Why would I want or need an isolated USB to NMEA
0183 gateway?
When software running on a PC needs access to NMEA 0183 data from a particular
device, or alternatively, may need to send NMEA 0183 data, a communication
port needs to be created. However, until the
USG-1 was
designed, there was no solution that worked in
every
case.
The Actisense USB to Serial Gateway (
USG-1) product developed out of the
requirement to solve
3 fundamental problems with interfacing
the marine industry NMEA 0183 communications standard to a PC:
A) Ground loops. When the PC and the NMEA 0183 system
have different ground potentials (or are totally different ground altogether),
data can become corrupted and permanent damage can occur (to the PC and
NMEA device).
B) Different standards. When you buy a standard USB to
serial converter, they normally provide PC standard RS232 port, whereas
NMEA 0183 uses a standard called RS422. This results in incompatible voltage
levels and electrical driver types - causing communication problems.
C) The PC has no serial port. Most modern PCs do not come
with serial ports any more as these are being replaced by the new standard
of USB.
Solution for problem A - Ground loops
The primary problem encountered when using a standard USB to serial converter (or a standard
RS232 port) is that the ground of the PC is then shared with the NMEA 0183 system ground.
PCs are often powered from a mains inverter, generator set or direct from mains supply when
in dock, whereas the marine electronics are normally connected to the current battery set.
This means that when you connect the two systems together, you are joining two different power
systems. This can result in no visible problems at first, but more often it results in one
of three consequences:
1. Data corruption - the data becomes garbled as the electrical data signal now floats on a
noisy ground current flowing between two systems.
2. The PC crashes intermittently as ground currents flow across its sensitive electronic circuitry.
This can cause permanent damage.
3. In the case of large ground loop faults, some components can melt / catch fire / fuses blow
or earth leakage devices trip.
The
USG-1 solves all these problems by providing a safe, opto-isolated barrier between the
two systems.
Because the signal travels across this barrier as light, the signals do not share
the same ground, and safety is assured as no current can flow between the two power systems.
In addition, a built-in power isolator completes the isolation.
