AT509551A1 - CIRCULAR DIVING UNIT WITH A MOUTHPIECE - Google Patents

Description

- 1 -

14757

The invention relates to a rebreather with a mouthpiece which is connected via a inhalation hose and an exhalation hose to a breathing gas circuit, wherein at least one gas sensor for measuring the partial pressure of a respiratory gas component is arranged in the respiratory gas circuit.

One differentiates between open diving equipment, half-closed and closed rebreather devices.

Open diving devices have a breathing gas storage bottle which is filled with compressed air or another breathing gas mixture, and a one- or two-stage pressure reducer, which reduces the pressure of the gas in the bottle to ambient pressure. The exhaled air is released into the surrounding water, but only a small part of the oxygen in the breathing gas is really consumed. Thus, about 3% of the inhaled gas is consumed at the water surface, while at a depth of, for example, 20 meters through the increased by two bar ambient pressure only a third of this value, ie 1% of the oxygen of the inspired gas is consumed. Thus, for a dive to a depth of twenty meters, one hundred times as much breathing gas has to be carried along as it actually consumes.

Semi-closed and closed rebreathers are used to circumvent system-related low breathing efficiency of open diving equipment. These devices are breathed in a cycle. The exhaled air is purified in rebreathers by means of a C02 absorber of carbon dioxide and re-enriched with oxygen. Furthermore, such devices are characterized by a one- or two-part counterlung, which can hold the exhaled gas volume. With rebreathers, the efficiency of gas consumption can be increased up to 100%. While open diving equipment normally breathes a gas with a breathable oxygen content, semi-closed rebreather systems determine the oxygen partial pressure (p02) in the circuit based on the amount of gas supplied and the diver's metabolism. In electronically controlled closed devices, the oxygen partial pressure is kept at a certain level by means of a control loop. Electronically controlled closed rebreathers are known, for example, from the publications GB 2 404 593 A, US 2003/188744 A1 and WO 2005/107390 A2. In manually controlled closed rebreathers, the diver manually sets the oxygen supply and thus manually controls the oxygen partial pressure. In an electronically controlled closed cycle device is

Oxygen usually added with an electromagnetic control valve. This solenoid valve is usually housed in the housing of the carbon dioxide filter. The actual control loop is implemented in one or - for redundancy reasons - in several microcontrollers. The oxygen partial pressure of the breathing gas must be within certain limits in order to be breathable. Generally, 0.16 bar is considered the lower limit and 1.6 bar the upper limit. An oxygen partial pressure below or above these limits is classified as life-threatening. It can be seen that a constant monitoring of the oxygen partial pressure is necessary for rebreathers. Closed units require p02 sensors for manual and / or electronically controlled regulation of the oxygen partial pressure in the breathing gas circuit. The p02 sensors used are usually electrochemical liquid-electrolyte sensors which have to be calibrated at the surface with air or 100% O 2 before the dive.

A correctly functioning p02 sensor for use in rebreathers has an output signal (current or voltage), which depends linearly only on the oxygen partial pressure in front of the diaphragm of the sensor.

However, pO 2 sensors designed as liquid electrolyte sensors are very error-prone. Typical errors that can occur are: • nonlinearity; • Current limitation: in this case, the p02 sensor becomes non-linear at a certain oxygen partial pressure because the output current of the sensor (or output voltage) can not rise above a certain level due to an error. This results in too low sensor signals at high oxygen partial pressure; • faulty signals from one or more sensors or the sensor signal processing; • incorrect calibration;

The error rate of the p02 sensors is attempted to be countered by the redundant use of p02 sensors. Thus, in closed rebreathers usually 3 oxygen sensors are used. If one sensor fails and therefore its output differs from that of the other two, it will be reset by comparing all three sensor signals with a "voting algorithm". detected, and this sensor is no longer used to control the p02 (see GB 2 404 593 A or WO 2004/112905 Al).

A faulty sensor can thus be determined. However, this method fails with the following errors: «I # ·« · I # · • * «4« «« · · · · ····· · · · _ 2 ·· ·· ··· ♦ · * ··· · • Failure of 2 sensors, but with the same output; • same nonlinearity of at least 2 sensors (> = 2 sensors from the same production lot, same age, same conditions ...); • same current limitation of at least 2 sensors.

An alternative is described in WO 2008/080948 A2. A calibration / validation device allows the flow of an oxygen sensor with a gas of known composition. Thus, a sensor can be easily checked for correct function.

In addition to the susceptibility to fouling, 02 liquid electrolyte sensors have further disadvantages: • Short life of a maximum of approx. 1.5 years; • May give erroneous signals at high humidity (condensation on the sensor membrane); • Electrolyte may leak from the sensor housing; • Long response times (t90) of typically 6 s; • Relatively large dimensions; • The relatively long response time makes regulation of the oxygen partial pressure relatively difficult. In a closed rebreather usually the oxygen partial pressure is measured with oxygen partial pressure sensors and then with the aid of a control circuit (usually with a microcontroller) an electromagnetic control valve is controlled, with which oxygen from a supply bottle is supplied to the circuit. In the worst case, this can temporarily lead to high oxygen partial pressure spikes in the circuit, which must be regarded as life-threatening, but are not recognized with the conventional sensors due to their long response time, since the long response time causes an averaging of the signal.

A carbon dioxide absorber (chemical filter, soda lime, carbon dioxide filter, scrubber) absorbs the exhaled carbon dioxide in a rebreather. A proper function of the carbon dioxide absorber is vital, since with an increase in the carbon dioxide content in circulation threatens carbon dioxide poisoning, which in turn is classified as life-threatening. The following errors can occur: - 4 - • · + + ···· • soda lime is defective • Maximum absorption capacity is reached, no further carbon dioxide can be absorbed; • The absorber is too cold and the chemical reaction is insufficient; • Water has entered the circulation and this has made the soda lime unusable; • Directional valves in the mouthpiece are defective - pendulum breathing occurs and the carbon dioxide filter is not flowed through, so no carbon dioxide can be absorbed.

Many projects have been involved in the development of a CO2 sensor for rebreathers to detect a carbon dioxide filter malfunction and / or an increase in CO2 in the circuit. Optical C02 sensors are mostly based on the absorption of infrared light. However, due to the high humidity (condensing) in a rebreather, this method is not very reliable. It is known to arrange a moisture barrier or hydrophobic membrane to increase the reliability in front of the measuring cell of the infrared C02 sensor. Another way to increase the reliability of such C02 sensors is to increase the sensors / sensor element to a temperature greater than the gas temperature in the rebreather to preclude condensation. Furthermore, to check the function of the carbon dioxide absorber, the temperature of the carbon dioxide filter can be measured (US 2003/074154 A1).

It is the object of the invention to avoid said sources of error in the partial pressure measurement of gas constituents in the respiratory gas.

According to the invention this object is achieved in that the gas sensor is designed as a solid state electrode. The solid-state electrolyte sensor can be embodied as 02 and / or as a CO 2 gas sensor.

Solid state electrolyte sensors are based on special materials that are conductive to gas ions. Normally, however, these materials are conductive only at elevated temperatures (typically 500-700 ° C). Typical materials include zirconia and ceria for oxygen and nasicon for c02.

Potentiometric solid electrolyte sensors for oxygen have been known for a long time, and find application in engine controls (lambda sensor) or in industrial combustion controls, among others.

Conventional sensors such as e.g. used in a car, but have the disadvantage that they are relatively large, therefore, require a high electrical heating power (> 10Watt) and a reference measuring chamber with a reference gas is necessary (potentiometric sensors, Nernst potential). These disadvantages have not permitted the use of these sensors in rebreathers until today.

Miniaturized gas sensors are used inter alia for in-situ and bypass measurements of Ox, COx, H2, CxHy, NOx in medical and environmental engineering, e.g. used in the performance diagnostics of astronauts or for residual gas analysis in space, (see http://tu-dresden.de/die_tu_dresden/fakultaeten/fakultaet_maschinenwesen/ilr/ rsn).

Thick-film miniature solid-state electrolyte sensors have the advantage of a long service life and a very fast response time. The actual sensor elements are available in the size 2.5x2.5x2mm3 and can be easily integrated into a rebreather. Due to the small design only low heat outputs (1-2 watts) are required, which allows conventional batteries or rechargeable batteries to operate for several hours.

The high operating temperature prevents condensation-related disturbances. The fast response time allows precise control of the oxygen partial pressure. The high response speed of less than 100 ms even allows to determine the heart rate, as the p02 / pC02 signal of the exhaled air is modulated with the heart rate.

The small dimensions allow integration of the gas sensors directly in the mouthpiece. Thus, the oxygen partial pressure of inhaled and exhaled gas can be detected separately. Favorable placement in the gas stream can also be used to measure the mass of the gas with these solid-state electrolyte sensors and thus deduce the minute volume of the diver and the respiratory rate. The high temporal resolution of the sensors allows a high-precision determination of small and short-term oxygen partial pressure changes.

By recording minute volume and respiratory rate, the load on the diver can be recorded and this, in turn, can be used as a factor influencing the decompression calculation.

Planar miniature solid-state electrolyte sensors for the partial pressure measurement of CO 2 and O 2 thus have the following properties: Very fast response time < 100 ms; 9 · »t1 · 1« «1 ···· · 1 · · · *. # 2» 21 · ♦ 2 ♦ 1 1 · 1 · · · Operating temperature 650 ° C (02) and 550 ° C (CO 2). Due to the high operating temperature problems with high / condensing humidity can be excluded; • 02 sensor: unlimited life; • C02 sensor: ~ 2000 operating hours; • The 02 sensor is an amperometric sensor - so no reference measuring chamber is needed; • In the C02 sensor, a solid electrolyte reference is integrated, so this also requires no reference chamber; • low operating costs; • Sensors are very small (actual sensor element ~ 4mm2); • The high response rate even allows to determine the heart rate, as the p02 / pC02 signal of the exhaled air is modulated with the heart rate.

Applying a 02 and a C02 solid-state electrolyte sensor in a rebreather results in the following benefits: • High operational safety, as the sensors are very robust and error-resistant; • Because the sensors are very small, they can also be integrated directly into the mouthpiece of a rebreather; • Since the sensors have a very short response time (<100ms), o the oxygen partial pressure in the system can be better and more accurately controlled; o measure differences in the gas composition of inhaled and exhaled gas (when integrated in the mouthpiece); o This allows conclusions about the oxygen metabolism of the diver. 1

Since the sensors are kept at high temperature, these can be used as 2

Gas mass flow meter can be used. By appropriate placement of the sensors in the gas flow, the gas flow can be measured (inhalation and exhalation volume, minute volume), which allows: o conclusion on the activity of the diver (stress, high physical stress, ...); o Determining if the diver is breathing at all, and how fast-which, in turn, can be used as input to the controller. • The following can be checked with a C02 sensor: o Correct function of the C02 filter; o Correct operation of the directional valves in the rebreather (if the directional valves are damaged, this can quickly lead to a local C02 increase (C02.-buildup) o conclusions on the metabolism of the diver (high physical stress, stress, ...) o Checking the oxygen sensor: Normally, the difference between the oxygen partial pressure of the inhaled and expired gases should be approximately equal to the difference in the partial pressure of carbon dioxide.

The large number of advantages thus allows o an optimized control of the oxygen supply; o a collection of physiological data (metabolism, tidal volume, minute volume, respiratory rate, O 2 content in inhaled and exhaled gas, CO 2 in exhaled gas) - this can be used to check the oxygen control;

Find influence in the decompression calculation (important point); o Increased safety of the system due to different sensor systems (02, C02 and mass flow sensor) I * * * * * * * * * 11 * * * • • I * * * * * * * * * * * * * * # g, M * «« «·· ·· ··· *

To control and read the sensors electronic circuits are necessary. These usually consist of a microcontroller that takes over the heating control and an analogue circuit, which typically consists of amplification and analogue filters. With today's technology, such a circuit can be highly miniaturized, so that the entire electronics requires less than 1-2 cm3 of space. Such a small circuit can easily be placed directly next to the sensors in the mouthpiece.

Using miniaturized solenoid valves, the oxygen supply control valve in the breathing circuit can also be integrated directly into the mouthpiece.

Together with a miniaturized electronic control unit, the complete control circuit of the rebreather can thus be integrated in the mouthpiece.

By integrating the complete control electronics and the control valve, there are numerous advantages in the mouthpiece: o no long cables and signal distortions caused by them, since sensors, solenoid valve, electronics and power supply (battery) are integrated directly next to each other; o cost-effective construction; o The mouthpiece contains all the electronics. Recirculation units without electronic control can be easily upgraded by replacing the original mouthpiece with the fully integrated mouthpiece

The invention will be explained in more detail below with reference to FIGS.

1 shows a known rebreather and FIG. 2 shows a part of a rebreather according to the invention.

Fig. 1 shows a closed rebreather according to the prior art. The diver exhales through the bite piece 19 connected to the mouthpiece 1 via the exhalation hose 2 into the exhalation counterlung 4. In C02 filter 7 ("scrubber"), carbon dioxide is chemically absorbed from the exhaled air. The breathing gas then passes into the inhalation counter lung 5. About the bite piece 19 of the mouthpiece 1 and the inhalation tube 3, the breathing gas is inhaled again. In order to replace the used oxygen, fresh 02 gas from an oxygen storage bottle 11 via an electromagnetic control valve 9, which is usually accommodated in the housing of the CO 2 filter 7, is replaced by .phi..sub.p. φ φφ φ · φφ φ φ φ φ φ φ φ φ φ φ

φ · φ φ · φ φφ φφφφ φφ

Supplied breathing gas circuit. A pressure reducer 12 reduces the cylinder pressure to a pressure of typically 7-10 bar. The storage bottle 11 contains pure oxygen 02. In addition to the electromagnetic control valve 9, the control circuit also has a microcontroller 10 and one to four oxygen sensors 8, via which the oxygen partial pressure p02 in the breathing gas circuit is measured. Dive relevant data are displayed on a display 15. If the partial pressure of oxygen drops below a certain value, then pure oxygen 02 is added to the respiratory gas cycle via the electromagnetic control valve 9. When diving, the breathing gas is compressed in the breathing gas circulation. To compensate for the pressure-related loss of volume, diluent gas from a supply bottle 13 is supplied to the breathing gas circuit 26 via a manual valve 16 or an automatic valve. Via the two pressure reducers 12, 14, the cylinder pressure is reduced to typically 8-10 bar above atmospheric pressure. Excess gas can escape through a pressure relief valve 6.

Fig. 2 shows a simple embodiment of the invention. The integrated mouthpiece 1 is connected via a breathing tube 3 and an exhalation hose 2 to the breathing gas circuit 26. The two directional valves - inhalation valve 18 and exhalation valve 17 - specify the gas flow direction. With 19 is the actual rubber bite piece, which holds the diver with his teeth. The O 2 sensor 20 and the C02 sensor 21 are designed as solid electrolyte sensors and mounted in the cavity of the mouthpiece 1 between the directional valves 17, 18. By means of a control valve 23 formed by a miniature solenoid valve which replaces the control valve 9 of FIG. 1, oxygen can be supplied to the breathing gas circuit 26 via an opening 27 from an oxygen storage bottle and an oxygen supply line 24 which are not shown in FIG. The feed into the breathing gas circuit 26 takes place after the exhalation valve 17 in order to guarantee a good mixing and at the same time to avoid short-term peak increases in the oxygen partial pressure in the inhaled gas. The control of the control valve 23 via an electronic control unit 22 via a waterproof cable 25, a display unit and an external battery power can be connected. The electronic control unit 22 and the control valve 23 are water and pressure-tight integrated in the mouthpiece 1.

In the context of the invention, further options may be provided. Thus, a disc or roller-like closure for the bite piece can be integrated into the mouthpiece 1, in the event that the diver if the bite piece 19 is removed from the mouth. Furthermore, it is conceivable to integrate a switching roller in the mouthpiece 1, which allows a Umschatten from closed circuit to open circuit. In this case, a so-called second stage (low-pressure stage) of an open dipping system is expediently integrated into the mouthpiece 1. The second stage can also act as an auto diluent control valve in closed mode.

Claims (9)

PATENT CLAIMS 1. Rebreather with a mouthpiece (1) which is connected via a inhalation hose (3) and an exhalation hose (2) to a breathing gas circuit (26), wherein in the breathing gas circuit (26) at least one gas sensor for measuring the partial pressure of a respiratory gas component is arranged , characterized in that the gas sensor is designed as a solid electrolyte sensor. 2. Rebreather according to claim 1, characterized in that at least one solid electrolyte sensor is designed as an O 2 sensor (20). 3. Rebreather according to claim 1 or 2, characterized in that at least one solid electrolyte sensor is designed as a C02 sensor (21). 4. Rebreather according to one of claims 1 to 3, characterized in that at least one solid electrolyte sensor in the mouthpiece (1) is arranged. 5. Rebreather according to one of claims 1 to 4, with at least one in the breathing gas circuit (26) via an electrical control valve (23) opening oxygen supply line (24), characterized in that preferably designed as Minimagnetventil electrical control valve (23) in the mouthpiece ( 1) is arranged. 6. rebreather according to claim 5, characterized in that the oxygen supply line (24) in the region of the mouthpiece (1) in the breathing gas circuit (26), preferably in the exhalation hose (2) downstream of an exhalation valve (17), opens. 7. rebreather according to one of claims 1 to 6, characterized in that with the gas sensor and / or with the electrical control valve (23) connected electronic control unit (22) in the mouthpiece (1) is integrated. 8. rebreather according to claim 7, characterized in that the electronic control unit (22) is connected to an external display unit and / or an external power source. 9. Rebreather according to one of claims 1 to 8, characterized in that at least one battery for powering the electronic control unit (22) in the mouthpiece (1) is arranged. Patent Attorney 2010 02 25; Fu Dlpl.-ln® M ^ MSRlBabeluk A-i150, Wfcn) MSi ^ l ~ era3rt5r 39/17 Te !: (+421) 892 8933-0 Ftuc (* 431) 89289333