Dive computer
A dive computer or decompression meter is an electronic device used by a scuba diver to indicate the diver's decompression requirements for the depth and duration 'profile' of a dive. Its main purpose underwater is to display either the 'no-stop' time or the depth and duration of any required 'decompression stops'. 'No-stop' time is the time remaining before a diver must surface for his own safety in order to avoid getting decompression sickness. A Decompression stop is a period of time the diver must spend at a constant depth in shallow water at the end of a dive in order safely to eliminate gas from the diver's body to avoid decompression sickness.
An alternative to dive computers are dive tables used with a watch and depth guage. The diver must plan from the table and avoid exceeding the planning maximum depth and duration.
The equipment
Inside the watertight case, a battery-powered electronic computer uses a pressure gauge and timer to track the dive profile. It supplies that information to a decompression algorithm to estimate the amount of nitrogen that has been dissolved in the diver's tissues and calculate a decompression schedule. An LCD display on the face of the dive computer indicates the decompression information to the diver.
Examples of decompression algorithms are Buhlmann's algorithm, the Multi Tissue Model, the Varying Permeablity Model and the Reduced Gradient Bubble Model.
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Display information
Dive computers also display the current depth, the amount of time the diver has been underwater, and the maximum depth reached during the current dive, so the diver can keep true to his original dive plan and surface after the agreed-upon dive duration. Most dive computers log this information for at least the last ten dives so the diver can later write this information down in his diver's log book.
Some dive computers display information such as:
- Water Temperature
- Display of excessive ascent rate and audible alarms
- "Time to Fly" display showing when the diver can safely board an airplane
Features
In addition to air dives, some dive computers are able to calculate decompression schedules where the diver uses, at some stage during the dive, breathing gases such as nitrox or pure oxygen, or even helium mixes such as trimix or heliox.
Most dive computers calculate decompression for 'open circuit' SCUBA where the proportions of the gases involved are constant for long periods. Other dive computers model 'closed circuit' [rebreather], which maintain constant partial pressures of gases by varying the proportions of gases in the mixture.
Some dive computers also connect to the diving regulator and monitor gas consumption.
Some dive computers can connect to a personal computer allowing detailed analysis of dives and logging of dives.
Cautions
Scuba instructors recommend that divers follow the limits of the dive tables they receive as part of their training, forming a dive plan and then following it. This approach need more rigour, discipline and caution - just the qualities needed in a hazardous sport. On the other hand, dive computers allow divers to perform big dives with little planning are too forgiving. Following a dive plan is good procedure and will help protect divers if they lose their dive computer in the water, or if it runs out of batteries or even if its software crashes.
Different brands and models of dive computers are called more "conservative" or "liberal", where "conservative" means the computer limits diving time more in order to increase the margin of safety against decompression sickness. Experienced divers may want to use a more "liberal" computer, but this may increase risk. Complicating this choice is the fact that susceptibility to decompression sickness is not well understood, and it seems to vary depending on the diver's fitness, age, weight, fatigue, and even recent illness, as well as the water temperature and the altitude.
Many computers go into a "lockout" if the diver violates the safety limits, to discourage continued diving after an unsafe dive. While in lockout mode, these computers display depth and time only, while flashing various warning signs telling the diver that he or she should surface. After a lockout, many computers remain locked out for 24 hours.
Referenced By
Diver training | SCUBA Equipment
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