 |
|
Why would I want or need an NMEA Data Multiplexer?
The NMEA 0183 standard allows any suitably designed marine electronic device
to share its gathered information with any other device on a vessel. Unfortunately,
there is one very large drawback with this standard - only one device on
a connected network can actually send data (a single 'talker' device),
with multiple devices (determined by the current limit of the sending unit)
listening to that data (multiple listeners).
If the vessel owner has an instrument that ideally requires the data output
of two or more devices, for example a chart plotter, then the owner has
no alternative but to settle on connecting only the most important device,
usually the GPS.
|
|
What happens if the owner prefers the vessels gyro compass output to that
of the GPS, or requires that the current depth be displayed on the plotted
chart to help avoid the possible case of running the vessel aground on
a shifting sand bank? The NMEA 0183 standard cannot supply an answer to
those questions: "one transmitting / talking device only".
The Actisense™ NMEA Data Multiplexer's ( NDC-2 & NDC-3)
can solve all these problems and more with their simple, easy and flexible
designs.
|
 |
|
|
|
|
The autoswitched NMEA output is connected to one of the NMEA Data Multiplexer's
inputs. In this way the highest priority device's NMEA data is autoswitched
into the complete NMEA system and the actual device supplying the NMEA
data can be determined (and displayed if required and possible) to help
the user.
|
|
|
|
How can the NMEA Data Multiplexer reduce the congestion
on my NMEA network?
Some NMEA instruments output a large number of NMEA sentences every period
(usually 1-3 seconds), some of which are of no use to the average boat
owner, and just clog up the NMEA network. GPS units are especially guilty
of this and not all allow the user to reduce the number of unwanted sentences
that are transmitted. Of those that do, the procedure can often be fiddly
and time consuming.
|
|
The Actisense NDC-3 cannot filter the incoming
NMEA data - if you require the ability to remove any sentences that are
deemed unnecessary, please view the Actisense NDC-2 which
has full NMEA sentence filtering capabilities.
|
|
|
|
How do I give my GPS unit priority on the NMEA
Data Multiplexer network?
The Actisense NDC-2 and NDC-3 have
many useful features, among which is the ability to prioritise their input
ports. The usefulness of this feature becomes apparent when the NMEA network
is running over 50% loading/capacity (most setups). At this point a standard
NMEA Multiplexer could start to delay the important information by an unacceptable
amount and may even lose it altogether.
The Actisense NDC however, will always transfer the highest priority input's
NMEA sentences first, keeping the delay to the minimum
possible. The remainder of the inputs will have their NMEA sentences transferred
in turn, until all data is either transferred or no more time / bandwidth
is available in the NMEA output.
|
|
For example, the most relied upon unit e.g. GPS, should be attached to
input port 1 (the highest priority).
The Actisense NDC-3 'Port Priority' is the same
as the port number, i.e. port 1 is the highest priority and port 4 the
lowest. On the Actisense NDC-2 this
is the default port priority, which can be re-configured as required -
please view the Actisense NDC-2.
|
|
|
|
|
|
If your system requires the ability to re-configure the input
Baud rates, please view the Actisense NDC-2 which
is fully configurable.
|
|
|
|
|
|
B) If you have not already purchased an NDC, the new NDC-3-USB has
a USB port built in for easy connection to a PC.
Simple Plug'n'Play installation and operation makes either of these options
a perfect solution.
|
|
|
