Technical information

38
3. Meridian as a dive computer
SCUBAPRO MERIDIAN
3. Meridian as a dive computer
pressure oxygen, and can vary in terms
of the exact level of partial pressure they
happen at. It is commonly accepted that
partial pressures up to 1.4 bar are tolerable,
and several training agencies advocate
maximum oxygen partial pressures up to
1.6 bar.
Long exposure effects to oxygen partial
pressures over 0.5 bar due to repeated and/
or long dives. These can affect the central
nervous system, cause damage to lungs or
to other vital organs. Long exposures can
be divided to more severe Central Nervous
System effects and less dangerous long
term Pulmonary Toxicity effects.
Meridian treats high ppO
2
and long
exposure effects in the following ways:
Against sudden effects: Meridian has
an MOD alarm set for a user-defined
ppO
2
max. As you enter the oxygen
concentration for the dive, Meridian shows
you the corresponding MOD for the defined
ppO
2
max. The default value of ppO
2
max
from the factory is 1.4bar. This can be
adjusted to your preference between 1.0
and 1.6bar. It can also be turned OFF.
Please refer to chapter 3.2 Gas settings
for more information on how to change this
setting.
Against long exposure effects: Meridian
“tracks” the exposure by means of the
CNS O
2
clock. At levels of 100% and
higher there is risk of long exposure effects,
and consequently Meridian will activate an
alarm when this level of CNS O
2
is reached.
Meridian can also warn you when the CNS
O
2
level reaches 75% (see section CNS
alarm). Note that the CNS O
2
clock is
independent of the value of ppO
2
max set
by the user.
The CNS O
2
clock increases when the
oxygen partial pressure is higher than
0.5bar, and decreases when the oxygen
partial pressure is lower than 0.5bar.
Hence, while on the surface breathing air
you will always be decreasing the CNS O
2
clock. During the dive, the depth at which
0.5bar is reached for various mixes is as
follows:
Air: 13 m / 43 ft
32% 6 m/20 ft
36%: 4m/13ft
F
NOTE:
• the O
2
concentration of Gas d can
only be set to a value higher than the
O
2
concentration for Gas 1.
• O
2
concentration setting shown “- -“
means that gas is disabled.
• Meridian requires that the MODs of
Gas 1 and Gas d be at least 3m/10ft
apart.
• Setting the ppO
2
max value to OFF
applies to Gas 1 only. Gas d is
always limited to a maximum value of
ppO2max of 1.6bar.
• For oxygen concentrations of 80%
and higher, the ppO
2
max is fixed at
1.6 bar and cannot be changed.
• The MOD for Gas d is the switch depth
for that gas. This is what Meridian
uses for its calculation, warnings and
suggested switch point.
• When diving with more than one gas
mixture, the Nitrox reset time function
(described in section 2.3.5) has the
following effect:
• Gas 1 is set to 21%
• Gas d is set to OFF.
3.10.1 Diving with two gas mixtures
Meridian is equipped with the ZH-L8
ADT MB PMG algorithm. PMG stands for
Predictive Multi Gas, meaning that when
you program more than one gas mixture,
Meridian will predict the switch to the
higher oxygen concentration gas at the
depth that you specified and alert you at
all times with a decompression schedule
comprehensive of both gas mixtures that
you programmed. In other words, you
get full credit at any point during the dive
for all the extra gas that you are carrying
with you. At the same time Meridian can
also show you what the decompression
schedule would be if you were to finish
the dive using only the gas mixture that
you are currently breathing from, so that
you can be prepared in the event that