AR50MAN.doc or AR50MAN.htm revised 12-7-05.
Underwater Acoustic Release System
Acoustic Release Model AR-50-AA
(underwater release unit)
Acoustic Release Interrogator Model ARI-50
(topside command unit)
Sub Sea Sonics, San Diego, CA
(619) 286-7546 (www.subseasonics.com)
OVERVIEW:
This
underwater acoustic release system permits the underwater release of such items
as an instrument package lifted by a float, a bungee that when released
performs a desired action, etc. The acoustic release interrogator (ARI-50)
sends a command to the underwater acoustic release (AR-50-AA). An additional
feature includes a command to make the release unit become a very low power
pinger to acknowledge operation or permit tracking (requires a special pinger
tracking receiver and antenna not included with this system).
Each
underwater release has a specific four digit unit identification number
assigned to it by Sub Sea Sonics. To send an action command to the underwater
release unit the following three steps are performed. First, the four digit identification number
is selected using the interrogator keys while viewing it on an LCD display (two line by 16 character each line).
Second, the specific action command is selected using the keys and LCD display.
Third, both are transmitted to the underwater release unit.
The
interrogator comes with a transducer on a cable that is placed in the water for
use. The interrogator must be connected to a 12 VDC battery such as a gell cell
or lead acid battery adequate to supply 5 amps during transmit.
DEPLOYMENT OF A RELEASE UNIT:
A. Installation of
batteries inside a release unit:
B. Verify that the
release unit is operating:
C. Installing a new
erosion release link:
D. Final deployment:
TRANSMITTING COMMANDS:
Hookup of the
acoustic release interrogator (topside command unit):
Supply
12 VDC from a gel cell battery or equivalent (needs 12 VDC at 5 amps for
transmit, but only 10 mA when not transmitting). Connect the transducer to the
interrogator and place the transducer in the ocean or very near the release
unit if testing in air. If testing is done in air the transmitting transducer
may have to be adjacent to the release unit body about six inches down from the
link. If poor results are observed then try moving the transducer slightly.
Maximum ranges of 3 inches to 3 feet in air are typical.
Operation of the
interrogator:
Use
the Stop (S) key to break out of the initial power up banner and get to the
main menu. Use the Next (N) key to move to the next item on the menu and the
Accept (A) key to accept an item from the menu. Likewise for the Select Action
sub menu. First, select the underwater unit identification number using the
Select unit Id menu item. Second, select the action desired using the Select
Action menu item. Third, Transmit the command using the Transmit once or
Transmit loop menu item. Transmit once sends the command just once. Transmit
loop sends the command repeatedly. Transmit loop should only have to be used if
acoustic transmission conditions are marginal for some reason and if so will
save operator time.
An example of sending
the command ‘Release with Ping’:
Prepare
a release unit (AR-50-AA) as indicated elsewhere herein. (If testing in air then something simulating
the conductivity of the water is needed to turn it on. A 270 ohm resistor across the contacts is
recommended or better yet install the BTL-50-AA battery test load). Connect the transducer (TD-50) to the
interrogator (ARI-50) and place the transducer in the ocean (or within a few
inches of the release if testing in air).
Supply 12 vdc to the interrogator. Hold S for main menu. Press N once to
get to Select Unit Id. Press A to be able to select the unit identification
number desired. Use the I or D keys to set the unit Identification number to
that matching the unit underwater. Once selected use the A key to accept the
one selected. The LCD display will flash the selected unit identification
number and return to the main menu. Use the N key twice to advance to Select
Action. Use the A key to accept the select action sub menu. Use the N key
repeatedly to get to ‘Release w/ Ping’. Use the A key to accept this action.
The display will flash the action accepted and return to the main menu. Use the
N key three times to advance to Transmit Once. Use the A key to accept and
perform this activity. To avoid an accidental release you will be asked to
verify that you want to perform a release with the choice of S for stop or R
for release. Press R. The unit will display TRANSMITTING…, etc. as the
transmission of the 2.5 second steady synchronization/wakeup pulse followed by
seven suppress spectrum/20 ms precisely timed pulses occur. The command will
have been completed when the LCD displays END XMIT CYCLE.
All
of the other command setups and transmissions are similar to this one.
Action = Pinger:
Sending
this action command causes the release unit to behave like a pinger for 60
seconds and then returns to listening. While acting as a pinger it emits a
single 20 ms ping once per second (1.00 sec +/- 2%). These pings can be picked
up on a sensitive pinger receiver if the sea is relatively quiet. If a pinger
receiver with tracking antenna is available the direction to the release unit
can be obtained. Note that the AR-50-AA
acoustic release unit has an internal pinger that only puts out about 10 mW of
power. Accordingly, if there is too
much ocean noise the pinging mode may not be able to be picked up. (A pinger receiver is not supplied with the
ARI-50 / AR-50-AA system).
Release unit time-out
times:
The
following time-outs are used to free the release unit for another command. Pinger Action = 60 sec (one ping per
sec). Fast Ping Check = 2 sec. Brief Erosion = 10 sec. Release with ping = 15 min. Release without ping = 15 min.
STORAGE:
1.
Keep a new or used or dummy erosion link installed on each
release unit when storing to protect the plastic threads and prevent accidental
erosion of the positive contact (the one the link spiral contact touches).
2.
If it is desired to prevent battery drain then keep the unit
off by washing any salt or other conductive material off the area near the link
and coil. Keep this area dry and free of any salt or contaminant that might
conduct current.
3.
Store out of direct sunlight.
4.
Store such that the top (erosion link) end is protected from
any heavy sideways impacts as it is possible to break this end off.
SAFETY WARNINGS:
1.
Remove the battery access end plug with extreme caution in
the event that the cavity leaked from underwater pressure or the batteries
developed a gas and built up a pressure inside the cavity.
2.
Do not touch the transducer while transmitting otherwise the
sustained 2.5 second part of the transmission may overheat body tissues or
cause other harm.
MISCELLANEOUS INFORMATION:
BUBBLES
OFF OF THE "COIL" WATER CONTACT:
The
stainless steel coil at the link end is the negative contact for the erosion
process. During the release while the link is eroding there will be bubbles
coming off of this coil contact. A deposit forms on the coil contact which can
be left there or occasionally brushed off.
EROSION
TIME VS. WATER TEMPERATURE:
Lab
tests indicate that the time to release increases 80% as the water temperature
is lowered from 70 deg F (21 deg C) to 28 deg F (-2 deg C).
EROSION
TIME VS. BATTERY VOLTAGE:
Lab
tests indicate that the erosion time increases about 150% (2.5x) as the battery
voltage decreases from 13.5 volts to 7 volts.
ACCIDENTAL
LINK COATING INHIBITING EROSION:
Neither
oil nor silicon spray applied as thick as possible right on the link erosion
points inhibit erosion. Both seem to disappear even when very gently submerged
into still water. However, if the contacts are covered with a thick covering of
grease this will prevent erosion if the covering is 100%. Tests show that a 90%
covering only doubles the erosion time.
Accordingly some accidentally deposited grease is very unlikely to cause
a problem.
LINK
CONTACT SMALL CAVITY LEAK:
Should
the link cavity (where the O-ring resides) happen to leak this will not prevent
a release. The majority of the electric current will still flow to the intended
erosion points. However, should the cavity have leaked there might be erosion
damage to the unit contact. It is a worth while precaution to inspect this
contact by pressing on it with a screwdriver to verify it is solid (not damaged
by crevice corrosion during a prior release).
VERY
LOW RELEASE BATTERIES:
If
the release unit battery voltage drops below 5.5 VDC due to unintended weak
batteries, a special supervisory circuit resets the micro controller which
shuts off any present activity (such as Release w/ Ping) and the unit returns
to listen mode. This is a friendly failure as the unit will be immediately
ready to try again. If this should happen wait for the batteries to recoup a
bit and try again. If trying again is selected consider sending a less current
using command such as the Brief Erosion command. If it is sent with Transmit
Loop it will turn the erosion on for 10 seconds once every other transmission
cycle (about 10 seconds out of every 25 seconds) thereby reducing the average
load on the batteries. But this is only a last resort and will not be necessary
if adequate batteries are used.
THEORY OF
OPERATION:
RELEASE RECEIVER:
The release unit receiver utilizes a low noise first stage
followed by a high pass filter, more amplification followed by a phase locked
loop detector.
RELEASE UNIT LISTENING MODE:
During normal deployment the release unit spends most of its
time listening for an on-frequency signal. To keep the total battery current
low (less than 200 micro amps) the receiver is turned on only once every 1.15
seconds (+/- 30%) to listen for a signal in the center frequency band (FM).
This only takes 20 ms and If none is heard (usually the case) the receiver is shut
off and the micro controller goes to sleep. This cycle keeps repeating until a
signal in the center frequency band is detected and lasts longer than 8 ms.
When this happens the receiver stays on and checks to see that the signal stays
on longer than 80 % of the time for the next full second. It then checks for
the signal absent for at least 300 ms. It then changes to pulse timing mode and
times the six time periods formed by a total of seven 20 ms pulses. (A
suppression frequency is transmitted before each pulse to suppress any on
frequency interference such as echoes, biological interference, or man made
signals. This combined with long times between pulses prevents interference
from echoes.) Each of these 6 times is converted into an octal digit for a
total of 18 bits. The first 12 bits contain the unit identification number. The
next 3 bits tell the action requested. The last 3 bits are a parity check. As
the times are received they are checked against the unit identification number
for that unit. If any one of them is wrong the unit immediately goes back to
listening mode where it will not respond to the additional 20 ms pulses left in
the command being transmitted.
RELEASE UNIT RELEASE MODE:
When the release command is received, the micro controller switches
on the release sub-circuit for the duration of the release mode time (e.g. 15
min). During this time the full battery voltage is applied to the ‘link’ (+)
relative to the ‘coil’ (-) water contacts. The current flow is approximately
200 mA for a LK-40 link with its two 0.025 inch diameter by 0.1 inch long
exposed points. A current limiting circuit limits the current to approximately
700 mA. A short across the ‘link’ to "coil" will not damage the
release unit but will drain the batteries. If a heavy load or weak batteries
cause the battery voltage to drop below 6 volts then a friendly reset of the
micro controller would occur and a new command would have to be sent to restart
the intended action.
NOTES REGARDING THE CHECKOUT OF AN AR-50-AA RELEASE UNIT:
Unit Identification Number: Each underwater release unit has
a specific "unit identification number" or unit Id assigned to it.
This number is between 0 and 4094 in decimal and is assigned by the factory. It
is 12 bits in binary. In the unlikely event that this number is lost it can be
read from a release unit by turning it on and observing the flashes on its
outside LED. Single flashes indicate bit one and double flashes indicate bit 0.
There is a spacing of about 1.2 second between each single or double flash. To
observe this remove the unit from the water to turn it off. Wait for up to 13
sec for the unit to check to see if it is still in water and if not to shut
itself off. (If unit was in the process of releasing then the wait for the
out-of-water check requires up to 60 seconds). Next, with a helper at hand,
make contact with a 100 ohm to 100,000 ohm resistor (or a wet rag) across the
‘link’ and ‘coil’ contacts until the unit starts flashing. Write down the flash
counts (ex. 11 11 11 1 11 1 11 11 11 1 11 1) flashes = 000101000101 binary.
Convert these to decimal (ex. 0325 decimal). This is the unit identification
number which must be used with the topside command unit (acoustic release
interrogator) to effect any of the actions that the release unit will perform.
This number can more easily be obtained by reading the number marked or tagged
on the outside of the release unit if one is still there. Note that the unit Id
goes with the electronics inside and cannot be changed. Unit Identification
Numbers are assigned by Sub Sea Sonics. This permanent assignment eliminates
the need for unit identification physical switches with their possibility of
switch contact failure. It also keeps
the assignment of numbers under the control of Sub Sea Sonics and reduces the
chance of two users selecting the same unit identification in the same region
of the ocean.
Listening Mode Of Release: When the release unit is turned
on (submerged or a resistor or a wet rag or equivalent placed across the ‘link’
and ‘coil’) it first sends out its binary unit id by flashing the outside LED
and then goes into its listening mode. In listening mode it wakes up from sleep
every 1.15 second +/- 30% and checks for any signal on frequency FM (35714 Hz
+/- 3%). If it does not hear one it goes back to sleep. This listening mode can
be confirmed by observing the outside LED on release link end flash once for
every ten wake ups which is once every 11.5 sec +/- 30%.
Actions By Release: When a command is sent by the Acoustic
Release Interrogator, the release will flash the LED in response. First it will
flash with very faint flashes every time a 3 bit symbol is received and
confirmed correct for that specific release unit. There are 6 of these symbols.
Next it will flash with normal brightness to indicate which command it received
as per the following:
|
One flash every 1.00 sec (60 sec total) => Pinger Action (unit pings once per flash also). |
|
20 very fast flashes (2 sec total) => Fast Pinger Check (unit pings once per flash also). |
|
100 very fast flashes (10 sec total) => Brief Erosion Check (unit pings once per flash also). |
|
No flashing occurs during Release w/o
Ping (release without pinging) and lasts 15 minutes. |
|
One flash every 1.50 sec (for 15 minutes) => release with ping (unit pings once per flash also). |
These actions can only be interrupted by turning the unit
off. To turn the unit off it must be
removed from water or the test resistor across the water contacts (link and
coil) must be removed. This must be followed by waiting for the unit to check
the these water contacts. This occurs every 11.5 sec +/- 30% for all but the 15
minute release which requires 60 seconds between am-I-in-the-water checks. [The
reason for these long wait times till off is to reduce water contact erosion by
stopping all current flow until specific check times. These check times last
about 0.5 seconds.] Interrupting the commanded actions by shutting off the unit
before the commanded action times out can save a lot of operator time in system
checkout.
ACOUSTIC RELEASE SYSTEM SPECIFICATIONS:
AR-50-AA:
Acoustic
release using fast electrolytic erosion of stainless steel for the release.
Multipath
interference resistant by use of:
·
Single frequency sent at any one time.
·
Pulses spaced at least 1.0 seconds to permit echo die out
before the next pulse.
·
Suppression frequency spectrum transmitted to block echoes,
noise, and interference.
·
Long pulses used (20 ms or greater) for ample energy
integration time.
Reception
frequency bands:
Detection
frequency set in phase locked loop 35714 Hz +/- 3%,FM.
Reception
sensitivity: 1.5 micro volt rms with a 3000 ohm driving impedance for a logic
level solid transition. (-27 dB relative to one micro bar.)
Reply
frequency for very low power pings:
Single
reply frequency 38462 Hz +/- 1%, FR.
Acoustic
output: 10 miliwatt (151.5 dB relative to 1 micro Pascal at 1 meter).
Command
reception: Seven pulses accurately time spaced preceded by a
wake-up/synchronization 2.5 sec steady signal all on frequency FM and each
pulse preceded by suppression frequency FS.
1,500
foot max. rated depth (2,000+ foot design)
80
lb. max. rated release load capability (80+ lb. design)
Main
housing made from 1.25 inch nominal schedule 40 and schedule 80 PVC pipe (1.667
inch OD), an end cap, a coupling and a battery access solid PVC end plug using
a double O-ring seal.
Total
length 22 inches. Weight 2.5 pounds, approx. one pound in water.
Accepts
link LK-40 (40 lb) or LK-80 (80 lb).
Powered
by a single 13.5 VDC internal battery pack made from 9 lithium Energizer L91
size AA cells (BAT-50-AA-L91). As an
alternate alkaline AA cells can be used but with significantly less performance
(about one fourth the life and number of releases and poor low temperature
operation and shorter shelf life).
Battery
current in listening mode is less than 200 microamps.
Accepts
BAT-50-AA-L91 battery pack and requires soldering two wires for replacement.
Unit
is reverse battery protected.
Unit
output is short circuit proof.
All
unit external contacts are electrostatic discharge resistant and have passed a
test during design checkout of 30 kV from a 25 pF capacitor..
ARI-50:
Acoustic
release interrogator (for use with AR-50-AA).
Command
transmission: Seven pulses accurately time spaced preceded by a
wake-up/synchronization 2.5 sec steady signal all on frequency FM and each
pulse preceded by suppression frequency FS.
35714
Hz +/- 0.1% 20 ms pulse used as the main frequency, FM.
31250
Hz +/- 0.1% 20 ms rapid pulse used to generate the suppress frequency spectrum,
FS.
Acoustic
output: 10 watt (181.5 dB relative to 1 micro Pascal at 1 meter).
Requires
12 volt 5 amp DC supply such as a lead acid or gel cell (user supplied).
Unit
identification number selected using Increase/Decrease keys.
Action
selected using Next/Accept keys.
Transmit
command selected from Menu using Next/Accept keys.
TD-50:
Transducer
for the ARI-50 interrogator. Made from a piezoelectric cylinder 1.0 inch OD by
0.5 inch high by 0.115 inch thick walls. Full electrostatic shield. Normally
supplied on a 50 foot cable with a BNC connector. It can be modeled with a 4.7
nf capacitor and a 3000 ohm resistor in parallel. Its in circuit electrical ‘Q’
is about four making the tuning of the resonant transformer that drives it not
critical. [The TD-50 is the same as the TD-60].
BAT-50-AA-L91:
Battery
pack for use with the AR-50-AA acoustic release. This battery pack is made by
wiring nine Eveready L91 lithium AA size cells in series using welded contacts
or a special factory verified soldering technique. Battery pack includes a
spine, internal rubber spacers and shrink tubing to hold all the cells in
place. Battery pack characteristics
include 13.0 volts sustained under heavy load, 2900 ma-hr, 10+ year shelf life,
excellent low temperature operation, high current handling capability, superior
to alkaline in most every way. Meets
transportation requirements of 49CFR 173.185 (b) and IATA special provisions
A45. Red wire = positive, black wire =
negative.
The battery pack can be tested before
connection into the acoustic release by using a 270 ohm 1 watt temporary test
load and measuring the voltage with an accurate voltmeter. A new battery pack should measure > 13.5
volts. A pack at mid life nominally measures 13.0 volts. Near expired pack nominally measures <
12.2 volts. This test does not
absolutely guarantee that the battery pack is good but it is a worth while test
that might catch a bad battery pack at this pre-installation stage.
For more information on the L91 lithium
batteries see www.energizer.com.
BTL-50-AA:
Battery
test load used for system checkout.
This is installed in place of a release link. It has a black wire with ‘coil’ contact clip that must be
connected to the ‘coil’ water contact.
It both turns the AR-50-AA underwater acoustic release unit on, puts a 270
ohm battery test load on the unit, has a red LED that indicates release voltage
present but doesn’t turn on if the batteries are below 7 volts (very low
batteries). Its brightness increases
for batteries above 7 volts. It has an
exposed stainless steel wire used for connecting to the positive lead of a
voltmeter. The negative voltmeter lead
goes to the ‘coil’ water contact. With
this voltmeter connection the battery voltage under this load can be measured
during system checkout in air.
LK-40:
Release
link for AR-50-AA. One use only. Load
rated at 40 lb on-axis load. Eroding strength members are two pieces of 0.025
inch diameter stainless steel alloy 308 wire configured as a loop. Erosion time
2 to 4 minutes at 1000 foot depth. This
release link type will typically give 35 or more releases plus 10 months of
operation using the BAT-50-AA-L91 lithium battery pack. Cut this in half for a large safety
margin.
LK-80:
Release
link for AR-50-AA. One use only. Load rated at 80 lb on-axis load. Eroding strength
members are two pieces of 0.035 inch diameter stainless steel alloy 316L wire
configured as a loop. Erosion time 4 to 8 minutes at 1000 foot depth. Uses about four times as much battery energy
as the LK-40. This release link type will typically give 10 or more releases
plus 10 months of operation using the BAT-50-AA-L91 lithium battery pack. Cut this in half for a large safety margin.