Velodyne VLS-128 User Manual

Appendix G • Time Synchronization
This section provides a detailed discussion of the GPS Qualifier and PPS Qualifier functions.
G.1 Introduction 116
G.2 Background 116
G.3 PPS Qualifier 117
G.3.1 Require GPS Receiver Valid 117
G.3.2 Require PPS Lock 117
G.3.3 Delay 118
G.4 GPS Qualifier 118
G.5 Application 118
G.6 Logic Tables 118
G.1 Introduction
These two new options control how the sensor utilizes the GPS information supplied to the sensor. The first control option
determines how the sensor utilizes the PPS signal (PPS Qualifier). The second control option determines how the sensor
utilizes the timestamp provided in a National Marine Electronics Association (NMEA) sentence (GPS Qualifier).
The new options, shown below in their default positions, can be found on the Configuration tab in the sensor’s Web Inter-
face.
Figure G-1 Web Interface PPS and GPS Qualifier Option Selections
G.2 Background
Your sensor maintains a counter representing the number of microseconds since the Top Of Hour (TOH). The TOH count
is incremented based on an internal oscillator. When the sensor is presented with a valid PPS signal the TOH count is adjus-
ted on the rising edge of each PPS to align the TOH with UTC Time. The TOH is sent as a four-byte time stamp in both the
data and position/telemetry packets.
The TOH is comprised of two separate counters. One counter maintains the number of minutes and seconds since the top
of the hour, and the other counter maintains the sub-second count ( Figure G-2 on the facing page ).
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Velodyne VLS-128 Specifications

General

Brand	Velodyne
Model	VLS-128
Category	Accessories
Language	English