary GNSS receiver to 1) set an
internal GPS and UTC offset with respect to POS time and 2) correct the drift in the internal clock.
The Primary GNSS receiver must have sufficient satellites visible when POS is started so that it will
generate the 1PPS and time message. Without this data POS will not be able to synchronize its internal
clock and navigation will not proceed. Once the internal clock is synchronized there can be gaps in the
Primary GNSS output of 1PPS and time message without adversely affecting POS performance.
The
Events
pane on the main POSView window, see page 5-6, displays the Universal Time, Coordinated
(UTC) time of the most recent PPS pulse transmitted by the primary GNSS receiver. The Count field for
PPS indicates the total number of signals recorded from the GNSS receiver.
Synchronizing External Equipment to POS
To synchronize external equipment time with POS, the external equipment must read and record the
1PPS signal and one of the corresponding time messages from POS. With this information the external
device can adjust its internal timing to match POS timing using either GPS or UTC as the time base. Any
data recorded by the external device can then be time stamped with a time synchronized to POS so that
the data can later be merged with POS data using a common time base.
Processing the time differential for each new 1PPS pulse and time
message allows the user to compensate for drift in the external device
clock.
The PPS pulse is present at the rear panel IO connectors and is configurable for pulse width and polarity
from the POSView
Settings
–
Events
window. Figure 124 shows the parameters of the 1PPS signal.
Figure 124: 1PPS Signal Characteristics
The time messages corresponding to PPS can be configured to be output on any COM port. All the
various 1PPS time message outputs provide the time of the previous 1PPS signal except the UTCT
+ Vdc
2
2
1 1
0 Vdc
0 Vdc
Configurable
1000 us (1 s)
t
t
1 = Positive pulse
2
p
= Negative pulse
+ Vdc