EP2097312B1 - Method for operating a rebreather and a rebreather - Google Patents

Description

The invention relates to a method for operating a rebreather, in which oxygen is metered into the respiratory gas, the content of the oxygen being monitored by at least one oxygen sensor, and wherein the oxygen sensor is checked by flushing with a gas having a known oxygen concentration.

Open diving equipment is characterized by 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 water, whereby only a small part of the oxygen in the breathing gas was actually consumed. Thus, about 3% (25 l respiratory minute volume, 0.8 l spent oxygen, at rest) of the inhaled gas are consumed at the water surface; at a depth of, for example, 20 m, this value is only one due to the increased ambient pressure of 2 bar Third, that is 1%. Thus, for a dive at 20 m one hundred times as much breathing gas must be carried along as is actually consumed.

Semi-closed and closed rebreather systems are used to circumvent the systemic low efficiency of open diving equipment (SCUBA, SCBA) for breathing gas consumption. These devices are breathed in a cycle. The exhaled air is purified in these devices by means of a carbon dioxide absorber of carbon dioxide and re-enriched with oxygen. Furthermore, such devices are characterized by a one- or two-part counterlung, which can absorb the exhaled gas volume. With rebreathers, the efficiency of gas consumption can be increased up to 100%.

The present invention relates to such semi-closed and closed rebreathers and to a method of operating such devices.

A rebreather and method having the features of the preamble of independent claims 1 and 10 are known from GB 2 329 343 ,

While normally breathing a gas with breathable oxygen content always takes place in open scuba diving equipment, in semi-closed rebreathers the pO ₂ in the circuit is determined by the amount of gas supplied and the diver's metabolism and kept at a certain level in electronically controlled closed equipment by means of a control loop ( GB 24 045 93 A . US 2003188744 A1 . WO 2005/107390 A2 ). In manually controlled closed rebreathers, the diver will manually adjust the oxygen supply and thus the oxygen partial pressure regulated manually. The oxygen partial pressure of the breathing gas must be within certain limits to be breathable. Generally, 0.16 bar is considered the lower limit and 1.6 bar the upper limit. A PO ₂ below or above these limits is classified as life-threatening. It can be seen that a constant monitoring of the pO _{2 is} necessary for rebreathers. Closed units require pO ₂ sensors for manual or electronically controlled regulation of the pO ₂ in the circuit. Electrochemical sensors are usually used as pO ₂ sensors, which are calibrated on the surface with air or 100% O ₂ before the dive.

A correctly functioning pO ₂ sensor for use in rebreathers has an output signal (current or voltage), which depends linearly only on the pO _{2 in} front of the diaphragm of the sensor.

1. a. Nichtlinearität;
2. b. Stromlimitierung: in diesem Fall wird der pO₂ Sensor ab einem bestimmten pO₂ nichtlinear da der Ausgangsstrom des Sensors (oder Ausgangsspannung) fehlerbedingt nicht über einen bestimmten Level ansteigen kann. Dies resultiert in zu niedrigen Sensorsignalen bei hohem pO₂;
3. c. Fehlerhafte Signale von einem oder mehreren Sensoren bzw. der Sensorsignalverarbeitung;
4. d. Fehlerhafte Kalibration;

pO ₂ sensors are very error-prone. Typical errors that can occur are:

1. a. Nonlinearity;
2. b. Current limitation: in this case, the pO ₂ sensor becomes non-linear starting at a certain pO ₂ 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 pO ₂ ;
3. c. Faulty signals from one or more sensors or the sensor signal processing;
4. d. Faulty calibration;

As already mentioned, pO ₂ measuring instruments are calibrated on the surface with air or 100% O ₂ under normobaric conditions (at sea level therefore ~1000 mbar ambient pressure), whereby the sensitivity of the sensors is determined. The maximum achievable pO ₂ is therefore 1.0 bar. Since dO often results in a pO ₂ higher than 1.0 bar, it is important to check the sensors for a) and b). (Example of a calibration with 100% O ₂ : ambient pressure: 1000 mbar, output voltage signal: 50 mV -> sensitivity = 50 mV / bar pO ₂ )

The susceptibility to failure of the pO ₂ sensors is countered by the redundant use of pO ₂ sensors. For example, three oxygen sensors are usually used in closed rebreathers. If a sensor fails, therefore, its output signal is different from that of the other two, this is by comparing all three sensor signals with a "voting algorithm" ( GB 240 45 93 A . WO 2004/112905 A1 ), and this sensor is no longer used to control the pO ₂ .

• e. Ausfall von zwei Sensoren, die jedoch ein gleiches Ausgangssignal haben;
• f. gleiche Nichtlinearität von mindestens zwei Sensoren (>= zwei Sensoren aus der gleichen Produktionscharge, gleiches Alter, gleiche Bedingungen ...);
• g. gleiche Stromlimitierung von mindestens zwei Sensoren

A faulty sensor can thus be determined. However, this method fails with the following errors:

• e. Failure of two sensors, but with the same output;
• f. same nonlinearity of at least two sensors (> = two sensors from the same production lot, same age, same conditions ...);
• G. same current limitation of at least two sensors

Furthermore, for a detailed dive analysis a continuous recording of all dive relevant data is necessary, depth profile, time and pO _{2 are} often stored in an internal memory of the pO ₂ meter and can be transferred to a personal computer after the dive, the temporal resolution and the maximum length of the recording depends on the internal memory size and is therefore limited.

For transfer to the personal computer usually special interface cables are needed. Especially for the effective treatment of diving accidents, a quick evaluation of the dive data is important. Often, however, the right interface cable is not available on-site. The ability to read the dive data without such special cable with any standard PC is therefore desirable.

The invention as claimed in independent claims 1 and 10 is therefore the object of a pO ₂ measuring device in such a way that errors in the pO ₂ sensor signals, non-linearities of pO ₂ sensor signals, a possible current limitation of pO ₂ sensors reliably detected and a detailed record the dive-relevant data are made possible.

From the US 4,939,647 A For example, a method is known which at least partially solves the problems described above. An oxygen sensor is calibrated by purge with pure oxygen. This allows calibration at an oxygen partial pressure of 1 bar. However, it has been found that such a calibration is not sufficient to reliably detect the error cases presented above.

According to the invention this object is achieved in that the test is triggered automatically. It will be so after a necessary and prescribed Calibration performs a check that is not started manually, but is triggered automatically. The test is thus independent of any stress situation in which the diver is located. Especially in such a stress situation, however, due to an increased oxygen demand and an increased respiratory rate, as well as the associated increased production of CO _{2 increases} the probability of failure of a sensor. Depending on the setting, type of deviation and the like, the test can lead to an alarm signal, trigger a changeover to emergency operation or cause a correction of the calibration.

Preferably, the test is carried out under water taking into account the ambient pressure. Essential to the present invention is the fact that the ambient pressure in the test is also crucial for the choice of the time of the test. In this way one can perform the test at an oxygen partial pressure which is in the upper range of the usual measuring range. This means that, in particular, the partial pressure of oxygen is in the range of the upper limit of the partial pressure of oxygen which, for medical reasons, can be expected of humans. This means, for example, that at a depth of 6 m, a purge with pure oxygen is carried out, in which the partial pressure is then about 1.6 bar. The rinsing is carried out until a reliable signal is obtained, which corresponds to pure oxygen. This will usually take four to six seconds.

In particular, the linearity of the oxygen sensor and the function in the important range of higher oxygen partial pressures can be checked by this test of the first type. This makes it possible to detect sources of error which can not be detected during a calibration or on-shore test, since the maximum oxygen partial pressure is limited here to 1 bar. This test of the first kind is usually carried out during descent, when the above-described depth of about 6 m is reached. As a result, ongoing further checks, namely tests of the second kind can be carried out, for example, to discover when an oxygen sensor is impaired by condensation in its function. Since these checks are usually carried out at greater depths, they are not carried out with pure oxygen, since otherwise unacceptably high partial pressures would be achieved. The test is carried out with mixed gas, in which case the oxygen partial pressure may well be below 1 bar.

Furthermore, the present invention relates to a rebreather with at least one pressure bottle for oxygen and another pressure bottle for a thinner gas and with a valve for the supply of oxygen and / or thinner gas in the circuit, which valve is controlled in response to the signal of at least one oxygen sensor, wherein means for purging the oxygen sensor is provided with a gas having a known oxygen concentration.

According to the invention, this rebreather device is characterized in that the device is in communication with a pressure sensor and is controlled in dependence on the signal of the pressure sensor in order to test the oxygen sensor.

The gas requirement for the inspection of the oxygen sensor can be minimized in particular by the fact that the reference gas injection is mounted directly in front of the sensor membrane and so only the space in front of the membrane is rinsed.

A memory card slot allows dive-related data to be stored with high time resolution and a personal computer with memory card slot is sufficient to read the data.

The measuring device is characterized by one or more integrated reference gas feeds. A microcontroller with suitable software is used for signal processing, for the calculations, for the control of the solenoid valves, for outputs on the display and the storage of data on a memory card. As stated above, as a reference gas on the one hand pure oxygen and the diluent gas in closed rebreathers, or the supply gas in semi-closed rebreathers, used. By means of a solenoid valve, the reference gases can be injected directly in front of the membrane of the oxygen sensors. The injection duration is preferably between 5 and 10 seconds, depending on the response time of the oxygen sensors. Thus, for the duration of the gas injection, the oxygen sensor only measures the oxygen partial pressure of the reference gas, while the gas mixture in the circuit in front of the sensor is displaced by the comparison gas flow. From the depth, which is usually determined with a pressure sensor, the ambient pressure is calculated and calculated together with the known oxygen content of the reference gases, the actual oxygen partial pressure upstream of the sensor diaphragm (setpoint) and the actual value (calculated from the sensor signal and the sensitivity determined during the calibration ) of the sensor. Furthermore, the maximum comparison mass flow is limited to 1 to 2 bar l / min by integrated orifices.

It should be noted that the function of the rebreather during these checks is not affected and the diver can breathe normally. Also, the timed amount of oxygen in the 100% oxygen test is approximately equal to human psychological oxygen consumption per unit of time and should therefore not lead to a significant increase in the oxygen partial pressure in the circulation.

The checks a), b), c) and d) described below are performed automatically by the μ-controller.

• In einem bestimmten Zeitintervall (beispielsweise alle 2 min) wird vom µ-controller der pO₂ Messvorrichtung Verdünnergas bei geschlossenen Kreislaufgeräten oder das Versorgungsgas bei halbgeschlossenen Geräten vor die Membran des Sensors eingespritzt. Durch den Vergleich der Soll- und Istwerte kann der pO₂ Sensor dann auf ein korrektes Funktionieren überprüft werden. Ebenso kann mit dieser Überprüfung auf korrekte Kalibration geprüft werden.

To verify the correct operation of a pO ₂ sensor, the following procedure is used:

• At a certain time interval (for example every 2 min), the μ-controller of the pO ₂ measuring device injects diluent gas in the case of closed rebreathing devices or the supply gas in semi-closed devices into the membrane of the sensor. By comparing the setpoints and actual values, the pO ₂ sensor can then be checked for correct functioning. Likewise, this check can be checked for correct calibration.

• Die pO₂ Messvorrichtung wird an der Oberfläche mit Luft oder dem Versorgergas kalibriert. In einem bestimmten Zeitintervall (beispielsweise alle 2 min) wird vom µ-controller der pO₂ Messvorrichtung Versorgungsgas (bekannter Sauerstoffgehalt) vor die Membran des Sensors eingespritzt. Durch den Vergleich der Soll- und Istwerte kann der pO₂ Sensor auf Linearität überprüft werden.

Linearity check on semi-closed rebreathers:

• The pO ₂ measuring device is calibrated on the surface with air or the supply gas. At a certain time interval (for example every 2 minutes) supply gas (known oxygen content) is injected by the μ-controller of the pO ₂ measuring device in front of the membrane of the sensor. By comparing the setpoints and actual values, the pO ₂ sensor can be checked for linearity.

• Die pO₂ Messvorrichtung wird an der Oberfläche mit 100% Sauerstoff (1,0 bar pO₂) kalibriert. Am Beginn des Tauchganges wird vom µ-controller automatisch in einer Tiefe von vorzugsweise 5 m bis 7 m 100% Sauerstoff vor die Membran des Sensors eingespritzt. Der tatsächliche Wert des pO₂ des Gases vor der Sensormembran ist demnach 1,5 bar - 1,7 bar. Ein Vergleich mit dem tatsächlichen Sensorsignal lässt eine Beurteilung des Sensors auf Linearität zu. Prinzipiell ließe sich auch das Sauerstoffventil des Regelkreises einsetzen um den Raum vor den Sensoren zu fluten, um so eine automatische Linearitätsüberprüfung durchzuführen. In diesem Fall sollte der Taucher für die Zeit der Überprüfung den Atem anhalten, um nicht das Messergebnis zu verfälschen.

Linearity check for closed rebreathers:

• The pO ₂ measuring device is calibrated on the surface with 100% oxygen (1.0 bar pO ₂ ). At the beginning of the dive, the μ-controller automatically injects 100% oxygen into the membrane of the sensor at a depth of preferably 5 to 7 meters. The actual value of the pO _{2 of} the gas in front of the sensor membrane is therefore 1.5 bar - 1.7 bar. A comparison with the actual sensor signal allows an evaluation of the sensor for linearity. In principle, the oxygen valve of the control loop could also be used to flood the space in front of the sensors in order to perform an automatic linearity check. In this case, the diver should hold his breath for the duration of the check so as not to falsify the measurement result.

These linearity checks are just as suitable for testing the sensors for current limitation.

These test methods, in contrast to the voting algorithm, allow for real testing of an oxygen sensor during the dive. The error cases a), b), c), d), e), f) and g) can be reliably detected. In particular, one is Checking the sensors for correct functioning during the whole dive at certain intervals possible.

Thus, in principle, the safe operation of a closed rebreather with only one oxygen sensor is possible.

If setpoints and actual values deviate from one another, the diver is alerted by an alarm function. For closed-loop rebreathers, only pO ₂ sensors are used for the control and have successfully passed the automatic function check.

Due to condensation of water directly on the membrane (water droplets) of oxygen sensors, failure c) can occur. By means of the reference gas volume flow, such a drop of water can be blown away from the membrane. Thereafter, the pO ₂ sensor should return correct values.

Furthermore, the invention is characterized by an integrated memory card slot. Dive-relevant data such as sensor signals from one or more sensors, time, depth and battery voltage are written once per s to a Secure Digital memory card (file system FAT 12, 16 or 32). A 60-minute dive corresponds to a file of about 500 kbytes. This file can then be read by any personal computer equipped with a commercially available reader / card slot for Secure Digital memory cards.

Fig. 1

den grundsätzlichen Aufbau eines erfindungsgemäßen Kreislauf- tauchgerätes; und

Fig. 2

eine erweiterte Ausführungsvariante der Erfindung.

In the following, the invention will be explained in more detail with reference to the embodiments illustrated in FIGS. Show it:

Fig. 1

the basic structure of a circulatory diving apparatus according to the invention; and

Fig. 2

an expanded embodiment of the invention.

In Fig. 1 shows the basic structure of a closed rebreather. The diver exhales through the mouthpiece with directional valves 1 through the exhalation tube into the exhalation counterlung 2. By the pressure relief valve 3 excess gas can be discharged into the environment. The exhaled air is purified in the soda lime tank 4 of carbon dioxide. With the inhalation counter-lung 13 and the inhalation hose closes the cycle. The oxygen sensors 11 are mounted in the lime container. A μ-controller 12 calculates the pO ₂ from the signals of the oxygen sensors and displays the dive-relevant data on a display 14. If the oxygen partial pressure pO ₂ in the circuit is too low, is via the oxygen cylinder 5, the pressure reducer 8 and a solenoid valve 10 supplied oxygen. Furthermore, thinner gas can be supplied to the circuit via an automatic lungs-automatic valve or a bypass valve 9 from the diluting gas cylinder 6 and a further pressure reducer 7 (important when diving, when flushing the circuit, or when blowing out the mask). The pressure reducers reduce the cylinder pressure to a pressure ~8 - 12 bar higher than the ambient pressure. Furthermore, a pressure sensor 30 is used to determine the ambient pressure.

In Fig. 2 is the subject invention, which represents an extension for rebreathers, for example. The μ-controller 20 evaluates the signals of the oxygen sensor (s) 11. These are screwed in a suspension 24 on the outlet side in the lime container. Via a Serial Peripheral Interface (SPI short) connection 22, a display 21 is connected. Another SPI connection 23, a memory card slot 19 for Secure Digital (SD cards short) is connected. If Compact Flash cards are used, they are not described via an SPI connection but via a parallel connection. The μ-controller 20 can via a solenoid valve 10 from an oxygen cylinder 5 and pressure reducer 8 100% oxygen directly in front of the membrane (the) pO ₂ sensor (s) (s), wherein the flow rate (for example, 1 bar I / min) through an aperture 18 is defined. Furthermore, diluent gas of known oxygen content can pass from reservoir cylinder 6 via pressure reducer 7 and another solenoid valve 16 to the membrane of the pO ₂ sensor (s). Again, the maximum gas flow is defined by a diaphragm 17 (again, for example, 1 bar I / min). The leads are fastened by means of a holder 25 in front of the sensor membrane. It should also be noted that Fig. 2 an extension too Fig. 1 represents, that is, the solenoid valve 10 and the manual valve 9 are still part of the circuit.

Claims (14)

1. Method for operating a rebreather, in which oxygen is metered to the breathing gas, wherein the oxygen partial pressure is monitored by at least one oxygen sensor (11) and wherein the one oxygen sensor (11) is tested by flushing with a gas with known oxygen concentration, characterized in that the test is automatically triggered.
2. Method according to claim 1, characterized in that the test occurs under water considering the ambient pressure.
3. Method according to claim 1 or 2, characterized in that the flushing occurs by direct injection of gas with known oxygen concentration before the membrane of the oxygen sensor (11).
4. Method according to any one of claims 1 to 3, characterized in that the test is carried out as a function of the ambient pressure.
5. Method according to any one of claims 1 to 4, characterized in that a test of a first kind is carried out at a predefined ambient pressure by flushing with pure oxygen.
6. Method according to claim 5, characterized in that the test of the first kind is carried out at a ambient pressure, at which the oxygen partial pressure pO₂ is in the range of the upper limit of the oxygen partial pressure pO₂.
7. Method according to claim 6, characterized in that the test of the first kind is carried out at an ambient pressure, at which the oxygen partial pressure pO₂ is between 1.5 and 2 bar, preferably at about 1.6 bar.
8. Method according to any one of claims 1 to 7, characterized in that tests of a second kind are carried out at defined intervals by flushing with a gas with known oxygen concentration.
9. Method according to claim 8, characterized in that the tests of the second kind are carried out by flushing with diluting gas.
10. Rebreather apparatus with at least one pressure cylinder (5) for oxygen and an additional pressure cylinder (6) for a diluting gas and with a valve (9; 10) for supply of oxygen and/or diluting gas in the circuit, which valve (9; 10) is controlled as a function of the signal of the at least one oxygen sensor (11), wherein a device for flushing of the oxygen sensor (11) with a gas with known oxygen concentration is provided, characterized in that the device is in connection with a pressure sensor (30) and is controlled as a function of the signal of the pressure sensor (30) in order to automatically test the oxygen sensor.
11. Rebreather apparatus according to claim 10, characterized in that the oxygen sensor (11) has a membrane, at which a flushing nozzle for flushing of the oxygen sensor (11) with a gas with known oxygen concentration is pointed.
12. Rebreather apparatus according to any one of claims 10 or 11, characterized in that a control device (20) is provided, which triggers the flushing with oxygen when a defined ambient pressure is on hand.
13. Rebreather apparatus according to claim 12, characterized in that the control device (20) has a memory card slot (19).
14. Rebreather apparatus according to any one of claims 10 to 13, characterized in that an aperture (18) is provided which reduces the flow rate of the gas.

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