Oxygen control system
(Note; Everything about the Ouroboros rebreather can be found
in the comprehensive manual which accompanies every unit)
This can be a mechanical or an electronically controlled device.
Which ever is chosen it is important that the control of the
oxygen level is maintained within certain limits. If decompression
is to be conducted using tables or a fixed PO2 dive computer,
the limits must be accurately maintained. Rapid excursions
to and from depth must also not generate excessively low or
high PO2’s. Ideally any such limits reached should generate
an alarm, as it cannot be relied upon that the diver will
notice, especially if in a multi-tasking situation. Some rebreather
designs, due to high flow rates within the oxygen circuit,
can generate massive PO2 spikes sufficient to cause convulsions
in a short space of time if left unchecked, this is an undesirable
design feature should an addition valve fail. Within the CE EN14143
and most Navy tests is a PO2 tracking control test as well
as a upper and lower limit test after rapid depth changes.
NOTES ON CELL
HEALTH
Before any dive a comprehensive screen menu check system
will occur. If any of the cells are not healthy then
the screen on the right will displays levels below 20%.
This screen is only shown after an oxygen calibration,
or if the cell health is low. It is also shown if the
pre dive checks have been restarted from the option
in the Setup screen and If cells are less than approximately
7mV in air or a wrong calibration gas has been used
so that the cell mV appears to be less than 7mV in air.,
A warning is given not to dive.
|
 |
Oxygen sensor isolation
The Ouroboros has the ability to automatically deselect faulty
oxygen sensors. However there may be instances when you wish
to override the computers decision. This can be done by manually
turning off sensors in the O2 screen on page 61.
O2
sensor Screen
This screen allows the operator to view individual cell
levels and status. The cells can also be disabled in
the event of failure. When on the surface, the O2 sensors
can be calibrated.
1;-From the O2 sensor screen, the operator
can:
Enable/Disable sensor – Short
press of both buttons
This allows the operator to toggle the sensor between
an enabled (Y) and disabled (D) state. A disabled sensor
will not be used in the sensor averaging. An enabled
sensor will be used as long as its reading is in close
proximity to the other enabled cells. The rebreather
will not use cells that are out of range (displaying
and N). It will also not use cells that have a dissimilar
reading to the other cells. See o2 sensor polling on
page 63 of our manual for more details on automatic
disabling and averaging.
|
Above left; Dry Screen
Above right; Diving Screen |
2. Turn off rebreather
oxygen solenoid control using all cells disabled (D)
If all 3 cells are turned to disabled (D) state, then
the rebreather will stop controlling the oxygen solenoid.
The diver will be prompted:
If the diver replies ‘yes’, then another
warning screen appears and asks:
If the diver again replies ‘yes’,
then the solenoid control system is turned off and the
decompression algorithm will follow an internally selected
setpoint on the Primary display. The solenoid control
system can be turned back on again (as will the cell
tracking decompression) by changing one of the cells
to ‘Y’ again.
ONLY ONE CELL WILL BE
TURNED ON AGAIN THE NEXT TIME THE OUROBOROS IS TURNED
OFF THEN BACK ON AGAIN. ENABLE CELLS AS APPROPRIATE.
3. Scroll down list – Short
or long press of right button
This allows the operator to enter scroll down the list
of cells |
|
4. Enter CAL mode
SURFACE ONLY – Long press of both buttons
This allows the operator to enter the o2 sensor calibrate
screen. This is used to calibrate the po2 sensors
and thus ensure that the rebreather is controlling
as accurately as possible, and that the decompression
calculations are using the appropriate po2 value.
O2 sensor Calibrate
Screen
This screen allows the operator to calibrate the po2
sensors and thus ensuring that the rebreather is controlling
PO2 as accurately as possible, and that the decompression
calculations are using the appropriate po2 value.
|
 |
| NOTE:
ANY SENSORS THAT THE OPERATOR THINKS ARE NOT WORKING
CORRECTLY SHOULD BE REPLACED BEFORE ENTERING THIS SCREEN
FROM THE O2 sensor Screen.
From the O2 sensor screen, the operator
is prompted to perform ‘flush now’ with
the Calibration Gas
When this has been done, a press
of the right switch moves the operator to next screen.
The operator is then prompted to ‘Vent’
the breathing loop momentarily by opening the mouthpiece
and closing it again to equalize the pressure in the
loop.
|
 |
When this has been done,
a press of the right switch moves the operator to next
screen. The rebreather is then checking all the sensors
for a stable reading. The rebreather will then automatically
calibrate the sensors. Alternatively the user can use
a short press of both switches to force the rebreather
to calibrate. This is not advised, but in extreme cases
can be used where the operator has no alternative but
to use very unstable sensors.
When the calibration is complete, the operator is then
taken to the first of the On screen Pre-dive checks.
Now that the rebreather has an updated calibration,
all pre dive functionality checks should be done to
ensure the calibration is correct. |
|
Calibration Gas
The calibration gas is setup from the Gas Adjust Screen.
The calibration gas is the gas used in the rebreather
O2 cylinder. This is normally 99% oxygen. However, should
a slightly weaker O2 be used, then the CAL gas should
be adjusted accordingly. Then the calibration of the
O2 sensors will be adjusted accordingly.
Atmospheric Adjustment
Atmospheric adjustment is carried out automatically,
during calibration, by multiplying the calibration
gas O2 level by the current ambient pressure in Bar.
This ensures the most appropriate PO2 is used by the
rebreather.
Example: 98% O2 x 0.950 bar atmospheric = 0.931 Bar
|
Before deselecting a sensor, the PO2 should
be confirmed by doing a diluent flush (with oxygen injection
temporarily disabled). The PO2 of your selected diluent at
the current depth is displayed on the dive Decompression Screen
Summary on page 70 of our manual.
Calibration
It is not necessary to calibrate the unit prior to every dive
but it is vital to do a pre-dive calibration check. When prompted
to do so in the Pre-dive check screen (page 28), complete
the following.
1. Make sure the diluent cylinder via the
ADV cannot add gas into the loop (isolate the shut-off).
2. Evacuate the loop and close the mouthpiece.
3. Fill the loop with oxygen until the over pressure valve
just releases.
4. Without adding exhaled air into the loop evacuate it
again.
5. Fill and evacuate again twice, leaving the loop full
of oxygen at the third fill.
6. Follow the on screen instructions.
7. Quickly open and close the mouthpiece to equalize the
pressure in the loop with the surrounding ambient pressure.
8. Check the Backup display by pushing the top button to
see the PO2 and re calibrate as required.
9. Check the Primary display and confirm the PO2 is correct
on all 3 sensors to within 0.05 of the ambient PO2 with
100% oxygen.
10. If the PO2 is not correct, go to the GAS screen (page
58) and select Oxygen as the calibration gas. Now calibrate
the unit.
11. Flush once more with oxygen and confirm the readings.
12. If the readings are still wrong you must abort the Pre-dive
checks and open the Dome and expose the sensors to atmospheric
air for 5 minutes. Now select the milli-volt function on
the Backup display by pushing both buttons together. If
any of the cells are below 7mVolts they need replacing.
13. Before replacing the cells remove and clean the jack
plug connection to each cell. Check the ‘in-air’
reading again.
14. Replace and re calibrate as required.
Calibration at altitude is covered
on page 64 of our official manual.
Oxygen sensor
tests
If the cells become affected by moisture or are nearing
the end of their life they may read incorrectly. Items to
look for when a cell is suspect:
1. When flushing with oxygen, look for a cell reacting slowly.
There may be moisture on the face. Remove the cell and dry
it gently by applying tissue paper to the face. Do not apply
pressure to the face.
2. Periodically check that the cells read greater than 7mV
in air by pushing the bottom button on the Backup display.
If a cell appears to go out of calibration quickly, flush
the loop with oxygen. Calibrate the cells on the Primary
and Backup displays. Leave the loop closed for one hour
full of oxygen and then check the cells again on the Backup
display without switching the main electronics on. They
should all be within 0.1 PO2. Now flush with air, leaving
the electronics off. The PO2 on the Backup should read between
0.23 and 0.19.
Calibrating the Backup Display
1. Ensure the battery is good.
2. When running the pre-dive sequence, once you have the
loop flushed with oxygen, monitor the PO2 on the Backup
Display and decide if any of the three displays need adjusting.
3. Turn the large blank cap on the rear of the Backup Display
corresponding to the un-calibrated cell. If you run out
of range on the control, try screwing it right in and start
again. DO NOT SCREW THE CAP RIGHT OUT TO EXPOSE THE SEALING
O RING AS THIS WILL FLOOD THE BACKUP DISPLAY, IF DIVED.
If the backup will not calibrate then confirm the cell millivolt
reading (by pushing the bottom button on the display) in
air is above 7 millivolts and start the calibration routine
again. Screw the cap right in and out again.
4. With the loop still full of oxygen, make sure the Backup
Display oxygen reading is the same as the calibrated Primary
Display readings.
5. If you completely undo the cap, clean
and re-grease the waterproof cover O-ring and the internal
O ring and refit the cap, being careful not to cross-thread
the it.
| PO2
Cell Calibration menu options
1. Flush Now
A short press of the right button confirms that the
breathing loop has been properly flushed with the
Calibration Gas.
2. Vent Now
A short press of the right button confirms that the
breathing loop has been vented at the mouthpiece (quickly
open and close) to ensure there is no overpressure
in the breathing loop.
3. Calibrating..
After the ‘vent now’ operation is confirmed,
the rebreather now monitors the active sensors, and
performs the appropriate calibration calculations.
This process can be stopped by a press of the left
button. The process can also be manually confirmed
by a short press of both buttons, in case the unit
is taking an excessive time in getting a stable reading
– e.g. because of water on the cells. However,
normal practice would be to let the unit continue
to calibrate automatically to ensure the best accuracy.
O2 Sensor Polling
The rebreather has a method of automatically removing
O2 sensor cells from the PO2 averaging. This is based
on a set of rules. If the operator considers these
are not appropriate for a particular type of cell
failure, then any individual cell can be turned off
manually. See the O2 sensor Screen.
Rules:
1. If all cells have been disabled by the user the
rebreather control system is turned off. See Dvo Screen
and O2 sensor Screen for how to turn it back on.
2. If a single cell is below 0.15
bar or above 3.00bar, then it will be disabled, the
system denotes this with a ‘N’ next to
the cell.
3. If after item 2, all 3 cells are
disabled for the same fault, then all cells will be
re-enabled – this ensures that if the O2 is
very high, or very low and all the cells agree, then
the O2 is probably very high or low accordingly.
4. If all cells are enabled and have
no faults, then each cell is checked to see how many
other cells it is within 0.20bar of.
a. If all cells are within 0.20bar of each other,
then all cells will be enabled.
b. If two cells are within 0.20bar of each other and
one cell is not, then the cell that is not within
0.20bar of the others will be disabled.
c. If no cells are within 0.20bar of each other, then
all cells will be kept enabled.
5. If all 3 cells are disabled with
the same fault at this stage, then all will be re-enabled.
6. All enabled cells are then used
in the PO2 averaging. Any cell disabled in these calculations
will have a D or N shown against it in the O2 sensor
Screen.
7. Examples:
a. Cell 1 = 0.5bar, cell 2 = 0.60bar, cell 3 = 0.70bar.
All cells used (rule 4a)
b. Cell 1 = 0.3bar, cell 2 = 0.60bar, cell 3 = 0.70bar.
Cells 2 and 3 only used (rule 4b)
c. Cell 1 = 0.3bar, cell 2 = 0.60bar, cell 3 = 0.14bar.
Cell 1 and 2 only used (rule 2)
d. Cell 1 = 0.3bar, cell 2 = 0.60bar, cell 3 = 0.90bar.
All cells used as no obvious fault in any single cell
(rule 4c)
To
Purchase cells please use the contact page to give
us a call
|
|
|
|
|
|
|
|
|
|
|
