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© 2009 Active Research Limited
USG-1 solutions
Solution #1 - Ground loops
The first 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 connected
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
marine 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, 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 the two power 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.
Solution #2 - Different standards
PC serial or “COM” ports use the RS232 standard. This
uses a ground and a receive pin to get data from a
connected system. Data is sent as voltages referenced
to ground on a single transmit line. This type of drive is
known as “single-ended”.
In contrast, RS485 systems use a “differential” system,
where a “Positive” data line and a “Negative” data line
move in opposition to each other.
Many installations without isolated outputs have been
seen where the negative data line on a differential drive
system has been connected to the ground of the PC. If
you’re lucky, this may work, but if not, you will either simply
get no data, or at worst, damage your equipment.
The USG-1-485 solves this by using ingenious circuitry
unique to Actisense in its bi-directional transmitter
circuit. Please refer to the
information.
Solution #3 - PC has no serial port
Many laptop and desktop PCs do not come equipped
with RS232 type serial ports (which could be converted to
an RS485 type using a simple converter) any more. The
USG-1-485 solves this by creating a standard RS485 port
from any PC USB port.
This port appears on the PC system as a regular “COM”
port, and so can be used with all standard navigation and
display software.
Features
Standard USB connection -
Equipped with a type “A”
USB connector to connect to a USB port or hub (USB v1.1
or v2.0 compliant).
Opto-isolated ISO-Drive transceiver technology
creates a transceiver, unique to Actisense, that is isolated
to 1500 volts - say goodbye to ground loop issues!
ISO-Drive allows a completely “floating” output to be
created, making a safe connection to a PC an easy
task. You can use the ISO-Drive output to safely transfer
data to an RS485 device, or to another PC. The output
automatically changes between differential and single
ended drive depending upon the type of instrument it is
connected to.
When not transmitting, the USG-1-485 automatically
switches to receive mode. The output becomes
a differential input fully compliant with the RS485
specification. This allows the USG-1-485 to work correctly
with long cable runs and in a noisy environment. Typical
operating voltage is 2.0v to 12.5v. The unit can withstand
-8/+12.5v continuously, and +/- 40v transients. The input
is also compatible with RS232 signal levels.
PC USB drivers supplied on disc
- the drivers allow the
USG-1 to appear as a standard “COM” port on the PC.
Low current consumption
- the USG-1-485 is powered
directly from the USB port on your PC, so no extra power
cables are required.
Tough Polycarbonate case
- certified to IP54 (Splash
and dust proof) when used with both supplied cables.
Software updates
The USG-1 has no built-in firmware, but Actisense will
be providing updates to the PC USB drivers free on
our website,
when they become
available.
Summary of Contents for USG-1-B-485
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