DE102004022988A1 - Gas mixing device for divers comprises an automatic safety unit for monitoring the gas mixture using an oxygen sensor - Google Patents

Abstract

Gas mixing device comprises an automatic safety unit (10) for monitoring the gas mixture (13) using an oxygen sensor (11). Compression of gas mixtures with too high an oxygen content is prevented by the compressor. The safety unit introduces safety measures as soon as the signal (14) from the oxygen sensor indicates a rise in oxygen content of the gas mixture above the safety limit. Preferred Features: The mixing path has several abrupt changes of the cross-sectional surface (18) at which the gas stream experiences a sudden speed change.

Description

technical area

professional and scuba divers use not only ordinary as breathing gas Air, but occasionally mixtures of air and oxygen, so-called Nitrox to mature Shorten decompression phases or minimize the risk of decompression sickness. Nitrox is also used in respiratory protective equipment of the fire brigade or in civil protection, about the physical capacity the respirator to increase.

object The invention relates to a gas mixing device which is a compressor upstream and sucked in by the compressor Air enriched with oxygen and mixed with it to nitrox and a method for safe operation of the gas mixing device.

Gas mixing devices for the Production of breathing gas mixtures of earlier design, with which compressed gas cylinders be filled for diving equipment should, need to operate either specially qualified personnel working in the Able to analyze the mixed gas and adjust the dosage accordingly the analysis result constantly adjust, or are complex pressure regulator, regulating valves, flowmeter and related agents required to increase the ratio of the components of the breathing gas mixture to keep constant [1]. As compressed gas cylinders of the immersion technique typically filled to 200 to 300 bar pressure will be for Such mixing devices numerous expensive high-pressure components needed. In addition, for the oxygen content is an expensive oil-free compressor needed its maintenance and operation very demanding and just in exotic Diving travel destinations is hardly practicable. These disadvantages of High-pressure gas mixing processes have the worldwide breakthrough Nitrox diving prevented so far, although thereby extends the dive time and the risk of decompression sickness can be reduced.

A relatively new method, the oxygen content of ordinary Compressed air enriched by a permeable membrane [2], required for Realization also expensive and in addition costly expensive High pressure installations. Since the oxygen is taken from the air here will, and the unwanted Nitrogen content is released back to the atmosphere, but before had to be condensed In this process the operating costs are significantly higher than at the filling of diving tanks with compressed air, Furthermore There is still no sufficient experience, whether such membranes under the harsh operating conditions of a commercial dive center a sufficient one Lifetime, would be conceivable For example, contamination of the membrane by oil from a defect become a compressor. Since the additional proceeds through the Nitrox diving for one Diving center is rather low, can replace the membrane before Expiry of their calculated life an economic disaster be.

A Method to mix the Nitrox gas under atmospheric pressure and then compacting in a compressor, appears as the cheapest Alternative, whose operating costs are also better calculable. earlier such solutions [3] need but still an expensive oil-free Compressor, since the gas mixture in a pipe spiral is insufficient, and the compressor phased a mixture with too high an oxygen content can suck. In [3], therefore, not even the attempt taken, the oxygen content of sucked by the compressor Gas analysis, but the analysis is only after the mixing in the compressor. This has the further disadvantage that the Latency through the compressor setting the oxygen dosage very difficult and makes it a game of patience.

An improved solution [4] with a turbulent mixing section, on the other hand, can achieve such a homogeneous mixing that even an analysis of the gas mixture taken in by the compressor supplies meaningful measuring results. Thus, an ordinary compressor can be used, which is carefully cleaned for operation with oxygen-enriched mixture and then operated with a specially suitable and approved for gas mixtures with increased oxygen content lubricating oil. At the present state of the art of lubricating technology, gas mixtures of up to 40% oxygen content can be compressed without an acute danger of explosion. Exceeding this oxygen content - for whatever reason, for example due to failure of the oxygen dosage, or fluctuations in the intake capacity of the compressor - but after exceeding a certain safety limit of the oxygen content is an acute risk of explosion. To avoid accidents, it must be prevented that the compressor compresses a breathing gas mixture with an excessively high oxygen content beyond the danger limit. In the gas mixing device [4] this backup is done by the operating personnel who constantly observed the display of an oxygen analyzer and manually sets the Sauerstoffdosierventil manually, so that the gas mixture reaches the desired target value. It is to be assumed that this method of operating the gas mixing device, which in [4] is even the subject of an underan is caused by carelessness or technical failure or fluctuations in the power supply of the compressor to an accident sooner or later. Further disadvantages of the gas mixing device according to [4] for the named field of use are the nature of the turbulent mixing system used. It is based on vanes in the gas stream, which impose alternating changes in the direction of rotation about the central axis of the gas stream. Such and other guiding elements in the gas stream are difficult to clean and therefore a filter on the air inlet side of the mixing section is necessary. In case of contamination of the guide elements, the effectiveness of the mixing may suffer and there is then the danger that the oxygen analyzer does not recognize a dangerously increased oxygen content due to insufficient mixing. Experience shows that especially in remote exotic destinations, the temptation to simply remove a dirty filter instead of replacing it. Apart from these disadvantages, which are based on human weaknesses and the conditions in some developing countries, such a mixing system also has purely technical disadvantages. The mixing tube diameter with the guide elements contained therein must be adapted for optimal mixing of the air flow rate of the compressor. In [4] a range of 1: 5 is achieved for smaller air flow rates with a first embodiment of the mixing section, with a second embodiment a range of 1: 2. With these two versions, a range of 1:10 can be covered, which agrees sufficiently with the typical field of application, compressor stations with an air throughput of 80 liter / min to 1000 liter / min. However, it would be desirable to cover this area with one and the same embodiment of the gas mixing device. Another problem of the mixing method of [4] lies in the need for a good mixing large length of the linear mixing line used, which. the installation just in tight spaces, as they are relatively common in practice in the compressor rooms of dive centers or especially on dive safari boats, difficult.

From this Various tasks arise for the gas mixing device according to the invention.

First is to provide an automatic safety device, which is a Compaction of gas mixtures with too high oxygen content over the Danger limit is prevented. Second is an improved turbulent Provide mixing section, the most compact design over a huge Range of air intake a nearly homogeneous gas mixing can guarantee. Third, this improved mixing section should be as possible no vanes contained within the gas stream, first, the production cost to lower and second, to simplify cleaning, so that a more complex Suction filter can be omitted. Fourth, the automatic security device is self-testable as well be self-calibrating to avoid maintenance and operator errors which is often poorly qualified in exotic diving destinations Exclude operating personnel. Fifth should the oxygen sensor of the safety device by special constructive measures be operated under optimal conditions and before moisture, about due to condensation, be protected.

These Tasks are in accordance with the claims of Invention solved. The object of the invention is based on an inventive combination of known components whose very good activity for the mentioned Purpose due to the amazing simple construction can also astonish professionals. Those Further developments of the subject invention, the particular Protecting the oxygen sensor from moisture or disturbances of its Prevent pressure compensation system, based on earlier, at the time not yet published in this application inventive activity one of the two inventors [6], [7], [8].

presentation the invention

The fundamental Obstacle, an automatic safety device for a gas mixing device of the kind described above [4] lies in itself too slow response of galvanic oxygen sensors available on the market [9]. An alternative to these sensors is for the purpose of gas analysis in the intake of a compressor previously unknown, because there are no on a different physical principle based oxygen sensors available, which has grown permanently to the harsh operation in a compressor station would, even in the intake of the compressor, and the cheap and cheap are maintenance free. From many years Experience with galvanic oxygen sensors for the analysis of oxygen-containing Have breathing gas mixtures in gas mixing devices of the type of [4] these oxygen sensors are proven - but this only applies to normal operation, if the oxygen dosage as in the method of [4] manually very slowly and carefully turned to a setpoint so that the oxygen sensor to follow the event despite its reaction, which is too slow in itself can. For a safety device designed to detect incidents and timely Safety measures trigger is sufficient, the slow response of the available oxygen sensors in usually not far from.

One typical example is intended to illustrate this. In case of failure of the Oxygen dosage, which is a quick, small, but already dangerous Increase in the oxygen content in the sucked by the compressor Mixture leads, can the slow response of the oxygen sensor according to data sheet [9], who for the operation in the intake of a compressor experience straight is still robust enough, typically 12 ... 15 seconds long delay until the discovery of this accident by cause the evaluation electronics. Another delay results itself in that a subsequent shutdown command to the oxygen supply because the transit time of the gas through the gas mixing path does not immediately cause that the Compressor only sucks in harmless air. So it could happen that in this or a comparable scenario the compressor for half Minute or longer a gas mixture with already dangerous high oxygen content sucks and compressed. An emergency shutdown the compressor as a supplement to the Although interrupting the oxygen supply could help a bit the requirements for the reaction time of the safety device to diminish, but the thereby possible time savings in the Usually still not enough to slow the oxygen sensors compensate. Although there are special versions such oxygen sensors that react faster (about twice so fast), but they have one on their gas-sensitive side much thinner Diffusion membrane on, the continuous operation in the intake system of a compressor not according to experience has grown - it threatens a rapid tear of the Diaphragm and thus a failure of the sensor.

Of the average expert must therefore for Come to an end that such Oxygen sensors for such an automatic security device not in principle are suitable, as this would then react too slowly. Therefore is for a gas mixing device of the type mentioned currently not automatic Safety device on the market, on an oxygen sensor based and yet fast enough to interfere with Oxygen dosage reacts.

In the gas mixing device according to the invention The reaction time will be through some tricky action across from the currently known state of the art so far reduced that the safe operation the gas mixing device according to the invention only possible is, although commercially available galvanic oxygen sensors - or others for the stated purpose per se too slow oxygen sensors of others physical principles of action - used can be.

The first measure consists of the sensor signal originating from the oxygen sensor for signs of an increase in the oxygen content of the gas mixture over a Safety boundary beyond. This happens preferably through a computer program in a so-called microcontroller, the part of the evaluation electronics of the automatic Safety device is. This is the drift and offset-free Realization of predictive Signal evaluation method possible, who can already recognize an imminent danger before the oxygen content of the gas mixture sucked in by the compressor exceeds the actual danger limit.

The second measure consists in the mixing section by a special shaping a preferably to give low latency. This succeeds through a turbulent one Mixing process in which the gas flow on the way through the mixing section is gradually accelerated gradually. This is achieved by in a certain way stepped largely abrupt cross-sectional changes in the mixing section, where also the turbulence arise, which cause the mixing.

These activities bring together with the latency in the compressor (up to its high pressure stage, where the actual danger source sits), just enough time ahead, by automatically triggered precautions such as interruption or reduction of oxygen flow, rapid shutdown of the compressor, opening a safety valve at the high-pressure stage of the compressor, Injecting inert gas into its intake tract, or switching one Flap in its intake tract from the mixer to the air down to just a few of the possible ones precautions to name a compression of gas mixtures with too high oxygen content Effective beyond the danger limit by a connected compressor to prevent.

further developments the gas mixing device according to the invention relate to a particularly compact shaping of the mixing section, the Protection of the oxygen sensor against harmful environmental and operating conditions and the stabilization of the oxygen dosage against temperature fluctuations due to the inevitable cooling off the oxygen fittings by the relaxation of the oxygen gas operational.

Finally will a method for safe operation of the gas mixing device according to the invention discloses the essential parts realized in a computer program can be that from the microcontroller of the automatic safety device accomplished becomes.

This succeeds, an amazing one to provide a gas mixing device constructed in a specialized manner, which ensures a very good homogeneous gas mixing of the sucked air from the compressor with the injected oxygen gas for the production of so-called nitrox - breathing gas of diving technology and respiratory protection, and due to a fast-acting automatic safety device as far as possible against accidents and Faulty operation is secured. The gas mixing device can be used by other gas injectors, such as helium, and connection of appropriate gas analyzers for the production of other respiratory gases as nitrox.

There The prior art apparently assumes that for continuous operation In the intake of a compressor suitable and available oxygen sensors in principle too slow to be part of a safety device for a gas mixing device the type described above to respond in a timely manner, and Thus, the combination of such a gas mixing device with a Safety device of the type presented above represents a novelty, becomes a protective right for each Kind of gas mixing devices coveted that for the production of gas mixtures is determined from air and oxygen or other respiratory gases, the Gas mixture downstream in one of the gas mixing device Compressor on one for filling suitable for diving tanks or respirators suitable high pressure is brought, and which is characterized in that an automatic Safety device is present, which is an oxygen sensor contains which monitors the gas mixture at a suitable location, wherein a compression of gas mixtures with too high oxygen content through a connected Compressor over the Danger limit is further prevented by the fact that the automatic Safety device automatically precautions initiates as soon as the signal originating from the oxygen sensor Signs for an increase in the oxygen content of the gas mixture over a Safety limit addition.

Aufzählung the drawings

1 shows the basic principle of the novel gas mixing device with an attached compressor, which compresses the originating from the gas mixing device gas mixture and filled on scuba tanks.

2 shows a particularly advantageous embodiment of a turbulent mixing section for the novel gas mixing device, in which the cross-sectional areas gradually decrease from the inlet side of the mixing section to its outlet side, and in which a plurality of manifolds are present to give the mixing section an advantageous, as very compact serpentine shape.

3 shows a detail of a further developed embodiment of the novel gas mixing device, in which the pressure compensation of the oxygen sensor is not carried out by the ambient air, but by a gas mixture taken from the gas mixing section.

description the invention with reference to the figures

1 shows by way of example and schematically the basic principle of the novel gas mixing device. According to the known state of the art, the gas mixing device has an air inlet ( 3 ), which is connected to the atmosphere, a gas injector ( 4 ) near the air inlet, a metering valve ( 5 ) for supplying oxygen gas to the gas injector ( 4 ), a turbulent mixing section connected to the air inlet ( 6 ) for mixing atmospheric air with the gas from the injector oxygen gas, an output terminal ( 7 ) at the end of the mixing section where a compressor ( 8th ) can be connected so that the suction of a compressor connected to the output terminal a gas flow ( 9 ) causes in the gas mixing device, which causes the mixing process, and is characterized in that an automatic safety device ( 10 ), which by means of an oxygen sensor ( 11 ) the gas mixture ( 13 ) is monitored at a suitable location, wherein a compression of gas mixtures with too high an oxygen content by a connected compressor beyond the danger limit is further prevented by the fact that the automatic safety device reduces the oxygen supply to the gas injector or interrupts and / or the compressor off, and / or more Protective measures as soon as the sensor signal originating from the oxygen sensor ( 14 ) Indicates an increase in the oxygen content of the gas mixture beyond a safety margin.

As an indication of an increase in the oxygen content of the gas mixture beyond a safety margin, not only the instantaneous value of the sensor signal ( 14 ), but also the speed of the rise of the sensor signal. In this way, despite an inherently slow reaction of the oxygen sensor and despite the latency through the mixing path, the automatic safety device is able to anticipate future events and react with protective measures before the compressed gas mixture in the compressor has even reached a critical oxygen content. This artifice is crucial for a timely response of the automatic security device. I was trying It has been found that all practically relevant malfunctions of the oxygen metering in the described gas mixing device can be detected much earlier by the evaluation of the speed of the rise of the sensor signal than by the instantaneous value of the sensor signal alone.

In practical implementations of the invention, such an evaluation of the signal originating from the oxygen sensor is preferably carried out by a computer program executed in a microcontroller, since the realization of the evaluation of the rise of the sensor signal with purely analog circuit technology encounters fundamental difficulties, especially offset and drift-free differentiating circuits With the necessary large time constants, if at all, only high-quality and therefore expensive precision components can be realized, which is also detrimental to the robustness under harsh environmental conditions. The microcontroller is part of the evaluation electronics ( 12 ) of the automatic security device. The evaluation electronics usually contains. a display unit ( 25 ) for the oxygen content or for messages. It is also expedient to use a switch ( 24 ) to manually switch the mixing process on and off, and an alarm sounder ( 26 ). If in a compressor station only Nitrox be filled, then. the desk ( 24 ) also be an additional contact set of the relay for the compressor motor.

Preferably, the automatic safety device acts on the oxygen supply. This usually takes place from an oxygen storage reservoir ( 1 ) via connected pressure reducing and pressure indicator fittings ( 2 ). The gas mixing device is removed from the valves ( 2 ) Oxygen under reduced pressure - about 2 to 5 bar - supplied, wherein the setting of the per unit time of the mixing section supplied oxygen preferably via a metering valve ( 5 ), which is the gas injector ( 4 ) is connected upstream. This metering valve is usually a manually adjustable needle valve for reasons of reliability, and not an electrically activated valve. For the same reason, the sole use of the fittings ( 2 ) to adjust the oxygen supply, although this would be a cost savings.

To now the evaluation electronics ( 12 ) of the automatic safety device to be able to interrupt the supply of oxygen, it must be provided via an actuator means ( 15 ), which they have via a control line ( 16 ) and that acts on the supply of oxygen. This actuator means, for example, as shown in the figure, be an electric solenoid valve in the oxygen supply line the metering valve ( 5 ) is connected upstream. Alternatively, however, the actuator means could also be an electrically adjustable metering valve. However, this would then be followed for safety reasons again a purely mechanically acting Durchflußbegrenzer, so that the solution with the solenoid valve and the manually adjusted metering valve is preferred.

In addition to the protective measures already mentioned - reduction or interruption of the oxygen supply or shutdown of the compressor - other protective measures are occasionally possible, such as separation of the intake line ( 20 ) of the compressor from the mixing section and switching to the ambient air by means of electrically triggered valves, or blowing larger amounts of an inert gas, such as nitrogen, in the suction line of the compressor via an electrically triggered valve. The actor agent ( 15 ), via which the evaluation electronics ( 12 ) the automatic safety device initiates the protective measure, must be adapted accordingly.

In order to avoid disadvantageous guiding elements in the gas stream, the gas mixing device according to the invention preferably uses a turbulent mixing method which; on largely abrupt changes in the cross-sectional area ( 18 ) of the mixing section ( 6 ). At these points, due to the suction process of a compressor connected to the gas mixing device, a largely abrupt change in the flow velocity of the gas flow with turbulent vortices (FIG. 17 ), which the mixing of at ( 3 ) sucked air with the at ( 4 ) cause injected oxygen. The pulsating suction of a reciprocating compressor or diaphragm eccentric compressor enhances the mixing effect. In particular, for operation with screw compressors, it is advantageous if the mixing section a plurality of manifolds ( 19 ), since these compressors produce with their high intake capacity in the manifolds further mixing vortex, which reinforce the attenuated mixing effect due to the lack of Pulsationsvorgangs again.

For the sake of completeness, it is also shown in the figure, what with the from the high-pressure outlet ( 21 ) of the compressor ( 8th ) is usually done compressed gas mixture. This is done via a fill bar ( 22 ) with the associated fittings on scuba tanks ( 23 ) filled. In the case of the gas mixing device according to the invention, advantageously no complicated modification of these high-pressure installations usually present in diving bases is necessary, it is sufficient to clean them accordingly for operation with nitrox.

For the gas mixing device, a turbulent mixing section ( 6 ) with a particularly short lead time for the gas mixture, which is the delay until the effect of the auto mated safety device triggered protective measures. This mixing section with a particularly short throughput time is characterized in that it has several largely abrupt changes in the cross-sectional area (FIG. 18 ), at which a largely sudden change in velocity of the gas stream ( 9 ) in conjunction with the pulsating suction of the compressor can cause a turbulent mixing of the intake air with the injected oxygen over a relatively short total length.

The smallest delay results when the cross-sectional areas gradually decrease from the beginning of the mixing section to the end, so that the gas stream with each stage assumes a higher flow velocity. The oxygen sensor ( 11 ) is expediently placed at the end of the mixing section or near the end of the mixing section.

In a further developed embodiment, such a mixing section can also be several manifolds ( 19 ), which on the one hand in the range of high gas flow rates (screw compressors) further improves the mixing by further turbulence arising at the manifolds, but on the other hand allows a very compact design of the gas mixing device by the gas mixing section is brought by means of the manifold in a snake shape.

A field-tested dimensioning of a particularly advantageous mixing section for Kompressorsansaugleistungen of 80 liters / min to 1000 liter / min is now with reference to the 2 described in more detail. The mixing section is made of tubular segments with circular cross section ( 28 ) and a tee ( 29 ), and is powered by 90 degree manifolds ( 19 ) brought into a serpent form. The air intake ( 3 ) has 50 mm inner diameter. This is followed by a first pipe segment with a length of 255 mm. The of the oxygen supply line ( 27 ) fed gas injector ( 4 ) has its mouth 50 mm away from the air inlet in the center of the first tube segment. This is followed by a first manifold ( 19 ) with a radius of 65 mm, with respect to the center line in its center, followed by a second tube segment ( 28 ) with a length of 35 mm, a first largely abrupt reduction of the cross-sectional area ( 18 ) over a length of 17 mm by reducing the inner diameter of the tubes from 50 mm to 34 mm, followed by a third tube segment ( 28 ) of 58 mm length, a second manifold ( 19 ) with radius 43 mm, a fourth tube segment ( 28 ) of 255 mm length, a third manifold ( 19 ) with radius 43 mm, a fifth tube segment ( 28 ) of 55 mm length, a fourth manifold ( 19 ) with radius 43 mm, a sixth tube segment ( 28 ) of 26 mm length, a second largely abrupt reduction of the cross-sectional area ( 18 by reducing the inner diameter of the tubes from 34 mm to 24 mm, followed by a seventh tube segment ( 28 ) of 135 mm length, and a 100 mm long tee ( 29 ) for the connection of the oxygen sensor ( 11 ). Connected to this, but no longer absolutely necessary for the mixing process, is a fifth manifold ( 19 ) with a radius of 35 mm and an eighth pipe segment ( 28 ) 104 mm in length, at the end of the output terminal ( 7 ) of the gas mixing device is located. The latter two components facilitate assembly of the mixing section in a housing that is 50 cm wide, 40 cm high and 8 cm deep, and also accommodates the oxygen dosing valve and automatic safety device components. The entire gas mixing device then has only about the size of a briefcase, which currently represents a world record in terms of the smallest possible design for the stated application.

The theoretical analysis of the mixing process is due to the additional Effect of the pulsating suction of the compressor, which Resonances and additional Turbulence fills, extremely difficult. The effectiveness of the mixing process in the particularly advantageous Mixed range was over in the trial a very wide range of gas flow rates from 80 liters / min to 1000 liter / min detected.

The method for safe operation of the gas mixing device according to the invention is as follows:
Make sure that the metering valve ( 5 ) and the switch ( 24 ) is set to "Off" for the mixing process. 8th ) turn on. At the filling bar ( 22 ) turn on a valve to which no dip tank is connected. Oxygen supply to the gas mixing device on the valves ( 2 ) turn up. The display of the evaluation electronics ( 12 ) - there is an automatic self-test of the measuring amplifier and then a self-calibration of the oxygen sensor to 21% oxygen content, which is known because still air is sucked. If there are serious deviations from the stored self-calibration value of earlier filling operations, there is reason to believe that either the oxygen sensor has become defective or has arrived at the end of its service life, or that a valve ( 5 . 15 ) in the oxygen supply line is leaking or not completely closed. In this case, the display shows a corresponding fault message and refuses to release the oxygen supply. On the other hand, if the self-calibration succeeds without such suspicion, the automatic safety device, after activation of the mixing process, will be activated by manual operation of the switch ( 24 ) Free the oxygen supply via its actor agent. Now the dosing valve ( 5 ) turn it up very slowly while observing the indicated oxygen content until the setpoint is reached, for example 40%. After a certain waiting time, the high-pressure system is flushed through and this gas mixture is applied to the filling line.

As a result, any number of diving bottles can be filled. The automatic safety device constantly evaluates the sensor signal. Should that come from the oxygen sensor ( 11 ) sensor signal ( 14 If there are signs of an increase in the oxygen content of the gas mixture beyond a safety margin, it will initiate one or more protective measures, as a rule this means interrupting the supply of oxygen via the actuator means ( 15 ) and the delivery of an alarm tone ( 26 ). Then the oxygen supply to ( 2 ) manually turned off and the compressor off. Depending on the design of the system and the shutdown of the compressor can be triggered by the automatic safety device itself. After the investigation and elimination of the cause of the fault, the procedure can be repeated from the beginning.

If there is a fault and all tanks are filled, then at the filling bar ( 22 ) turn on a valve to which no dip tank is connected. Oxygen supply to ( 2 ) shut down. After a short wait, the dosing valve ( 5 ) shut down. Switch ( 24 ), whereby the automatic safety device releases the actuator means ( 15 ) also brings into a position in which the oxygen supply is interrupted, in the case of a solenoid valve, this is automatically closed. After a certain waiting time, in which the compressor only sucks in air, the high-pressure system has been flushed through to the filling line with air again. Then turn off the compressor. Since it can not be avoided even in the proper operation of the gas mixing device that nitrox gas is released into the atmosphere, especially in the rinsing, must be paid to absolute cleanliness in the vicinity of the filling and good ventilation. Where this is not possible, flushing must take place via a separate exhaust air duct into the open air.

The one Part of the just disclosed method for safe operation of the gas mixing device according to the invention, which focuses on activities of the automatic safety device may be in the microcontroller the evaluation electronics are programmed. If this microcontroller via a nonvolatile Storage. has, then It is particularly advantageous in this memory past signal values of the oxygen sensor when operating with switched off oxygen flow - so on Air - to lay down, which are obtained in the described self-calibration phase. The comparison of these signal values from past self-calibration phases with the current self-calibration value allows a statement about the Functioning of the Oxygen sensor. Usually Its sensor signal in air gradually decreases during its life cycle. At the end of its life, this signal attenuation accelerates. On this way, the end of the lifetime of the sensor can be reliably detected become. In contrast, should the diffusion membrane on the gas-sensitive Greased side of the sensor or even torn, then the sensor signal rises in air usually clearly opposite earlier Values before the sensor dries out and thus no signal at all delivers more. All these errors can be saved by comparison with earlier Self-calibration values are automatically detected.

Becomes the measuring amplifier for the sensor signal a multiplexer upstream, under the control of the microcontroller In addition to the sensor signal and reference signals such as the zero point or the expected maximum of the sensor signal to the sense amplifier can, then the automatic safety device is also in the situation is offset, the entire measuring channel automatically and also to test for correct function during operation.

On this way, it succeeds the automatic security device in a further developed version the invention a self-test and Selbstkalibrationsfähigkeit to give, characterized in that a self-calibration of Oxygen sensor is carried out in air that the thus obtained new self-calibration value with at least one earlier obtained self-calibration value is compared to the sensor to check for normal aging and the absence of suspicious abnormalities, and that the new self-calibration value as comparison value for later self-calibration operations in a non-volatile Memory (for example EEPROM or a RAM with backup battery) is stored so that it also after switching off the gas mixing device and restarting after a longer time Time - weeks or months - again to disposal stands.

Of the regular self-test of the measuring channel is characterized in that the measuring amplifier not only the sensor signal, but also solid. Comparison signals are supplied, the result after the reinforcement and the analog / digital conversion in the automatic security device as well is compared with setpoints stored there.

In the case of high oxygen supply capacities, it may happen during operation of the gas mixing device that components of the oxygen supply gradually cool down gradually over time, up to the outer icing of the relevant components. in the especially the fittings cool ( 2 ) of the oxygen storage reservoir ( 1 ) strongly. Due to the sinking oxygen temperature increases the mass flow of oxygen through the metering valve and at constant suction capacity of the compressor, which is the rule, the proportion of oxygen in the gas mixture increases. Although this effect is in most cases negligibly small for practical purposes, since the supercritical pressure ratio mass flow is proportional to 1 / root (T) of the absolute temperature T of the oxygen, it can be alleviated by passing the oxygen in front of the metering valve Heat exchanger is performed. Preferably, the heat exchange takes place with the ambient air. Any conceivable implementation of such a heat exchanger is suitable which fulfills this purpose. A particularly cost-effective implementation of the heat exchanger is obtained when a portion of the oxygen supply line is wound around the outer wall of the mixing section and is in good thermal contact with this.

Should under particularly difficult conditions of use the measure of Heat exchanger not sufficient for stability the oxygen content at a once set to target content metering valve to ensure, then the automatic security device can also be used to to regulate the oxygen content to the target value by virtue of the measured data from the oxygen sensor an electrically operated valve in the oxygen supply line controls accordingly.

Like in the 3 is shown by way of example, the necessary for the pressure balance of the sensor interior gas can be removed from the mixing section to an optimal pressure equalization of the electrolyte chamber ( 30 ) of the oxygen sensor via the below its printed circuit board ( 31 ) pressure compensating diaphragm ( 32 ) to ensure. This prevents that the suction of the compressor - negative pressure and pulsations - long term damaging the sensitive diffusion membrane on the gas-sensitive front of the sensor, whereby the life of the oxygen sensors in the gas mixing device is significantly improved.

To condensation of moisture from the intake air to the electronic components on the circuit board ( 31 ) and electrical connectors: ( 34 ) within the oxygen sensor, the gas withdrawn from the mixing zone can be dried by drying ( 35 ) before being led into the interior of the sensor.

As in [6], the oxygen sensor ( 11 ) are in a separate chamber which seals it against the environment, wherein the pressure equalizing gas is supplied from the mixing section to the chamber interior.

However, according to [8], a closure body ( 37 ), which tightly seals the back of the oxygen sensor, whereby the gas required for pressure equalization from the mixing ( 6 ) via a connecting piece ( 39 ) and via a pressure equalization line ( 40 ), for example a hose, into the interior of the closure body ( 37 ) to be led.

The closure body may, for example, with coil springs ( 38 ) be releasably secured to the housing of the mixing section and thus holds the oxygen sensor securely in place.

If necessary for climatic reasons - especially in the tropics - a dry cartridge ( 36 ) are interposed in the pressure equalization line. The drying cartridge contains a desiccant which removes the water vapor passing through it during pressure equalization operations, for example silica gel.

The Amount of the drying agent can be measured so that its Service life of the oxygen sensor corresponds, before especially when between the gas mixing section and the desiccant There is a bidirectional valve assembly, in which the valves open only when a pressure difference must be compensated.

In such a pressure compensation device for the oxygen sensor, the drying agent can be avoided if the electronic and electrical components of the oxygen sensor are protected against condensation moisture by casting with a permanently plastic potting compound. Then, the oxygen sensor has it characteristic Vergusskanäle that lead into its pressure equalization chamber [7]. These potting channels are preferably used as generous cut-outs in the PCB ( 31 ) of the oxygen sensor realized.

The invention succeeds in a surprisingly simple way to provide a safe and stable functioning gas mixing device, which can be connected upstream of a compressor in order to compress the gas mixture in this. The particularly advantageous embodiment of the mixing section in the form of a coil with stepped reduced cross-sectional areas and a plurality of bends allows a cost-effective and very compact implementation. The invention is particularly suitable for the safe production of oxygen-enriched air immersion technology, so-called nitrox, the current state of oxygen-compatible lubricant technology with up to 40% oxygen content. It is also suitable for mixing breathing gases with other components such as helium. Compared to the prior art, the inventions It is much cheaper to produce, easier to clean, more compact, which facilitates installation in confined spaces, especially in dive safari boats, the gas mixture is of near-optimal homogeneity, the desired oxygen content is easier and more stable, and one and the same design is suitable for a variety of applications large gas flow rates that can vary over approximately one order of magnitude. The automatic safety device also allows operation by semi-skilled helpers without special qualifications, which is a not-to-be-underestimated advantage especially in exotic dive destinations in distant countries.

literature

• Lubitzsch et al., US 4219038
• [2] Delp, US 5611845
• [3] Wells, "Continuous Nitrox mixer", US 4,860,803
• [4] Cowell, "Pre-compression nitrox in-line blender", US 5 992 464
• [6] Engl, "Gas sensor device for respiratory equipment ", German patent application 10259988.2
• [7] Engl, "Castable Gas sensor and casting method therefor ", German Patent Application 10328356.0
• [8] Engl, "Pressure compensation device for gas sensors ", German patent application 102004004265.9
• [9] Datasheet for Oxygen sensor OOI-105, Envitec-Wismar GmbH, Wismar, Germany

1

Oxygen storage reservoir

2

Fittings of ( 1 ), in particular pressure reducer

3

air intake at the entrance of the gas mixing device

4

gas injector for the oxygen

5

metering valve for the oxygen

6

mixing section

7

Output connection of the gas mixing device

8th

compressor

9

gas flow

10

automatic safety device

11

oxygen sensor

12

evaluation electronics

13

to be monitored mixture of gases

14

sensor signal or line for the sensor signal

15

actuators means (for example, electric solenoid valve)

16

control line to the actuator means

17

turbulent whirl

18

modification the cross-sectional area

19

elbow

20

suction of the compressor

21

High pressure outlet of the compressor

22

Filling panel

23

tanks

24

switch to activate the mixing process

25

display unit

26

sounder

27

oxygen supply to the gas injector

28

Pipe segments)

29

Tee

30

electrolyte chamber of the oxygen sensor

31

circuit board of the oxygen sensor

32

Pressure compensation diaphragm of the oxygen sensor

33

Pressure equalization chamber of the oxygen sensor

34

Connectors of the oxygen sensor

35

desiccant

36

drying cartridge

37

closure body

38

spiral spring

39

connecting branch

40

Pressure equalizing line

Claims (19)

Gas mixing device for compressor stations, with - an air inlet ( 3 ), which is connected to the atmosphere, a gas injector ( 4 ) near the air inlet, - a dosing valve ( 5 ) for oxygen supplied to the gas injector, - a mixing section connected to the air inlet ( 6 ) for mixing the air with the gas from the injector oxygen gas, - an output terminal ( 7 ) at the end of the mixing section, for connecting a compressor ( 8th ), that - the suction of a compressor connected to the output terminal a gas flow ( 9 ) in the gas mixing device, - that the mixing section is designed so that the gas flow turbulent vortex ( 17 ), which effect the mixing, characterized in that - an automatic safety device ( 10 ), which by means of an oxygen sensor ( 11 ) the gas mixture ( 13 ), whereby compression of gas mixtures with too high an oxygen content by the compressor beyond the danger limit is prevented by the safety device automatically initiating protective measures as soon as the signal originating from the oxygen sensor ( 14 ) Indicates an increase in the oxygen content of the gas mixture beyond a safety margin, wherein the protective measures may be one or more of the following: reduction of the oxygen flow to the gas injector, or shut down of the oxygen flow to the gas inlet - opening of a safety valve at the high pressure stage of the compressor, or - injecting inert gas into the intake duct of the compressor, or - switching a flap in the intake duct of the compressor so that it can only suck in air, or - any other protective measure required by an automatic security device ( 10 ) via actor means controlled by it ( 15 ) can be triggered automatically and which is capable of preventing a compression of gas mixtures with too high an oxygen content beyond the danger limit. As actuator means can be used: - an electrically adjustable metering valve ( 5 - a solenoid valve upstream or downstream of the metering valve, - a relay for switching off the compressor motor, - a controllable safety valve at the high pressure stage of the compressor to discharge the gas inside it, - a controllable flap in the intake tract of the compressor, - any other one automatic safety device controllable actuator means that can prevent or interrupt the compression of gas mixtures with too high an oxygen content beyond the danger limit. Gas mixing device according to claim 1, characterized in that as an indication of an increase in the oxygen content of the gas mixture beyond a safety margin not only the instantaneous value of the sensor signal ( 14 ), but also the speed of the rise of the sensor signal. Gas mixing device according to claim 1 or 2, characterized in that the mixing section ( 6 ) several largely abrupt changes in the cross-sectional area ( 18 ), at which the gas stream ( 9 ) is in each case subjected to a largely sudden change in velocity, whereby turbulent vortices ( 17 ), which cause the mixing of the sucked air with the injected oxygen. Gas mixing device according to claim 3, characterized in that the mixing section ( 6 ) several largely abrupt changes in the cross-sectional area ( 18 ), wherein the cross-sectional areas from the beginning of the mixing section at the air inlet ( 3 ) to its output terminal ( 7 ) gradually decrease, so that the gas flow ( 9 ) assumes a higher flow velocity with each stage. Gas mixing device according to one or more of claims 1 to 4, characterized in that the mixing section ( 6 ) several manifolds ( 19 ) having. Gas mixing device according to claim 5, characterized in that the mixing section ( 6 ) is designed in a particularly compact snake shape, resulting from the series connection of a first pipe segment ( 28 ), which controls the air intake ( 3 ) and the gas injector ( 4 ), a first manifold ( 19 ), a second tube segment, a first largely abrupt reduction of the cross-sectional area ( 18 ), a third pipe segment, a second manifold, a fourth pipe segment, a third manifold; a fifth pipe segment, a fourth manifold, a sixth pipe segment, a second largely abrupt reduction of the cross-sectional area (FIG. 18 ), a seventh pipe segment, and a tee ( 29 ) for the connection of the oxygen sensor ( 11 ). Method for operating the gas mixing device according to claim 1 to 6, characterized in that - the beginning of the oxygen supply is still closed, so - that the compressor ( 8th ) via the air inlet ( 3 ) of the mixing section ( 6 ), that the automatic safety device carries out a self-calibration of the oxygen sensor to the known oxygen content of the atmospheric air - 21%, - that the automatic safety device releases the oxygen supply after successful self-calibration, whereby the mixing process can begin; Safety device during the mixing process monitors the gas mixture for signs of an increase in oxygen content beyond a safety limit, and interrupts or reduces the oxygen supply or initiates other suitable protective measures as soon as it detects a hazard. A method as claimed in claim 7, characterized in that the new self-calibration value obtained in air self-calibration is compared with at least one previously obtained self-calibration value to test the sensor for normal aging and the absence of suspected anomalies, the success of self-calibration only then, assuming normal aging and suspected anomaly, and - otherwise, in the event of abnormal aging or presence of anomalies, the procedure is terminated with an error message indicating, in particular, an abnormal aging or the presence of sensor abnormalities is then recognized when the new self-calibration value compared to the comparison value substantially ge ringer is or is significantly higher, - that is successfully stored self-calibration of the new self-calibration value as a comparison value for later self-calibration steps in a non-volatile memory, so that it is also after switching off the gas mixing device and the reconnection after a long time available again as a comparison value. Method according to one of claims 7 or 8, characterized - that the automatic security device has means to the Measuring amplifier for the sensor signal not only the sensor signal itself, but optionally also others supply fixed comparison signals to be able to their result after reinforcement and optionally an analog / digital conversion in the automatic Security device compared with setpoints stored there becomes, - that this comparison to a regular self-test of the measuring channel is used - that an error message and the creation of a safe state takes place, for example, a shutdown of the oxygen supply, as soon as a deviation from the setpoints is detected. Gas mixing device according to one or more of claims 1 to 6, characterized in that a heat exchanger is present, which is a heat exchange of the metering valve ( 5 ) causes the supplied oxygen gas with the ambient air. Gas mixing device according to claim 10, characterized in that that the heat exchanger a Lead is around the outside wall the mixing section is coiled. Gas mixing device according to one or more of claims 1 to 6 and 10 to 11, characterized in that the automatic Safety device is used to reduce the oxygen content of the To regulate the gas mixture to a desired value, by doing that from the Oxygen sensor derived signal evaluates and a controllable Valve in the oxygen supply line according to a control law stalking. Gas mixing device according to one or more of claims 1 to 6 and 10 to 12, characterized in that the pressure equalization of the oxygen sensor ( 11 ) necessary gas of the mixing section ( 6 ) and is supplied to the interior of the oxygen sensor so that at its pressure compensation membrane ( 32 ) is substantially the same pressure as at the gas flow ( 9 ) in the mixing section ( 6 ) oxygen sensitive front side of the oxygen sensor. Gas mixing device according to claim 13, characterized in that the pressure equalization of the oxygen sensor from the mixing section removed gas by a desiccant ( 35 ), which largely extracts the water vapor from the gas before it enters the interior ( 33 ) of the oxygen sensor. Gas mixing device according to claim 13 or 14, characterized in - that the oxygen sensor is located in a separate chamber, the opposite him the ambient air seals, and - that of the mixing section removed gas is supplied to the chamber interior for pressure equalization. Gas mixing device according to claim 13 or 14, characterized in that - to its pressure compensating diaphragm ( 32 ) leading opening of the oxygen sensor ( 11 ) with a closure body ( 37 ) is tightly closed, - that the gas taken from the mixing section for pressure equalization is supplied to the interior of the closure body. Gas mixing device according to one or more of claims 14 to 16, characterized in that the drying agent ( 35 ) in a drying cartridge ( 36 ) is located. Gas mixing device according to one or more of claims 14 to 17, characterized in that the drying agent the supply side of the mixing section forth a bidirectional valve device upstream, which is a pressure equalization process in both possible flow directions admits by in the presence of a pressure difference to be compensated between the mixing section and the interior of the oxygen sensor, a valve the bidirectional valve device opens, and that the valves closed in the absence of a pressure difference to be compensated are. Gas mixing device according to claim 13, characterized in that - the electronic and electrical components of the oxygen sensor are protected with a permanently plastic potting compound against condensation moisture, - that the circuit board of the oxygen sensor has openings which are large enough so that the permanently plastic potting compound in the pressure compensation chamber ( 33 ) of the oxygen sensor can flow in unimpeded manner, that the gas taken from the mixing section to equalize the pressure of the oxygen sensor acts on the permanently plastic encapsulant, which largely unaffected the gas pressure to the pressure compensating diaphragm ( 32 ) of the oxygen sensor gives.