User manual

Poseidon MKVI User Manual
Chapter 2
Page 45
Figure 2-10.
Test 50 – Closed-Circuit mouthpiece position.
IMPORTANT:
Do NOT adjust the mouthpiece position again after completing Test
50, until the pre-dive tests have completed. 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 congured to be. The
system will start by injecting pure oxygen directly on the primary oxygen sensor for 20 continu-
ous seconds, thereby ooding 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 solenoidvalve. In doing so, this test both calibrates the
sensors, and conrms that the correct gas mixtures are in the respective cylinders.
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 by the
“Open-Circuit” icon on the Primary Display. At Test 50 (Figure 2-10), the icon disappears from
the Display, the letters “CC” ash in the upper left corner of the LCD, the HUD vibrates, the
HUD and battery LEDs ash, 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.