Raven RPR 110, Инструкция по установке и обслуживанию

Страница: 7 / 20

5
PPS OUT
The PPS output is normally used to provide a timing signal to another device. PPS
stands for Pulse Per Second and that’s what the signal does. Once each second the
signal pulses to indicate the start of a GPS second. The GPS second is a time
reference, which can be used to synchronize systems. If your application requires
very accurate time then the PPS output may be required.
The PPS output can also be used as a RADAR or Speed Log output as described in the
following sections.
RADAR OUT
The receivers can simulate a Doppler RADAR commonly used on agricultural equipment
for detecting speed. The GPS receiver is always calculating speed and can generate
the signals, which can be used by equipment requiring RADAR input. The receiver is
normally configured at the factory for RADAR output.
To use this feature you will need a special cable from Raven. It should be noted
that the GPS can only determine speed when it’s navigating. If a tree line blocks
too many satellites or if for some other reason the Receiver is unable to navigate,
then the RADAR output could become invalid.
The scaling factors and timing controls that govern the operation of this feature
can be controlled via a serial configuration message as defined in the Serial
Protocol Definition document. The receiver uses default settings that should
provide reasonable operation without the need for special configuration.
ADVANCED MESSAGE FORWARDING
The RPR 110 receiver supports advanced message forwarding in systems where the
application is designed to take full advantage of this feature. When enabled, all
messages received on Port B of the receiver will be time tagged with GPS time and
output on Port A in a special format.
The special format is basically just a prefix that includes the time tag. The time
tag is very important since it is referenced to GPS time and provided with
millisecond resolution. It can be used to completely eliminate latency issues.
Latency is usually only an issue in systems where GPS positions are used to locate
data coming from another sensor. If not accounted for, the latency of output can
show up as positional errors.
The advanced message forwarding takes care of latency problems in systems where the
other sensor can output NMEA style messages. This feature would also be useful in
systems with limited serial ports if the application developer were to take
advantage of this feature.