How Does Pdis Work; Special Considerations When Diving With More Than One Gas Mixture; Diving With Pdis - Uwatec Aladin H User Manual

3.9.2

How does PDIS work?

The mathematical decompression model
in the Aladin H, called ZH-L16 ADT MB
PMG, tracks your decompression status
by dividing your body into 16 so-called
compartments
following the uptake and release of
nitrogen in each with the appropriate laws
of physics. The various compartments
simulate parts of your body such as central
nervous system, muscles, bones, skin and
so on.
The depth of the PDI stop is calculated as
that at which the leading compartment for
the decompression calculation switches
from on-gassing to off-gassing, and the
diver is advised to perform a 2-minute
stop above the displayed depth (this is the
opposite of a decompression stop, where
you are asked to remain just beneath the
displayed depth). During this intermediate
stop, the body is not taking up any more
nitrogen in the leading compartment, but
rather releasing nitrogen (though under
a very small pressure gradient). This,
combined with the relatively high ambient
pressure, inhibits bubble growth.
It should be noted that the 4 fastest
compartments, up to 10 minutes half-
times, respectively, are not considered
for the determination of the PDI stop
depth. This is due to the fact that these
compartments are only "leading" for very
short dives, for which an intermediate stop
is not required at all.
F
NOTE: The PDI stop is not a mandatory
stop and it is NOT a substitute for the
3-5 minute safety stop at 5m/15ft.
Even when performing a PDI stop, you still
MUST perform a safety stop at 5m/15ft for 3
to 5 minutes. Performing a 3 to 5 minute stop
at 5m/15ft at the end of any dive remains the
best thing you can do for yourself!
34
and mathematically
WARNING
3.9.3 Special considerations when
diving with more than one
gas mixture
Switching to a higher oxygen concentration
mix during the dive influences the PDI stop.
This needs to be accounted for, in line with
the predictive nature of multi-gas handling
in ZH-L16 ADT MB PMG.
When diving with more than one gas
mixture, the Aladin H displays the PDIS
depth according to the following rules:
• If the PDI stop calculated for the bottom
mix (gas 1) is deeper than the switch
depth, than this calculated value is
displayed.
• If the PDI stop calculated for gas 1
is shallower than the switch depth to
gas d, then the displayed PDI stop is a
function of gas d.
In case of a missed gas switch, the Aladin
H reverts to the PDI stop for the actively
breathed mix.
3.9.4

Diving with PDIS

F
NOTE: To use the PDIS feature, you
must enable PDIS (see chapter:
Settings, section: Setting PDIS).
PDI Stop depth PDIS icon
When the calculated PDI stop is deeper
than 8m/25ft, the Aladin H shows it on
the display and continues to do so until
you reach the displayed depth during
an ascent. The displayed value changes
during the dive as the Aladin H tracks the
uptake of nitrogen in the 16 compartments
and updates the PDIS depth accordingly to
reflect the optimum at all times.
ALADIN H USER MANUAL