NO831476L - DEVICE FOR INDICATING DIVE PARAMETERS. - Google Patents

Abstract

The device is based on at least one memory containing the decompression parameters of a table of diving depth and times. It estimates and compares measured values of diving depth and times with those contained in the memory. At each moment of the diving, the total climbing time (15) including the imposed decompression stages (16) depending on the duration (13) and on the depth (14) of the diving may be displaced, and/or there is provided a device which transforms, for going to a new depth, the real base time in a time equivalent to this new stage. A single air/water interchangeable pressure sensor is used comprising preferably a piezoresistive cell. LED diodes are lit, if the maximum climbing speed is exceeded (10), if a decompression stage is reached (11) and if the device is out of work (12) by exceeding the time and/or the depth.

Description

The invention relates to a device for indication

of the parameters for a diving operation, such as e.g. current depth, maximum achieved diving depth, elapsed diving time or the like, which indicating device is operated by means of a) at least one storage for the decompression parameters at a number of diving depths and diving times, and, b) an evaluation and logic stage for the measured values of the depth gauge and timer, with the values stored

in the warehouse.

During diving with compressed air, a pressure equilibrium is established using the diving apparatus (demand regulator). This means that the air inhaled by the diver has the same pressure as the water that surrounds him.

With increasing water depth, the diver inhales air with higher pressure, which causes more air to dissolve in the diver's body. The various gases of which the air is composed enrich the various tissues of the human body.

me to varying degrees, in accordance with given saturation factors.

During ascent, the opposite occurs, the tissues

depletes itself.

If now the ambient pressure falls too quickly as

as a result of too rapid ascent, the air dissolved in the blood and tissues cannot be exhaled. sufficiently quickly.

This applies in particular to the dissolved nitrogen as the excess of oxygen and carbon dioxide is considerably smaller. This happens because a large part of the oxygen consumed

res of the tissues, and that the carbon dioxide leaves the organism faster than other gases due to its high diffusion rate.

If nitrogen is present in excess during too rapid a pressure reduction, it can go out of solution and form bubbles. This leads to diving sickness, which can avoid

occurs if the nitrogen is allowed to release itself so slowly from the blood and tissues that no gas bubble formation occurs.

The way in which gas bubble formation causes disease lies in the fact that the nitrogen gas bubbles cause damage to the tissues, and that they appear in the blood vessels and remain trapped in the last branches of these, the capillaries. The gas bubbles prevent there. the blood and oxygen supply to the surrounding tissue.

If this blocking state of a blood vessel (embolism) persists, the affected areas can no longer be supplied with nourishment and are destroyed.

To avoid diving sickness, the diver must not ascend at a speed greater than 10 m/min., and after exceeding the so-called zero time, he must take breaks (decompression stays) during ascent.

The duration and depth of the decompression stays depend on the diver's tissue saturation. The tissue saturation is affected in turn. of different factors.

Without stating reasons and without claiming completeness, some of the most important points must be stated here:

- maximum diving depth

- diving trail d

- the diving course

- air pressure at the water surface (diving site's Jiøyde above

(height of the dive site above sea level)

- duration of stay at the dive site before. the diving

- previous dives within 12 hours

- physical exertion under water

- Individual tissue composition for the diver

(corpulent or athletic physique)

- composition of the breathing gas or breathing air.

As long as the diver can return to the surface at any time without risk of diving sickness, he is in the zero-time diving zone.

The zero time means the time during which a diver can stay at a certain depth, so that he does not have to make any decompression stops during his ascent.

Nevertheless, the pressure chamber laboratory at the University of Zurich recommends that a minimum stay of 3 minutes at a depth of 3 meters should be observed for each dive.

To be able to return to the surface without a decompression accident, every diver must know the ascent conditions. These conditions are the rate of ascent and the decompression intervals that the diver must allow to pass during ascent. The decompression intervals depend on the duration and depth of the dive and must. spent at specific depths.

Currently, the diver determines the ascent conditions by hand, using the diver's watch, the depth gauge and the dive chart. Determining the jay decompression intervals in the diving table is very simple, but is also inaccurate with regard to optimal decompression due to the fact that easy processing of the tables can only be achieved at the expense of a loss of accurate recording of the diving parameters.

To achieve the optimal decompression for each diving operation, the diving sequence must be accurately recorded and the corresponding decompression conditions must be calculated. It is of course impossible for a diver to carry out this work himself, due to the fact that for this purpose he would have to register a large number of data records and evaluate these using complicated calculations. Currently, amateur divers and professional divers therefore use tables from which they can read the decompression conditions. Such recognized tables are, for example, the tables of

- Groupe d'Etudes et de Recherches Sous-marine (France)

- Royal Navy (England)

- U.S. Navy (USA)

- Druckkammerlabor der Universitat Ziirich (Switzerland).

These tables are based on experiments on humans and on calculations in which there is a limited number of tissues with different saturation factors. been simulated on a. large calculator.

The diver's requirements with regard to the table are:

. Simple treatment

. Decompression conditions for each dive" with only the necessary safety margin.

These two requirements are mutually contradictory due to the fact that simple processing of the table requires few table input values, but few input values make accurate recording of the diving course impossible. It is thus impossible to determine the decompression conditions that are precisely necessary for each dive.

All tables are therefore based on the compromise that they. few table input values are at the expense of the maximum decompression time, and the diver.finds the decompression that is precisely necessary in the.extreme case.

In all other cases, the diver decompresses for far too long.

This means that most tables that currently

can be achieved, is calculated for a linear descent (approx. 30 m/min.. ), a stay at a given depth and a direct ascent.

The decompression conditions can thus be read from

the table using the maximum diving depth and the total diving time (the time from the start of the dive to the start of the ascent).

However, if different tables are compared with each other, it turns out that significant differences occur with regard to the decompression conditions for the same total diving time and the same maximum diving depth.

This occurs:

- because most tables are intended for diving at sea level and diving in mountain water can only be taken into account with difficulty, apart from variations in atmospheric pressure as a result of weather conditions;

- because diving before. a current dive cannot be taken

in consideration at all with many.tables, and with other tables can only be considered with difficulty;

- because the decompression conditions depend on the duration of the stay at the diving site and on the height of the diving site above sea level, and this is not taken into account in all tables; - because only a few tables take into account an altitude range for which the .decompression conditions are valid; - because a safety factor of varying size has been used in the various published tables.

Tables 1-4 for heights of 0 - 700 m above sea level and 5 - 8 for heights of 701 - 1500 m above sea level can be found at the end of the description.

The main differences between the tables of the Pressure Chamber Laboratory at Ziirich University (Druckkammerlabor der Universitat Ziirich) compared to all other tables are the following: 1. The tables of the Pressure Chamber Laboratory are. unique in that they take into account a work factor, i.e. these tables are designed in such a way that a diver who performs physical work under water can decompress in accordance with these tables without risk of any decompression accident. 2. The tables for the Pressure Chamber Laboratory are among the few exceptions that are not designed for one imaginary height above sea level, but for a height range above sea level.

As the tables are on the one hand complicated, but on the other hand require a large number of records of measured data, the most diverse devices and aids for the diver have been developed. By. aside from different types of depth gauges and diving watches, these include e.g. a decompression meter, an instrument that simulates the body's gas saturation. that gas is forced out of a flexible bag through a piece of sintered ceramic and into - a chamber with rigid walls. A pressure gauge connected to this chamber indicates the pressure there. The longer and deeper the instrument Tædtaes..during a dive, the higher the pressure rise behind the sintered plug. The pressure gauge thus gives the diver approximate information about the increasing saturation of his body tissue.

As the currently available decompression measuring instruments can only reproduce the saturation of the human body tissues in a very inaccurate manner, this instrument must never be used alone for determining decompression. Currently, decompression must always be determined with the help of additional factors, such as dive depth and dive duration, using a decompression table before each dive. The "Dekorneteret" can therefore at best be brought along for control purposes. The reason for this is that the decompression meters work

in accordance with Boyle-Mariotte's law and can only simulate the effect of nitrogen under high pressure on the human body. Decompression gauges can. never work accurately because the gas diffusion through the sintered filter takes place at the same speed in both directions. IN

however, the human body (especially during short-duration dives) never behaves in uniform conditions. A decompression meter is no guarantee of preventing a decompression accident.

Another common measuring instrument is the so-called bottom timer. The bottom timer is an automatic instrument for measuring the diving time. It is pressure-controlled and thus engages itself automatically when a calibrated depth is reached. In the same way, the bottom timer disconnects itself again just before it reaches the water surface. In reality, it is nothing more than a waterproof "stop watch" that engages and disengages itself using a simple - pressure-controlled - mechanism. The bottom timer informs the diver of the effective diving time. However, this diving time can also be read on a normal diving watch (adjustable using a setting ring).

Diving time and diving depth are certainly important factors, but they are not the only factors for determining decompression.

On the other hand, a diving calculator could gather or collect all data accurately and could evaluate these accordingly. It would be ideal if the diving calculator simulated a diver composed of a limited number of standard tissues. Degree: of. saturation for the individual tissues, as a function of depth and saturation factor for the relevant tissues, would then be integrated over time. By means of continuous comparison of the critical degree of saturation with the degree of saturation for the individual tissues achieved up to the relevant time, the decompression conditions could be determined.

Now a proposal has already been put forward

an ideal decompression meter in analog technique, which makes use of RC elements. to simulate the degree of saturation of the individual tissues. In this case, problems arise, on the one hand, in that the degree of saturation cannot be transformed, by means of calculation, into the equivalent decompression conditions, and on the other hand, the process of saturation and desaturation of the tissues can only be reproduced to a limited extent degree using RC networks, due to the fact that the different tissues have nitrogen half-lives of 5 - 635 minutes. This requires enormously large time constants for the RC joints (up to 635 minutes), which leads to very large problems with regard to the construction of the RC joints. In addition to this, the proposed, analogous treatment would be far too imprecise for practical use. This proposal has therefore never been realised.

Various diving calculators are already commercially available, but with these hardly any progress has been achieved, due to the fact that the diving calculators produced so far have not done anything more than digitize all previously known instruments (such as depth gauges, bottom timers , decompression gauges). Above all, all previously known devices suffer from the disadvantage that they only take into account the maximum achieved diving depth and the maximum diving time as parameters for determining the decompression conditions. This means that a diver, in accordance with the indication of these devices, must comply with the same decompression conditions, regardless of whether he has spent most of his time at shallow depths, perhaps even at a zero-time depth , and has only reached the maximum diving depth briefly, or whether he has spent the entire diving time at the maximum depth.

The result of this inaccurate indication is that divers draw conclusions from the indicated decompression conditions on the basis of the current times and depths, which they themselves again only estimate and thus come into danger.

The invention is based on the problem of making it possible to indicate the decompression conditions more accurately

basis of the relevant diving times and diving depths.

According to the invention, this is achieved by

total ascent time, depending.on the depths reached and the elapsed times during the dive, and including the prescribed decompression stays, can be indicated at any time during the diving operation, and/or that there is an

net a converter device for converting the current base

time in each case, upon entering a new diving depth step, to the equivalent bottom time for this new diving depth step.

In order to further increase the accuracy of the indicating device, extra measures are provided so that the air pressure, preferably measured with a measuring instrument,

must be taken into account by means of the converter device. Thus, it can air pressure that really exists

present at the diving site, depending not only on the altitude, but

also of the weather conditions, are also taken into account. - In the past, it was only possible to use very broadly divided or graded tables that differed in accordance with the altitude, while the weather conditions, which have a very large influence

ning, was not taken into account at all.

It would now be conceivable to use two different pressure gauges, one to measure the water pressure and the other to measure the air pressure, but it is preferably ensured that a single pressure sensor, preferably consisting of a piezoresistive load cell, can be connected to the circuit which contains the converter device, both for ..the air pressure and the water pressure. Thus, not only costs can be saved for an additional pressure sensor, but the device's handling is also maintained, which is important for carrying under water.

If, however, a single pressure sensor is used for pressure measurement above or below water, where the pressure conditions are very different, either a relatively expensive pressure gauge with a wide measuring range must be used, or appropriate measures must be taken. so that the pressure sensor's measurement range can be selected in each case for measuring air or water pressure using a switching device.

^The switching device preferably comprises at least one FET switch which is followed by an impedance converter for decoupling with respect to the input of the subsequent stage, in particular an analog/digital converter.

The converter device itself consists appropriately

of a calculator as well as a store or stores for bottom times, decompression times and/or repeatedly occurring groups ("repetition groups"), which stores can be e.g. table-store.

In particular, a differentiation stage is connected to the output of the pressure sensor, on the one hand due to the fact that the rate of ascent can be controlled. On the other hand, it is also possible that the switching device for switching from air to water pressure measurement will comprise a step change detection step for the pressure, which is formed e.g. using the differentiation step.

Other possible forms of this switching device are a manually actuated switch (whose actuation could of course be forgotten) or a switch that is actuated by a humidity sensor. Although the latter version could cause switching errors during initial rain showers or on arrival at the surface as a result of residual moisture, reliable switching and indication is ensured by the step change detector stage. In this case, the question of the step change detector step could also be solved in other ways than: by means of a differentiating step, for example by means of a threshold switch, with memory circuits and suitable comparator steps or the like.

However, it can. also for other reasons, e.g. for an evaluation and logic stage with a limited working range, be advantageous with range switching, for example when changing the gain or bit range of an analogue/digital converter which is connected in front of the evaluation and logic stage, by means of a switching device. It is thus possible to use cheaper components, such as an evaluation and logic stage with a smaller capacity. The switching device can then be formed by the same equipment that also performs the switching of the pressure sensor.

The possibilities for switching which are indicated as examples above are indeed very practical, but in many cases they are too expensive. In practice, one is therefore preferred. solution in which a reference voltage source is arranged which can be switched using the switching device and which is appropriately followed by an analog/digital converter.

If the relevant air pressure is also to be included in the calculation alongside the water pressure, it is necessary to work with an indicating device with a main switch that can be affected as desired, especially manually, due to the fact that the device's start of operation cannot be detected automatically. In this case, it is advantageous if, in addition to this main switch, especially for connecting the pressure gauge,

in addition to the pressure gauge, a second switching device is provided for switching on additional parts of the equipment when diving in water. Also in this case, the above-mentioned switching device can take over the role of this second switching device, in order to save costs for additional components.

On the one hand, any automatic device is subject to possible malfunctions. On the other hand, not all possible faults of a diver can be detected at reasonable expense. In such cases, the indicating device may give incorrect indications. However, this would entail an additional danger for the diver. Based on an indication device with at least one detector circuit for an abnormal function, e.g. for one. incorrect action by a diver, it is therefore suggested that a bypass or parallel circuit be arranged for the converter equipment and that this parallel circuit is arranged to be switched on by means of the detector circuit, while a warning signal and/or a slave or secondary indicator for the maximum, "achieved" diving depth can be engaged by means of this parallel circuit in case of occurrence of the abnormal function, e.g. if the main switch is first operated under water, if the storage capacity is exceeded or similar. In this way it is ensured that if the capacity is exceeded or in the case of another failure of the normal function, at least the indication achievable by known devices is provided. In this case, it is particularly advantageous if a segment indicator in an indicator device with at least one such indicator can be alternately connected to indicate different display data, e.g. e.g.

to the relevant decompression depth before* the occurrence of the abnormal function and to the maximum diving depth thereafter. On the one hand: this saves on components, and on the other hand it saves the diver from overloading the equipment, which can only prevent work underwater and can also do? .the indication less clear, and furthermore of course can cause dangerous errors.

In order to reduce the current consumption of the indicating device, which will usually be battery-powered, it is appropriate that an astable multivibrator circuit is arranged for the pulsed activation of at least one display device or indicator, e.g. with 3-4 signals per second.

A further increase in the indication accuracy can be achieved if the circuit which includes the converter equipment also contains a memory or storage for the repeatedly occurring groups (repetition groups) obtained by repeated diving with equivalent diving time obtained with the help of the converter device, via possible decompression, as account is taken of the decompression parameters and also of the time periods on the surface. In the case of repeated dives with an intermediate period of time on the surface, a residual saturation with nitrogen of. the diver's tissues still occur due to the previous dive, if this has not already become zero due to a suitably long stay on the surface. In the latter case, the expression "Repetition group zero" is used, which means that the diver can dive without any handicap. If, on the other hand, the repetition group is not equal to zero, it can, in accordance with the above proposal, go again immediately, into the calculation of diving. For. for this purpose, table stores are preferably provided for the repetition group tables, which are known in themselves, while table stores can also be provided in the converter equipment for the bottom times and decompression times.

Such table stores simplify construction. Furthermore, however, it is also appropriate that the converter equipment has a memory; or storage circuit for the diving depths in the elapsed times, as well as for the resulting correction values, where such are applicable.

The invention will be described in more detail in the following in connection with embodiments which are schematically shown in the drawings, where fig. 1 and 2 show curves for different diving operations, fig. 3 shows a diagram for explaining the meaning of the air pressure, fig. 4 and 5. show curves for various repeated divings, fig. 6 shows a highly schematic block diagram of an indicating device according to the invention, fig. 7 illustrates the indications that can be obtained with the indication device. fig. 8 shows a detail of the timer, fig. 9A and 9B show a circuit core of the indicating device according to the invention, fig. 10 shows details of the indicator drive device in fig. 9B,

fig. 11 shows the code used in the device, fig..12 and 13 represent alternatives to a circuit detail in fig. 9A, fig. 14 shows the main program sections for the indicating device according to the invention, fig. 15 shows a stock-busy schedule, fig. 15A - 15D show the data arrangements for the plan according to fig. 15, fig. 16 shows the program structure, and fig.

17 and 18 illustrate details of the program sequences.

Fig. IA - 1H shows dives of different types.

According to them. tables that have been common in the past, despite the differences, decompression conditions, which depend only on the maximum depth reached and the total duration, must be observed for all dives. ; Even if, for example, only 38m was achieved in one dive, it would be necessary to round to 40m because the tables are only divided into 5m increments. Only in such a dive as shown in fig. IA, the tables' decompression plan would be fully utilized, i.e. only with a very rapid descent to the maximum depth and sustained stay there until ascent to the surface.

In that in fig. The example shown by IB is a stop shot at 19 m during the ascent. According to the tables, this does not count as a decompression stay. but must be counted towards the diving time. The decompression conditions will thus only be fully utilized in the diving shown in fig. IA, while the decompression in the case of fig. IB, due to the necessary safety margin for the diving according to fig. IA, would have to go on for far too long. Most divers are of course also fully aware of this and are then tempted to shorten the decompression time found in the table, at their own discretion.

On this subject it should be noted that the complete ascent tables of the Pressure Chamber Laboratory at the University of Ziirich (Schweizerische medizinische Wochenschrift 103, No. 10, 1973) consist of five sets of tables of similar construction, for altitudes above sea level of 0 -

700 m (tables 1 - 4), 701 - 1500 m (tables. 5 - 8)., and also 1501 - 2000 m, 2001 - 2500 m and 2501 - 3200 m, and the table sets in each case include a • decompression table, a zero time table, a surface interval table and an additional time or recurrence table.

As the tables are only divided into steps of 5 metres, this will be explained below. some . few points;;regarding the determination of the "bottom time", first for the descent phase. It is assumed that the dive in question has not been undertaken by anyone else within the last 12 hours. In accordance with the division in the tables, "depth step" shall be understood to mean the range from a depth value; in the table to the next greater depth value in the table (where the top or first depth step begins at zero meters), a "repeat dive" means a dive that is repeated within 12 hours, the "surface interval time" means the time at the surface between two dives, and the "current bottom time" means the bottom time that applies until the transformation calculation. As long as the diver is in the first (top) depth step, the bottom time is equal to the total diving time, i.e. the time that has passed since the beginning of the descent.

If the diver descends from the first depth step to the second, it is possible to transform the previous bottom time into an equivalent diving time (bottom time) corresponding to the second depth step. This is, of course, only meaningful if a gain.in the bottom line occurs with the help of.this transformation.

This conversion calculation method is based on the fact that the previous dive, in case of a change of depth step to a greater depth, is considered as a completed dive which is now followed by a further dive with a surface time interval of zero within the framework of a repeat dive.

This conversion of the bottom time for one depth step to the equivalent bottom time of the next, larger depth step can be performed on each depth step change from a higher to. a deeper depth step and would be described as gradual or stepwise descent.

The transformation itself is carried out using the two depth steps and the relevant bottom time in the additional time table. Examples IA to 1H: See Tables 9 and 10 at the end of the description. and fig. IA - 1H.

Diving operations in the area from 0 to 700 m above sea level.

Fig. 1A shows a dive with repetition group zero, based on the decompression tables. When ascending to the surface in point e, after a total diving time of 34 minutes and a maximum, achieved depth of 33 m, a decompression stay of 5 minutes must be made according to Table 1 at

6 m and a stay of 17 minutes at 3 m.

Fig. IB shows a dive with a repetition group of holes, in which the ascent takes place step by step

- but within the so-called zero time limit. This zero time limit (Table 2, or Table 6 for 701 - 1500 m above sea level) indicates the limits of a dive up to which no decompression needs to take place, i.e. up to which the diver can return to the surface immediately at any time (obviously he complies with the maximum ascent time of 10 m/min.). In this area, any previous, total diving time can now be transformed, by passing through a depth step, into the equivalent diving time

for the next depth step, using Table 4 (or Table 8 for 701 - 1500 rn above sea level).

The current dive time at any point of the dive: is equal to the equivalent dive time for the previous point plus the time that has actually elapsed since then. If a depth step at this time of the dive is passed in a downward direction - or upwards provided that the diver is within the zero time limits - this relevant diving time is transformed into a new, equivalent diving time, by first deducting any repeated additional time that is included in the value, and then transform the remaining current diving time into the new depth step - always rounded up - after which the repeated addition corresponding to this new depth step is added again. As long as the diver is within the zero time limit, the transformation is carried out in accordance with the additional time or repetition table (Tables 4 or 8), and otherwise in accordance with the decompression table (Tables..1 or 5).

If.rounding errors creep in due to diving down or.up several times, these will be eliminated by comparison with the transformation to it; final depth step, if a shorter equivalent diving time is obtained from this.

In the example of fig. IB is found for point b (15 minutes, 33 m) in Table 4, rounded up; to the table value of 17 minutes at 35 m, the equivalent time value of 34 minutes for the new depth step of .19 m (rounded up to 20 m). The equivalent diving time is therefore now 34 minutes at 20 m. The zero time limit (see Table 2) has thus been exceeded, and the prescribed decompression stay according to Table 1 finally amounts to 7 minutes at 3 metres.

The diving shown in fig. 1C, shows a step-by-step ascent which, however, already takes place" beyond the zero time limit. In this case, also in accordance with the decompression tables of the Pressure Chamber Laboratory at the University of Ziirich, no equivalence conversion can be performed, and decompression must take place as if the total diving time had expired at the maximum, 'achieved' depth.

Fig. ID shows a dive, also here with a repetition group. zero, at which the descent takes place step by step., but. within zero time. As can be seen from Table 5, every time a depth feed step is passed, a conversion to an equivalent diving time can take place, which ultimately gives a gain in diving time of a total of 10 minutes, compared to conventional calculation, and this also gives a gain in decompression time. in 13 minutes. In accordance with the tables of the Pressure Chamber Laboratory at the University of Ziirich, the calculation: of the step-by-step descent would theoretically be permitted, but in practice this has proved to be far too complicated every time this possibility was used. It is first the indicating device according to the invention that has here provided the opportunity to realize these time gains which are possible according to the tables.

Finally, Fig. 1E shows a dive with repetition group zero in which the ascent takes place step by step, but outside the zero time limit. The transformation can be carried out in the same way as with stepwise descent within zero time.

The dives according to fig. IA, IB and 1C end - as shown in the figures - with the diver in repetition group J. After, a surface interval time of e.g. 185 minutes at

0 - 700 m above sea level, the diver is in repetition... •' tion group B, like this. it can be realized from Table 3/_To_find this, the next, shorter time indicated_in the table must be selected In each case Rounding up or down, or interpolation is not allowed.

A dive in which the diver dives again after a seed. surface interval time with repetition group B, is shown in fig. 1F. In this case, the repetition group is used for the first time on the equivalent diving time after 7 minutes and a depth of 30 m and is later carried forward continuously. After the dive, which in reality only lasted 26 minutes, decompression must take place as if the dive had lasted 34 minutes.

From the diving according to fig. IB (repetition group J) and a later surface interval of 150 minutes, the diver is in repetition group C. As shown in fig. 1G, followed by a short descent to 19 m and a later repeated dive with a gradual ascent. After the ascent beginning at point a, the conventional calculation method would give repetition group D, and at point c a decompression plan for 75 minutes at. 20 m depth with a total of 18 minutes: decompression time at 3 m. After very short dives ..now the repetition ion group remains unchanged, i.e. every time the line for repetition group A in the additional time or repetition table. not be exceeded. For 20 metres, this shows a time of 8 minutes, while the dive in fig. 1G only had a duration of 4 minutes (not counting the ascent time). In point b, the repetition group C is taken into consideration of the diving time of 9_ minutes for the new dive,

with an addition of .16 minutes (from Table 4, at a depth of 20 m). As the diver is still in the 18 m depth step at point c, he remains within the zero time limit, although rounding to 20 m would occur to fix the relevant _ ./decompression conditions and the zero time limit would therefore be exceeded by 30 minutes. The same applies to point d, the zero time limit for the 18 m depth step. (50 minutes) has been achieved, but at this point the diver is in the 12 irt depth step, i.e. at an equivalent, diving time of .113 minutes at 12 m, and thus has not yet exceeded the zero time limit of 200 minutes for 12 meters. The repeated diving which takes place after, the short descent and re-ascent in fig. 1G, proceeds in accordance with the second minute scale indicated below the time abscissa.

Fig. 1H shows, finally, a dive which the diver starts with the repetition group E that follows from the previous dive 1C and a surface interval of 110 minutes. The diving sequence consists of a short descent and a later repeated dive with changes of depth. The conventional calculation method would give repetition group F after the ascent beginning at point a, and at point g the decompression plan for 72 minutes at .20 m, i.e. a decompression stay of 18 minutes at 3-m. With the converter device according to the invention, however, the repetition group E (unchanged because line A in the repetition table (10 minutes at 15 m) has not been exceeded) is taken into account when calculating the current or equivalent diving time, as soon as the repetition table's line A is exceeded , at the added time of 34 minutes. A descent to the depth step of 18 m in point d finally gives an equivalent dive time of 37 minutes at 20 m, while the ascent and further descent in points e and f allow two different calculation methods. According to the first, a conversion to the depth step is first carried out. 12 m, which would give an equivalent dive time of 97 minutes at 12 m for point f. According to the second method, the correction method, the transformation can be carried out at point e to the depth step 15 m, which has the effect that the whole i", dive sequence from to point f is only entered at 87 minutes at 15 m, as a result of which the diver can decompress at point g with only 5 minutes at 3 m, while according to the former method he would have needed 10 minutes and according to the conventional method 23 minutes.

By means of the conversion with the indicating device according to the invention, an equivalent diving time is achieved with a smaller excess safety margin, so that it pays for the diver to convert if the equivalent is shorter than the one we see in the picture. "diving time./ During the ascent, the relevant diving time must also be determined in each case, but here the Pressure Chamber Laboratory prescribes that all stays during the ascent (outside the zero time limit) must be included in the diving time in its full duration, including the ascent time from the maximum, achieved depth to the stay.

In the following examples (see Figs. 2A - 2G) "bottom time" means the current or any reshaped (equivalent) bottom time in each case, and "Deco" denotes the prescribed decompression conditions.

2A) Diving with repetition group G after previous dive ID and subsequent surface interval of 25 minutes in the range from 0' to _J7.00 m above sea level; repeated diving. with gradual descent.. In point f and for repetition group G

provides conventional calculation methods the decompression schedule

for 82 min/85 m; 10 minutes at 6 m and 38 minutes at 3 m.

Point a: Stepwise descent

Conversion of 17 min/9 m to 12 min/12 m;

saving in time 5 minutes.

Point b: Repetition group G is taken into account in the bottom time calculation after the repetition table's line A . (12 min/12 m). is exceeded. Bottom time = 13 min + repetition time addition 85_min_= 98_ minutes.

Point c: Stepwise descent taking into account repetition group G.

Bottom time 108 min/ 12 m

Zero time limit exceeded (75 min/15 m) Bottom time 85 min/15 m - Deco: 3 m/5 min.

Point d: Stepwise descent taking into account repetition group G.

Bottom time 87 min/15 m

Bottom time 64 min/20 m - Deco: 3 m/18 min.

Point e: Stepwise descent taking into account repetition group G.

Bottom time 61 min/25 m - Deco: 6 m/3 min

and 3 m/30 min.

2B) Diving at 701 - 1500 m above sea level, (see Tables 5-8)

after previous diving 1E and

- a subsequent surface interval of 110 minutes at 0 - 700 m above sea level - then repetition group D follows from H, - and then a surface interval of 80 minutes at 701 - 1500 m above sea level - then repetition group A follows from D.

Compared to this, repetition group B would be achieved with a surface interval of 190 minutes at 0 - 700 m above sea level. 1 point.f dg with repetition group A, the conventional calculation methods give the decompression plan for 54 min/

20 m - Deco: 4 m/5 min and 2 m/19 min.

Point a: Repetition group A is taken into account in the base time calculation after exceeding the repetition table's line A (12 m/13 min).

Bottom time = 14 min + repetition time allowance

+ 13 min = 2 7 min.

Point b: Incremental descent taking into account repetition group A.

Bottom time 47 min/12 m

Zero time limit.exceeded. (30 min/15 m) Bottom time 41 min/15 m - Deco: 2 m/8 min.

Point c: Stepwise descent taking into account repetition groupv.A.

Bottom time 47 min/15 m

Bottom time 34 min/20 m - Deco: 4 m/3 min and

2 m/9 min.

2C) Extreme case diving without previous load, repetition group zero, at 0 - 700 m above sea level. Deep diving beyond the table values - "Out of range"

("Out of range", on the figure).

The points.a - h: Stepwise descent within zero time with a maximum jtimesgevihst" of" 11" minutes: ,

Zero time limit exceeded (0 min/45 m)

Bottom time 5 min/45 m - Deco: 3 m/4 min.

In the case of excessively slow descent from point a to point h, it would be quite possible that the maximum time gain of 11 minutes would not be achieved, if a bottom time of 7 minutes or 9 minutes at 45 m occurs, with a corresponding effect on the decompression plan .

Item i: Bottom time 11 min/45 m - Deco: 6 m/2 min and<v>

3 m/6 min.

Point k: Bottom time 16 min/45 m - Deco: 6 m/3 min and

3 m/11 min.

Point 1: Transformation 18 min/45 m more. 16 min/50 m; Time gain 2 minutes; Bottom time 16 min/5 0 m - Deco: 6 m/5 min and 3 m/17 min.

Total diving time 27 min.

Point m: Transformation 18 min/50 m to 17 min/55 m;

Time gain 1 min; Bottom time 17 min/55 m.,-Deco: 12 m/l min, 9 m/4 min, 6.m/8 min and

3 m/24 min.

Total, diving time 42 min..-

Point n: Bottom time 21 min/55 m - Deco: 12 m/2 min,

9 m/7 min, 6 m/10 min and 3 m/32 min.

Total diving time 56 min.

Point o: Transformation 23 min/55 m to 22 min/60 m;

Time gain 1 min; Bottom time 22 min/60 m - Deco: 15 m/2 min, 12 m/2 min, 9 m/10 min,

6 m/10 min and 3 m/35 min.

Total diving time 64 min.

Point p: Conversion 24 min/6 0 m to 2 3 min/65 m;

Time gain 1 min; Bottom time 23 min/65 m - Deco: 15 m/2 min, 12 m/4 min, 9 m/10 min,

6 m/13 min and 3 m/40 min.

Total diving time 75 min.

Point q: Bottom time 26 min/65 m - Deco: 18 m/l min,

15 m/2 min, 12 m/8 min, 9 m/14 min, 6 m/18 min

and 3 m/46 min.

Total diving time 95 min.

Item r: Bottom time 31 min; diving depth 65 m. For this point, no decompression conditions can be determined - table values are exhausted. An "Out of Range" LED illuminates, decompression conditions and ascent time are erased, maximum depth achieved is output.

2D) Extreme case diving without previous load, repetition group zero at 0 - 700 m above sea level. Deep diving beyond 70 m. Table values exhausted - "Out of range".

Points a-f: From point a, the decompression conditions are continuously increased as each of the depth steps is run down to point f.

a: Bottom time 1 min xx sec - Deco for 10 min/45 m - 3 m/4 min b: Bottom time 1 min xx sec - Deco for 10 min/50 m - 3 m/5 min c: Bottom time 1 min xx sec - Deco for 10 min/55 m - 9 m/l.min

6 m/2 min d: Bottom time 1 min xx sec - Deco for 10 min/60 m - 9 m/l min 6 m/3 min 3 m/5 min e: Bottom time 1 min.xx sec - Deco for 10 min/65 m 12 m/l min 9 m/2 min 6 m/3 min 3 m/6 min Point f: Bottom time 2.min xx sec - Deco for 5. min/70 m - 9 m/2 min 6 m/4 min 3 m/5 min Total diving time 18 min. Point g: Bottom time 6 min xx sec - Deco for 10 min/70 m - 12 m/2 min 9 m/3 min 6 m/4 min 3 m/6 min Total diving time 22 min. Point h: Bottom time 11 min xx sec - Deco for 15 min/70.m - 12 m/2 min 9 m/3 min 6 ra/10 min 3 m/20 min Total diving time 4 2 min.

Point i: Diving beyond the 70 m depth step - the "Out of range" LED lights up, surface time and decompression conditions are erased, maximum depth achieved is output.

2E) Diving with repetition group zero at a mountain lake height of 701 - 1500 m above sea level (see Tables 5 - 8). Realistic diving at varying depths.

Point a: Stepwise descent

Conversion 15 min/10 m to 13 min/12 m; time gain 2 min.

Point b: Stepwise descent

Conversion 13 min/12 m to 11 min/15 m; time gain 1 min.

Point c: Stepwise descent

Transformation 11 min/15 mJitil 8 min/20 m; time gain 3 min.

Point d: Stepwise descent

Zero time limit at the 20 m depth step (15 min/ 20 m) exceeded.

Transformation 15 min/20 m to 23 min/15 m.

Point e: Stepwise descent with correction calculation Conversion 25 min/15 m to 21 min/20 m Correction calculation

Bottom time = Bottom time for the 20 m depth step at point d plus elapsed time since point d.

Bottom time = 15 min + 2 min = 17 min/2 0 m Zero time limit (15 min/20 m) exceeded. Bottom time 17 min/20 m - Deco. for 20 min/20 m - 2 m/4 min.

Point f: Bottom time 21 min xx sec - Deco. for 25 min/2 0 m -

2 w/6 min.

Point g: Stepwise descent

Transformation 25 min/20 m to 20 min/25 m Bottom time 20 min/25 m - Deco. for 25 min/25 m-4 m/4 min and 2 m/8 min.

Point h: Start of ascent at 10 m/min.

Bottom time 25 min xx sec.

Point i: Departure from the ascent cone; the bottom time is increased by the time spent in the ascent cone.

Bottom time 25 min xx sec - Deco. for

30 min/25 m - 7 m/3 min, 4 m/4 min and 2 m/9 min.

2F) Dive after previous dive 2E and a subsequent surface interval of 70 minutes at 701 - 1500 m above sea level - this results in.repetition group D from G - and then a surface interval of 80 minutes at

0 - 700 m above sea level - this results in repetition group B from D.

1 comparison with this wild, repetition group A

be achieved with a surface interval of 150 minutes at 701 - 1500 m above the hub.

In point h, the conventional calculation method gives the decompression plan for 44 min/40 m with 12 m/2 min,

9 m/7 min,

6 w/20 min and

3 m/4 0 min ,

where departure from the decompression phase has not yet been taken into account.

Point a: Repetition group A is taken into account in the bottom time calculation after the repetition table's line A (40 m/4 min) has been exceeded.

Bottom time = 5 min + repetition time allowance 4 min = 9 min.

"Point b: Zero time limit (10 min/40 min) exceeded.

Conversion 10 min/40 m to 10 min/35 m.

Point c: Zero time limit (15 min/35 m) exceeded.

Transformation 15 min/35 m to 22 min/30 m. Bottom time 22 min/30 m - Deco. for 25 min/30 m - 3 m/5 min.

Point d: Stepwise descent with correction calculation

Bottom time 26 min/35 m

Correction calculation

Bottom time = Bottom time at point c at 35 m plus the time that has passed since point c.

Bottom time 25 min/35 m - Deco. for 25 min/35 m - 3 m/9 min.

Point e: Bottom time 25 min xx sec - Deco for 30 min/35 m - 3 m/12 min.

Point f: Bottom time 31 min xx sec - Deco for 35 min/35 m -

6 m/5 min

3 m/17 min.

Point g: Bottom time 36 min xx sec - Deco for 4 0 min/35 m -

6 m/7 min

3 m/20 min.

Point h-: Beginning of ascent for decompression with

10 m/min.

Point i: Descent during the decompression phase to more than 3 m below the deepest decompression stage (7 m).

The entire decompression time up to this point is added to the bottom time, i.e. Bottom time = 40 min + 5 min decompression time

= 4 5 min.

Bottom time 45 min/35 m - Deco for 50 min/35 m -

9 w/ 3 min

6 m/10 min and 3 m/35 min.

Point k: New start of decompression, but now for 50 min/35 m.

2G) Extreme case diving without preload. Repetition group zero at 0 - 700 m above sea level.

1. Diving with an emergency return to the surface.

2. Diving in which the diving calculator is first switched on underwater. 1. Point a: Zero time limit (0 min/45 min) exceeded.

Bottom time 2 min xx sec - Deco. for 10 min/45 m

- 3 m/4 min.

Point b: Start of emergency ascent.

Point c: Entry to the decompression stage.

DECO LED lights.

Point d: Arrival, to the surface without including the prescribed decompression stay. The "Out of Range" LED lights up. The decompression conditions, the surface time and the DECO LED are removed, the maximum diving depth achieved is output. _.. 2. Point a: The diving calculator is connected under water.

The "Out of range" LED lights up, maxi-. template achieved diving depth is output as se-customer indication.

In any event, it is important that any diver who remains above the zero time curve with regard to dive time and maximum dive depth is in the zero time diving area and therefore does not need to make any decompression stops on ascent to the surface (although a 3 minute break at a a depth of 3 m is recommended when ascending). However, as long as the diver is within the zero time, the method of determining the equivalent bottom time described above for the descent can also be transferred to the ascent, due to the fact that the diver can in any case return to the surface at any time without decompression.

Under these conditions, an additional time can also be provided from the additional time table for the subsequent cycle during the ascent (for a repetitively occurring diving sequence). Now, however, the problem arises that with general use of this method for all depth steps and with reshaping of the relevant bottom time, when moving beyond a depth step into the bottom time of the higher depth step, significant rounding errors are introduced. This has a particularly large impact if the diver first floats up a number of depth steps and then dives again to the maximum depth step. The solution to this problem conveniently consists in the previous dive at a greater depth only being transformed into the depth step for the previous diving depth if the relevant bottom time has just become as great as the zero time for the maximum diving depth. At the time of converting the bottom time to the current diving depth, it is only necessary to record a correction time and to use the previous bottom time as the correction bottom time. However, these two correction values are only necessary if the diver again returns to the maximum diving depth step within a short time.

It is then necessary to compare whether the sum of the correction bottom time and the correction base time recorded at the time of return is less than the real bottom time that has elapsed up to this point. If this is the case, the real bottom time must be corrected by setting it equal to the sum of the correction bottom time and the correction time. Otherwise, the transformation has been worthwhile.

By means of this new method a significant improvement is achieved as it is in this way possible for a dive, both in the descent and to a certain extent in the ascent, to be considered as consisting of successive, repeated dives in accordance with the tables, and thus providing the necessary conditions for digitalisation.

So much attention has been devoted to the digitization of the diving sequence because the values necessary for determining the decompression conditions, the bottom time and the maximum depth can be optimally determined in this way. With the bottom time and the maximum depth, the associated decompression conditions are read from the decompression table.

The decompression conditions mean the decompression times in the individual decompression steps in the decompression tables, times which must be observed by the diver.

The existing rules are somewhat different for

the case where a dive is preceded by another dive within 12 hours. As already explained using the previous conversion examples, each dive is assigned a repetition group at the beginning of the surface interval, corresponding to the degree of nitrogen saturation in the diver's tissues, to determine the appropriate additional value for the decompression parameters. Traditionally, the repetition group for the end of the surface interval is determined at the beginning of the repetitive dive.

In contrast to this conventional method, however, it is advantageous if the repetition group is tracked continuously during the surface interval in order to shorten the surface interval table which is necessary for this purpose, and thus, after all, save storage space for the indicating device according to the invention. The result, i.e. the repetis ion group obtained at the end of the surface interval, is the same. The continuous determination of the repetition group will be described later together with the explanation of the program sequences.

The repetition group is usually only taken into account at the beginning of the ascent because, upon inspection of the table, the transformation of the bottom time had to be carried out, taking into account the repetition group in each case. If, however, as in accordance with the invention, a suitable converter device is provided, the corresponding correction can easily be carried out automatically.

It is therefore appropriate if the repetition group at the end of the surface interval is taken into account by a repeatedly occurring time addition at each change of depth step during the descent. It will thus be possible to inform the diver at all times about the minimum ascent time including decompression time. With the conventional methods, the decompression times suddenly increase at the beginning of the ascent, i.e. the correction would be significantly more complicated due to the fact that when determining the descent time

(in accordance with the above explanations) corrections must already be made anyway, and an additional correction value only leads to additional complications.

If thus the bottom time should. is transformed during the descent, taking the repetition group into account, then the repeatedly occurring additional value from the previous depth step change is subtracted from the relevant bottom time before the transformation of the relevant bottom time into the equivalent bottom time, then the transformation is carried out in the manner described above, and to finally, the repeatedly occurring time addition for the next deeper depth step is added to the relevant bottom time. The previous dive and the preload of the tissues that this causes are thus superimposed on the values for the dive at each change of depth step to a greater depth. As described above, these values may already be present in digitized form.

The problems that arise in connection with air pressure being taken into account will now be explained with the help of fig. 3. If it is assumed that the temperature is the same at the different altitudes, the air pressure decreases with increasing altitude in accordance with an exponential function. In an accurate calculation of the air pressure, account must be taken of the fact that the temperature decreases with altitude. In order to obtain as accurate a picture as possible of the atmospheric pressure up to an altitude of 4000 m, this is calculated in accordance with the international altitude formula which takes into account to an annual average temperature of 15° C at sea level and an annual average atmospheric pressure at sea level of PQ = 101.325 kPa. The formula is valid up to an altitude of 11,000 m and has the following form:

In order to obtain as realistic a picture as possible of the air pressure curve, the meteorological variations in air pressure that occur as a result of sudden changes in the weather and can amount to - 5 0 mbar;. at sea level, is taken into account. This is a relative error of 5 .\% which is superimposed on the barometric pressure curve as a spread area.

The air pressure curve shown in fig. 3, is approximated by means of a straight line 4 through the points (0/1) and (3300/0.67), with AL being the maximum air pressure variation at sea level and S being the spread area for the air pressure variations, which amounts to about. 5%. The figure also shows the altimeter resolution A per 100 m, the altimeter's maximum error FM, and also the minimum error Fgmj_n°9the maximum error Fgraaks of the height measured by atmospheric pressure, which in the transition area from one height step to another can lead to the selection of the next set of tables.

This shows that the relative error of 5% of the air pressure results in a significantly larger relative error with respect to height.

When considering the individual altitude step limits (700/701, 1500/1501 etc), the relative error at the maximum rises to +72% (-500 m on 700 m) and remains at a minimum above 10% (+350 m on 3200 m).

These enormous deviations of the cartographic height above sea level from the atmospheric pressure height are taken into account with safety factors in the sets of tables from the Pressure Chamber Laboratory at the University of Ziirich, so that the diver is not put in danger.

Example:

According to the map, a diver is on a mountain lake at 1300 m above sea level and uses the table sets for the height step (700/1500) m above sea level for. his diving.

However, as a result of a sudden change in the weather, the prevailing atmospheric pressure may have risen so much that it now corresponds to an equivalent height of less than 700 m above sea level. The diver could now use the table set for the height step 0 - 700 m above sea level, if, he. should use an altimeter instead of the map for selection of. the table set.

In order to achieve a greater accuracy for the selection of the table set than with the help of a map, it is not necessary to have any precision altimeter. The relative error of this altimeter must be less than the minimal relative error of the cartographic height related to the height equivalent to the barometric pressure. The relative error of this altimeter thus only needs to be less than 10%. The indicating device according to the invention takes into account the atmospheric pressure in an adequate manner and therefore, under the conditions of the given example, correctly refers to the table set for 0 - 700 m above sea level, which corresponds to the prevailing atmospheric pressure even if the diver is located at 1300 m above the sea.

On the other hand, the water height provides the pressure

■i3

If it is assumed (Pw) = bar and ^r^O = 10 kg/m , we get:

(2) Depth in meters 10 - P

Because the water depth cannot be determined independently of the prevailing atmospheric pressure (P^), the latter must be taken into account. The water pressure (Pw) is the difference between the absolute pressure (pabs) and the air pressure (P^). Therefore, the following applies to the depth in meters and the pressures (paks) r (Ph) in bar:

(3) Depth = 10 . (Pab's" Ph)

To determine the depth during dives at different heights above sea level, a sensor for absolute pressure must be selected and the depth must be calculated in accordance with (3).

The density of seawater is approx. 3 = 1.02.5 g/cm , and the density of fresh water is approx. = 1.0 g/cm3.

Due to the fact that the diving depth must be determined both in

in

seawater and fresh water, a short fault analysis shall be given below.

If the depth at a real depth of 10 m is determined in accordance with (3), taking into account 3, 10 m is obtained as depth in fresh water and 10.25 m in sea water. The relative error of the depth in seawater in relation to the real depth is thus 2.5%. This accuracy is sufficient, and further the error is on the safe side. and too small a depth will never be determined. because of the error.

Thus, the specific requirements are achieved for a pressure measuring system as it will be used in a preferred embodiment of the indicating device to be described later, namely for an absolute value pressure sensor from 0 - 10 bar, so that the altitude range 0 - 4,000 m above sea level and the water depth range 0

80 m can be covered.

In order to guarantee a sufficiently high accuracy for the height measurement and the depth measurement, the relative error must not exceed 3.5%.

The sensitivity

must be so large that a

pressure change of 0.01 bar = 100 nu air column.= .10 cm water column produces a voltage change which, after amplification and analogue/digital conversion, corresponds digitally to at least one digit of

the least significant space; expressed as a binary value

(<E>)2^ (<1>)2. It has already been mentioned that repeated dives within 12 hours must be taken into account when determining the decompression parameters. This topic will be treated in more detail below. It has also been mentioned that the different repetition groups are denoted by letters and lead to an additional time in accordance with the additional time table. Fig. 4 shows a graphic representation of a repeated dive with a diving time T2 after a previous dive with a diving time T-^ and a decompression time D, and after a surface interval Oi. For example, the diving time T is equal to 50 minutes and the decompression time D, based on this diving time and the depth (10 m) is 3 minutes, whereby after ascent to the surface and at the beginning of the surface interval a repetition group F is obtained. As shown in fig. 4, the surface interval Oi amounts to 100 minutes. During this time, the excess gas content in the diver's body decreases and you reach a repetition group C corresponding to a smaller gas content. This is evident from the surface interval table. The diver, who is now in repetition group C, wants to dive. 30 m. In the C line of the additional time table and in the 30 m column, he finds the additional time of 10 minutes. This means that there is still as much gas in the diver's body as if he had already stayed at 30 m for 10 minutes. To determine a reasonable decompression, the additional time must now be added to the new, real diving time. If, for example, the actual diving time is now 20 minutes, he must select the decompression plan for 30 minutes at 30 m. A repeated dive as shown in fig. 4, with constant height, is admittedly the most common case. By means of fig. 5, however, it must be discussed what happens if the diver changes the water mass and height.

At a higher altitude, the times with which a given repetition group is achieved are shorter. It is allowed to calculate the surface interval at a height with a lower set of tables, but the reverse is not allowed.

Example according to fig. 5

A first dive is carried out at a height of 450 m above sea level, for 40 minutes at 30 m. After the prescribed decompression under water, the diver is out of the water at 11.01 and is now in group J. The diver is now flown by helicopter to a mountain lake at 14 00 m above sea level... At 12

he has risen above the height limit of 700 m above sea level. At this point, the diver is in group G, which allows him a flight height of up to 2000 m above sea level. At 12.55 the diver is ready for the new dive.

According to the surface interval table for 0 - 700 m above sea level, the diver was in group F after 12.06. The diver takes into account the remaining 4 9 minutes of surface interval time in the table set for .701 - 1500 m above sea level, passing at 12:55 from group.F to group D. The diver now dials up the additional time in accordance with his new diving depth. At 13.30 the dive is finished and the diver is now in group G. At 15.10 the diver goes below the height limit of 700 metres.

In the table set for 701 - 1500 m above sea level, the diver was in group C after a surface interval of 90 minutes (ie at 15:00). The additional surface interval after 15:00 is taken into account in the table set for 0 - 700 m above sea level, as the surface interval table for 701 - 1500 m above sea level is no longer valid after going below the limit of 700 m above sea level.

Structure of the indicating device according to the invention: The preceding statements show that the processing of the tables is relatively complicated, and with the tables it is therefore impossible to give the diver the information he would actually need at any time during a dive. The previously known diving calculators have only automated the reading of the tables, without at the same time making it possible to transform the real bottom time into the equivalent bottom time,

to take into account the real atmospheric pressure (which may be subject to considerable variation as shown in Fig. 3) or the repeated time increments, or to give a continuous indication of the required ascent time. All in all, the data that can be obtained from the tables is thus subject to major inaccuracies. The purpose of the invention is to remedy this condition and to provide the diver with the most accurate information possible, particularly with regard to the decompression parameters.

Fig. 6 shows an embodiment of the invention by means of which this purpose can be achieved. In this embodiment, the ambient pressure (i.e. both air and water pressure) is supplied as an input variable to a converter equipment 5 from at least one pressure sensor 6. A further input variable is supplied by means of a timer (hour) 7 which - as it will appear from the following description - can also be integrated in the converter equipment. Finally, a power supply circuit 8 must be arranged which can be switched on via a main switch 9 which in turn can be influenced as desired, i.e. by direct manual influence or via a remote control.

In the converter equipment 5 is recorded not only the beginning and the end of a diving operation, together with its development course., but preferably also the previous history, in order to be able to take account of repeatedly occurring time additions. For this purpose, it is of course necessary that the associated table data is stored in the converter equipment 5 itself and/or memory or storage devices which are connected to it. The processing of the signals is suitably carried out in digital form, and it will therefore be necessary, at least for the pressure sensor 6, which emits analogue signals, to arrange an analogue/digital converter inside the converter equipment 5.

As output variables from such converter equipment 5 can be determined, a guideline value At for the expected ascent time (calculated decompression time), the decompression parameters D (i.e. depth steps and times for decompression), the depth data Tm (such as actual depth and maximum depth), and the total dive time Tt. Furthermore, however, it is also appropriate if abnormal functions are indicated, i.e. incorrect behavior of the diver and/or of the indicating device itself. An indication Va can thus be provided if the diver exceeds the maximum ascent speed, and at least one further indication An which emits a battery monitoring signal in the event of insufficient power supply and/or emitted signal if values which are not present in the stored tables occur, for example because the diver, in violation of the rules, has exceeded the maximum depth of 70 m.

Although the indicating device must of course be placed in a pressure-tight enclosure, a leak detector with a corresponding indication can also be arranged. Although the indicating device must also be able to be securely attached to the diver's body, preferably to the arm, it can nevertheless, in the event that it is lost

(for example removed because the device prevents work under water), include a motion detector which, in the absence of movement caused by the diver, after a short time activates an optical, acoustic or otherwise localisable signal to facilitate the recovery of the device.

If the indication An comes into operation to indicate that the end of a table has been reached, the decompression parameters (output variable D) can no longer be determined accurately. It will be described later that, for this case, a bypass (by-pass) can be arranged to the converter equipment in question, by means of which it. current depth and dive time. remains indicated for the diver, but the decompression conditions and ascent time are deleted due to the fact that the latter can no longer be calculated, as a result of abnormal behavior of the diver. For example, in the case of an emergency ascent without observing the prescribed decompression stops, in order not to leave the diver completely without information, the maximum depth reached can also be indicated, so that he can improvise a decompression plan for himself using of the dive time and the maximum depth achieved.

All in all, an embodiment of the indicating device according to the invention is constructed so that the diver only has to turn it on using the main switch 9 - before entering the water 1 - or off. The equipment then works fully automatically, and the operation of the equipment is reduced to observing the display device or the indicator. The diver will appreciate this ease of handling because the diver's ability to concentrate is reduced due to anesthesia with increased depth, and this state of confusion increases with depth. In extreme cases, this narcosis can degenerate into so-called "deep ecstasy". which has already spelled doom for many divers. This increases the importance of a clearly legible and understandable display device, in which only the values that the diver really needs are indicated.

As any fully equipped diver often has to carry numerous instruments, it is advantageous if the indicating device according to the invention also takes over the function of other instruments. It can thus easily replace the conventional depth gauge and diver's watch. In the same way must

it takes on the function of an altimeter with a resolution of at least 100 m. In order to be able to calculate the ascent conditions, the equipment must further, by means of software, detect whether the diver:

- located on land or in the water,

- floats, on the surface of the water,

- dives down,

- rises in accordance with the rules,

- rises faster than 10 m/min,

- rises too slowly,

- divers with or without preload..from. previous dives,

- has exceeded the values of the table to be processed,

- has exceeded the zero time limit,

- must decompress,

- has.begun decompression,

- has completed decompression in the prescribed manner,

- terminates decompression in violation of regulations,

- has switched on the indicating device - before the water level drops.

If a time clock is also included in the indicating device, the duration of the operational capability of the indicating device also lasts for several days. The time clock would otherwise not be.worth bringing along..If a time clock is. included, is further, the operation is no longer limited to switching on and off the device, due to. that this clock can also be set and must provide an independent opportunity for the diver to read the time.

Fig. 7 shows the display or indicator panel

in a practical embodiment of the indicating device according to the invention. As already indicated, the display device must provide different indications in different operating conditions. The most important operating states are "Deco calculation" (the normal case) and "Out of range". Additional operating states are subordinate to these main operating states: 1. Maximum ascent rate exceeded ("Ascent rate") 2. Countdown for the decompression stays ("Decompression countdown", only subordinate. "Deco calculation")

3. Power down

4. Software part.

In one practical embodiment, the display device is made with four.4-digit numerical LCD display units 13 - 16 and with three LED indicators 10 - 12. LCD display devices are admittedly more advantageous due to their lower power consumption and their good legibility with.diffused and focused, incident.light, but LED indicator devices must be selected for the most important indications due to. that. LCD display devices at maximum depth, and especially in the dark, can only be read with great difficulty or cannot be read at all. To save power with the LED indicators, these can be operated in one. pulsed mode if desired. Theoretically, for example, actuation using an astable multivibrator with a mark-gap ratio of 1:1 would already save 50% of the required energy, but. in some cases, a smaller on-off ratio, e.g. 1:2 or 1:3, be sufficient. If desired, a switch can be provided by means of which the LED indicators or some of these can be optionally switched from continuous to pulsed operation. A variable resistor may also be provided in the circuit for the astable multivibrator, to vary the mark-gap ratio. The setting control for this variable resistance is then suitably combined with the control for the above-mentioned turns, to form a single control ring.

In the one in fig. 7 shown embodiment, it is arranged

three LED indicators 10,. 11, 12, with the following functions:

The light-emitting diode 10 lights up every time the maximum permissible ascent speed of 10 m/min is exceeded.

The light-emitting diode 11 is used to indicate that the counting of the decompression time has started. It ignites as soon as the deepest decompression depth step for. a given dive has been achieved, and expires at the end of a decompression, regardless of whether this has been completed in accordance with or contrary to the regulation. If necessary, incorrect behavior of the diver can be indicated by means of a flashing signal from this light-emitting diode 11.

The light-emitting diode 12 indicates whether the end of the stored tables has for some reason been exceeded or if the indicating device for some reason deviates from its normal function. This light-emitting diode 12 can then only be extinguished again by briefly turning off the main switch at the water's surface.

It appears from fig. 7 that, in addition to the LED indicators 10, 11 and 12, liquid crystal display devices (LCD units) 13 - 16 with four digits in each case are also arranged. These serve to indicate numerical values and are designed as segment indicators.

It has already been mentioned that the main operating states are denoted by their names. "Deco calculation" and "Out of range", and that the light-emitting diode 12 turns on in the latter case. This indicates that the function of at least the indicator 16a has been changed by means of a switching device, e.g. that the liquid crystal indicator 16 has been connected by switching to another signal source, which possibility is. made visible in fig. 7 in that the left field of the indicator 16 bears the inscriptions DEDEK and DEMAXD. In this way, an indicator is saved, which means an advantage both with regard to cost and space.

"Deco calculation" is the name given to the state of the indicating equipment as long as it can work, in accordance with the stored table values, and. their treatment specification, i.e.

- if the diver has switched on the indicating device out of the water (before the diver.goes into the water), - if the diver does not return to the surface until he has fully decompressed in accordance with the specified decompression conditions, - as long as the dive does not exceed the maximum values of the stored tables , and - as long as the indicating device does not enter a software error.

During the "Deco calculation" operating mode, the following values shall be displayed: - The total diving time (in minutes) extending from the start of the descent until the surface area is reached:

DIVET in field 13.

- The existing diving depth, with an accuracy of half a metre: DEPTH in field 14. - The ascent time (including the prescribed decompression time in each case) in minutes (UPDIVT in field 15) which the diver must expect at all times during the dive if he ascends at the maximum allowable rate of ascent. - The existing decompression step in each case, i.e. during the dive the deepest decompression depth in each case and, during decompression, the depth at which decompression is now to be performed, with an accuracy of 1 meter:

DEDEK in field 16a.

- The existing decompression time in minutes (DEKOT in field 16b. This is the prescribed decompression time in each case in the decompression depth step DEDEK.

These indications can be seen in fig. 7, while at the same time the light-emitting diode 12 remains off and the two light-emitting diodes 11 and 10 only light up if the corresponding case occurs.

In the main operating condition "Out of range" the transducer equipment 5 (see Fig. 6) is over-voltaged by means of a pre-bypass circuit (appropriately provided in a single integrated circuit), so that the indicating device now only performs the function of a depth gauge with a secondary indicator and a diving timer. The indication mode "Out of range" comes into operation as soon as the indication device can no longer work in accordance with the stored table values and their processing regulations.

In the operating state "Out of range" the decompression times, decompression depths and ascent time are no longer calculated, and the UPDIVT, DEDEK and DEKOT values displayed up to this point are removed. Instead of DEDEK, the maximum depth achieved so far in the dive, DEMAXD, which was previously stored without being displayed, is now displayed in field 16a..

As mentioned, a switching device which is arranged in the indicating equipment and is appropriately included in the integrated circuit, is used for this purpose. If the light-emitting diode 11 should happen to light up at the time of entry into this main operating state, it is extinguished in this state, just as the display devices 15 and 16b are emptied. Only the light-emitting diode 12 lights up continuously to indicate the changed operating state, while, on the other hand, the light emitting diode 10 continues to complete its normal function.

In addition to these main operating conditions, four additional operating conditions were mentioned, in front. Regarding these, it has already been explained that the diode 10 lights up in the "climb speed" state, i.e. if the maximum permissible climb speed is exceeded, and. that the diode 11 lights up at the beginning of the "Decompression countdown" state, i.e. with the beginning of counting the decompression time from the moment the deepest decompression step is reached in each case.

It. third operating condition mentioned, "Power down", is an operating condition in which the indicating device must draw attention to/that the battery voltage has dropped to a critical value. In practice, this can be done by causing the LCD indicator or indicators in the effective main operating state to flash, e.g. at 0.5 second intervals as soon as the battery voltage has. fell below a value sufficient for the next two hours. Like already. explained, power is saved by the indicators being driven by means of an astable multivibrator, which is important in this particular operating condition.

The fourth operating state mentioned, "Software Error", is the state in which an error occurs for reasons related to the program. This presupposes that the programs have been correctly compiled for the indicating device, i.e. in practice the programs are :.constructed so that the indicating device itself can detect an error in the chronological order of the programs and thus switches the display device over to the "Software error" state. From this point on, all functions of the indicating device are inactive. Only an "E" appears in the first digit of the dive time display to indicate an error. The LEDs are all off.

The execution of. the invention is based on the considerations summarized below: To work with the tables, the calculator needs the data for the diving, mainly the depth and the time. The depth is determined from the water pressure, the time is kept in an internal clock.

In a display device, it must be possible to indicate the calculated data and any error indications for the diver.

It must be possible for the diver to switch the device on and off and to reset the device to its initial state. If provision has been made for the operation of a time clock, the diver must be able to enter the time and possibly switch. the display mode•to indicate the time.

When designing the indicating device that is necessary to achieve these purposes, account must be taken of the fact that the equipment must be battery powered, i.e. an operating voltage of approx. 5 - 8 V is available. Any voltage above this value or with a different polarity must be generated from the battery voltage at corresponding costs. To avoid excessively rapid discharge of the battery, the circuit must be designed so that it consumes as little power as possible. The battery voltage must be monitored, and if it falls below a certain minimum value, this must be indicated. To avoid changing batteries in the water- and pressure-tight enclosure, it is appropriate to use a rechargeable accumulator battery.

The device must be mounted in an enclosure or box which. is pressure-tight to a water depth of 100 m, i.e. external connections, such as the charging connection for the battery, switch spindles etc, represent a large mechanical expense and should be reduced to a minimum.

The heart of the converter equipment 5 is a microprocessor 27 (Fig. 9A) which, among other functions - when it is occupied with a program - works as a calculator and which will therefore mostly be referred to as the calculator in the following. For one embodiment of the indicating device according to the invention, a single-chip calculator 8748 from Intel is used. This contains lk EPROM and 64 RAM location units (including normal registers and stack), i.e. space for 64 variables.. If the stack and normal registers are disregarded, there is still approx. 45 variables for use according to desire. lk is available for the tables and the program. The ROM and RAM areas can. can be expanded with additional modules.

A calculation of the size of the tables shows that 3k additional storage (ROM) will be required for the tables.

The selected calculator has an internal timer/counter that runs parallel to and independently

of. the program. This timer/counter is necessary to increment all timers in the program and to synchronize the program with the clock time. The main program can communicate with the timer/counter in the following ways:

- Setting the timer/counter

- Interrogation of the timer/counter

- Start of the timer/counter

- Stop the timer/counter

- Polling a timer flag indicating a timer overflow.

The timer can intervene directly in the running program by means of an interrupt ("Timer interrupt") (in case of any timer overflow).

Depending on whether a pure counter or, a timer is required, an input Tl or the calculator clock pulse (divided by 32 by means of a divider stage 23) can be switched

to the timer/counter, as shown in fig. 8.

For this purpose, a switch can be connected to one of two clamps 18, 19 or to a stop clamp 20. From the block diagram in fig. 8 also shows the most important instructions and their effects.

To start the main program at 0.5 second intervals, the timer/counter will be connected to an interrupt timer. As a result, the quartz oscillator frequency must be determined for the calculator clock pulse and a timer interrupt program (HTIME) must be written.

6 MHz is chosen as quartz oscillator frequency. The calculator's cycle frequency is 15 times less than the quartz frequency, i.e. 4 00 kHz. For every 32 machine cycles, i.e.

for every 80 ys, the interrupt timer is incremented by 1. The interrupt timer is an 8-bit register. By means of the controlled setting of this register, times between 80 ys and 256 x 80 ys = 20.48 ms can be produced. These times are far too short for the intended application and must be extended, using an auxiliary timer program that generates the 0.5 s timer pulse from 25 timer interrupts.

Since the timer interrupt transfers control approximately every 20 ms from one point or another in the main program to the auxiliary timer program, the auxiliary timer program should need as few registers as possible,

as these can no longer be used by the main program.

At least one register must be reserved either as an auxiliary timer or as a display for the auxiliary timer. One aims at a program which, as far as possible, only needs one register for the auxiliary timer and for setting the interrupt timer.

To achieve as individual an auxiliary timer program as possible, the interrupt timer is allowed to run full several times and is initialized with a correction value each time before branching into the main program (for the first pass).

Determination of the correction value for the interruption timer

- Time interval of 24 "normal" timer interrupts: 20.4 ms - Time for 24 timer interrupts: 24 x 20.48 ms = 4 91.52 ms

- Time difference to half a second: 500 - 491.52 = 8.48 ms

- Number of required timer interrupts: 8.48 ms/80 ys

= 106 - To achieve a timer overflow (which initiates the interrupt) at the desired time, the interrupt timer must be initialized at 256 - 106 = 150. The above-mentioned auxiliary timer program HTIME will be dealt with later in the description of the programs. Out. from the above it can under all circumstances be realized how the timer 7, which is described in connection with fig. 6,

can be constructed in a practical embodiment.

As the power supply circuit 8 (Fig. 6) may be of conventional design, it will not be described further. Instead, the input of the third input value, namely that from the pressure sensor 6, and the remaining circuit will be described in connection with fig. 9A and 9B.

Some requirements for the pressure sensor have already been stated above. It must also be resistant to fresh and salt water, it must emit an electrical output signal for further processing and it must also have small dimensions and be cheap.

The most commonly used systems for electrical pressure measurement are load cells with adhesively attached deformation gauges (stretch flaps) and piezoresistive sensors.

For the indicating device according to the invention, a piezo-resistive system has been chosen due to the fact that this has the following advantages compared to the systems with strain gauges: - It gives a larger output signal and therefore only requires a simpler amplifier circuit or none at all. - It is then also less sensitive to disturbance signals, such as thermoelectric voltages etc. - The single crystal material with internally diffused resistors is not bound by adhesive as with deformation gauges, and thus has much less hysteresis (no creep of the adhesive) and no fatigue phenomena (as long as the cell

operated within its nominal range).

- Manufacturing in compliance with the laws of semiconductor physics is easier and allows production in large series at much lower prices.

The selected pressure sensor also has the advantage of a pressure range from 0 to 10 bar and thus a measurement range to 90 m water depth, and it is located in a robust steel case, while the external pressure acts on a steel membrane which is resistant to salt water .

The continuous signal from the pressure sensor 6, amplified by means of an amplifier 21, is to be appropriately transformed into a calculator-compatible, quantized signal, and for this purpose an analogue/digital converter 22 is arranged for receiving the amplified: output signal from the pressure sensor 6. An analogue/digital converter with 8-bit resolution is used because the calculator can only process 8 bits in parallel. To be able to measure sufficiently precisely with 8-bit resolution at the zero point/, for ..measuring the height above sea level, it must be possible to change the measurement range. This is possible in the following ways: - By switching the gain to the input amplifier (differential amplifier) 21 as shown in fig. 9A, - when switching the reference voltage source 39 to the analog/digital converter 22 as shown in fig. 9A, - when connecting an analog/digital converter with a higher resolution, so that either the upper or the lower 8 bits are connected to the bus depending on the required resolution.

In order to feed the pressure sensor 6, in principle an accurate current source would be required, and also an accurate reference voltage source would be required. However, it can. both stabilized sources are looped if it is recognized that the pressure sensor with the reference voltage source 24 in practice forms a resistance bridge which can be connected directly to the operating voltage in the well-known manner, while the reference voltage of the reference voltage source 24 with a simple resistance voltage divider is also connected to the operating voltage, so that the effects cancel each other out, while the signal obtained at the output of the analog/digital converter 22 is exactly proportional to the signal from the pressure sensor 6 and thus to the water depth.

To save stabilized reference sources, the pressure sensor is connected directly to the 5 V operating voltage (instead of to 14 V). Because of this, the output signal of the pressure sensor drops. This signal is far too small for the analog/digital converter 22 and thus must be amplified approximately by a factor of 12, so that it lies between 0 and 4 V. The amplifier 21 must then be designed so that one can manage with an operating voltage of only 5 V, and so that the amplifier 21 itself can follow a small input signal to zero. (Normal operational amplifiers usually require a supply of + and - 15 V, and the output signal only comes within , about 2 V of the supply voltage). A differential amplifier 21 was chosen for this amplifier, and this will be discussed further at a later stage.

Of the additional circuit parts which appear in fig. 9A and 9B, mention must be made of a comparator stage 41 which is arranged after the differentiation stage 26 and whose purpose will be described later, and above all the calculator 27 which, together with a memory or storage stage 28 (EPROM), forms the core of the converter equipment for conversion and selection of the real or equivalent bottom time, taking into account the other parameters mentioned. Between the bearing 28 and the converter 27, an intermediate bearing (locking circuit = latch) 29 is also connected for addressing the bearing 28.

Thus, the following peripheral components are arranged for the calculator 27:

- A table and program store, both in store level 28,

- the intermediate bearing (lock circuit) 29,

- the analog/digital converter 22,

- the liquid crystal display devices 13-16,

- the light-emitting diode indicators 10 - 12,

- two additional switches S3 and S4 if a time indicator is required.

To drive these components, the calculator 27 has:

- an 8-bit bidirectional data bus 42,

- two locked I/O ports, each of 8 bits,

- two test inputs TO and Tl (one of which, with suitable programming, can serve as an input for the counter and the

others such as timing pulse output),

- an interrupt input 38.

In order to make full use of the calculator and to manage with as few extra components (locking circuits, drivers etc.) as possible, all input and output lines will be used in the following way: The data bus will be used for data transfer from storage 28 or from anlog /digital converter.22 to the calculator. In order not to activate both components at the same time, the correct module must be selected with. a control signal (control wire: Port 2, bit 4).

The port Pl is used to drive the display device, with the following bit assignment:

The binary chip address is transformed in a 1-of-4 decoder 36 into chip-enable signals. Since the data is only accepted by the LCD decoder driver with each positive edge of the chip open signal, this signal must not be present continuously. For this reason, the 1-of-4 decoder is pulsed with the ALE signal.. (The ALE signal appears each time during each calculator cycle.)

The port P2 is used for page addressing of the storage, for selection between the analog/digital converter 22 and the storage 28, and for activating the LEDs (10 - 12).

Bit Allocation:

The LED diodes 10 - 12 are activated by means of a step detector f and driver step .35 which will be described later.

The address for a value in the external storage 28 is formed from the page address (Port. 2, bits 0 - 3) and an address on the data bus. The address section or part of the address, which is transferred on the data bus, must be held in a latch circuit 29 (CMOS buffer storage).

Inputs:

To indicate that the battery is almost exhausted, a power-down detector (battery voltage threshold switch) TO is used. Logical "0" on input TO means that the calculator must point out the limitation of the diver's remaining time by means of a flashing display. The calculator 2 7 thus takes over the function of an astable multivibrator.

If a clock function is to be provided, the inputs Tl and 38 must be used for setting the time and for switching the display mode.

Porten Pl. and Gate P2 bits 5 and 7 in the calculator 27 lead to a display circuit which is shown schematically in fig. 9B. This contains the three light-emitting diodes 10 - 12 and the four liquid crystal indicators 13 - 16, each of the latter being preceded by a decoder and driver stage 30 - 33. The structure of these decoder and driver stages 30 -

33 is shown in fig. 10 and shall be described briefly below.

For the decoder and driver steps 30 - 33 (LCD decoder driver), the Intersil module ICM7211 Type AM has been chosen. This module contains an oscillator as well as all the decoder and driver stages which. are required to drive the er^4 digit indicator. A capacitor that determines the frequency,

is required, as an external component. This type of AM is microprocessor compatible and has a code that allows the suppression of a digit. It is thus possible to suppress leading zeros in the indicator.

It can be realized from fig. 10 that:

- The data must be transferred one digit at a time with the corresponding digit address. (The digit address. is a 2-bit

BCD words).

- The relevant chip is selected by means of a chip selection wire, while a data transfer can only take place on a positive edge or flank on this wire.

For this circuit, as shown in fig. 10, the code shown in fig. 11. Regarding this code, the following points should be noted: - To take. away or remove a digit., it is only necessary to send the binary value. 1111 to the corresponding numerical address. - With this code, it is also possible to use the letter "E" as a special character for an error signal.

In fig. 11 shows Column B the binary code and Column HD shows the hexadecimal code.

As the last mentioned figures 10 and 11 only serve

to explain fig. 9B very schematically, a comparison must now be made between the detail 39 in fig. 9A and two alternative versions as shown in FIG. 12 and 13.

During the discussion of the analog/digital converter 22, it was mentioned above that this only has a resolution of 8 bits. It was further stated that area switching therefore had to be carried out. In this way is. where possible, to get by with cheaper components, e.g. with it. 8-bit A/D converter (ADC) compared to an ADC with a higher number of bits. In a similar way, area switching can also be advantageous if the pressure sensor 6 is not directly able to measure both the water and air pressure. For both cases, a single switching device can be used with which the reference voltage source 24 is switched in a suitable manner.

It has already been pointed out above that the amplification of the impedance converter 40 can be switched for this purpose as shown in fig. 12, where the reference voltage source 24' is simplified. In this figure, as well as in fig. 9A (switching step 34) and fig. 13, are the switches, which are more conveniently in the form of. FET switches, for clarity shown as normal switches.

The reason why FET switches are preferred lies in the following: In order not to consume too much power, the transverse current through the voltage divider must be kept as small as possible. This means that the voltage divider. must be designed with as high a resistance as possible. In order not to load the voltage divider with the A/D converter's input, the voltage divider is connected to the A/D converter .22 via an impedance converter 40.

Another variant appears in fig. 13 where the voltage divider 24" is switched before the impedance converter 40. The impedance converter 40 can be the same in each case. Although both variants (which are shown in Figs. 12 and 13) are possible, they have the following disadvantages: - All commercially available FET -switches^- must be operated with supply voltages of + 15 V and - 15 V; - with a "normal" FET, the blocking voltage is exposed to too much large spread to eat one. such FET should be able to be operated with CMOS levels; - the only available CMOS FET switch (4066) also cannot be used in the above circuit configuration due to its On resistance of typically 3-5 kfi, although it only needs one. 5V supply.

As shown in fig. 9A, a switchable reference voltage source 39 has therefore been chosen because it is the solution in which the switch's On resistance has no effect on the accuracy of the switching of the reference voltage, even though a CMOS switch can be used. This circumstance takes into account the fact that the FET switch in the switching stage 34 is in each case located in the input branch of the impedance converter 40, in which practically no current flows, and as a result no voltage drop is expected due to the On resistance . As can be seen from fig. 9A, the switching stage 34 contains two switches S1, S2 which are opened and closed alternately. In relation to this, an advantage can be seen for those in fig. 12 and 13 showed alternatives at N that only a single switch S is required for the switching.

For the selection of the resistors, the following conditions have been found to be particularly appropriate:

The zero point on the pressure sensor 6 can then be adjusted with the trim potentiometer R4, and the system's sensitivity can be adjusted with the help of the trim potentiometer P^ in the reference voltage source 24 of the analog/digital converter 22.

As already explained in connection with fig.

7 and the diode 10, the maximum rate of ascent must on

10 m/min is monitored and an indication is given if this is exceeded. This monitoring can be carried out either in digital or analogue form. In both cases, the "deep signal" must be differentiated.

To save space, a software solution would be desirable. To achieve a reasonably realistic indication, a pressure change over 2-3 digital steps must be considered, as the last bit of any digital value can jump. :Then. a depth step in reality corresponds to 0.5 m, the diver must be monitored, with an ascent rate of 10 m/min over a distance of 1 - 1.5 m, or over a time interval of 6-9 seconds, which with cyclic measurement with intervals of 0.5 seconds require approx..12 - 18 variables, the difference of which would have to be formed continuously to be able to differentiate the signal digitally. The large number of variables that will be required for this differentiation, with only 45 variables available in total, gives preference to the analog differentiation step. The differentiation step 26 which is now provided generates from the depth signal. (position signal) a speed signal which must be compared with a signal which is proportional to the limit value of the rate of ascent. The output signal from this comparator circuit then controls the LED indicator 10.

Programs and operation of the indicating device: In order to be able to record the diving operations in their entirety using the input values pressure and time, the complete program is divided into four main program sections as shown in fig. 14. Each of these program sections or program sections also corresponds to a section of the dive. During a dive, the diver can run through these sections or sections in the most widely varying sequences. This means that the program sections must also run correspondingly one after the other.

These program sections will now be explained in connection. with. the operation of the indicating equipment. When the main switch 9 (fig. 6) is closed, all the electronics are connected to the supply voltage, and the calculator 27 (micro-processor) is switched on, after which it sets the program counter to zero and there branches to the address for the Restart program (RSTART) .. The restart program initializes all variables, timers, and counters to their initial or initial values. At the end of the resurrection, the abort timer is initialized, enabled, and started.

Every 0.5 seconds the main program is now restarted using the auxiliary timer program ( HTIME ) and then proceeds as follows: The pressure is entered in the program section PSNORC, and then the control is handed over to the Check-and-Set program ( CHKSET ). Program section CHKSET supervises all timers and counters as appropriate and passes control to one of the program sections

Surface area ( SURFAC).

Diving (DIVE)

DIVEUP

Decompression (DECO)

Display (DISPLY)

The program section DISPLY serves the display and

then enters a waiting loop that must never run to completion as the auxiliary timer must restart the main program before this time. If the wait loop does not terminate at least once (after about 1.5 seconds), the program .enters the software error mode.

In order for all programs to work correctly, a collection of subroutines (LIB) is also necessary. These sub-routines are called individually by the different programs.

The individual program sections must be described

by means of fig. 16.

By means of fig. It should be 15. however, first a few points regarding the memory or storage configuration are introduced.

As the storage 27 only has an 8-bit index register and the external storage can only be read by indexed addressing, it must be divided into pages of 256 information units or "bytes" (corresponding to the index pointer area). The storage of tables must therefore also take place. page by page, in the same way for all five tables (for the individual, elevation steps above sea level), so that the tables can be read with the same programs. With this storage system, there are necessarily empty "spaces" or "gaps" in the storage as the data does not always need a full page. This formation of gaps or voids is exacerbated due to the different table lengths.

(The table length decreases with increasing height above the hub).

If all this is taken into account, the 3k table values need approximately 4k of storage, i.e. one height step needs 3 pages or 3/4 k. If thus 4k of ROM is used, there is still one page (256 bytes) left for other data or programs.

It has already been mentioned that the calculator 27 (Fig. 9A) has an internal storage of lk. Considering the large amount of data to be processed and the scope of the necessary program, this capacity is however in no way sufficient for program storage.

In order not to have to use even more extra modules, the 4k EPROM storage is connected so that it can be used as program and data storage. As the complete, main program, including all sub-routines, needs a storage space of over 2k, significantly more than 2k remains for the tables to be stored. Three tables can be accommodated in this space. As the normal sports diver usually does not dive. altitudes of more than 2000 m above sea level, will only the three tables for. the altitude steps 0 - 700 m, 701 - 1500 m and 1501 - 2000 m will be stored.

The storage-busy time table then appears as shown in fig. 15, where the first half of the program is contained in the internal storage 17a of the calculator 27 (fig. 9A), the second half of the program in 17b, the sub-routines in 17c and the tables in 17d - 17f in the storage. 28. Using pages 7 - 9 in the right part of fig. 15 it is e.g. shown that Page 7 (17g) contains the first half of the decompression table, Page 8 (17h) contains the second half of the decompression table and the surface interval table, and finally Page 9 (17i) contains the zero time table and the recurrence or repetition table. The storage of the tables certainly seems to be difficult, but is nevertheless cheaper, with regard to the components used, than if one wanted to calculate the specified values by only storing the mathematical connections (as far as this is possible).

In order to be able to read the tables, a plan must be created for the data structures and table processing routines. By means of fig. 15 it has been shown that the indi-. vidual tables are housed in given pages in the warehouse. This is forced due to the limited addressing possibilities and the requirement that all tables must be read out with the same sub-routines. It now only remains to determine the arrangement of the individual values in each table, so that each value can be reached as quickly and easily as possible. (The selection of the correct page and table will be described later).

Only a linear representation is possible in the table storage, i.e. all tables, whether they are linear (such as the zero-time table), two-dimensional (such as the repetition group table), or also three-dimensional (such as the decompression table), must be and stored in a linear form. To represent a multidimensional table in linear form, positional markers (identifiers) must be introduced in the table for end of line, end of table, etc.

In order to achieve as small a table as possible, an attempt must be made to accommodate more than one value or one value and one or more identifiers in one storage location (storage cell).

To work with the decompression table, the following routines will be necessary: - With the maximum depth and bottom time, the sum of the decompression times for a dive, the repetition group and the depth of

the first decompression stay is determined.

- With the depth, bottom time and the instantaneous decompression depth, the decompression time at this depth must be determined. - With the real depth, the associated depth step (according to the decompression table) must be determined.

With the input values depth.and. bottom time, a line in the table must therefore be selected for each time. The table must therefore be provided with time and depth step identifiers in such a way that...at. the identifiers can be found easily and can be compared with the input values.

Thus, in fig. 15A showed data arrangement selected, where STID denotes a depth step identifier, ZID a time step identifier, RG the repetition group, ZEND a line end marker, STEND a depth step end marker and TABEN.D a table end marker.

The following points are now worth noting regarding the existing tables:

- With one exception, all values are less than 64.

- All depth steps, with one exception (12 m), are multiples of

5. The largest value is 70.

- The bottom time steps are also multiples of 5, largest value 250. - The repetition groups go from A to L. If these are transformed into numbers and a value (M) is also introduced for the case where there is no repetition group, the values go from 1 to 12.

- The value 0 never occurs.

If the above recognition is taken into account, the following package concept is achieved: - The line in which the decompression time 70 minutes appears (the only value greater than 64) is omitted. - The depth-step identifiers are stored after division by 5.

(Special rule for the depth step 12 m).

- The bottom time step identifiers are also stored after division by 5.

If this is done consistently, all values are less than 64 and can be represented by 6 or 8 bits.

This means that 2 bits are free for identifiers and markers.

Selected identifiers: ZEND: Bit.6 set

STAND: Bit 7 set

TABEND: Value 0, as this identifier must be the same in all tables.

The markers ZEND and STEND can. thus be stored together with the repetition group (which is always located at the end of the line).

The data arrangement of the decompression table now appears as shown in fig. 15B.

The most important part of the programs for reading the decompression tables: The selection of a line can be achieved relatively easily by "thumbing through" the table and comparing it in

the table stored identifier with the input values. Readout program (Selecting a line in "Pseudo-Pascal")

SET POINTER TO Ist. TABLE VALUES ; Ist depth stageid.

FETCH VALUE(POINTER)

DO WHILE DEPTHSTAGEID. < CONVERTED INPUT DEPTH

BEGIN: DO. WHILE .NOT STAND

BEGIN: INCREMENT POINTER

FETCH VALUE(POINTER)

END

INCREMENT POINTER

FETCH VALUE (POINTER) •,. Depth gauge owned.

END

INCREMENT POINTER

FETCH VALUE(POINTER) ; Time identifier

DO WHILE TIMEIDENTIFIER < CONVERTED INPUT TIME

BEGIN: DO WHILE NOT ZEND

BEGIN: INCREMENT POINTER

FETCH VALUE(POINTER)

END

INCREMENT POINTER

END

; The pointer now points to the first value of the desired ; line

On the basis of this program section, the desired values can be easily determined: - The depth of the first decompression stay is the first value in the selected line. - The sum of all decompression times for a dive is equal to the sum of all values between the start of the selected line and the ZEND identifier. - The repetition group is located in the same storage cell as the ZEND identifier. - Based on the real decompression depth. the position of a decompression time within the line, and thus its value, can be determined.

To read out values from the decompression table, the following three subroutines were written:

BDECOW: Determines the following values:

Sum of the decompression times for a dive.

Depth of it. first decompression stay. Decompression time for the first decompression stay.

BDEKOT: Determines the decompression time for a given decompression depth step.

BRPDEC: Determines the repetition group 1 decompression table.

The selection of a line mainly takes place in the subroutine XDECTB which is used in the above subroutines.

The transformation of a real depth into the corresponding depth step is carried out (since.in the main only.multiples of 5 appear here) with a rounding formula in the subroutine BDEST, without using the decompression table.

Repetition or Repetition Tables:

To work with the repetition table, the following routines are necessary: - With the depth and the repetition group, the additional time must be determined.

- With the depth and the time, the repetition group must be determined.

- With the real depth step, the next, deeper depth step (in relation to the repetition table.) must be determined.

With the one input value - the depth - the value's position in the line can therefore be determined. The second input value is either the repetition group which, when correctly selected, indicates the number of the line in which the additional time is to be found, or the time with which, by comparison with the value in the table, the line whose position corresponds to the repetition group can be found .

Taking this knowledge into account, a data arrangement was chosen which does not contain ..any identifiers, but only end-of-line marks. The position of a value in the repetition group is known if the row and column in which the value is located are known. The column corresponds to the position of the value in a line. To be able to determine this position of. the value in a line, the header for the repetition table (the line with the depth steps) is stored as a pointer line, separated by a TABEND tag, before the actual data. The position of the desired value in this line can now be determined by comparing the input value "Depth" with the values in the indicator line. Identification of the line is not necessary as the repetition groups have been chosen so that they agree with the position of the lines in the table.

The selected data arrangement for the repetition tables appears in fig. 15C as far as the index line is concerned, and of FIG. 15D when.it concerns the table values. The repetition table's data is stored linearly, starting with the header. The program section. for reading the repetition table, namely the determination of the position of a value in a line, can be made to compare the input depth with the indicator line.

Expressed in "Pseudo-Pascal" language, the following is obtained for the determination of the position in the line:

SET POS = 1

SET POINTER TO BEGIN OF POINTERTAB.

FETCH VALUE (POINTERS)

DO WHILE VALUE (POINTER) < INPUT DEPTH

BEGIN:. INCREMENT POINTER

INCREMENT POS

FETCH VALUE (POINTERS)

END

The variable POS now contains the value's position in the line.

The variable POS is not actually "counted", but is determined from the difference, in the pointer value at the start and end of this program section.

On the basis of the above program section, the desired value can be easily determined: - The additional time can be determined by moving the pointer forward by the number of lines.

The "Pseudo-Pascal" program for this is as follows:

DO WHILE REP. GROUP ^ 0

BEGIN: DO WHILE NOT ZEND

BEGIN: INCREMENT POINTER

FETCH VALUE (POINTERS)

END

DECREMENT REP. GROUP

END

POINTER = POINTER + .(POS. IN THE LINE)

- The repeat ion group can be determined by reading the value in the correct POS in each line and comparing it with the input time.

"Pseudo-Pascal" program for this operation:

SET POINTER TO BEGIN OF DATA

AUXPOINTER = POINTER + (POS. IN THE LINE)

FETCH VALUE (AUX POINTER)

DO WHILE VALUE (AUXPOINTER) < TIME

BEGIN: DO WHILE VALUE (POINTER) / ZEND

BEGIN: INCREMENT POINTER

FETCH VALUE (POINTERS)

END

AUXPOINTER = POINTER + (POS. IN THE LINE)

END

The next deeper depth step can be determined in the indicator line without using the additional table values. The position in the line is determined easily and the next value is read, but in the indicator line itself.

For reading values from the repetition table, the following subroutines have been written:

BZZU: Determination of additional time

BRPGUW: Determination of the repetition group (underwater) BDESTN: Determination of the next, deeper depth step.

The determination of the position within the line finds

mainly takes place in the subroutine XREPTB which is used by the above three subroutines.

The zero time table is stored and read in the same way as the repetition table. Thus, one pointer line and (unlike the repetition table) only one data line is stored.

For reading (such as with the repetition table) the position in the line is therefore first determined and with this the necessary zero time.

If, on the other hand, the surface interval table is considered, it can be realized that the difference from column to column is approximately the same in each line. This is also understandable because a diver always goes from a repetition group to the next, lower group after a given time, and these times must be the same, regardless of the starting group.

For this reason, only the lowest diagonal is stored instead of the whole. the table. As this table only works with the repetition groups and only one (diagonal) line is stored, this can be stored in such a way that the repetition group corresponds exactly to the position in the line.

Under these circumstances, working with this table is simplicity itself.

The surface interval time (according to the repetition group) is looked up in the table and compared with. the value stored there. As soon as the two values are equal, the surface interval time is set to zero and the repetition group is decreased by 1.

So far, only the way in which a given value is looked up within a table has been described. It will now be explained how the page in which the table is located in the external storage is found, and how the cursor is set to the start of the table within this page.

To select the table, an offset must be determined depending on the height step and corresponding to the page in the first table for this area. To this offset must be added a further offset corresponding to the table's position within the set of tables. The sum of these two offsets shall be used as the page address of the lowest 4..bits. of gate 2. When the page has been determined in this way, the table must still be selected then, in many cases two tables are accommodated on one page. If the table is not at the start of the page, the values on the page must therefore be "thumbed through" to the first TABEND mark, to set the pointer to the beginning of the second table.

To find the start of the table, the subroutine FNEXTT has been written. This.looks up a storage area for the TABEND tag and sets the pointer to the value.after this tag.

In the previous description of the display device, it was shown that it must react to two types of errors, namely: Out of area: If the diver enters an area (in posi tion or time) which is no longer covered by

the tables.

Software error: If the calculator enters an "overflow" or "underflow" during a calculation, or if the timing device fails.

In order to detect these errors, the following is performed in all table processing routines: - the table limits are monitored, and if these limits are exceeded, the Out of Range flag is set; - during any multiplication, the result is monitored, and if this can no longer be represented by 8 bits, the Software error flag is set; - similarly, the result would be monitored during a division, or a check would be performed as to whether a division by zero had been performed. However, this monitoring becomes redundant in the present case as a division by zero can never occur. In reality, the divisor is always loaded with a constant that is always greater than zero, one instruction before the deviation routine is called.

Now that the storage and handling of the tables has been described, the program sequence and program structure will be described. Tables 11 - 18 and 20 - 22 mentioned in the description can be found at the end of the description.

Each main program is described by the program documentation and the associated flowchart. The program documentation is structured so that it describes the flowchart verbally and coherently. With the help of the flowchart and the program documentation, any desired point can be found quickly and easily in the assembler code.

As shown in this program structure shown in fig. 16, the program begins, after the main switch 9 has been switched on (see fig. 6), with the Restart program RSTART. This is carried out as shown in Table 11.

Every 0.02 seconds, the auxiliary timer program HTIME is executed as shown in Table 12, and in the process it generates the timer pulse of' 0.5 s, with which it starts the main program cyclically every 0.5 s, starting with the program section "Detect. ; press" - PSNORC.

To be able to detect entry into the water by means of a pressure change, the latter must be 0.02 bar in 1 second. The pressure change of 0.02 bar corresponds to an air column of 200 m. True, no human can move a vertical distance of 200 m in 1 second in air without jet propulsion, but the diver achieves a pressure change rate of 0.02 bar/s when he passes from the air, to the water. A water height of only 20 cm is sufficient to produce the pressure of 0.02 bar, and any diver will dive to a depth of 20 cm within 1 second of descent into the water.

This water height of 20 cm appears on one

on the one hand based on the resolution of the pressure sensor 6, and on the other hand based on the fact that the change in pressure must amount to at least 2 digital quantities. If, due to a fault, the indicating equipment is first switched on under water (an abnormal case), this is detected by means of a test that ascertains whether the initially measured pressure is greater than 1.2 bar. This is essential as the air pressure in such a case could not have been determined in advance.

The reason for choosing the limit of 1.2 bar is that the air pressure at sea level can reach a maximum of 1.06 bar. If the case where the diver dives in a lake below sea level is ruled out, the test can without doubt be carried out at 1.2 bar.

Thus, if the main switch 9 is actually first actuated underwater, the indicating equipment works on the assumption that the atmospheric pressure at the diving site is equal to 1 bar. From this point on, the depth gauge in the equipment according to the invention is only as good as most conventional depth gauges which do not distinguish between diving in mountain water and in the sea. The pressure value of 1 bar then corresponds to the atmospheric pressure at sea level and is thus, for the present system, the zero point from which either the water depth or the height above sea level is determined.

The program sequence for the program section PSNORC appears in detail from fig. 17 and also of Table 13.

In the figure, 4 3 denotes a test regarding whether the indicating equipment has been switched on underwater, 44 denotes a test regarding whether the diver has gone down into the water, and 45 denotes a transformation of the pressure, so that it is adapted to the gain = 1.

At this point it should be mentioned that in each case (in the calculator 27 and in the analog/digital converter) 10 bar corresponds to 200 bits, so that one bit gives a resolution of 0.5 m. The depth gauge is thus also accurate to 0, 5 m, while the preparation of the data for use in the tables becomes very simple as the depth, determined digitally, when divided by 2, corresponds exactly to the real depth in metres. The ratio of 10:200 means, however, that the numerical value of the pressure processed further in the calculator is too large by a factor of 20 when compared with the real pressure. It should also be mentioned that the calculation of the diving depth using the pressures PNEU . and PNULL is reduced to:

DEPTH = (PNEU - PNULL)

This means that the diving depth included in the calculator is greater than the real diving depth by a factor

Oh A

at 2.

It is further apparent from fig. 16 that the program section PSNORC is followed by the program CHKSET whose details appear in Table 14.

At this point, the fig. 16 displayed library programs are discussed.

All the used subroutines are contained in this program section.

These are:

- All the table processing routines described above.

- A few mathematical programs.

To this end, the library program has:

- A subtraction with direct access to the minuend..

- A sub±raction with indirect access to the minuend.

(Both subtractions transfer the sign information in the meant bit and can thus also be used for comparison

of two numbers).

- A multiplication with direct access to the multiplier. (This multiplication of 8 x 8 bits gives a 16-bit result. The 16-bit result, consisting of lower 8-bits and upper 8-bits, is only used in the main program DISPLY, otherwise calculations are only carried out with the lower 8 bits .) - A division with direct access to the divisor. (The original 16-bit with 8-bit division has been changed to an 8-bit with 8-bit division as the calculator works with 8-bit values. the bit, which is set in case of a flood,

. used.)

- A subroutine that converts 8-bit and 16-bit binary numbers into BCD numbers, in order to be able to transfer the values to be indicated to the display device in BCD code,

This subroutine also detects leading zeros and sets FH„ex instead of the leading BCD zero, so that the code required in FIG. 11 for the blank ("blank"), can be provided. In principle, it would be advantageous if the program is not saved as a coherent program block, but the individual subroutines are instead introduced into the main program, so that as many pages as possible are fully utilized, i.e. that few "gaps" occur in program-1 the warehouse and few side jumps are necessary. For the described program structure is. however, this is not advisable, due to the fact that the complete program occupies a warehouse of approx. _2 1/4 k, " i.e.^_;. it is "necessary to work with storage group switching.. For the sake of simplicity, all subroutines are placed after the 2-k limit, so that the storage group ( memory bank ) only has to be switched before. and after each "subroutine" call, and the main program never goes beyond the 2-k boundary, which must be avoided wherever it. is possible., as it would complicate the bearing-group switching ... to a significant extent.

While still in the program section CHKSET, a decision is made, depending on the values and differences determined in this program: which of the programs that follow CHKSET in fig. 16, which must be carried out.

The sequence of program section SURFAC is shown in fig. 18 and in Table 15. Details of the program section DIVE appear in Table 16. In fig. 18 denotes 46 a test of whether the diver snorkels; 4 7 is a test of whether the diver leaves the water; 4 8 is a test of whether the diver has changed to diver status; 49 is a test of whether the diver is in a surface interval, and 50 is a test of whether the repetition group has become zero. Ascent program DIVEUP: To be able to control the ascent at a minimum speed of 8 m/min, the diver must be "observed" over a longer period of time. This "observation" consists in checking whether the diver is in the "ascent cone".. The ascent cone means the area through which the diver moves in the period of 30 seconds, ascending at least 4 m in the vertical direction and not diving below the depth step at which the ascent took place - started. A new ascent cone is set every 30 seconds provided the diver has not left the ascent cone before then and continues to ascend. The sequence of this program is shown in Table 17.

The decompression program DECO is described in detail in Table 18.

As can be realized in particular from fig. 7, all these programs lead to some type of indication assigned to the display program DISPLY.

In order to be able to drive the four display units 13 - 16 (see Fig. 7, 9B) with four-digit numerical indicators, a total of 16 digits must be addressed. These sixteen digits are addressed using a 4-bit code word which has the structure shown in Table 19. The code word for selecting digit No. 3 in the indicator.15 is thus

Using this code word structure it is very easy to send the individual output values to the display device (indicator) .. In reality, a display counter (DISPCO) can be incremented from zero to 15, and the relevant digit can each time be sent in BCD code to the display device. Table 20 illustrates the flow chart for this program section.

Now that the individual program sections have been described, reference should be made to Table 21 in which all program sections are shown in a storage occupancy time table for program storage. In addition to this, Table 22 contains a list of all variables and subroutines that are used.

Furthermore, the status and flag conventions are shown in the subsequent tables 23 and 24.

It should be noted that in the previous statements it has been shown that the tables of the Pressure Chamber Laboratory at the University of Zurich are mainly stored in the table stores, due to the fact that these tables are particularly suitable for the compilation of the entire dive from individual diving sections, they have the possibility of evaluating previous dives during a repeated dive, and they concern not only dives at sea level, but also in mountain waters up to an altitude of 3200 m. Above all, digital processing can be easily carried out with these tables. It is clear, however, that the invention is in no way limited to the use of these tables, but that other tables, for example the tables of the American Navy, can also be used.

Although no particular indicator for the relevant time has been shown and described in connection with fig. 7, it was mentioned in the description that it is advantageous to use the stopwatch (timer), which is present in all circumstances, to indicate the time. This requires that the power supply to the circuit parts required for this time display must be maintained, also after the main switch 9 has been switched off.

Decompression table for 0 - 700 m above sea level

Repetition system for 0 - 700 m above sea level

Decompression table for 701 - 1500 m above sea level

Repetition system for 701 - 1500 m above sea level

Claims (16)

Device for indicating the parameters for a diving operation, such as e.g. current depth, maximum depth achieved, previous diving time or similar, which device is operated with the help of a) at least one store for the decompression parameters at a range of diving depths and diving times, and b) an evaluation and logic stage for the measured values of the depth gauge and the timer, with. the values stored in the warehouse, characterized by the fact that the required total resurfacing time, depending on the diving depths and diving times, including the prescribed decompression stays, can be indicated at any time during the dive, and/or that a converter device (5) is arranged for converting the relevant bottom time, upon entering a new diving depth step, into the equivalent bottom time for this new diving depth step. 2. Device according to claim 1, characterized in that the air pressure, preferably measured in each case using a measuring instrument (6), is also taken into account using the converter device (5). 3. Device according to claim 2, characterized in that a single pressure gauge (6), preferably comprising a piezoresistive measuring cell, for both air pressure and water pressure is connected to the circuit containing the converter device (5). 4. Device according to claim 3, characterized in that the measuring range of the pressure gauge (6) can be switched for measuring air or water pressure by means of a switching device (34). 5. Device according to one of claims 1-4, characterized in that a differentiation stage (26) is connected to the output of the pressure gauge (6). 6. Device according to claim 4 or 5, characterized in that: the switching device (34) comprises a step detection step (35) for the pressure, and which is formed, for example, by the differentiation step (26). 7. Device according to claim 4, 5 or 6, characterized in that - for example for an evaluation and logic step with a limited working area - an area change can be carried out by. using the switching device (34), when switching the gain or the bit range to an analog/digital converter. (22) which is connected before the evaluation and logic stage. 8. Device according to claim 7, characterized in that there is arranged - a reference voltage source (24; 24'; 24") which can be switched using the switching device (34) and which is suitably followed by an analog/digital converter (22) . 9. Device according to one of claims 4-8, characterized in that the switching device (34) comprises at least one FET switch. 10. Device according to claim 9, characterized in that an impedance converter. (40) is connected after the FET switch for disconnection with regard to the input to the subsequent stage, in particular the analogue/digital converter (22). 11. Device according to one. of claims 1 - 10, characterized in that a warning signal (12) and/or a secondary indicator v. (16a) for the maximum achieved diving depth, in the event of the occurrence of an abnormal function can be switched on by means of a detector circuit consisting of a time -setting device (7) and a pressure sensor (6). 12. Device according to one of claims 1-11, characterized in that the converter device (5) comprises a calculator (27) and stores for bottom times and/or decompression times and/or repetition groups. 13. Device according to claim 12, characterized in that the bearing or bearings are of the table bearing type (28). 14. Device according to one of claims 1-13, characterized in that the converter device (5) comprises a storage circuit for the diving depths and diving times in each case, as well as the obtained correction values where such are used. 15. Device according to one of claims 1-14, with at least one segment indicator, characterized in that the segment indicator (16a) can be switched alternately - for example before and after the occurrence of an abnormal function. - to display different data. 16. Device according to one of the preceding claims, characterized in that an astable multivibrator circuit is provided for cyclic activation of at least one display device (10 - 12).