Poseidon SE7EN User Manual
Appendix 3 Page 99
Figure 2-10.
Test 50 – Closed-Circuit mouthpiece position.
IMPORTANT:
Do NOT adjust the mouthpiece position again after completing
Test 50, until Test 54 prompts for switching back to OC mode. In
order to complete Test 53 (oxygen sensor calibration) successfully,
the mouthpiece must remain in the Closed-Circuit (CC) position.
Oxygen sensor calibration (Test 53)
Test 53 (Figure 2-11) calibrates the oxygen sensors. Part of this test is to ensure that the
oxygen supply is really oxygen, and that the diluent supply is what it is configured to be. The
system will start by injecting pure oxygen directly on the primary oxygen sensor for 20 continu-
ous seconds, thereby flooding the entire oxygen sensor chamber with enough oxygen to also
calibrate the secondary sensor. The use of oxygen to perform Test 49 (PPLT) helps this test
complete properly, because the breathing loop will have already been pre-charged with
oxygen. After the calibration constants for oxygen are established, the system then injects
diluent (air) via the diluent calibration solenoid valve. In doing so, this test simultaneously cali-
brates the sensors, confirms the correct gas mixtures are in the respective cylinders, and
confirms that the calibration solenoid valves are mechanically functional.
This procedure can be followed on the display where graphs are plotted.
Figure 2-11.
Test 53 – Oxygen Sensor calibration.
Closed circuit mouthpiece position (Test 50)
The mouthpiece should have been left in OC position following Test 43, as indicated in the
information field. At Test 50 (Figure 2-10), the information text “Switch mouthpiece to Closed
Circuit” appears, the HUD vibrates, the HUD and battery LEDs flash, and the audio speaker
sounds. All of this indicates that the mouthpiece should be placed in the Closed-Circuit (CC)
position. As soon as the mouthpiece is in the Closed-Circuit position and is detected by the
HUD, the test will pass. The system allows 2 minutes for this test to be completed, before
timing out.
As with the Open-Circuit mouthpiece position (Test 43), if the mouthpiece appears to be in the
closed-circuit position, but Test 50 does not pass, then make sure that the mouthpiece switch
is fully in the CC position. If the test still will not pass, then make sure the HUD is positioned
correctly in the mouthpiece, and is not twisted or otherwise adjar from its proper position. If no
amount of repositioning of the mouthpiece lever or HUD allows the system to pass Test 50,
then contact an authorized Poseidon Service Center.
IMPORTANT:
While Test 49 is being conducted, be careful not to manipulate
the counterlungs too much, or do anything that might affect
the internal loop pressue, independently of the gas injected by
the metabolic solenoid valves. The test can be performed while
wearing the rebreather, as long as there is not too much motion
or instability of the counterlungs. It’s recommended that you don’t
let the mouthpiece and loop rest against the counter lungs during
test 49, as this might cause the test to fail.
This test is by far the most important of all the pre-dive tests, as it is determining whether the
oxygen sensors are providing true values for the partial pressure of oxygen (PO
2
). Failure of this
test can occur for a number of reasons, all of which the user should be familiar with. Most causes
relate directly to the oxygen sensors themselves – either bad or aged sensors failing the test, or
the presence of condensate on the sensors from a prior dive. If Test 53 fails persistently, verify
that the gas cylinders are connected to the correct regulators, and make sure they contain the
correct gas mixtures. If the test continues to fail, one or both of the oxygen sensors may need
replacing. When changing oxygen sensors, it’s very useful to keep track of which oxygen sensor
was placed in which position, by noting the individual oxygen sensor serial numbers.
