Shearwater GF Computer Manual de usuario
Shearwater GF
Computer
DANGER
This computer is capable of calculating deco stop requirements. These calculations
are at best a guess of the real physiological decompression requirements. Dives
requiring staged decompression are substantially more risky than dives that stay well
within no-stop limits.
Diving with rebreathers and/or diving mixed gasses and/or
performing staged decompression dives and/or diving in overhead
environments greatly increases the risk of scuba diving.
You really are risking your life with this activity.
WARNING
This computer has bugs. Although we haven’t found them all yet, they are there. It is
certain that there are things that this computer does that either we didn’t think about,
or planned for it to do something different. Never risk your life on only one source of
information. Use a second computer or tables. If you choose to make riskier dives,
obtain the proper training and work up to them slowly to gain experience.
This computer will fail. It is not whether it will fail but when it will fail. Do not depend
on it. Always have a plan on how to handle failures. Automatic systems are no
substitute for knowledge and training.
No technology will keep you alive. Knowledge, skill, and practiced procedures are
your best defense. (Except for not doing the dive, of course.)
Overview
Features
•Depth, time and oxygen sensor display
•Buhlmann algorithm with gradient factors conservatism
•Imperial and metric displays
•Two set points, each of which can be set between .4 and 1.4
•A menu system that adapts to diving status
•Automatic turn off after 30 minutes on the surface
•Depth sensor to rated to 450 feet
•Any combination of oxygen, nitrogen, and helium
•Open and closed circuit, switchable during a dive
•5 CC and 5 OC gasses
•Gasses can be changed and added during a dive
•CNS tracking
• No lockout
• Automatic setpoint switching (configurable)
• Battery life of over 500 hours of diving or years of standby
• Backup battery to allow battery change without losing tissues
Decompression and Gradient Factors
The basic decompression algorithm used for the computer is Buhlmann ZHL-16C. It
has been modified by the use of Gradient Factors that were developed by Erik Baker.
We have used his ideas to create our own code to implement it. We would like to give
credit to Erik for his work in education about decompression algorithms, but he is in no
way responsible for the code we have written.
The computer implements Gradient Factors by using levels of conservatism. The
levels of conservatism are pairs of number like 30/85. For a more detailed explanation
of their meaning, please refer to Erik Baker’s excellent articles: Clearing Up The
Confusion About “Deep Stops” and Understanding M-values. The articles are readily
available on the web. You might also want to search for “Gradient Factors” on the
web.
The default of the system is 30/85. The system provides several settings that are
more aggressive than the default.
DO NOT USE THIS SYSTEM UNTIL YOU ARE SURE
YOU UNDERSTAND THE SETTINGS.
Graph from Erik Baker’s “Clearing Up The Confusion About Deep Stops”
Display
The display has five areas. There are two title areas
and three data display areas.
Across the top line is the title for the first row of
information. This area only changes during the
display of the dive log. The first data area shows
depth, battery warning, dive time, ascent rate, first
stop depth, and first stop time. It is showing a depth
of 34.7 meters, a low battery alarm, 15 minute dive
time, a 6 meter per minute ascent rate, and a stop at
24 meters for 1 minute.
The low battery indicator flashes when it is on.
The ascent rate indicator shows 6 levels of ascent rate. Each block represents either
10 fpm or 3 mpm. When the ascent rate is greater than 6 units, the whole block will be
filled in, and it will flash.
If you are above the indicated stop depth, the stop depth will flash.
The next line has the three O2 sensor readings. They will show in PPO2 normally, but
if both buttons are pushed together, the display will switch to mV for a few seconds. If
a sensor is voted out, it will display the current value, but it will flash and the value will
not be considered in the average PPO2.
The next area is the title for the bottom line. This title changes frequently in the menu
system to provide additional information about the bottom line. The last line shows
that the computer is in closed circuit (CC) mode with a gas containing 21% oxygen and
0% helium.
If there is a gas programmed in the current mode (OC or CC) that would normally be
used at the current depth, the system will flash the gas contents to remind you to either
switch gases, or remove the gas if you aren’t using it.
The no decompression limit (NDL) is zero since we are in decompression, and the
time to surface (TTS) is 15 minutes.
The computer works in both metric and imperial for depths and temperatures. The
depth shows a decimal point when the depth is between 0 and 99 meters. It shows no
decimal point if the display is set to feet.
Buttons
Two buttons control the system. The functions can be summarized as follows:
The left button (MENU) is used to scroll through the menu or increment the display.
When the “Switch Setpoint” menu item is displayed, MENU will move to the “Select
Gas” menu item.
In the “Select Gas” menu, MENU increments the gas number.
The right button (SELECT) is used to accept the current choice. In some cases that
means save the current value, in others, it means execute the command. For
example, when a gas is displayed in the “Select Gas” menu, SELECT will select the
displayed gas. When the “Switch Setpoint” menu is displayed, SELECT will switch the
setpoint.
There are several other button pushes that the system recognizes.
To turn the computer on, press MENU then immediately press SELECT.
When the system is not in a menu, pushing SELECT will bring up information displays
with various dive status information.
Pushing both buttons at any time will change the PPO2 display to a millivolt (mV)
display. The mV display is not subject to calibration. It displays the raw mV on the
sensor without regard to whether the sensor is calibrated or whether is has been voted
out.
MENU
•In the menu system, the menu button moves to the next menu or increments
the current number
•When the computer is off, pressing MENU and then immediately pressing
SELECT will turn the computer on.
SELECT
•In the menu system, the confirm button saves the current value or executes the
command.
•Out of the menu system, the confirm button brings up information displays.
BOTH BUTTONS
•Pushing both buttons at any time changes the PPO2 display to the mV display.
The computer works in both metric and imperial for depths and temperatures. The
depth shows a decimal point when the depth is between 0 and 99 meters. No decimal
point is shown if the display is set to feet or if the depth is greater than 99 meters.
Menu
The system is designed to make the selection of the common operational functions
while diving easy. The menu selections are separated into two sets. The “Operation”
menu is to provide easy access to commonly used functions. The “Setup” menu is to
change system settings.
The system will continue to read the sensors and update the sensor display while you
are in the menu system.
If no buttons are pushed for a few minutes, the menu system will time-out. Anything
that had been previously saved will be retained. Anything that was in the middle of
editing will be discarded.
The menu structure is below:
•Turn Off
•Calibrate
•Switch Setpoint
•Select Gas
•Switch to Open Circuit
•Dive Setup
oEdit Low Setpoint
oEdit High Setpoint
oDefine Gasses
oExtenal PPO2 On/Off
•Dive Log
oDisplay Log
oUpload Log
•System Setup
oAuto SP Switch
oSet Conservatism
oSwitch to Feet/Meters
oSet Backlight Time-out
oSet Backlight Brightness
oSet Time
oSet Date
Some menu items are not applicable in some operating modes.
The status screens are:
•Max depth, CNS, setpoint and average PPO2
•Diluent PPO2 and Conservatism setting
•Water temperature, loop temperature and voltage
•Date and Time
•Surface interval
•Serial Number, Model, and Version
Basic Setup
Before using the computer there are several things that need to be configured. This is
not an exhaustive list of the pre-requisites for diving the system, but a suggestion of
key tasks.
In the System Setup menu, select the Auto SP Switch parameters, and set the units to
your preference.
Enter the gasses that you will use for the closed circuit portion of your dive, and enter
the gasses for open circuit bailout.
The system will use the closed circuit gasses that are available in the order of oxygen
content during the Time To Surface (TTS) calculation. The system will use to the next
available gas that has a PPO2 of less than 1.0 for closed circuit diving.
If the system is switched to open circuit during a dive, the system will calculate the
TTS based on the configured open circuit gasses that are available. It will use the next
available gas that has a PPO2 of less than 1.6 for open circuit diving.
NOTE: These gasses are used automatically only for TTS calculations. The gas used
to calculate the current tissue load and the current ceiling is always the gas actually
selected by the diver.
Calibrate the oxygen sensors.
Example Dive
This is an example of the displays that might be seen on a dive.
This example shows a complicated dive with multiple CC gasses and multiple OC bail-
out gasses. A normal, single diluent CC dive wouldn’t have any button pushes at all,
so there wouldn’t be much to show.
The first step is to calibrate. Since we are on the surface and not diving, MENU will
bring up “Turn Off”, then “Calibrate.” Once the loop is flushed with oxygen, CONFIRM
will bring up the confirmation display, and another CONFIRM will calibrate.
Next, we check the closed circuit gasses that we have programmed.
Entering the gas selection function by pressing CONFIRM with the “Select Gas” menu
item showing, will display the first CC gas that is available. MENU will increment to the
next gas available. Another MENU takes us back to the “Select Gas” menu item.
Those are the only two gasses configured.
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