NMEA Data Multiplexer - NDC-4
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© 2015 Active Research Limited
The NDC-4-ASW Autoswitch
The
Actisense
NMEA Data Multiplexer / Combiner /
Autoswitch (NDC) has been designed with the ability to
operate as a Multiplexer / Combiner OR an Autoswitch.
For systems that have multiple NMEA devices of an
identical type (e.g. two GPS’s or two depth sounders),
automatic selection of the highest priority device is
normally a vital requirement. However, the NMEA 0183
standard has no method of automatically switching
between different devices, so this requirement is usually
fulfilled with a manual changeover switch: not a very good
solution, but the only one available until now.
If the NMEA data from two (or more) devices are simply
combined together, the NMEA listener(s) will not be able to
differentiate between the various sources and will get very
confused, often jumping between them. If this creates a
‘jumping’ position fix, vessel safety is seriously affected.
The NDC-4 Autoswitch mode is the perfect solution to this
problem - automatically selecting a single device from the
multiple ‘same data type’ devices available.
Autoswitch mode will automatically select the highest
priority device from up to 4 connected input devices, with
NMEA port 1 as the highest priority through to NMEA port
4 as the lowest. This creates a system capable of
automatically selecting the next priority device if the higher
priority device fails for one of three reasons:
• A complete failure to send any NMEA data.
• An invalid NMEA sentence checksum.
•
If the validity flag(s) contained within the received NMEA
sentence indicate that this data is not valid and should
only be used with caution.
With the addition of two fully Baud rate configurable
outputs protected by ISO-Drive technology, that can also
incorporate NMEA filtering to remove any unwanted
sentences before the switching process, the NDC-4
Autoswitch mode is the most flexible available.
Having the ability to filter out NMEA data before the
autoswitch process can be particularly useful to avoid
unwanted sentences from causing the Autoswitch to
change input channels due to invalid data, leaving only the
required sentences to switch on.
If ordered as an Autoswitch, the NDC-4 will be pre-
configured as an NDC-4-ASW and be ready to work out of
the box. Alternatively, any NDC-4 can be configured using
Control Centre to operate in Autoswitch mode.
Setting the NDC-4 as an Autoswitch
The NDC-4 can easily be changed between being a NMEA
Data Multiplexer / Combiner and an NMEA Autoswitch
using Control Centre.
In the ‘Port Configure’ tab click on the button labelled
“Change To Autoswitch” to change the NDC’s operation
mode to Autoswitch.
Figure 12 – “Change To/From Autoswitch” message
A warning message will be displayed, requesting that the
user confirm the request to change to Autoswitch mode.
Selecting
‘Yes’
will automatically send the new
configuration to the unit, and the NDC-4 will now Autoswitch
its inputs instead of Combining them.
To revert back to Combiner mode, click on the (same)
button (now labelled
‘Change To Combiner’
). Again, the
user must confirm the operating mode change is required
and the NDC-4 will now Combine its inputs instead of
Autoswitching them. There is no need to click the
‘Send to
Hardware’
button, this configuration change is automatic.
Summary of Contents for NDC-4
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