EP0550649B1 - Device for monitoring portable breathing apparatus - Google Patents

Abstract

A monitoring device for portable breathing apparatus has a manometer that detects the pressure in the pressure reservoir (5) of the breathing apparatus and an emitter (2) that emits at regular intervals a signal that corresponds to the pressure. The emitter further has a signal generator that generates an identification signal charactheristic for the emitter. The pressure signal and the identification signal are received and checked by a receiver (3). When the identification signal matches an identification comparison signal stored in the receiver, the pressure measurement value is displayed on a display (4).

Description

The present invention relates to a monitoring device for mobile breathing apparatus. Such mobile breathing devices are e.g. used by divers, firefighters in fire fighting or generally when the air is contaminated with pollutants that make free breathing impossible. Mobile breathing devices usually consist of one or two metal bottles, which e.g. carried on the back of the user and in which a highly compressed oxygen-gas mixture with a pressure of e.g. up to 350 bar is included. This oxygen-gas mixture is referred to in the following simply as breathing air or simply air. The breathing air is taken from the bottles via a shut-off valve and inhaled by the user using a so-called lung regulator.

• Beim Gerätetauchen werden heute, im professionellen Einsatz, Tiefen von über hundert Metern erreicht, und auch beim Sporttauchen werden von geübten Taucher beträchtliche Tiefen erzielt.

The problem of using such breathing apparatus is first described using the example of scuba diving:

• Today, in professional use, scuba diving reaches depths of more than a hundred meters, and even deep diving is practiced by experienced divers.

With increasing water depth, the hydrostatic pressure acting on the diver increases, which leads to the fact that the body tissue has a higher amount of inert gases, i.e. in particular absorbs nitrogen. This process is reversed when it appears and the pressure is reduced. If the pressure is reduced faster than the released gas can be discharged and exhaled, the decompression sickness arises, which in minor cases can lead to temporary health impairment, in more severe cases it can lead to permanent health damage and even death. In order to prevent the inert gases from being released too quickly, divers must therefore take longer pauses in surfacing at certain depths when they reappear after a longer stay, which are referred to as so-called decompression stops. The duration of the necessary decompression stops is difficult to calculate because the human body has a large number of different types of tissue, which differ both in terms of their saturation and desaturation behavior depending on the depth and time of diving, and in terms of medical risk. For this reason, divers usually use diving tables in which the decompression times are given as a function of the diving depth and the diving time reached, or they use diving computers in which the saturation and desaturation behavior of a selected number of tissue types is mathematically simulated and the decompression times thus determined are given to the diver by means of corresponding ones Display facilities are shown.

An overview of the problem of decompression gives e.g. the work of A.A. Bühlmann: Decompression-Decompression Sickness, Berlin, Heidelberg, New York, Tokyo 1984, ISBN 3-540-13308-9 and in particular pages 1-62 of the medical aspect, and pages 63-67 about the decompression calculation. Pages 68 - 82 contain decompression boards for divers.

Before the diver undertakes such a dive, he must ensure that the air supply he has carried is sufficient for the planned length of stay and for the ascent time.

However, determining the required air supply poses considerable difficulties: the amount of air consumed by the diver per minute is not constant, but changes e.g. with the physical strain. In the case of anxiety and panic conditions, air consumption can skyrocket due to so-called hyperventilation. Furthermore, the amount of air removed is of course dependent on the respective ambient pressure and thus depends on the depths the diver visits.

The diver therefore needs a monitoring device in order to be able to estimate the actual air consumption and the possible length of stay under water.

At present, divers use pressure gauges to monitor the air supply, which are connected to the breathing apparatus via a hose and display the current pressure of the air supply in the container. Since the pressure drops as the air is removed from the bottle, the remaining breathing time can be estimated to a certain extent, provided experience has been gained.

It has also been suggested, see e.g. US Patents 4,794,803 or 4,586,136 to design a monitoring device in such a way that the remaining time still available for the diver can be determined and displayed directly from the measured bottle pressure. However, these devices have the disadvantage that they are connected to the breathing apparatus via a hose and are therefore very unwieldy to operate and can also impair the diver's freedom of movement.

In order to counter this problem, in the Australian patent document AU-B-78218/87, which was used to form the preamble of claim 1 and claim 33, an ultrasound transmission between the pressure sensor on the bottle and one has been proposed instead of the hose Provide display device. In this case, the reception and display device is arranged on the face mask of the diver.

However, the use of such monitoring devices, especially if they work with wireless signal transmission, is only justifiable if certain security requirements are met.

It must be ensured that the signal transmission from the transmitter to the receiver is correct under all circumstances, i.e. that movements of the diver and the water, external disturbances etc. have no influence on the transmission of the measurement signal.

It should be taken into account that the ability to think from a depth of about 30 m is impaired by the high N2 partial pressure, which exerts a kind of narcotic effect (deep intoxication). If the monitoring device e.g. incorrectly indicating that the air supply is too low, this can lead to rash, panicky reactions even for experienced divers. It should therefore be ensured that the monitoring device never, if not briefly, displays an incorrect signal.

The problems described above for scuba diving apply, in a correspondingly modified manner, also to the use of breathing apparatus for fire and disaster control and other applications. Here, too, the user needs an exact specification of the breathing time still available, e.g. to be able to start its return journey in good time. Furthermore, the user is usually in a particular state of stress, and care must be taken to avoid incorrect measurements and incorrect information as far as possible.

• Diese Aufgabe wird erfindungsgemäß durch den Gegenstand des Anspruches 1 gelöst.
• Das erfindungsgemäße Verfahren ist Gegenstand des Anspruches 33.
• Zu bevorzugende Weiterbildungen der Vorrichtung sind Gegenstand der Unteransprüche.

The present invention is therefore based on the object of providing a device for monitoring mobile breathing apparatus, by means of which the user is at least informed about his air supply and which works reliably and in particular free from external interference and whose display can be read off in a simple manner. It is also an object of the invention to provide a corresponding method for monitoring mobile breathing devices.

• This object is achieved by the subject matter of claim 1.
• The method according to the invention is the subject of claim 33.
• Preferred developments of the device are the subject of the dependent claims.

The monitoring device according to the invention consists of a transmitting device and a receiving device separate from it. This design has the advantage that the receiving device, which is generally combined directly with the display device, can be arranged in the user's field of vision without the user's freedom of movement, e.g. is unnecessarily restricted by a hose device and without special handling being necessary for reading the display device.

The receiving device can thus be carried by the user in any manner. It is preferable that the receiving device is arranged directly on the user's wrist. Compared to an arrangement on a face mask, this has the advantage that the user has no accommodation difficulties when reading the display. In addition, he does not always have the display instruments in view, which could irritate or distract him. The arrangement on the wrist enables the user to easily read the corresponding displayed data even if he e.g. does any kind of work with your hands.

On the other hand, wireless signal transmission poses considerable risks for the security of data transmission. With this conception, the receiving device could produce interference signals such as e.g. are caused by movements of the diver, but also by external sources, as a pressure signal and thus indicate incorrect or more frequently changing values to the user. It is then no longer possible for the user to reliably read the data.

A risk that should not be underestimated in the case of wireless transmission also assumes that corresponding operations or dives are generally not undertaken alone, but that several people carry out the operation or the dive together. Since identical devices are often used for all members of such a group within a rescue organization or diving center, the risk is very high that a receiving device will pick up the signals from the transmitting device of a neighbor and thus display incorrect values to the user.

It is possible to solve the problem of using several monitoring devices within a group by assigning an individual transmission frequency to each device, which can only be received by a correspondingly set receiving device. However, this design has some disadvantages. If one wanted to provide a larger number of such monitoring devices with different frequencies, the frequency band remaining for the individual device would have to be very narrow. However, this requires a relatively high technical effort on the receiver side in order to reliably filter out the frequency intended for the respective receiving device from several received frequencies. This makes the receiving device complex and the likelihood of possible errors increases.

The fact that the intensity of the received signals decreases with distance is not sufficient to ensure a clear assignment of the devices in this case.

On the one hand, a somewhat constant reception intensity could only be achieved if the transmitter and receiver are arranged at a relatively short distance from one another and always have the same spatial allocation to one another. However, this is not the case if the transmitter is installed on the pressure vessel and the receiver is installed in the area of the head or, for example, a face mask of the user. In this case, just one turn of the head is enough to change the spatial assignment and thus the reception intensity. If the transmitter is installed on the pressure vessel and the receiver is installed on the user's wrist, strong fluctuations in the reception intensity can be expected depending on the movement of the user. In addition, other disturbances, such as air bubbles when diving, can also influence the reception intensity.

Furthermore, the distance from different users, e.g. when collecting objects or people together, be very small, so that the distance-related difference in intensity no longer plays a role. This applies e.g. then when a diver tries to help a colleague in difficulty.

The monitoring device according to the invention solves these problems very reliably. The use of an identification signal ensures that each receiving device always receives and processes only those signals that are transmitted by the assigned transmitting device. This not only prevents signals from other devices from being received; due to the rigidly predetermined identification pattern, signals from external disturbances, e.g. from any other channels. This is achieved in that the signal is only processed if it exactly corresponds to the respective identification pattern. It is very unlikely that interference signals from other, arbitrary transmitters contain corresponding identification patterns.

According to a preferred embodiment, the data and the identification signal are transmitted digitally. As a result, greater reliability of the data transmission is achieved, and it is also possible to select a large number of identification patterns by combining this signal from a correspondingly high number of individual bits.

It is possible that a certain receiving part or vice versa is assigned to each transmitting part already during production. However, this has the disadvantage that e.g. in the event of a failure of the receiving part, the associated transmitting part also becomes unusable and vice versa.

According to a preferred development of the invention, it is therefore proposed to make the assignment between the transmitting part and the receiving part changeable.

In this case, it is preferably provided that the transmitting part and the receiving part to be used therewith can be brought into an identification signal change mode, which enables the receiving part to record and store the identification signal of the transmitting part assigned to it. According to a preferred development, this assignment or pairing mode has several security levels, so that an unintentional and incorrect assignment of the transmitting part and the receiving part is avoided.

According to a preferred development, the transmitting and receiving parts are designed so that the identification signal change mode is always triggered by a device, and preferably by the transmitting part, this device then preferably also having a fixed, unchangeable identification signal.

The possibility of freely assigning the transmitting part and receiving part has considerable advantages in practical use. Organizations such as a diving base, a fire brigade unit and the like usually have a large number of mobile breathing apparatuses which are each provided with a transmitting part and a receiving part when using the monitoring device according to the invention. Falls in such a group e.g. a transmitting part and a receiving part of an unassigned pair would make a total of two monitoring devices unusable if the assignment could not be changed. If a changeable assignment is used, the remaining devices could continue to be used.

Finally, it is also not necessary to store the receiving section and the transmitting section in such a way that the devices cannot be mixed up. If it is determined that the devices do not match, a new assignment can be made at any time.

Furthermore, especially if the monitoring device is to be used when diving, the battery required both in the transmitting part and in the receiving part must be arranged pressure-tight in the respective housing and can therefore not be changed by the user himself. Since it is to be expected that the batteries of the transmitting part and receiving part will be used up at different rates, depending on the respective usage profile, both devices of such a combination would fail for the time of changing the battery of a device which can usually only be carried out by the manufacturer. This disadvantage is also avoided by the changeable assignment.

The variable assignment has the further advantage that two receiving devices can also be assigned to one transmitting device. It is then possible, for example, that a diving instructor uses two receivers with which he can observe his air supply and the air supply of a student diving with him. if the Devices are also equipped with an air consumption measurement, the diving instructor can also use this display to assess the stress level of his student.

Finally, it is also conceivable that, in particular for the receiving device, which can be combined with other functions, different device models are offered which the user should be able to use without having to procure a new transmission part in each case.

Furthermore, the manufacture of the monitoring device is significantly simplified by the changeable assignment.

The identification signal change mode is preferably triggered in that the transmitting device is caused by a manual operation to send out a specific signal, the identification control signal, which indicates to the receiving device that an assignment process is to take place. In order to prevent the assignment of several receiving devices to one transmitting device, appropriate security measures can be provided by the receiving device.

The actual assignment takes place in that the identification control signal also transmits the identification signal of the transmitting part. The receiving device brought into the identification signal change mode receives this identification signal and stores it in a corresponding memory until it receives another identification signal as part of a new assignment.

A third, arbitrary transmitter is unlikely to emit a pattern that corresponds to the identification signal. The remaining small uncertainty factor can be greatly reduced by a further safety measure, which also serves to reduce the effect of signal interference, e.g. caused by movements of the diver.

One of the preferred goals of the monitoring device is to calculate the breathing time still available to the user of the breathing apparatus. This breathing time is preferably calculated by a computing device which is installed either in the transmitting device or in the receiving device. This allows the user of the breathing apparatus to be shown how long the breathing air will still be sufficient under the current conditions.

According to a preferred development of the invention, this computing device is installed in the receiving part and continues the air consumption calculation in the sense of a forecast if no signal is received from the transmitting part. This means that a signal received after an interruption can be checked for plausibility.

If the receiving device does not receive a signal due to a disturbance, it continues to calculate the air consumption based on the previous measurements until the next signal is reliably received. Then it is checked whether this received signal is within a certain tolerance range of the extrapolated air consumption. If this is the case, the signal is displayed as a new value. If this is not the case, there is no display. Preferably, as long as the reception situation is unclear, no display value is output.

This design has the advantage that the receiving device can be reliably prevented from displaying an incorrect value due to an incorrectly received signal, which could irritate the user.

The transmission of the signals from the transmitting part to the receiving part can be carried out using all methods suitable for signal transmission. If the monitoring device is used under water, the data can be transmitted using ultrasound. When used underwater, however, it is particularly preferred to use radio signals, and here in particular to use signals in the long-wave range, i.e. the use of radio signals with a frequency of 5 Hertz to 100 Kilohertz.

Investigations by the inventors have shown that a frequency range between 5 Hertz and 50 Kilohertz is particularly suitable for the electromagnetic transmission of the signal in water in order to transmit the desired signals.

Both the transmitting and the receiving part can be provided with further functions.

If the monitoring device is used when diving, it can, according to a preferred development of the invention, be combined with a decompression computer. This computer is preferably housed in the receiving part and is connected to a pressure sensor which measures the hydrostatic pressure of the water and thus the depth of the dive. A further timer is also provided, by means of which the diving time can be measured. A computer circuit is used to determine the saturation or desaturation behavior for a finite number of tissue types from the measured values of depth and time, as is shown, for example, in the work by Bühlmann cited. From these values it can be determined and the diver can be shown how long the ascent to the water surface takes, and at what depths decompression stops with which length are to be inserted. By combining the calculation of the decompression times with the air consumption calculation, it can then be calculated and the diver can be shown how long he can stay at the corresponding depth level, before he has to start the ascent in order to have enough air supply for a medically safe ascent.

It is known from diving medical research that the saturation and desaturation of the tissues depends not only on the depth and time of the dive, but also on whether the diver performs physiological work or not. If the diver does work during the dive, the required decompression times can increase by up to 50 percent. A corresponding increase in decompression times can also result if the diver, e.g. while scuba diving, not actually doing any work, but e.g. must keep its location against a stronger current, so that a higher physiological work output is also required.

According to a preferred development of the present invention, the physiological work output is included in the decompression calculation with the aid of the monitoring device according to the invention. Air consumption measurement is used as a yardstick for work performance. The air consumption measurement can take place both relatively and absolutely.

In the case of an absolute air consumption measurement, the decrease in pressure for a known bottle volume determines the amount of air the diver takes in per unit of time. This value is used to infer an average or an increased physiological work performance, which is then taken into account in the decompression calculation.

The relative air consumption measurement only determines how high the diver's average air consumption is, which is averaged over a certain period of time. If the air consumption increases compared to this value, an increased physiological work output is assumed.

Both the absolute and the relative air consumption measurement can be continued while surfacing to further influence the decompression calculation. This makes it possible to record a physiological work performance during the decompression phase, which generally shortens the decompression time. In addition to the air consumption measurement, the pulse frequency of the diver can also be detected by means of an appropriate sensor and transmitted to the decompression meter. The pulse frequency also provides a measure of the physiological work performance. If the pulse frequency is e.g. Taken off via electrodes, which are arranged in the chest area of the diver, the values can e.g. forwarded by means of a cable connection to the transmitter on the diving bottle and from there transmitted wirelessly with the monitoring device to the receiver worn on the wrist.

If the monitoring device is used for fire and disaster control, several additional functions can also be integrated in the receiving section. In addition to the display of the current pressure in the pressure vessel of the breathing apparatus, the remaining breathing time and / or the breathing frequency can be calculated and displayed. Furthermore, it is possible to provide measuring sensors in the receiving device which give the user information about the state of the air surrounding him. For example, during fire fighting, the carbon monoxide content of the air is measured and displayed, so that the user of the breathing apparatus e.g. is informed about the danger to people to be rescued. Of course, in addition to gas detectors, sensors can also be used for all other types of measurable damage (e.g. Geiger counters and the like).

• Fig.1: Eine schematisierte Funktions-Darstellung eines mobilen Atemgerätes mit einem Ausführungsbeispiel der erfindungsgemäßen Überwachungseinrichtung;
• Fig.2: eine schematisierte Darstellung des Sendeteils des Ausführungsbeispiels gemäß Fig. 1;
• Fig.3: eine schematische Darstellung der Funktionsmodi des Sendeteils des Ausführungsbeispiels gemäß Fig. 1;
• Fig.4: eine schematische Darstellung der Codierung des Sendesignals des Ausführungsbeispiels gemäß Fig. 1;
• Fig.5: eine schematisierte Darstellung des Aufbaus des Sendesignals im Normalbetrieb des Ausführungsbeispiels gemäß Fig. 1;
• Fig.6: eine schematisierte Darstellung des Aufbaus des Sendesignals im Identifikationsänderungs-Modus des Ausführungsbeispiels gemäß Fig. 1;
• Fig.7: eine schematisierte Darstellung des Empfangsteils des Ausführungsbeispiels gemäß Fig. 1;
• Fig.8: eine schematisierte Darstellung eines weiteren Ausführungsbeispiels der Erfindung, bei der die Empfangseinrichtung mit einem Dekompressionsrechner kombiniert ist.

An embodiment of the present invention will now be described with reference to the figures. In it show:

• 1: A schematic functional representation of a mobile breathing apparatus with an embodiment of the monitoring device according to the invention;
• 2 shows a schematic representation of the transmitting part of the exemplary embodiment according to FIG. 1;
• 3 shows a schematic representation of the functional modes of the transmitting part of the exemplary embodiment according to FIG. 1;
• 4: a schematic representation of the coding of the transmission signal of the exemplary embodiment according to FIG. 1;
• 5 shows a schematic representation of the structure of the transmission signal in normal operation of the exemplary embodiment according to FIG. 1;
• 6: a schematic representation of the structure of the transmission signal in the identification change mode of the exemplary embodiment according to FIG. 1;
• 7 shows a schematic representation of the receiving part of the exemplary embodiment according to FIG. 1;
• 8: a schematic representation of a further exemplary embodiment of the invention, in which the receiving device is combined with a decompression computer.

The first exemplary embodiment of the invention explained with reference to FIGS. 1 to 7 is intended to be used in connection with a diver's breathing apparatus. However, with appropriate modifications, it can also be used for breathing apparatuses, such as e.g. used in fire and disaster protection, find use.

1 shows a highly schematic representation of the monitoring device, which is designated overall by 1 and which has a transmitting part 2, which contains the transmitting device, and a receiving part 3, which contains the receiving device.

The transmitting part 2 is, in the present example, (not shown in the figures) firmly attached to a diving bottle 5. The diving bottle is a conventional steel bottle with a volume of e.g. 7 to 18 liters and a maximum storage pressure of e.g. 350 bar, which can be closed with a manually operated shut-off valve 6. The shut-off valve 6 is opened during use, and the pressure of the air supplied to the user is regulated via a schematically indicated pressure regulating valve 9. This valve 9, which is usually referred to as a regulator, can have one of the different designs known in the prior art. The user then removes the air from the breathing apparatus, e.g. via a hose connection (not shown) by means of a mouthpiece.

A pressure sensor 7 is arranged between the shut-off valve and the regulator, which detects the pressure prevailing in the bottle. The arrangement of the pressure sensor after the shut-off valve 6 has the advantage that the pressure sensor is not subjected to the device pressure during storage of the bottle; furthermore, as will be explained, this has advantages with regard to the security design of the monitoring device.

When used, the receiving part 3 is used at a spatial distance from the transmitting part 2 and is coupled to a display device 4, which is usually integrated directly into the housing of the receiving part.

The transmitter part 2 shown schematically in FIG. 2 has a housing 10 made of non-magnetic material, preferably plastic, in which the electrical and electronic components of the transmitter part are accommodated. The interior of the housing 10 of the transmitting part 2 is completely filled with electrically non-conductive oil, silicone or the like. The area of the housing 10a in which the pressure sensor 7 is arranged is designed such that it is exposed to the pressure in the bottle 5 during use. This is shown schematically by the connecting piece 11, 12. The remaining part 10b of the housing is also sealed to prevent water from entering.

In the housing 10, a battery 13 is also housed, which supplies the transmitting part with electrical energy, and which is thus also exposed to the pressure in the housing.

The structure of the electrical components of the transmitting part will now be described with reference to FIG. 2.

The pressure sensor 7 is connected to a signal conditioning circuit 20 via electrical lines, which are only shown schematically here and below. All commercially available sensor types can be used as pressure sensors, provided that they can be operated with a battery voltage of less than 5 V and use as little energy as possible. Pressure sensors that operate on the piezoelectric principle are therefore particularly preferred.

The analog signal of the pressure sensor is converted into a digital signal in the signal conditioning circuit 20 by means of an A / D converter. The signal conditioning circuit 20 is also connected to a quartz-controlled timer 21, the purpose of which will be explained below. The digitally processed signal is fed to a commercially available microprocessor computing unit 22. The microprocessor computing unit 22 is connected to a memory 23 and also receives the signals of the timer 21. The memory 23 (and the corresponding memory in the receiving part) can be constructed entirely from RAM memory elements. However, it is also possible to use a mixed memory consisting of ROM (read-only memory) and RAM memory elements. Since the battery voltage is permanently available, the memory contents can be saved in the long term even when volatile memory elements are used.

The microprocessor 22 converts the pressure signal and the other signals to be transmitted into a transmission signal according to a program stored in the memory 23 and supplies it to a transmission output stage 25. The signal is transmitted from the transmission output stage 25 to the antenna 26.

The antenna 26 consists of a ferrite core which is wrapped with copper wire. An inductance of the transmitter coil in the range between 10 and 50 mHenry has proven to be particularly favorable.

Different operating modes of the transmitting device will now be described with reference to FIG. 3, in which the different functional modes of the transmitting part are plotted over the time axis 40.

In time segment 41 in the left part of the figure, the transmission device is in stand-by mode. In this mode, the signal conditioning circuit is caused to carry out a pressure measurement at certain time intervals, which is characterized by columns 42. A time interval of approximately 5 seconds has emerged as the preferred time interval. The microprocessor 22 is always switched between two measurements in a stand-by mode in which it consumes very little energy. This makes it possible to operate the transmitter with a lithium battery for about 5 years with a typical usage profile.

The start signal for the pressure measurement comes from the timer 21 of the transmission device. The mic Processor 22 is then activated and the pressure is measured by means of pressure sensor 7.

As soon as a certain switch-on criterion is met, the transmission device is switched from stand-by mode to transmission mode. Various criteria can be used as the switch-on criterion. It has proven to be particularly advantageous to compare the result of two successive pressure measurements and to switch to the transmit mode when the pressure rises. The switch-on criterion is preferably dimensioned such that the transmission mode is switched on if the pressure rises from below 5 bar to e.g. 30 bar or more is determined. This increase is achieved in any case when the user of the breathing apparatus opens the shut-off valve 6 of the bottle 5 and thus acts on the pressure sensor 7 with the bottle pressure. Random pressure fluctuations, e.g. caused by temperature changes, changes in altitude etc. are not sufficient to meet this switch-on criterion.

After switching on, a so-called identification change mode or pairing mode takes place in the time segment 43, which will be explained later.

The identification change mode is followed by the actual normal mode in time segment 45, which represents the actual use phase of the device. As shown schematically in FIG. 3, a measurement interval 46 and a transmission interval 47 alternate in this mode. It has proven to be advantageous to work with a time interval of the pressure measurements of 5 seconds even during normal mode. After each measurement value has been recorded, the transmission signal is then generated by the microprocessor and fed to the antenna 26 via the transmission output stage 25.

The time interval between the pressure measurement and the transmission of the signal is not constant, but is varied by the microprocessor according to a random process within a predetermined time range. The signal is always sent before the next measured value is recorded. This time variation has the advantage that, in the case of two monitoring devices which operate simultaneously at a short distance and which monitor different breathing apparatuses, a collision of transmitted signal values can only take place accidentally. If the time interval between the measurement interval and the transmission interval were always the same, the unfavorable constellation could arise that the values emitted by two transmission parts collide with one another for a longer period of time.

As soon as a predetermined switch-off criterion is met, the transmitting device is switched back to the stand-by mode, which is shown in time segment 49. The switch-off criterion is met when there is no longer a decrease in pressure for a predetermined number of measuring intervals.

The signal transmission from the transmitting device 2 to the receiving device 3 takes place by means of an electromagnetic radio wave of constant frequency. The quartz-controlled timer 21 is used to control the transmission frequency. Since the frequency of the quartz crystal is 32,768 Hz, the structure of the transmission part is simplified if a frequency is used which is derived from this frequency with the divider 2 _n . The frequencies 32,768 (n = 0), 16,384 (n = 1), 8,192 (n = 2) and 4,096 (n = 3) are therefore particularly preferred. Experiments have shown that particularly good data transmission under water is achieved by using a carrier frequency of 8,192 hertz.

In the interest of data transmission that is not susceptible to interference, the data signals to be transmitted are digitally encoded in the transmitting part 2. In order to transmit the digital values, there are various methods in the prior art in which the frequency, the amplitude or the phase position of the carrier signal are changed.

A known method, which could also be used for the monitoring device of the type shown, is the frequency change of the transmission signal using what is known as frequency shift keying. In this method, the bit information contents 0 and 1 are assigned different frequencies. However, this means that 2 frequencies have to be transmitted, which increases the effort on the sender and receiver side.

The best way of transmission has been to influence the phase position with the so-called "phase shift keying" (PSK), a special variant of the PSK method being used in the present exemplary embodiment, namely "differential phase shift keying" (DPSK) .

In this method, the transmission signal experiences a phase jump when a 1 is transmitted; if a 0 is to be sent, the send signal remains unchanged. Since with this method the first bit of the transmitted bit pattern contains an uncertainty, it must not serve as an information carrier.

An example of this digital encryption is shown in FIG. 4. A bit pattern consisting of bits 011010011 ... is shown in diagram 60 over a time axis 61 and a number axis 62.

In diagram 64, a voltage signal 67 is plotted over the scaled time axis 65 and the voltage axis 66, which has a constant frequency, but to which the bit pattern is impressed as a phase change by the DPSK modulation described above.

Within each transmission interval, a signal sequence is transmitted which, as shown in FIG. 5, is composed of a preamble, the identification signal, a data block and a postamble. The preamble serves to enable the receiving device to synchronize with the transmitted signal. The identifica tion code contains the transmitter-specific identification. The actual data block to be transmitted follows the identification code. In any case, the data block contains the measured pressure value, but in a preferred embodiment can also contain a temperature value which is detected by a corresponding temperature sensor. It is also possible to transmit the respiratory rate derived, for example, from the measurement of the pressure signal in this data block. Of course, other data can also be transmitted if this is of interest in the specific application. This is followed by the postamble, which is used, among other things, to correct errors.

In the exemplary embodiment shown, the synchronization interval comprises 16 bits, the identification code 24 bits, the data block 32 bits and the postamble 4 bits. So each signal is 76 bits long.

Experiments have shown that it is favorable for the DPSK used to transmit a total of 8 periods of the carrier frequency at 8196 Hertz per bit. This results in a total transmission time of 0.976 msec / bit or a total signal duration of approx. 74 msec.

The structure of the receiving part will now be described with reference to FIG. 7.

The receiving part 3, separate from the transmitting part, is accommodated in a plastic housing 70 and has no mechanical connection or by means of electrical lines to the transmitting part 2. The plastic housing 70 is filled with electrically non-conductive oil, silicone or the like and has a battery 71 in order to supply the electrical and electronic components with electrical energy. A flexible wristband (not shown) is also arranged on the housing 70 and enables the user to fasten the receiving part to the wrist like a wristwatch.

The housing is designed so that it withstands the water pressure even at the greatest depths that can be reached by divers and has no movable electrical switching devices on its outer surface facing the water. In order to be able to put the device into operation and to confirm the assignment in the pairing mode, several electrically conductive metal pins 73 are embedded in the housing, which the diver e.g. can be bridged with his fingers, which under certain circumstances is interpreted by the receiving part as a switching event.

The receiving part has one or two ferrite antennas 80, as shown schematically in the figure. The received signal is first fed to a signal processing and amplification stage 81, which is followed by a digitizing stage 82. Both components correspond to the usual design.

The digital signal is fed to a comparator 83. This comparator determines whether the received and processed signal contains the identification signal or the identification control signal. If this is the case, the signal is fed to a microprocessor 85 which, controlled by a program stored in a memory 86, takes over the further processing.

The use of the upstream comparison stage has the advantage that the microprocessor 85 is only subjected to the signal when it is certain that the individual receiving device has been addressed.

The receiving part is timed by a timer 84.

The data derived from the received signal and possibly further data are shown to the user on the display 87. For this purpose, the display 87 is arranged behind a transparent area in the wall of the housing 70 of the receiving part 2. The pressure in the bottle 5 and preferably also the remaining breathing time are shown on the display. For this purpose, a further pressure sensor 89 is required, which measures the respective ambient pressure. The remaining breathing time is determined in that the microprocessor determines the current air consumption from the decrease in pressure measured per unit of time, taking into account the ambient pressure. The air consumption can be averaged either for a short time ago or over a longer period in order to obtain realistic values. The expected time until complete air removal is then extrapolated from this.

The respective data are shown in the display until new data are determined after a new measurement and the transfer of the values.

The receiving device also has a switching device 88, shown only schematically, with the metal pins 73 already mentioned. The metal pins 73 can also be arranged at a greater distance from one another or on different sides of the housing in order to prevent accidental contact bridging.

How the assignment or pairing of the transmitting part and receiving part is carried out within the identification change mode is described below.

As already explained, each transmitter part is permanently assigned an identification signal during production, which is only ever issued once. In the above embodiment, a 24-bit signal is used, resulting in a total of 16.7 million different identification options. This high number ensures that there are never two transmitters with the same signal.

The identification signal of the transmitter part is stored in a read-only memory area of the memory 23 of the transmitter part 2. It is also possible to read the identification signal in a RAM memory area gene; in this case, however, the signal must be fixed elsewhere in the device, for example by using it as a manufacturer number at the same time, so that the signal can be read in correctly when the battery is changed.

The identification change mode is started every time the transmitter is put into operation. As explained above, this is preferably done by a defined switch-on criterion, e.g. turning on the device valve 6 of the bottle 5. The transmitting part then goes into the identification change mode and, as shown in FIG. 6, sends a signal which consists of a preamble, an identification control signal, the actual identification signal and a postamble. In the exemplary embodiment, the preamble is 16 bits, the postamble is 4 bits, and the identification control signal and the identification signal are each 24 bits long.

The identification control signal is understood by all receiving parts of the corresponding series. As soon as a receiving part receives this signal, it is switched to the identification change mode by the microprocessor. The processor then asks on the display whether the identification signal of the transmitting part should be adopted. If this is confirmed by the user via the switching device 88 by means of the metal pins 73, the identification signal of the transmission part is adopted and stored in the memory 86 as an identification comparison signal.

The control program of the receiving part stored in the memory 86 can be designed such that the receiving part, as soon as it receives the identification control signal of the transmitting part in the identification change mode, checks whether its stored identification comparison signal matches the identification signal of the transmitting part. If this is the case, the receiving part can then indicate that it is set to this transmitting part so that the user knows that the two devices are assigned to one another.

In order to avoid inadvertent assignment of devices, the identification change mode has several security levels in the exemplary embodiment.

The first stage is the coupling of the start of the identification change mode to the switch-on criterion of the transmitting part. The identification change is only made immediately after the switch-on criterion has occurred. This reliably prevents an identification change from being started during normal use of the devices.

As a second security level, an energy measurement of the signal received in the identification change mode is carried out by the receiving part with a corresponding device. The program of the receiving part is thus designed so that whenever the identification control signal is received, an energy measurement of the overall signal is carried out. An assignment is only possible if the transmission energy exceeds a certain limit.

As is known, the transmission of energy from the transmitting part to the receiving part depends on the distance and, to a considerable extent, also on the respective alignment of the two antennas to one another. Only when the devices are arranged in a certain way with respect to one another in terms of space and angle does the energy absorbed by the receiving part become maximally high. The limit value for the energy measurement is therefore chosen so that an assignment can only take place if the transmitting and receiving parts are arranged at a small distance from one another and also have a predetermined angular orientation to one another. In order to facilitate the angular assignment, the antennas of the transmitting part and receiving part are preferably arranged in the respective housing in such a way that the maximum energy is obtained with a parallel or T-shaped arrangement of the devices to one another. In order to rule out coincidences here too, the identification control signal is repeated several times and only assumes sufficient signal energy if the measured value is above the limit value for a certain percentage of the transmissions.

Finally, and this represents the next level of security, the user must actuate the switch 88 to confirm the change of identification. For this, e.g. the three metal pins are used in such a way that only two can be bridged in the identification change mode. This prevents an identification assignment under water (in this case all three metal pins would be electrically connected). It is also possible to use three metal pins in such a way that a first pair and then a second pair must first be bridged.

• 1. Sende- und Empfangsteil praktisch unmittelbar nebeneinander in definierter Winkellage angeordnet sind;
• 2. in diesem Zustand das Absperrventil der Luftflasche geöffnet wird;
• 3. und die Identifikation durch den Benutzer manuell bestätigt wird.

An assignment only takes place if

• 1. transmitting and receiving part are arranged practically immediately next to each other in a defined angular position;
• 2. In this state, the shut-off valve of the air bottle is opened;
• 3. and the identification is manually confirmed by the user.

The following describes how the receiving device shown checks the plausibility of the received data.

As stated at the beginning, the monitoring device should, if possible, never be wrong, not even for a short time Show values. Due to the wireless transmission, however, it may happen that the reception of the entire signal transmitted during a transmission interval or of parts of the signal is impaired, for example by strong movements of the user or the like.

If two transmitting parts work in close proximity to one another, the situation could also arise in which the two transmitting parts transmit at substantially the same time, so that the signals overlap and are therefore no longer clearly identifiable.

Furthermore, even if this is unlikely, it could happen that a pattern which happens to correspond to the identification signal is created for a short time by the superimposition of different signals.

This problem can be countered by suppressing the corresponding display whenever the signal has not been recorded absolutely correctly.

In the exemplary embodiment shown, a plausibility check is provided as an additional security measure in order to rule out any risk of a false report. The plausibility check is carried out by calculating the expected pressure drop in the bottle of the breathing apparatus by the microprocessor of the receiving part.

In use, breathing air is essentially continuously extracted from the breathing apparatus, and the pressure in the bottle 5 drops correspondingly continuously, from which the current air consumption is determined. Based on the air consumption, the microprocessor calculates how the pressure drop in the bottle should continue to decrease with a continuous air extraction. With each pressure measurement, it is then determined whether the newly measured pressure is plausible compared to the previously measured pressure values. If this is the case, the new pressure value is shown on the display. If the pressure value is not plausible, or if no signal or a complete signal is not received in the predetermined time interval, then either no pressure value is displayed, or the last measured pressure value is displayed, but with an additional symbol or e.g. flashing of the display indicates that this is the result of a previous pressure measurement.

If no pressure signal is received for several measuring intervals, or if the signal cannot be clearly identified due to interference, this display is continued until a time frame defined in the control program of the microprocessor 86 is exceeded. From this point on it is assumed that reliable pressure values are no longer available and the calculation of air consumption is discontinued. This is indicated in the display 87 accordingly.

If pressure signals are received again that originate from the transmitting part assigned to the receiving part, these are displayed, but with an additional symbol, e.g. with a flashing indicator or the like, by which the user is informed that a plausibility check of these values is no longer possible.

In a further exemplary embodiment of the monitoring device according to the invention, which is shown schematically in FIG. 8, the monitoring device is combined with a decompression computer. The decompression computer could be arranged both at the sending device and at the receiving device. However, as in the exemplary embodiment shown, the receiving part of the monitoring device and the decompression computer are preferably combined in one housing, since the decompression computer then remains in operation even if the transmitter device fails.

Decompression computers of the type in question are known in the prior art. The patent applicant has such devices in large numbers in 1989 in Europe, the USA, Japan, Australia and many other countries e.g. sold under the name "Aladin pro". In decompression computers of this type, the current ambient pressure, which is a measure of the diving depth, and the total diving time are recorded via a corresponding pressure measuring device and a time measuring device. These input values are used to determine the saturation and desaturation behavior of a certain number, e.g. simulated six or sixteen different tissues. By comparing the load on the individual tissues, the computing unit determines which tissue is decisive for decompression, the so-called guiding tissue, and then determines the number, depth and duration of the necessary decompression stages. The diver is shown on a display the total diving time, the current diving depth, the next decompression stop and the total time required to reach the water surface with a certain, prescribed rate of ascent and the decompression levels. Furthermore, the decompression computer is provided with storage devices, a so-called log book, in which the dive profile of previous dives is stored, so that the diver can note down their respective diving times etc. after leaving the water. Furthermore, such a decompression computer is provided with a device to measure the air pressure before diving, so that it can also be used in lakes which are at a higher altitude than sea level, and to prevent air pressure fluctuations from being incorporated into the measurement result.

It is possible to use the receiving part of the monitoring device according to the invention and the computers unit for decompression calculation so that both are controlled by a common microprocessor.

Programming and design are simplified, however, if a solution with two microprocessors is used instead.

The exemplary embodiment of the monitoring device according to the invention shown in FIG. 8 works with a transmitting part, as explained in relation to FIG. 2 and therefore is no longer shown in FIG. 8. The receiving part has a pressure-resistant, non-magnetic housing 100, in which, as indicated by the dash-dotted area, the receiving device 103 and the decompression computer 104 are arranged together. The housing is filled with oil and has an internal pressure that is equal to the pressure of the water surrounding the housing. The dimensions of a sample of this housing, which is intended to be worn on the wrist, are approximately 75 mm (length transverse to the arm direction) and approximately 75 mm wide, measured along the arm. The housing has a thickness of approx. 20 mm.

The receiving part 103 is constructed as described above and has an antenna 110 and a first microprocessor 112 with a memory 113. The components essentially used for signal processing are summarized schematically in component 111.

The decompression computer has a microprocessor 120 with a memory 121 for program and data. The pressure of the surrounding water is detected by a pressure sensor 125. The other electrical components, such as timers, etc., are summarized schematically in component 127.

At least the battery 130 serving for the power supply, a display 132 embedded in the housing wall and a switching device 134 with four metal pins 136 are provided as common components.

A common display control device and a common timer and the like can be used as further common components.

• - der Druck in der Atemluftflasche in bar oder psi;
• - die verbleibende Zeit zum Aufenthalt auf der jeweiligen Tiefenstufe, unter Berücksichtigung der für den Aufstieg erforderlichen Zeit (remaining air time) in min oder mit einem Symbol, z.B. einer auslaufenden Sanduhr;
• - die gesamte Tauchzeit seit Eintritt in das Wasser;
• - die aktuelle Tauchtiefe;
• - der nächste Dekompressionshalt und die dort zu verbringende erste Dekompressionszeit;
• - die Gesamtauftauchzeit;
• - die maximal getauchte Tiefe;
• - die momentane Aufstiegsgeschwindigkeit.

The microprocessors are each controlled by their own program, but exchange data via a schematically indicated data line 138. From this, the following data are determined and shown on the display 132 with numbers and / or symbols:

• - the pressure in the breathing air bottle in bar or psi;
• - the remaining time to stay at the respective depth level, taking into account the time required for the ascent (remaining air time) in minutes or with a symbol, eg an expiring hourglass;
• - the total diving time since entering the water;
• - the current depth;
• - the next decompression stop and the first decompression time to be spent there;
• - the total ascent time;
• - the maximum depth immersed;
• - the current rate of ascent.

• - ein Signal, z.B. das Blinken der Druckanzeige, das anzeigt, daß der aktuelle angezeigte Flaschendruck nicht über die Luftverbrauchsprognose kontrolliert ist, da die Verbindung zwischen Sendeteil und Empfangsteil längere Zeit unterbrochen war;
• - eine Anzeige für eine kurzfristige Unterbrechung der Verbindung Sendeteil und Empfangsteil;
• - ein Signal, wenn die maximale Aufstiegsgeschwindigkeit den erlaubten Wert überschreitet (dieser Wert kann durch in kurzem zeitlichen Abstand erfolgende Druckmessungen mit dem Drucksensor 125 bestimmt werden).

In addition, the following functions or malfunctions can be displayed or output by flashing the corresponding values or by additional visual and / or acoustic warnings:

• - a signal, for example the flashing of the pressure indicator, which indicates that the current bottle pressure displayed is not controlled by the air consumption forecast, since the connection between the transmitting part and the receiving part has been interrupted for a long time;
• - A display for a short-term interruption of the connection between transmitter and receiver;
• a signal when the maximum ascent rate exceeds the permitted value (this value can be determined by pressure measurements with the pressure sensor 125 taking place at short intervals).

Furthermore, the monitoring device according to this embodiment can be coupled with displays which only become visible after leaving the water, e.g. a warning display in the form of an aircraft, which indicates to the diver that the use of an aircraft is not yet possible, a logbook display, etc.

As described above, the decompression data are determined by the microprocessor 120 by simulating the behavior of a specific number of tissue types. The permissible residence time at a certain depth results from e.g. iterative approximation by dividing the pre-calculated time, which is still sufficient for the air supply, into the remaining stay time and the total surfacing time, which is necessary to emerge from this depth after the stay time has expired.

In addition to the input variables pressure and time, the calculated air consumption can also be taken into account in the decompression calculation. Since air consumption is a measure of the physiological work performed by the diver, it can, according to the research results of diving medicine, the influence of physical work performance on decompression times should be taken into account.

Claims (33)

1. A monitoring device for a portable breathing apparatus having: a pressure measuring means, which detects the pressure in one or more pressure containers of the breathing apparatus by means of a pressure sensor and emits an electrical pressure signal, which is representative of the pressure;

a transmitter means which receives the pressure signal emitted by the pressure measuring means and transmits a transmission signal, corresponding to it;

a receiver means, which is to be carried by the user, and which is adapted to this receiving means, which receives the transmission signal, emitted by the transmission means;

a microprocessor means, arranged in the receiver means, which is controlled by a program, stored in a memory arranged in this receiving means, said microprocessor means calculating the pressure value, measured by the pressure measuring means from the received transmission signal,

a display means, which displays data as digits and symbols and which is connected to the receiver means and displays this calculated pressure value;
characterized in

that the transmitter means includes a control means, which causes, that the transmission signals are emitted in intervals,

that the transmitter means comprises a signal generating means, generating an identification signal which is characteristic for the individual transmitter means and unambiguously identifies the latter,

that the control means causes said identification signal to be transmitted at least once within each transmission interval,

that an identification comparison signal, which is assigned to that of an associated individual transmitter means is stored in the memory of the receiver means,

that the receiver means comprises a comparison means, which uses this identification-comparison signal for testing, whether a received signal includes the identification signal, belonging to the associated receiver means, and

that the receiver means only calculates and displays a pressure value from the received signal, if the identification signal, received by the receiver means matches the identification signal, stored in the associated transmitter means.

2. The monitoring device as claimed in claim 1, wherein a convertor means is provided which encodes the signals to be transmitted by the transmitter means in digital form.

3. The monitoring device as claimed in claim 1 or 2, characterized in that at least the control means and the signal generating means of the transmitter means are combined in a first microprocessor means which is controlled by a program stored in a memory.

4. The device as claimed in at least one of claims 1 to 3, characterized in that the identification signal is stored in the transmitter means as a digital number sequence with n bits and the identification comparison signal is stored in the receiver means also as a digital number sequence with n bits.

5. The monitoring device according to at least one of claims 1 to 4, characterized in that the identification signal stored in the transmitter means and/or the identification comparison signal stored in the receiver means is or are variable in order to match the identification signal and/or the identification comparison signal of the transmitter means and/or receiver means with one another.

6. The monitoring device as claimed in claim 5, characterized in that an identification control signal is generated by the signal generating means of the transmitter means, that an identification control comparison signal is stored in the memory of the receiver means and the comparison means switches over the receiver means into an identification signal change mode as soon as the comparison means recognizes that an identification control signal emitted by the transmitter means is identical to the identification control comparison signal stored in the receiver means.

7. The monitoring device as claimed in claim 6, characterized in that the transmitter means has a first detector means which recognizes the occurrence of a predetermined condition and switches over the transmitter means from a transmission mode, in which at least pressure signal and identification signal are emitted, into an identification signal change mode in which an identification control signal and the identification signal are emitted.

8. The monitoring device as claimed in claim 7, characterized in that the pressure signal measured by the pressure measuring means is fed to the first detector means and the latter recognizes as a predetermined condition when the pressure measured by the pressure measuring means rises by a predetermined value within a predetermined period of time.

9. The monitoring device according to at least one of claims 6 to 8, characterized in that the receiver means has a signal power measuring means with which the power of the signal received from the transmitter means is measured at least whenever the comparison means detects that an identification control signal transmitted by the transmitter means is identical to the identification control comparison signal stored in the receiver means.

10. The monitoring device according to at least one of claims 6 to 9, characterized in that the receiver means has a manually actuable switching means and an identification signal received during the identification change mode is only stored by the receiver means if this manual switching means is actuated.

11. Monitoring device as claimed in claim 10, characterized in that the switching means has electrical contact pins consisting of metal which are conducted through an electrically non-conductive housing region of the receiver means and can be touched from the outside.

12. Monitoring device as claimed in claim 5, 6, 9 and 10, characterized in that the receiver means only stores an identification signal received during the identification change mode if the power of the received transmission signal lies above a specific predetermined value and if the switching means is actuated.

13. The monitoring device according to at least one of claims 1 to 12, characterized in that the transmission of the transmission signal from the transmitter means to the receiver means takes place by means of ultrasonic sound.

14. The monitoring device according to one at least of the claims 1 to 12, characterized in that the transmission of the signals from the transmitter means to the receiver means takes place by means of electro-magnetic waves (radio waves).

15. The monitoring device as claimed in claim 15, characterized in that the frequency of the electromagnetic waves lies in the longwave range, preferably between 5 and 100 kilohertz, in particular preferably between 5 and 50 kilohertz and especially preferably between 5 and 15 kilohertz.

16. The monitoring device as claimed in claim 14 or 15, characterized in that the transmission of the data takes place via a change in the phase position of a sinusoidal signal (phase shift keying) and preferably via a differential change in the phase position (differential phase shift keying).

17. The monitoring device according to at least one of claims 1 to 16, characterized in that at least four bit sequences each with a predetermined number of bits are transmitted in each transmission interval, the first bit sequence being a preamble which permits the receiver to be synchronized to the transmitter, the, for example, second and third bit sequence being a data sequence which is representative of the measured pressure signal or which contains the identification control signal, and a, for example, fourth and last bit sequence as a postamble terminating each transmission interval.

18. The monitoring device according to at least one of claims 1 to 17, characterized in that the transmitter means has a timer unit and is controlled in such a way that the pressure measuring means measures the pressure in predetermined, fixed time intervals.

19. The monitoring device as claimed in claim 18, characterized in that the value determined during pressure measurement is converted into a transmission signal and transmitted before the next pressure measurement takes place and a random switching is provided which causes the time interval between the pressure measurement and the emission of the measured pressure signal to be random.

20. The monitoring device as claimed in claim 18, characterized in that the transmitter means has a second detector means which recognizes the occurrence of a specific event and which switches over the transmitter from a passive standby mode into an active transmission mode when this event occurs, and wherein a third detector means is further provided which recognizes that the measured value does not change over a predetermined number of successive pressure measurements and which switches over the transmitter means from the active mode into the passive mode.

21. The monitoring device according to at least one claims 2 to 20, characterized in that the expected reduction in the pressure or in the breathing air in the pressure container is extrapolated from the current breathing air consumption preferably by means of the microprocessor means of the receiver means.

22. The monitoring device as claimed in claim 21, characterized in that in the case of a brief disconnection of the connection between the transmitter means and the receiver means, the newly received pressure value is compared with the extrapolated pressure value and displayed if the extrapolated pressure and measured pressure differ by a predetermined amount.

23. The measuring device as claimed in claim 21 or 22, characterized in that the time how long the breathing air supply is expected to last is determined from the extrapolated breathing air consumption and, if appropriate, is displayed.

24. The monitoring device according to at least one of the claims 1 to 23, characterized in that both the transmitter means and receiver means are each arranged in a pressure-tight, preferably oil-filled housing so that the monitoring device can be used under water.

25. The monitoring device as claimed in claim 1, characterized in that the receiver means and display means are arranged in a common housing which can be attached in the arm or wrist area of the user with attachment means.

26. The monitoring device as claimed in claim 24 or 25, which is provided in particular to be carried during a dive, wherein the receiver means is coupled to a decompression computing unit which is connected to a second pressure measuring means and to a timer and, by means of a predetermined program stored in a memory of the decompression computing unit, calculates, taking into consideration the times spent at different diving depths, how long the user requires to reach the surface of the water without the risk of decompression sickness, in which case the overall resurfacing time and/or the next decompression stop and the time to be spent there and/or the fact that the maximum admissible ascent speed has been exceeded are displayed to the user.

27. The monitoring device as claimed in claim 26 and 21, characterized in that the microprocessor means of the receiver means and the decompression computing means, respectively, calculate and display, from the extrapolated time, the time for which the air supply will still last and, from the determined overall diving time, the time which the diver may still spend at the respective diving depth.

28. The monitoring device as claimed in claim 26 or 27 characterized in that the receiver and decompression computing means have separate microprocessor devices.

29. The monitoring device as claimed in claim 26 or 27, characterized in that the receiver and decompression computing means have a common microprocessor device.

30. The monitoring device as claimed at least in claim 3, or claim 3 and one of claims 1 to 29, characterized in that the first microprocessor means of the transmitter means continues to carry out at least partially the functions of the pressure measuring means and/or of the convertor means and/or of the first and/or of the second and/or of the third detection means and/or of the random circuit via the program stored in the memory.

31. The monitoring device according to at least claim 9, or claim 9 and one of claims 10-30, characterized in that the second mircoprocessor means of the receiver means carries out at least partially the function of the signal power measuring means via the program stored in the memory.

32. The monitoring device as claimed in claim 26 or 27, characterized in that the result of the air consumption calculation is supplied to the computing unit as a further input variable so that the influence of the air consumption can be taken into account as a measure of the psychological work performed by the diver in the calculation of the decompression parameters.

33. Amethod for monitoring a portable breathing apparatus with a gas/oxygen mixture stored in pressure containers, having a monitoring device which has a pressure measuring means, a transmitter means and a receiver means, characterized in that the transmitter means transmits the measured pressure values at transmission intervals, and that an identification signal which characterized the individual transmitter is transmitted at each transmission interval, the receiver comparing the transmitted iidentification signal with an identification signal stored in a memory of the receiver and further processing the transmitted pressure data and, if appropriate, further data only if the identification signal emitted by the transmitter and the identification signal stored in the receiver are identical.

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