Why would I want or need an isolated USB to RS485
gateway?
When software running on a PC needs access to RS485 network data, or alternatively,
may need to send data to the RS485 network, a communication port needs
to be created. However, until the
USG-1-485, there
was no solution that worked in
every case.
The Actisense USB to RS485 (
USG-1-485) Gateway
developed out of the requirement to solve
3 fundamental
problems with interfacing the industry RS485 communications to a PC:
A) Ground loops. When the PC and the RS485 system have
different ground potentials (or are totally different ground altogether),
data can become corrupted and permanent damage can occur (to the PC and
RS485 device).
B) Different standards. When you buy a standard USB to
serial converter, they normally provide PC standard RS232 port, whereas
RS485 uses a bi-directional signaling system. This means that a standard
USB to serial converter is incompatible with RS485 / IEC 61162-2 that use
the RS485 driver type.
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. Furthermore, RS485 signals are not directly compatible with standard
PC serial ports.
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 RS485 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-1-485 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.
