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35
VI
Diving with more than one gas mixture
VI UWATEC
®
Smart dive computers
VI
No change of gas
mixture:
Belated change of
gas mixture:
Submerging again
after a change
of gas mixture:
%
DECO STOP
4 sec
oxygen fraction of tank 1
%
DECO STOP
NO STOP
LEVELSTOP
change of gas mixture
confirmed
Changing the gas mixture
After immersion, TEC automatically selects gas mixture 1.
If during the ascent a diver reaches the depth
requiring a change of gas mixture (MOD gas mix-
ture D or 2), the imminent change is brought to
the diver’s attention by an audible attention signal
and the flashing of the tank symbol of the new
gas mixture, both lasting for 30 seconds.
Procedure: • switch to the regulator with the new gas mixture and start brea-
thing
• confirm the change by pressing and holding
(long beep)
within 30 seconds. The tank symbol will stop flashing.
If a diver fails to confirm the change of gas mixture, TEC will continue to cal-
culate with the previous gas mixture and adapt the decompression calculation
accordingly.
A diver can catch up on a required change of gas mixture until he reaches the
surface. By quickly pressing
the tank symbol of the new gas mixture will
start flashing.
Switch to the regulator with the new gas mixture and start breathing. Confirm
the change by pressing and holding
. The tank symbol will stop flashing
and the decompression calculation will readjust accordingly.
If after a change of gas mixture the Maximum Operating Depth (MOD) of the
current mixture is exceeded, the ppO
2
max warning will appear. ->20
Change to the gas mixture suited for this depth and select the appropriate tank
symbol or rise to the Maximum Operating Depth of the current gas mixture.
Failure to do so can result in oxygen poisoning.
WARNING
…
Examples for clarification of RBT and change of gas mixtures
The following figures show a dive profile and the display of various TECs in the following settings:
1. Start of ascent:
the TECs have different decompression prognosis, indicating the benefit of the travel
and/or decompression gases. However, the RBT is the same for all four, as it relates to tank 1 only. It
indicates that starting the ascent within the next three minutes the diver will have enough gas for the
ascent and the decompression obligations shown on TEC-1. At RBT=3 or less, the ascent arrow is sho-
wing: TEC suggests that the diver starts the ascent.
2. Slightly below MOD for 50% mix (MOD=22m):
The slow ascent has caused significant build-up of
decompression obligations. There is a marked difference in ascent times, indicating the benefit of
decompressing at high oxygen percentage.
3. Above MOD for 50%, missed switch:
TEC-2 adjusts its decompression prognosis to be same as TEC-
1. TEC-4 adjusts its decompression prognosis to be the same as TEC-3.
4. Again below MOD for 50%:
TEC-2 and TEC-4 once again show credit for the presence of the 50%
mix in their calculations.
5. Above MOD for 50%, switch carried out:
TEC-2 and TEC-4 show the tank pressure in the 50% tank.
The RBT agrees because also in TEC-4 it considers the 50% tank will be used to finish the dive. TEC-1
and TEC-3 are not receiving any signals from the transmitter on the 21% tank and show “- - -“.
6. Slightly below the MOD for 100% mix (MOD=6m)
: During the slow ascent from 22m, TEC-2 using
50% oxygen has caught up on the decompression schedule of TEC-3, which is still using 21% oxygen
but gives credit for the upcoming switch to 100% oxygen.
TEC-1:
set to 21% (tank 1)
TEC-2:
set to 21% (tank 1) and 50% (tank D)
TEC-3:
set to 21% (tank 1) and 100% (tank D)
TEC-4:
set to 21% (tank 1), 50% (tank 2) and
100% (tank D)
