Cochran GEMINI User manual

www.divecochran.com
Cochran
GEMINI
With
Monitor WU
Owner’s Manual
English –Imperial
Ver: Gemini.Mon.1.50
Manual Part Number: 4300812
For your records, please fill in the following:
Serial Number of the Tank Unit: _______________________________
Serial Number of the Wrist Unit: _______________________________
Your Name: _______________________________________________
Your Contact: _____________________________________________
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Purchase Date: ____________________________________________
Purchase Place: ___________________________________________
Address: __________________________________________________
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1
Product Introduction: Your GEMINI Dive Computer from Cochran Undersea Technology
is one of the most advanced instruments made for this application. The GEMINI consists of
two component parts, the Tank Unit (TU) and the Wrist Unit (WU), the TU contains the High
Pressure Transducer Assembly, Depth/Altitude Sensor, and the computer‟s electronics.
The TU performs the time-depth calculations and is where the detailed dive statistics and
profiles are stored. The GEMINI incorporates more user-programmable functions than any
other dive computer made, yet is one of the simplest to use. You may enter personal
preferences, dive site, and condition-specific settings. The GEMINI calculates these factors
in the background, displaying to you, the diver, the critical information you need, in an easy
to comprehend display. The GEMINI computers are one of the first dive computers to
implement a Training Mode, which enables the computer to record and store data in
shallow water training environments (swimming pools, shallow lakes, etc.). To get the
safest and most effective use of this instrument, it is important that the user fully
understand the product. Please read and understand this entire manual and know the
principles and practice safe diving before using this device. By using the GEMINI, the diver
specifically acknowledges that he has been adequately and thoroughly trained and certified
to engage in diving by a professional, competent, recognized training agency.
This Manual is divided into the following Sections:
Section Page
Operation as an Air/Single Blend Nitrox Dive Computer 1
Clock Operation 13
Touch Programming 13
Warnings 24
Oxygen & PO2 factors 26
Gas Blend Switching 28
Constant PO2 Operation 35
Configurable Items 49
Specifications and Maintenance 50
Liability, and Warranty 59
Itemized Index and Subjects 64
INSTALLATION: The Tank Unit (TU) high-pressure sensor installs into a high-pressure
port of your first-stage regulator. Your Authorized Dealer should do this at the time of
purchase. Should you choose to install the TU yourself:
1. Remove your current high-pressure hose or the high-pressure plug from your
first stage regulator.
2. Lightly lubricate the sensor O-ring only with a lubricant approved for use with
Enriched Air Nitrox equipment. DO NOT USE SILICONE GREASE.
3. Screw the sensor, HAND TIGHT, into the first-stage high-pressure port
4. Using a Scuba Tool, or thin 9/16" open-end wrench, snug the high-pressure
transducer connection taking caution to not over tighten.
CAUTION: DO NOT use tools such as vise-grips or channel lock pliers.
These tools can damage the transducer and such damage is not covered by
the limited warranty.
CAUTION: DO NOT use your hand to tighten the high-pressure connection.
This procedure should only be accomplished by using the appropriate tool
placed over the metal nut of the high-pressure connection. It must not be
over tightened.

2
With the first stage properly attached to a filled SCUBA cylinder, slowly open the cylinder
valve. Once the valve has been opened, listen to the TU‟s high-pressure connection for
any escaping gas. If possible, completely immerse the tank and regulator in water to see if
bubbles form around your connection. If any gas leak is seen or heard, immediately turn
the gas off by closing the cylinder valve and take the entire regulator system to the place
where you purchased your GEMINI.
The Tank Unit (TU) clips to a low-pressure hose close to the first-stage, it is recommended
that the TU be located on the divers left side. When clipping the TU onto the low-pressure
hose, a rolling motion will provide better results rather than pushing the TU straight down
onto the hose. The Wrist Unit (WU) may be worn on the wrist or attached to your
Buoyancy Control Device with the optional retractor.
Figure 49
Tank Unit Touch Contacts
TANK UNIT TOUCH CONTACTS: The Contacts are used to let the user command the
unit to do a number of functions, communicate with a PC for extracting information or
configuring the unit, and determining water conductivity. When Contacts 1 & 2 are shorted,
the GEMINI TU can detect the difference between wet fingers, metal objects, fresh water,
salt water, and a PC interface cable.

3
TURNING ON THE GEMINI TU: The TU will automatically activate when it senses a
cylinder pressure greater than 200 psi. Bridging touch Contacts 1 and 2, which are located
on the underside of the tank unit (see Figure 51), with wetted fingers for two seconds will
manually activate it also.
NOTE: If the TU is activated by cylinder pressure it will issue three beeps, if it is activated
by the touch contacts it will issue five beeps.
WRIST UNIT SIDE CONTACTS:
CONTACT #2
CONTACT #1
CONTACT #3
The Contacts are used to let the user command the unit to do a number of functions, or
obtain information and/or configuring the unit. When Contacts 1 & 2 are shorted, the
GEMINI WU can detect the difference between wet fingers, metal objects and water.
TURNING ON THE GEMINI WU: Although the GEMINI WU automatically turns on when it
is submerged in water, it is STRONGLY recommended that wetting two fingers and
simultaneously touching Contacts 1 and 2 for two seconds manually power the unit up.
This allows the diver to ensure that the unit is operating correctly and has adequate battery
capacity prior to entry. The WU will receive information from the TU from approximately 48
inches; the actual distance will vary depending on the orientation of the WU to the TU.
Once activated and in communications with the TU, the unit will remain on until the TU
turns off, usually 60 minutes. When the WU is beyond the communication range of the TU
the WU‟s display will flash. When the WU is back in communication with the TU the display
will cease flashing. Notice that when Contacts 1 & 2 is first bridged, a short beep is issued
which indicates that the unit is recognizing the touch. If the WU is activated and not in
communications with the TU, it will turn off after 15 minutes.
The GEMINI WU will not turn on if the battery voltage is less than 2.0 volts, or a fault is
detected during the self-test.
Bridging the wrist units touch contacts one can activate the WU and two with wetted
fingers. While the WU will activate upon entering the water it is highly recommended that
the WU be turned on manually as part of the divers pre-dive check.

4
As the GEMINI WU & TU first recognize a turn-on command, it begins a “Diagnostic”
function where many aspects of the system will be exercised and tested. This procedure
takes about five seconds and an audible beep is issued each second as certain tests are
successfully completed. During this time, all of the segments in the display are turned on
so that the user can confirm their operability. Should a test indicate a malfunction or
marginal test, the unit will turn back off again. The user should ensure that all of the display
segments are on and operating correctly.
CAUTION: After the WU is activated the “SERVICE” legend will be illuminated, this
indicates that the WU‟s memory is being updated with information from the
Tank Unit. It may take several minutes for this process to be completed. A dive
should not be started while the “SERVICE” legend is illuminated.
TURNING OFF THE GEMINI: After the Post Dive Interval following a dive, the GEMINI TU
will remain on for one hour before automatically entering its "Sleep Mode". During the
Sleep Mode, all calculations continue but the display is off. This is a power saving feature
of the GEMINI. The unit will continue calculating Surface Interval, compartment off gassing
as required, and any changes in altitude as it affects Nitrogen Loading. The current
Surface Interval and PreDive Predictions can be viewed by reactivating the units.
You cannot manually turn the TU off. The TU will turn off:
1. After 60 minutes if no tank pressure is sensed and no dive is made.
2. After all 16 half-time compartments are completely off-gassed on repetitive dives.
NOTE: The GEMINI TU will not enter the sleep mode or turn off as long as cylinder
pressure is being applied to the TU.
You cannot manually turn the WU off. The WU will turn off:
1. After 15 minutes after the TU and no dive is made.
2. If in a dive and the WU looses communications with the TU permanently. The WU
will turn off 60 minutes after the lose of communications. The touch Contacts are
disabled during this time.
MAIN GEMINI OPERATING MODES:
Surface Interval (No Nitrogen Residual)
Surface Interval (With Nitrogen Residual)
Dive Mode (Normal No Deco)
Decompression Mode
Post Dive Interval
Touch Programming
SURFACE INTERVAL –AIR ONLY/SINGLE GAS NITROX:

5
After completion of the Self-Diagnostic mode or after the Post Dive Interval following a dive,
the GEMINI enters the Surface Interval. This period has two screens, a Primary and an
Alternate. To switch to the Alternate Screen just tap once firmly on the face of the unit.
The Primary Screen displays, if applicable; current Surface Time, the previous dive‟s
Maximum Depth, the Current FO2 (normal Blend) oxygen percentage, Cylinder Pressure,
Gas Supply Time, Current Gas Consumption, and Altitude. The Alternate Screen displays
the previous dive‟s Bottom Time, Dive of Day number; current Time to Fly, current
calculated CNS and OTU value bar graphs. Figure 2 & 2a shows the display with no
residual Nitrogen (a clean Dive). Figure 4 & 4a shows the display with residual Nitrogen (a
repetitive dive). Figure 3 shows the alternate screen with no residual Nitrogen and Figures
5 & 5a with residual nitrogen.

6
The “Blend Identifier” displays the Oxygen percentage that the computer is using in its no-
decompression / decompression calculations. When the unit is on the surface it will display
„OF21‟ to indicate that the computer is calculating out-gassing using normal (Normonic) air
(21%).
“Surface Time” starts at zero after a dive and begins counting minutes. If the computer
shuts off and is turned on with Nitrogen residual left, the Surface Time continues to count.
If the computer shuts off and is turned on with no Nitrogen residual left, the Surface Time
will be zero.
“Dive of Day” starts at zero and increments after each dive regardless of the calendar day.
When there is no remaining Nitrogen residual, the Dive of Day is set to zero and the
computer is referred to as a „clean‟ system.
“Time to Fly” is displayed as the number of hours remaining until the nitrogen residual
reaches zero plus a twelve-hour safety factor. Flying is not recommended until Time to Fly
reaches zero.
“Barometric Altitude” is indicated in six ranges via the Ascent Rate Bar Graph as follows
(Altitude compensation is seamless up to 15,000 feet above sea level). The six ranges are
for display purposes only: The GEMINI actually senses and computes extremely small
altitude changes and hence, is called “Seamless”. The term “Barometric Altitude” is used
instead of just “Altitude” because the GEMINI measures Barometric Pressure to determine
Altitude. Barometric Altitude can vary from actual Altitude by over +/- 1000 feet! What is
important to the body when diving is Barometric Altitude.
0 Bars sea level to 2,500 feet 1 Bar 2,500 to 5,000 feet
2 Bars 5,000 to 7,500 feet 3 Bars 7,500 to 10,000 feet
4 Bars 10,000 to 12,500 feet 5 Bars 12,500 to 15,000 feet

7
The altitudes indicated are for reference only.
They do not appear on the WU display.
DIVE MODE –AIR ONLY/SINGLE GAS NITROX:
Whether in the Surface Mode, PreDive Prediction Mode, Programming Mode or the
Logbook Mode, The GEMINI will automatically enter the Subsurface Mode when the dive
computer senses a depth greater than five feet and is exited when the dive computer
senses a depth less than five feet.
NOTE: Remember, do not start a dive while the “SERVICE” legend is illuminated.
On the Primary Screen the Surface time will be replaced with the current bottom time,
Blend #1 set point is replaced with the calculated PO2value. Maximum Depth will be
replaced with current Depth, displayed in one-foot increments. Bottom Time will begin
once the GEMINI WU senses that the diver has descended below five feet and continues
until the diver has ascended above three feet. The maximum Bottom Time displayed is 9
hours 59 minutes.

8
The Alternate Screen will display the current FO2value that the unit is using in its NDC
calculations, the current CNS and OTU values and the Maximum Depth. (Figure 14 & 14a)
A Depth Alarm, which can be set to warn the diver should a certain depth be exceeded, is
set at 130 feet from the factory. The Depth Alarm issues an audible alarm and the
“WARNING” legend and Depth Digits will flash on and off for five seconds and be repeated
ever two minutes while below the user set depth. The depth alarm is disabled if in the
Decompression Mode since flashing depth digits have another meaning in this Mode.
The maximum depth achieved on the current dive is shown as “MAX DEPTH”. This is
updated once per second.
“REMAIN TIME” (NDC) is the remaining time (in hours and minutes) that the diver can stay
at the current depth without requiring decompression. A “Two Minute Warning” will be
issued when this time reaches two minutes or less. An audible alarm will be issued and the
“WARNING” legend and “REMAIN TIME” digits will flash. By immediately ascending to a
shallower depth, the diver may avoid a required decompression stop.
“REMAIN TIME” (O2) is the remaining time (in hours and minutes) that the diver‟s Gas
supply will last until the User Set Reserve is reached (normally 500 psi). A “Warning” will
be issued when this time reaches zero. An audible alarm will be issued and the
“WARNING” legend and “REMAIN TIME” digits will flash.
Temperature is measured for two purposes. One is to compensate the Depth Transducer
for Temperature variations. The other is to compensate the Nitrogen algorithm for changes
in Temperature that may affect the body. Both of these purposes require that the
Temperature be very slow reacting, just like the Depth Transducer and the body. This
slow-reacting Temperature is what is displayed. For Temperature effects on the body, the
amount of compensation can be set from NORMAL to REDUCED with the Analyst® PC
software Interface, if the diver is using a good dry-suit in cold water. Temperature