Dive computer

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Three different dive computers for the wrist

A dive computer helps the diver to plan and conduct dives in order to avoid decompression sickness ( diving sickness ). During the dive, the dive computer continuously measures the depth and time and calculates the profile of the dive. From this, dive computers calculate the current decompression obligation by simulating several types of tissue and their saturation with inert gases .

The dive computer is to be seen as a successor or as a supplement to the decompression table and the (historical) mechanically constructed decometer .

Devices that only display and partially record the depth and dive time, but do not calculate the decompression obligation, are called bottom timers .

history

Decompressiometer

When the US Navy published the first decompression tables in the 1930s - which reduced the risk of decompression sickness - the need for a device that automatically controls the dive and warns the diver if limit values ​​are exceeded was quickly recognized. In 1951, the Scripps Institution of Oceanography in San Diego was commissioned to develop the basis for such a device. Two years later the institute published a report that formulated four requirements for such a device:

  1. The device must be able to calculate the required decompression levels during a dive, for which the diver must carry it.
  2. Repetitive dives must be able to be included in the calculation.
  3. Multi-level dives must be possible.
  4. The device should allow more precise calculations than a decompression table.

In 1953 the authors recommended an analog-electronic implementation.

Since the electronics of those days were not developed enough to solve such complex tasks in the smallest of spaces, the Navy commissioned Foxboro (now Invensys ) to build a mechanical - pneumatic decompressiometer. The device presented in 1955 was called the Mark I and was criticized by the Navy because it was too imprecise and not very stable. Mark I simulated two types of tissue with a total of five flow resistances made of porous ceramic and had five bellows for data acquisition.

In 1959, Carlo Alinari introduced a commercial decompressiometer called SOS . It worked similarly to the Mark I , but was limited to a simulated type of tissue and replaced the bellows with a bladder. These devices were only widely used after Scubapro acquired the import rights for them in 1963. Although the correctness of simulating repetitive dives has been highly debated, it has been loved by divers around the world for its high reliability.

From the late 1960s to the early 1980s, many different decompressiometers were developed and sold by different companies. All were based on the mechanical-pneumatic concept, although some had the word "computer" in their names. Other well-known decompressiometers:

  • DCIEM Mark : Launched in 1962 by the Canadian DCIEM Institute, it simulated four different types of tissue.
  • GE Deco Meter : In 1973 General Electric presented a device that was based on semi-permeable silicone membranes instead of the ceramic membranes commonly found in decompression meters, which allowed deeper dives.
  • Farallon Decomputer : From 1975, Farallon Industries California offered a device that simulated two types of tissue and was particularly easy to read. However, since it differed greatly in practice from the Navy decompression table used at the time, it was withdrawn from the market a year later.

Analogue electronic decompressiometers

In parallel to the development of the mechanical-pneumatic decompressiometer, concepts were developed that consisted of an analog electronic computer . The tissue was simulated in a network of ohmic resistors and capacitors . These analog-electronic devices proved to be insufficiently temperature-stable and required a great deal of calibration effort before each dive. In terms of weight and size, the analog-electronic devices far exceeded the mechanical-pneumatic devices, as a powerful battery was required for their operation. The first analog-electronic decompressiometer was the Tracor , which was completed in 1963 by Texas Research Associates.

First digital dive computer

With the increasing efficiency and miniaturization of digital computers, it was also possible in the mid-1970s to evaluate measured values ​​and calculate the no-decompression limit in real time. However, the power supply of these mobile computers was still a major challenge, since the processors and memory modules at that time were not particularly energy-efficient and more powerful NiCd batteries were still very expensive and rare. The first digital dive computer was a device that looked like a cash register and stayed above the water. This desktop computer was able to simulate four types of tissue and correctly calculate the remaining no-decompression time. It was only used with surface-supplied divers who, in addition to the hoses for air supply and heating, carried an additional empty hose that enabled the dive computer to measure pressure. This digital device built for the laboratory with the relationship XDC-1 was completed by the DCIEM Institute in 1975 and used for research work. Its successor, the XDC-2 , was manufactured by CTF Systems Inc. and worked on the same principle as its predecessor. It was mainly sold in large numbers to institutions that dealt with hyperbaric medicine. Around 700 units of the successor model XDC-3 were sold between 1979 and 1982. It was so compact that it could be carried underwater, making the XDC-3 the first true digital dive computer. Four 9V batteries were required for the power supply, but the running time was limited to only around four hours. The XDC-3 was also marketed under the CyberDiver name.

From 1976 the diving equipment manufacturer Dacor (today Head ) built a digital dive computer, which did not carry out any tissue simulations, but only read out a stored Navy decompression table. The Canadian company KyberTec brought the CyberDiver II onto the market in 1980 , which also only read a decompression table but also had air integration. Its successor model, CyberDiver III , which appeared a year later, calculated the remaining no-decompression time , like the XDC-3 , using tissue simulations . In 1980 the US Navy began developing a dive computer called the UDC . He simulated nine tissues according to a decompression model by Edward Thalmanns and got along with mixed gases. In 1983 Orca Industries Inc. presented its Edge (Electronic Dive GuidE) model to the public, which was the first dive computer to have a graphic display and be able to calculate the no-stop time for multilevel dives. The Edge simulated twelve types of tissue and could run for about 12 hours on just a single 9V battery. In the USA, the Edge was very successful commercially and was sold in large numbers. In 1983, the development of a dive computer began in a collaboration between US Divers (now Aqua Lung International ) and Oceanic. The DataScan 2 or DataMaster II was not finished until 1987, when decompression computers were already available on the market.

Decompression computer

The first full-fledged decompression computer, which not only calculated the no-stop time, but also the decompression levels for complex multilevel dives in real time, was brought onto the market in 1983 by the Swiss company Divetronic AG in cooperation with the diving pioneer Hans Hass . This dive computer was called DecoBrain and it simulated 12 types of tissue according to Albert Bühlmann's ZHL-12 decompression model . The electronics engineer Jürgen Herman succeeded in 1981 at the ETH Zurich in implementing Albert Bühlmann's decompression model on an Intel microcomputer . By miniaturizing the hardware, he was able to design an energy-saving and lightweight dive computer with DecoBrain . The successor model produced from 1985, the DecoBrain II, was based on the ZHL-16 model and was powered by a NiCd battery, which was sufficient for an operating time of 80 hours. Divetronic AG also developed the Micro Brain model for Dacor and was involved in the completion of the US Navy's UDC before being taken over by Scubapro in 1989.

The Finnish diving instrument manufacturer Suunto introduced the SME-ML in 1986, a very compact and inexpensive decompression computer. It was based on the Navy table and, powered by a 1.5 V button cell , had a running time of 1500 hours. Its disadvantage was that it could only calculate a depth of up to 60 m. Today, Suunto is the largest manufacturer of dive computers.

In 1987 the Aladin model from the Swiss company Uwatec appeared, which was based on the ZHL-12 decompression model and was particularly popular in Europe. The French company Beuchat was involved in the development of the Aladin and sold it under its own brand. Uwatec is now a branch of Scubapro.

Current development

Numerous manufacturers now offer decompression computers. Standard models calculate zero and decompression times on the assumption that a predefined gas mixture is breathed during the entire dive. Higher-priced devices also include the remaining gas supply in dive planning, support switching between predefined gas mixtures or have an electronic compass. In some cases, the diver's breathing and heartbeat frequencies are also recorded wirelessly and included in the calculation. The latest developments are towards large color displays and apps , similar to what is known from smartphones . The Icon HD net ready model from Mares , which was presented in 2010, offers a 2.7 ”color display and the option to display it e.g. B. to be supplemented with maps.

construction

Schematic structure of a dive computer

The dive computer consists of a pressure-resistant housing in which a sensor (usually silicon pressure sensor ) for the water pressure (and possibly also for other physical quantities), a microprocessor and a LC - display , more recently, fully graphical OLED display at the Top. Because of the better sealing, electrical touch sensors (instead of mechanical buttons) are often used as operating elements. Most dive computers are worn individually on the arm, similar to a wristwatch. In so-called console models, the dive computer is connected to the diver's regulator via the high pressure hose. Such dive computers usually measure the gas pressure via this high pressure hose, but it is also possible to carry the dive computer with a separate pressure gauge (and other devices) in a console. Dive computers with head-up displays only have a very small market share. Such dive computers can form a monolithic unit with the diving mask or be held in front of the head with a separate strap. In both cases, the diver can keep all information from the dive computer in view at all times.

Dive computer with HUD. A person wearing the red mask will see the writing 2 m away

Calculation method

A dive computer indicates decompression obligations during a dive.

The basic concept of all common dive computers is to calculate the saturation of the tissue with the inert gas (s) (nitrogen, helium etc.) from the recorded data in order to determine the resulting decompression obligation. This takes place in short time intervals (in the range of a few seconds) so that the diver can read the essential elements of his decompression obligation at any time. The calculation is based on a mathematical model that is intended to map the medical-physical processes as precisely as possible. These calculation models can be roughly divided into one-phase and two-phase models.

In the so-called single-phase models (e.g. Bühlmann and Haldane) it is assumed that no gas bubbles form in the body. In the model, a certain number of different tissues (e.g. 16 in the known calculation method ZH-L16) is assumed, which saturate and desaturate at different speeds. These model tissues correspond to different tissue groups of the human body. According to the Bühlmann model, the assumed half-lives are between 4 and 635 minutes. Further assumptions about which oversaturation of the individual compartments can be accepted determine the depth and length of the decompression stops or up to which pressure (water depth) can still be surfaced.

In a two-phase model, e.g. B. RGBM, on the other hand, it is assumed that gas bubbles form in the body if the decompression regulations are complied with. Instead of the individual compartments, assumptions are now made about how the gas bubbles grow during the ascent, while decompression stops shrink, or what bubble size can be considered medically harmless. Two-phase models are often considered to be the more realistic variant, since the existence of symptom-free gas bubbles can be proven by ultrasound measurements. Depending on how the individual models are parameterized, very similar decompression plans can result in practice.

Since people react differently to an oversaturation of their body tissue and a subsequent pressure relief, the calculation methods of any kind can only cover a certain part of the collective. With the usual dive computers it is assumed that one to three percent of the users will have decompression problems despite adhering to the diving instructions given by the computer. These can be symptom-prone ( DCS I or II ) or symptom-free.

In contrast to a diving table, the application of which requires a standardized diving profile, a diving computer can calculate the ascent rule for almost any previous diving profile. However, there are also limits here, as identical dives lead to different levels of desaturation in different individuals in a group. In the case of repetitive dives, this can lead to a no longer precisely determinable inert gas presaturation in the individual diver when he begins the next dive. This is justified u. a. in that the removal of the residual inert gas remaining in the body during the surface interval varies greatly from person to person. Individual risk factors (obesity, alcohol or nicotine consumption, etc.) can hardly be included in the calculation.

Well-known calculation models and which manufacturers use them today (2013):

Decompression model Manufacturer
RGBM Mares , Suunto , Cressi-Sub
Haldanean PPS , Cochran, Delta, Uwatec
Randy drill Seiko
Bühlmann ZHL-12 Seiko, Uwatec
Bühlmann ZHL-16 Uwatec
DSAT PPS
VPM-B Liquivision

Functions

Dive profile in the logbook function of a dive computer.
  • lighting
  • Dive time
  • current diving depth
  • average depth
  • maximum diving depth
  • Water temperature
  • compass
  • Warning of too fast ascent (visual, acoustic)
  • remaining no-stop time
  • Display of safety stops
  • Display of deep stops , decompression stops and decompression time
  • Consideration of the desaturation during a repetitive dive
  • Warning if the depth or duration of the decompression stop is not respected.
  • No-fly time display: If a diver gets on an aircraft shortly after a dive and is not yet fully desaturated (exposed to lower air pressure), he may have a decompression sickness there too.
  • Manual or automatic adjustment of the water level above sea ​​level (important for mountain lake diving at an altitude of over 700  m ).
  • Warning if the set maximum diving depth is not reached
  • Alarm clock function
  • Log book function: Most dive computers have a log book function for the subsequent evaluation of dives, which enables the data from one or more saved dives to be called up.
  • PC interface: To transfer data to a computer using software for detailed evaluation (e.g. graphic display of the dive profile). Depending on the model, there is also the option of updating the device software, firmware and setting the dive computer (e.g. personalization function).

Model variants

Air-integrated dive computer

Dive computer with wireless air integration and nitrox functions

Air-integrated dive computers also include the pressure in the compressed air cylinder in the calculation and show the diving time for which the supply of breathing gas is still sufficient. Some devices include the diver's air consumption in the calculation of the nitrogen saturation or the decompression calculation.

Air-integrated dive computers are available on the market in two versions: with a transmitter or a high-pressure hose (high pressure hose). Models that are connected to the high pressure outlet of the first stage of the regulator using a high pressure hose sometimes replace the mechanical pressure gauge . In other models, the sensor for the cylinder pressure is located in a separate transmitter, which is screwed to a high-pressure outlet on the first stage. The transmitter transmits the pressure values wirelessly to the dive computer. At least in this case, the additional use of a mechanical pressure gauge is often recommended.

Dive computer for technical diving

In particular , dive computers developed for technical diving (so-called technical dive computers, trimix or mixed gas computers) can also u. a. offer the following options:

Web links

Commons : dive computer  - collection of images, videos and audio files

Individual evidence

  1. ↑ Thomas Kromp, Oliver Mielke: Handbuch modern diving . Kosmos, Stuttgart 2010, ISBN 978-3-440-12164-1 .
  2. ↑ Thomas Kromp , Hans J. Roggenbach , Peter Bredebusch : Practice of diving . 3. Edition. Delius Klasing Verlag, Bielefeld 2008, ISBN 978-3-7688-1816-2 .
  3. ^ Roland Zbinden: Dive computer and bottom timer. Dekostop GmbH, Schliern near Köniz, accessed on February 5, 2018 .
  4. ^ J. Corde Lane: Navy Dive Table Lecture. University of Maryland , accessed September 12, 2013 .
  5. ↑ a b Michael A. Lang: Introduction of the AAUS dive computer workshop. (PDF; 2.0 MB) Scripps Institution of Oceanography , accessed on September 13, 2013 .
  6. ↑ Foxboro Decomputer Mark I. Defense Technical Information Center, accessed on 12 September 2013 .
  7. ↑ a b c d e f g h i j Lothar Seveke: Development of the dive computer (only the technology, not the algorithms). Retrieved April 3, 2013 .
  8. ↑ Decompression Meter AKA Bendomatics. The Scuba Museum, Cincinnati Ohio, accessed April 3, 2013 .
  9. ↑ Frank Dolacek: Dive computer for deep diving. Retrieved April 3, 2013 .
  10. ^ Albrecht Salm: My little virtual dive computer museum. Retrieved September 12, 2013 .
  11. ^ Albrecht Salm: My little virtual dive computer museum. Retrieved September 12, 2013 .
  12. ^ Marion Kutter: History of the dive computer. Dive Magazine Ltd., archived from the original on November 2, 2013 ; accessed on September 13, 2013 .
  13. ^ Karl E. Huggins: Underwater decompression computers: Actual vs. Ideal. Department of Atmospheric and Oceanic Science, accessed September 16, 2013 .
  14. ↑ https://www.spektrum.de/magazin/die-physiologie-der-dekompressionskrankheit/822595
  15. ^ S. Lesley Blogg, Michael A. Lang and Andreas Møllerløkken: Proceedings of Validation of Dive Computers Workshop. (PDF) Norwegian University of Science and Technology, August 24, 2011, accessed September 16, 2013 .