NAUI Master Scuba Diver 22 Diving Equipment Memory (RAM) stores the information resulting from computations. A clock synchronizes the operations and serves as a timer. A battery supplies power for the operation of the circuitry, and a housing protects all of the components from the environment. There are two basic types of computers, tissue based and table-based. A tissue-based computer calculates nitrogen absorption in a number of theoretical body tissues and displays a warning or ceiling if the nitrogen level in any tissue approaches or exceeds programmed limits. A table-based dive computer compares time and depth data to the mathematical model of established dive tables. Warnings are displayed when the no-decompression limits of the tables programmed into the computer are approached or exceeded. A table-based computer does more than simply store a set of dive tables electronically. The computer compares time and depth input against the tables continuously to credit the diver for multi-level dives. This provides longer dive times than can be obtained using conventional dive tables. A table-based computer can also provide a repetitive group designation following a dive so the user can revert to the use of standard dive tables even following multi-level dives. Most dive computers do not take all of the factors affecting your body into consideration when making no-decompression calculations, so they must be used accordingly. Most make the same computations in cold water and in warm water, for older divers and younger ROM ROM Microprocessor divers, for those who are feeling well and for those who are not, for those who are exerting and for those who are not. You must, therefore, adjust and limit your dive profiles based on such factors. Some models can be adjusted by the user, depending upon the level of risk chosen. There are many different configurations of dive computers. Some models can be worn on the wrist (figure 1-18) or in a console (figure 1-17) and are independent units, others can be air-integrated incorporating a digital pressure gauge in the unit. There are even hoseless models that use a transmitter and receiver between the cylinder, regulator, and dive computer. There are also models that can be used with different gas mixtures, such as nitrox, and can be programmed by the user. As with any electronic device, there is always the possibility of operational failure. You should carry a back-up depth gauge and underwater timer in case of a failure of your computer. The possibility of a computer failure is quite low, but not impossible. If your computer should fail while diving, you are to ascend immediately and perform as a safety precaution a decompression stop of at least 5 minutes at a depth of 5 m (15 ft). Failure of a computer or accidentally switching one of these instruments off when it contains information from current diving activities poses a problem that can be handled only by delaying further diving for the number of hours required by the manufacturer. The delay in diving, which is not necessarily 12 hours, allows the instrument Device Housing Ambient Pressure Pressure Transducer Clock Power Supply A/D Converter Display FIGURE 1-23. DIVE COMPUTER BLOCK DIAGRAM
20047TC
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