COMPUTER USE

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THE IST GP4000+ COMPUTER

To Set the GP4000+ For EAN (Nitrox)

 

PARTIAL OVERVIEW OF THE COCHRAN EMC-14 COMPUTER

The metal buttons at the bottom of the display screen are numbered 1-2-3 from left to right. Touching the buttons with wet fingers will cause the computer to function one way. Touching the buttons with a metal object will cause the computer to function differently. Turn the Cochran EMC-14 on by holding wet fingers on buttons 1 and 2 for about 3 seconds.

After the computer runs through its display and the computer checks it will enter the Surface Mode. There are 2 screens that alternate every 8 seconds. One screen is the top one below and the second screen consists of the bottom 2.

The first screen (above) is mostly self-explanatory. However, the altitude is displayed in small bars. If there are no bars the altitude where the EMC-14 was turned on was below 2500'. Otherwise the bars displayed mean the following:

The second screen has 2 phases. If the clock has been activated by the dealer (or the Analyst Software) the current time will be displayed and a few seconds later the OTU will be displayed. On the 2 screens the FO2 will be displayed if that function has been activated by the dealer (or Cochran). (The meaning of Central Nervous System Toxicity (CNS), Oxygen Tolerance Units (OTU), and The Fraction of Oxygen in the breathing gas (FO2) is explained below.)

The battery voltage is 32 when the battery is new. When it drops to 24 (or 2 years have passed since the computer was first used) it is time to replace the battery. At 20 the EMC-14 will not operate. When the battery is remove all past data will be lost!

THE DIVING MODE OF THE EMC-14:

When you descend below 5 feet the EMC-14 will enter the diving mode and start recording all the underwater information gathered during the dive such as the depth, maximum depth, nitrogen in-gassing and out gassing, oxygen levels, water temperature. The computer remains in the Surface Mode until the descent is made. In that way surface activities do not become part of the dive profile. When the computer enters the Dive Mode the screen will appear as follows:

The Main Screen While Diving

The Alternate Screen While Diving

The Alternate Screen Time Alternates With The OTU. (Note: The Cochran graphic should have 22%, not 21%, in the parentheses!)

The Ascent Bars have the following meanings:

If the diver comes within 2 minutes of entering the Decompression Mode the EMC-14 will display that as follows:

Above, the diver is at 22' and should stop at 20' for 12 minutes.

The above is the Alternate Screen, 2 phases. It is in the Decompression Mode as well.

Above the diver has missed decompressing underwater. On the surface the 0 depth will flash until the decompression gas is eliminated. At that point the 10 minute surface interval will begin. If the diver enters the water before the 10 minutes is up the computer will assume the diver is still on the first dive.

CNS TOXICITY: PADI recommends that the partial pressure of the oxygen in the air be limited to 1.4 atmospheres or less. The Cochran EMC-14 computer has the same value. NOAA recommends that their divers not exceed 1.6 atm. If a diver exceeds their CNS toxicity level there is a greater chance that the high level of oxygen may cause mild to severe symptoms of oxygen poisoning, the severest being underwater convulsions. They are usually fatal unless someone else comes to the rescue!

Air has 21% oxygen so a person at sea level has 0.21 atm of O2 entering their body. The rest is 0.78 atm.of nitrogen or 78% of the air. If that person were to descend to 33' seawater they would be at double pressure which means the O2 partial pressure would now be 0.42 atm.

If a diver were breathing a 50-50 mixture of oxygen and nitrogen at the surface the partial pressure of the O2 would be 0.50 atm. At 33' that same gas mixture would have a partial pressure of 1.0 atm O2. So you can see that to avoid going over the PADI and Cochran's1.4 (or NOAA 1.6) oxygen pp limits a diver has to know what the percentage of oxygen is in the breathing gas as well as the depth.

Prior to diving the diver should be sure the FO2 is set to 21 if air is the breathing gas. If the diver is breathing Enriched Air Nitrox (EAN) the computer must be set to the oxygen percentage determined after analyzing the gas. The EMC-14 will take that setting along with the depth and constantly report what the CNS toxicity level is. The CNS level is displayed as a percent. If the CNS level reaches 100% it means the diver has encountered a CNS toxicity level greater than 1.4 atm of O2. That is dangerous and the dive should be safely terminated. The Cochran computer is defaulted at 50% of the maximum allowed. The diver may reset the computer to between 40% and 80%. When the percent is exceeded the alarm activates.

In the above underwater screen it is assumed the diver had set the CNS limit to 60% of the allowable 1.4 atm of O2. The diver exceeded the 60% and is now at 62% CNS exposure. The CNS Oxygen Toxicity reading is flashing. At the top the Warning Legend is flashing. Note that the diver is breathing air (F21). Because the depth is so great (115') the PO2 in the air is 0.94 atm. That is about 60% of the 1.6 atm maximum.

OXYGEN TOLERANCE UNITS (OTU): A person, diver or not, is limited to how much oxygen they should be exposed to over a period of time. On the earth we have adapted to a 21% of our breathing gas exposure, so breathing air for long periods of time makes us happy. If the percentage of oxygen is elevated, such as in a hospital cardiac treatment center or underwater at depth, the exposure increases. PADI has a 24-hour period limit of oxygen exposure for humans and that limit must be kept under 100%. If it is not, Pulmonary Oxygen Toxicity may occur leading lung irritation, coughing, burning in the throat and chest, and shortness of breath.

From the PADI DSAT Table, which shows the percentage of oxygen received from various PO2 levels breathed over time, if a person breathed 0.6 atm of oxygen for 720 minutes they would have received 100% of their OTU (maximum allowed in a 24-hour period). That would be similar to a diver breathing air for 12 hours at 66' (720 minutes at 0.21 PO2 x 3 atm). From that same table, breathing 1.0 atm of O2 for 300 minutes would also be 100% exposure. One last example: Breathing 1.5 atm of O2 for 60 minutes would result in 50% of the maximum 24 hour exposure. So, the PADI DSAT Table is a series of calculations of the amount of PO2 a diver is breathing, for how long (in minutes), all within a "moving" 24-hour period.

The EMC-14's algorithm will warn the diver when 50% of the allowable 24-hour exposure is exceeded. The percentage is programmable from 40% to 60%. The factor is kept track of for days if diving continues! The EMC-14 considers a diver at 1.6 atm PO2 to have received 100% of their OTU!

In the example above the level of oxygen (PO2) is 1.59 atm. The warnings are flashing because the PO2 exceeded the 1.4atm PO2 alarm.

THE EMC-14 SURFACE AFTER DIVING MODE:

The Surface Mode above is the primary screen.

The above is what the Surface Mode actually appears. It shows the 3rd repetitive dive of the day with a maximum depth of 126'. On this screen the surface interval alternates with the bottom time.

The Surface Mode Alternate screen is self-explanatory.

PROGRAMMING THE EMC-14 (ESPECIALLY FOR THE EAN MIXTURE):

With the EMC-14 on the surface and turned on (wet fingers on buttons 1 & 2 for 3 seconds), touch a coin (metal) to buttons 1 & 2 repeatedly and go to the 5th screen shown below. The screen is labeled EAn. That is the location for inserting the level of O2 (FO2) in the breathing air you will be using underwater.

Once you have the EAn screen touch buttons 1 & 2 with wet fingers. That will cause the right digit (0 in the screen above) to begin flashing. Let's say you tested an EAN tank with an oxygen analyzer and the reading was 36.4 % O2. You would want to change the right digit to 4. To do that touch the coin to the 2 & 3 buttons. With each touch the right digit will increase by 1. Once you set it to 4 in this example you would want to change the 2 digit to 6. Wet fingers on buttons 1 & 2 will cause the 2 to flash. A coin on buttons 2 & 3 will allow you to change the 2 to a 6. Repeat the above for the 3rd number if it needs to be changed. When the 3 numbers equal the % of O2 in the diving tank touch buttons 1 & 2 with a coin and the EAN mixture will be saved. It will remain at what you set until the setting is changed or the battery is removed.

Use the coin on buttons 1 & 2 to get back to the opening screen.

EMC-14 Specifications:

Click here to Download the EMC-14 Manual

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MODIFIED DIRECTIONS FOR USING THE EMC-16:

     The EMC-16 has 3 metal buttons on the right side. They are numbered 1, 2, and 3 from the bottom to the top. Touching the buttons with wet fingers will cause one thing to happen. Touching the buttons with a metal object, such as a quarter, will result in a different reaction!

To turn the computer on place wet fingers on buttons 1 and 2 for 2 seconds. There will be a beep. Without further activity the computer will remain on for 60 minutes and then shut itself off. The EMC-16 will not turn on if the altitude is > (greater than) 15,000', or the battery voltage is < 2.0 volts. The batteries should be replaced when the voltage is < 2.5, or they have been in the computer for 2 years or more. New batteries read about 3.2 volts.

The batteries are 2-1.5V Alkaline N OR 1 Lithium 3V. CR12600SE or CR2NP. Radio Shack 55026645. Do not allow the EMC-16 to be without battery power for more than 30 seconds. If you do, or if the battery voltage was allowed to fall to a very low point the computer may not turn on. If that happens remove the batteries for at least 30 minutes and then reinstall them. All prior diving data may be lost when this is done. The battery(ies) should be put into the computer + end first.

Once the EMC-16 is turned on, and after it goes through the computer checks, the Surface Screen is displayed: Figure 2 shows that screen. If the altitude is over 2500' those bars will be shown. The temperature is displayed in the upper right. The surface time (also the time since the computer was activated) is displayed. If the screen is tapped hard the Alternate Screen (Figure 3) is shown for a short time. Here the diver may verify the setting for the 21% of oxygen in the diving tank.

If you have surfaced after a dive and are still out-gassing the Surface Screen will look similar to the following (Remember the Alternate Screen is seen after tapping the computer's face.):

In the above underwater Alternate Screen the diver has reached 28% of the allowable amount of CNS Oxygen toxicity. Note that the diver is breathing air (F 21).

CNS TOXICITY: PADI recommends that the partial pressure of the oxygen in the air be limited to 1.4 atmospheres or less. The Cochran EMC-16 computer has the same value. NOAA recommends that their divers not exceed 1.6 atm. If a diver exceeds their CNS toxicity level there is a greater chance that the high level of oxygen may cause mild to severe symptoms of oxygen poisoning, the severest being underwater convulsions. They are usually fatal unless someone else comes to the rescue!

Air has 21% oxygen so a person at sea level has 0.21 atm of O2 entering their body. The rest is 0.78 atm.of nitrogen or 78% of the air. If that person were to descend to 33' seawater they would be at double pressure which means the O2 partial pressure would now be 0.42 atm.

If a diver were breathing a 50-50 mixture of oxygen and nitrogen at the surface the partial pressure of the O2 would be 0.50 atm. At 33' that same gas mixture would have a partial pressure of 1.0 atm O2. So you can see that to avoid going over the PADI and Cochran's1.4 (or NOAA 1.6) oxygen pp limits a diver has to know what the percentage of oxygen is in the breathing gas as well as the depth.

Prior to diving the diver should be sure the FO2 is set to 21% if air is the breathing gas. If the diver is breathing Enriched Air Nitrox (EAN) the computer must be set to the oxygen percentage determined after analyzing the gas. The EMC-16 will take that setting along with the depth and constantly report what the CNS toxicity level is. The CNS level is displayed as a percent. If the CNS level reaches 100% it means the diver has encountered a CNS toxicity level greater than 1.4 atm of O2. That is dangerous and the dive should be safely terminated. The Cochran computer is defaulted at 50% of the maximum allowed. The diver may reset the computer to between 40% and 80%. When that percent is exceeded the alarm activates.

In the above underwater Alternate Screen the diver has reached 10% of the allowable amount of O2 exposure (OTU) in a 24 hour period. Note that the diver is breathing air (F 21).

OXYGEN TOLERANCE UNITS (OTU): A person, diver or not, is limited to how much oxygen they should be exposed to over a period of time. On the earth we have adapted to a 21% of our breathing gas exposure, so breathing air for long periods of time makes us happy. If the percentage of oxygen is elevated, such as in a hospital cardiac treatment center or underwater at depth, the exposure increases. PADI has a 24-hour period limit of oxygen exposure for humans and that limit must be kept under 100%. If it is not, Pulmonary Oxygen Toxicity may occur leading lung irritation, coughing, burning in the throat and chest, and shortness of breath.

From the PADI DSAT Table, which shows the percentage of oxygen received from various PO2 levels breathed over time, if a person breathed 0.6 atm of oxygen for 720 minutes they would have received 100% of their OTU (maximum allowed in a 24-hour period). That would be similar to a diver breathing air for 12 hours at 66' (720 minutes at 0.21 PO2 x 3 atm). From that same table, breathing 1.0 atm of O2 for 300 minutes would also be 100% exposure. One last example: Breathing 1.5 atm of O2 for 60 minutes would result in 50% of the maximum 24 hour exposure. So, the PADI DSAT Table is a series of calculations of the amount of PO2 a diver is breathing, for how long (in minutes), all within a "moving" 24-hour period.

The EMC-16 Screen While Underwater:

The EMC-16 in a Decompression Mode:

The diver has reached 131' with a bottom time of 28 minutes. The amount of dissolved nitrogen is excessive and if the diver ascends to the surface DCS may occur. The diver must stop at 20' to outgas for 12 minutes. The diver is shown to be at the ceiling depth of 20'.

The above Alternate Screen shows that the gas mixture used on this dive was EAN28.

The factory preset for the PO2 alarm is 1.4 atm. Above the 1.4 has been exceeded (it is 1.5 atm) and the alarm is flashing.

The Analyst software can reset the alarm from 0.5 to 1.59 atm of PO2

.

The CNS exposure alarm is preset by the factory to 50%. Above the CNS alarm is flashing at 68%.

The Analyst software can change the alarm to activate anywhere from 40-80%. (1.6=100%)

 

The EMC-16 Screen When the Diver Surfaces:

If the diver descends again prior to the surface time reaching 10 minutes (above it is 8 minutes) the computer will assume the diver is still on the same dive (2 above). If the diver waits until 10 minutes have elapsed and then dives again they will be on dive 3 in this case.

The above is a typical display after diving and activating the Logbook function.

 

Changing the EAN (F O2%) Mixture in the EMC-16:

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Setting the Time on the EMC-16 (if it has been activated by the Cochran dealer or Analyst program):

 

To simply check the time without reprogramming the computer: Place metal on buttons 1 and 2. The CLC will appear. Use wet fingers on 1 and 2. CLC Al ON will appear. Use wet fingers on 1 and 2 to turn the alarm off. Bridge 1 and 2 with metal and the time will appear. To get back to the Surface Mode hold the metal on buttons 1 and 2 until it flips into the computer check mode and then the Surface Mode.

The following are the areas that may be programmed in the EMC-16 computer:

If the diver dives with 2 mixtures of oxygen, one being for the dive and the other for decompression, they may be programmed into the EMC-16 before entering the water:

The EMC-16 Specifications:

Click Here to Download the EMC-16 Manual

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OVERVIEW OF THE NITROX PRO AND PILOT/CLASSIC COMPUTERS

FEATURES:

The Nitrox Pro (those with the * are for the Classic) provides the following information to help you control your dive:

It gives the following warnings:

It gives the diver choices:

Additional features:

LCD DISPLAYS

The visual displays on the LCD will change according to the information being delivered. To protect the LCD from scratching you should apply one of the protective sheets that come with each unit, to the LCD surface. It is a removable sticker that can later be changed to a new one, once it comes worn out. The screen examples in the manual are shown in either metric or imperial units, but you should use the display with which you are most comfortable. The diagrams below show how the screen will appear during different aspects of the dive.

DIRECTIONS FOR USE

      To activate the computer wet two fingers and touch both NEXT buttons at the same time. At start-up all segments light for 5-10 sec showing unit self-test and adjusting to ambient pressure. If you forget to activate the unit prior to entering the water it will activate itself when it gets wet. However, the computer will assume you are at sea level if it turns on this way. It is wise to activate the computer in the atmosphere if diving above sea level so the altitude will be read by it.

BATTERY TEST:

     After the self-test procedure, the computer will perform a battery test. During this test the LCD will display numbers 9 (to 0). If the battery is sufficiently charged the LCD will show all segments and then begin working.

     If the battery is not giving full power the computer will run a function that will try to revive the battery. This will take max 10 minutes per cycle, and during this time the LCD display will count down from 9 to 0, if needed. If the battery revival is successful, the LCD screen will show all segments again then begin working. If it is not successful the computer will turn off, and a new reviving cycle is needed. EVEN A NEW BATTERY, WHEN TAKEN IN USE, MIGHT NEED SEVERAL CYCLES BEFORE BEING FULLY OPERABLE, IF IT HAS BEEN STORED FOR LONG AND/OR EXPOSED TO EXCESSIVE HEAT. AFTER THE REVIVAL CYCLES, THE BATTERY IS AS GOOD AS NEW! If, after several revival cycles, the unit still does not turn on, the battery should then be replaced. However, if you do not have a spare battery for immediate replacement, the computer can be turned on and used but the beeps and LCD light will not work. To turn the computer back on in this case connect the 3 function buttons simultaneously and wait for the 9 on the LCD to change to 8. The battery should then be replaced before the next dive.

FUNCTION BUTTONS - The Nitrox Pro has 4 function buttons that allow you to operate the computer:

Go Diving: After activation and the Self Test and Battery Test, the computer goes into Surface Mode.  You are now ready to enter the water without doing anything further. However, if the computer is turned on, but not used for 60 minutes it will turn off automatically.

While Underwater:

     There is only 1 screen that shows underwater. On that screen the diver simply reads the Dive Time (on the top), the time left until the diver enters the decompression mode (in the middle in the brackets), and the maximum depth (lower left). In the upper right the temperature will be displayed.

     On the Nitrox Pro there will be (on the right) a bar graph of the oxygen in the Central Nervous System (CNS), as well as the % of the same. Each bar, of 5, represents 20% of the allowable oxygen before oxygen poisoning may be encountered.

TAP SWITCH

     The tap switch operates the LCD light and warning beeps. To turn the functions on and off, tap the computer in the upper left corner of the screen with a hard object or fingertip (avoid scratching the unit though) as described below.

After the Dive:

THE COMPUTER TURNS ITSELF OFF:

     After a dive the computer will remain on for 15 minutes. It will then go into an energy efficient calculation mode. This is indicated with a clock icon on the LCD. The computer remains in this mode until the desaturation time is fully calculated down. Connecting NEXT+NEXT will bring the computer back to the Surface Mode.

    There are 3 screens in the Surface Mode. The computer will automatically scroll between the 3. Each of the screens shows different data related to the dive.

 In the Surface Mode:

     These functions are best explained using the Computer Instruction Manual with the computer in hand.

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     Here are copies of the pages in the manual for the Pilot and Classic computers:

 

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     The pages from the manual for the Classic/Pilot Nitrox computer:

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