ACO Experimenters Guide
If you have any questions
that are not coved in the Table of Contents below, please feel free to email or
call the appropriate person on the Contact page.
Customer Interface Information
General Questions.
- Where is Observatory deployed?
- Should I get into a group to propose a sensor
system to connect ?
-
Who will be responsible for system
operation?
I have questions about system integration.
- What is the data
interface ?
-
What are experiment
configuration options?
-
How
far away from the observatory can my experiment be placed?
- How do I prepare my instrument for installation?
I Have Questions About Power.
- How much power can I get ?
- My sensor has a large turn–on electrical
transient. Is that OK
- What happens if I draw
more current than allotted?
-
What about High-Voltage
Connections?
I Have Data Communication Questions.
- How much data can I send over the system to my desk?
- I want to send large amounts of data in bursts. Is
that OK?
- What happens if I use more bandwidth than
allotted?
- Can I send commands to my sensor to change its
configuration?
- Can I send commands to change software?
- I’d rather not connect to the system with a hard
wire. Can I connect with an acoustic data link?
- How secure is my
network connection and data link?
I Have Timing Questions
- Does the Observatory supply timing?
- What timing accuracy can I expect?
General
Questions
The ACO (Aloha Cabled Observatory is located
approximately 1.2 km SSW of Station ALOHA (22° 45'N, 158° 00'W). HOT
(Hawaii Ocean Time) assets are installed within a 6 km radius of Station ALOHA.
Combining compatible experiments into a sensor network that uses only one
observatory connector is likely to
be the most cost effective way to get your data from the ocean floor.
System operation
responsibilities will be relegated to the ACO STAC with the day-to-day operation
of the power and communication links to the
cable system the responsibility of the University of Hawaii. In the future, many observatories in the US will likely be operated
under ORION management.
System
Integration Questions
The Observatory is
basically a LAN. Your experiment can plug in either to a 10Base-T Ethernet port
or to a serial port. In principle, if the connection works in your lab on your
local network, then it should work on the ocean floor. Ethernet protocol is
preferred, but low-rate systems on long cables may be best accomplished using
RS-232 serial. Experiments on long cables (>100m) to the observatory that
require high data rates must be heavily tested. Ethernet has cable-length
issues, and the necessity to pass the signals through connectors may degrade
signal. For high-rate signals on long cables, it may be necessary to change the
electrical signal to optical in the cable connecting the experiment to the
observatory. This is new technology and developments should be watched
carefully.
There are several options to connect to the Observatory site,
1. Simple, reliable sensors that
can be attached to the observatory structure on deck. These sensors can be
installed when the observatory is brought to the surface for repair or
modification. The advantage of this
method is that an expensive wet-mate connector is not required.
The disadvantages are that your sensor will be brought to the surface
whenever the observatory is recovered, and that it cannot be deployed away from
the observatory structure.
2. Sensors installed permanently
near the observatory. These sensors will require a wet-mate connector pair to
install the sensor on the ocean floor using an ROV.
Connections to the observatory will be standard dry-mate marine
connectors, thus, the cost of the wet-mate connector will be born by the
experimenter.
3) Sensors installed at distances
greater than 150 m from the observatory. These sensors will need an emplacement
system compatible with the ROV being used for installation.
4) Sensor networks. Groups of
experimenters are encouraged to pool their interests and proposals for sensor
networks which can use a separate module to share the power and bandwidth
supplied by the observatory.
In all
cases, sensors must be tested at the SOEST
Observatory Test Bed prior to installation.
This insures that the sensor is compatible with the observatory and other
sensors.
There are two factors which limit the distance to
the experiment. One is the voltage drop in the cable. A low power
experiment on a heavy conductor can be placed farther away than a high-power
system or a system with a light conductor. We normally supply power at 48 VDC, but two 400 VDC user ports will be available
initially. The second factor is the ability to communicate via Ethernet over
the underwater cable.
The underwater-mateable
connectors cause impedance discontinuities and reflections on the cable. That
is why we say that your experiment must be tested on the submersible
umbilical
before shipping it for deployment.
RS422 serial can
communicate over longer distances, depending on Baud rate. Again, you should
test your sensor with the length of cable you hope to use. With the lower
frequency of the RS422 signal, the connectors probably have a negligible effect.
1. Check with the
Observatory operators to determine likely power and data allocations, and other
possible options and restrictions for your experiment. Since these factors could
be cost drivers, it is highly advisable to determine these parameters at the
proposal stage.
2. Check with the
Observatory operators to determine location, connector, pin assignments,
installation cruise opportunities.
3. Test your equipment to
your satisfaction using your own Internet connections.
4. Notify Observatory
operators that you are ready for a test at the Observatory test bed. If your
experiment is relatively simple, it should be possible to have observatory
personnel install it at the test bed and assign a URL for you to check your data
and commands from your office – just as though it was installed on the ocean
floor.
5.
Coordinate with the Observatory operators and users
group concerning installation procedures and options.
Power
Questions
Power from the cable is
substantial but limited (total of about 800 W available to users). This power
has to be shared by the entire community, and some experiments have a legitimate
need for more power by the very nature of the experiment. We are not therefore
allocating a fixed amount of power per experiment, but are providing “reasonable
guidelines”. In the interests of the larger community, we are asking each
experimenter to make a conscientious effort to conserve power.
A “reasonable
limit” below which there is probably no major concern is perhaps 25 Watts. With
this kind of conservation, we can probably supply up to 100 Watts or even more
on a case-by-case basis to power-hungry systems. At present we have very little
feedback on power requirements, so let us know what you have in mind.
Each user node is powered
through a remotely programmable 8-step circuit breaker. The current limit for
each user will be set to allow a reasonable start-up transient. This is
necessary in order to safely manage the power system for the other users.
If your equipment
intrinsically requires a large surge current, we may have to temporarily
increase your breaker setting for turn-on. The limit will then be set back to a
safe limit for normal operation. If the transient exceeds the limitations of
the circuit breaker, then the user will be required to buffer current transients
with a battery or other method.
A programmable circuit breaker will trip causing the 48 volts supplied to the
user interface to be shut off.
The Observatory also
provides two higher voltage and power (400 Volts at 200 Watts) user ports for
experiments or sub-multiplexer nodes that are located a considerable distance
from the Observatory site. This higher voltage reduces cable power loss by a
factor of 50.
Data
Communication Questions
The initial ACO
infrastructure will support a single 100-base T Ethernet link to shore.
Individual users will be able to access 10-Base T data link. Future expansion
could increase the available bandwidth by a factor of 4. Care must be taken with
high data rates, in that high-speed Internet connection costs can be
prohibitively expensive. For example click on the url below to see some examples
on pricing.
http://www.broadbandbuyer.com/chartbusiness.htm
.
An intense burst of data
on one channel may cause latency problems for another time-critical
experimenter. In order to provide the best possible service to all of our
experimenters, we may limit the bandwidth available to an individual. Your data
will still get through, but it may take a bit longer. If you have an experiment
that requires burst data, please contact the operators.
Bandwidth for individual
users is controlled by using a
bandwidth manager. Once set, uplink and
downlink speeds will be limited at a predetermined rate.
Yes, in the same way
that you do it while testing in your shop. Power changes above the allotment
will trip your circuit breaker.
An Ethernet experiment
can be reprogrammed, but not serial RS-232
experiments.
It should be understood that acoustic modems interfere with each other, so
only one such link can be operational at a time.
The other alternative is to have a shared acoustic link.
In this scheme, the Observatory link would poll the
individual experiments.
Experimenters desiring
acoustic modem connections to the observatory will be supported, but the
acoustic modem will be part of the experiment- not part of the ACO
infrastructure.
Since data transmission and connectivity rates
are controlled by the ISP (Internet Service Provider) we cannot guarantee 100%
connectivity or 100% security.
Timing
Questions
IRIG-B timing signals
synced to a GPS receiver at the Shore Station will be available to users along
with a 1-sec pulse line.
Ethernet experiments can use NTP (Network Time Protocol) for a time base.
While this is still an open question, if
your sensor system can read the IRIG time code supplied by the Observatory, and
convert it to a time stamp in your data, then time should be accurate to better
than 1ms. If you do not use this
feature, you should still be able to correct your data timing to better than 1
s.
Page Last Modified
09/24/2008
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