DE102018129165A1 - Gas pressure measuring device with hollow fiber membrane bundle - Google Patents

Abstract

Device for determining a total gas content dissolved in a liquid, comprising: a gas-filled measuring volume (2A, 2B) which is separated from the liquid to be measured by a semi-permeable, i.e. liquid-tight but gas-permeable, membrane (3), and a pressure determination means ( 4), in particular a pressure sensor (41) arranged in the measuring volume with connected evaluation electronics (42), the semi-permeable membrane being designed as a bundle (3) made up of a multiplicity of hollow fibers (30), and each of the hollow fibers being connected via a Has interior and the interiors of the hollow fibers (31) of the hollow fiber bundle (3) are in fluid communication with each other.

Description

The present invention relates to a device for measuring the total pressure of a gas or gas mixture dissolved in a liquid according to the preamble of claim 1, a printer or a printing press with such a device, and a measuring method using the device.

Gases dissolved in liquids are relevant in a variety of technical or physiological situations. Examples are the oxygen content, also oxygen saturation, of the blood in medicine, the nitrogen content of the blood when diving, the oxygen content of water in marine biology and fish farming or the oxygen content of printer ink or binder liquid for 3D printers. Another example are the (hydrocarbon) gases and gas mixtures that arise when operating an oil-cooled transformer, from which conclusions can be drawn about the type and extent of defects on the transformer.

In many cases, such as the last-mentioned example, it is desirable to know the proportion of a particular gas as precisely as possible. In some application-relevant cases, however, knowledge of the total content of the gases dissolved in the liquid is sufficient or even of sole interest. The proportion of the oxygen dissolved in the water can again serve as an example for the former case. This can be determined from the total proportion of the air dissolved therein via the known, temperature-dependent ratios of oxygen to nitrogen and the remaining components of the air (trace gases). When monitoring oil-cooled transformers, damage and faults in the device can also be recognized by the total partial pressure of the dissolved gases.

Situations in which the total content of dissolved gases is the relevant variable in itself are, for example, the monitoring of fish farms, since too much dissolved air can damage the gills of fish. Furthermore, knowledge of the total content is also relevant in the field of printing, be it conventional two-dimensional printing or 3D printing, which is becoming increasingly important today, since too high a content of dissolved gases, usually air, to form gas bubbles in the Can cause printer nozzles, which affects the print image and print quality.

To measure the total content of gases dissolved in a liquid, measuring devices are known in the prior art, usually referred to as TDG (Total Dissolved Gas) sensors, in which the liquid passes through a semi-permeable membrane, i.e. a membrane which contains only particles in the gas phase , not in the liquid phase, can be penetrated, is separated from a gas-filled measuring volume. Gases dissolved in the liquid can now pass through the semi-permeable membrane and into the measuring volume of the TDG sensor, so that a pressure is set there that corresponds to the partial pressure of all dissolved gases in the liquid. A measurement of the pressure in the measuring volume by means of a pressure sensor thus provides information about the total pressure of all gases dissolved in the liquid. The proportion of gas in the liquid can also be determined by an additional measurement of the total liquid pressure.

In the prior art, gas pressure sensors with a single flat or tubular membrane are used in order to separate the liquid from the measurement volume. This choice of shape has the disadvantage that the membrane has a comparatively low surface density, ie only a relatively small area is available per gas volume for gas exchange between the measurement volume and the liquid. This limits the response time of the sensors and their accuracy for a given sensor volume. Conversely, this choice of membrane shape leads to a very large sensor volume if a certain accuracy is specified.
Although it is known in the prior art to increase the surface density by corrugating or corrugating the membrane, this results in only a comparatively small increase in the surface density.
In the TDG sensors from OTT Hydromet known in the prior art, which have a tubular membrane according to the U.S. Patent 5,763,762 an additional disadvantage is the large wall thickness of the membrane (approx. 1mm outer with 0.1 mm inner diameter), which is necessary to prevent the hose from being pinched off.

The present invention is therefore based on the object of creating a measuring device for determining the total pressure of the gases or gas mixtures dissolved in a liquid, which nevertheless enables a highly accurate and responsive measurement in a compact design.

This object is achieved by a device having the features specified in claim 1, which is used in particular in accordance with claim 14 in a printer or in a printing press and using the measuring method in accordance with claim 17.

An essential element of the total gas pressure measuring device according to the invention is the Using a membrane in the form of a bundle of hollow fibers. Each of these fibers is a long, thin tube made of semi-permeable (membrane) material. “Long and thin” initially only means that the extension of the fiber in a longitudinal direction is significantly greater than in the perpendicular direction. With regard to the absolute length and the absolute diameter of the hollow fibers, a wide range of values is compatible with the basic idea of the present invention. Outer fiber diameters can be in the range of 1 mm or below, in particular 400 micrometers and below, fiber lengths in the range of 1 cm and above, in particular 10 cm and above. The wall thicknesses, ie membrane thicknesses, of the hollow membrane fibers used according to the invention are less than 500 micrometers, in particular less than 50 micrometers.
The cross-sections of the hollow fibers in the most general embodiment of the present invention are likewise of no great concern, as long as there is sufficient interior space for gas exchange or for the liquid to be measured to flow through. The wall thickness of the hollow fibers, that is to say the thickness of the membrane, can thus also be chosen largely independently of the diameter of the hollow fibers.

According to the invention, these hollow fibers are combined into a bundle and connected to one another in such a way that their interiors are in fluid communication, that is to say form a common, coherent volume. In principle, the fibers can all be connected to any number of other fibers at any point along their extension. A fluidically favorable configuration, however, consists in particular in that all hollow fibers of the bundle converge at one point, or all are connected at one end to a hollow distributor structure.

The hollow fiber bundle of the measuring device according to the invention comprises a large number of such hollow fibers, at least three, better a few tens, hundreds or even thousands of fibers.

The pressure determination means can be a pressure sensor, in particular a piezoresistive pressure sensor in connection with evaluation electronics. Alternatively, a mechanical pressure sensor can also be used. The pressure sensor is arranged in or adjacent to the measuring volume.

By designing the semipermeable membrane as a hollow fiber bundle, the present invention can increase the surface density, that is to say the membrane area per volume, and thus, for a given volume, achieve a more rapid and more accurate gas pressure measurement. The reaction speed is increased because a change in the gas pressure in the liquid leads more quickly to a measurable change in the pressure in the measurement volume due to the increased membrane and gas exchange area. For this reason, the accuracy is also increased when measuring a signal that changes over time, i.e. total gas pressure. Conversely, a measuring device according to the invention with a desired measuring accuracy can have a significantly smaller volume than total gas pressure meters (TDG sensors) according to the prior art.

In the configuration of the hollow fiber bundle with an internally hollow distributor structure, from which the fibers of the bundle branch off, an arrangement of the pressure determination means inside or in the wall of the distributor structure is particularly advantageous. Such an embodiment is particularly suitable for use in tanks or basins filled with the liquid to be measured or, for example, in free water. However, use in a liquid flow is also conceivable, for example a tube through which the measuring device according to the invention is introduced through a lateral opening, the distributor structure sealingly closing the opening.

In some configurations of the present invention, the membrane hollow fiber bundle is arranged within a housing. On the one hand, this serves to protect the hollow fibers from mechanical damage, for example due to strong flow within the liquid or objects floating around in it, or also damage during transport and installation of the measuring device. On the other hand, a housing, insofar as it is gas-tight, also enables embodiments in which not the interior of the hollow fibers but rather the part volume of the housing interior complementary to the hollow fiber bundle and, depending on the embodiment, optionally a distributor structure, serve as the measurement volume.
In simple embodiments, the housing is a hollow cylinder closed at both ends. However, other shapes can be more advantageous in the context of various configurations of the measuring device according to the invention.

In any case, the housing must have at least one opening as an inlet and / or outlet for the liquid. Other embodiments provide more than one opening. For example, a large number of openings could also be provided in order to correspondingly facilitate the exchange of liquid between the housing exterior and interior and thereby accelerate the reaction of the invention to a change in the total gas content in the liquid. In one embodiment of the present invention there is at least one side the housing with a lattice structure. Alternatively, all of the housing sides can also be designed essentially as a lattice structure and thus the housing as a whole as a lattice cage. As a result, with only a slight increase in weight compared to the embodiment without a housing, a certain mechanical protection of the comparatively sensitive hollow fiber membrane bundle is connected with an almost undisturbed liquid exchange.

In another embodiment of the present invention with basically at least liquid-tight housing, two openings are provided that communicate with the partial volume of the interior of the housing that is complementary to the hollow fiber bundle. This advantageously ensures that the liquid to be measured can flow into the housing through one of the openings and flow out again through the other. It is thus possible to switch the measuring device according to the invention on or in between a tube or a hose transporting the liquid to be measured. The flow resistance or the pressure drop caused by the device is advantageously minimized if the openings are on opposite sides of the housing and / or the housing interior, including the arrangement of the hollow fiber bundle, is aerodynamically shaped.
In these embodiments, the gas-filled measurement volume that is monitored by the pressure determination means is the inside of the hollow fiber bundle and the distributor structures that may be connected to it. For the aerodynamic configuration of the housing interior, it is proposed to arrange this in the region of the inlet opening when using a distributor structure.

Another embodiment that can be flowed through provides for the liquid to be measured to flow through the interior of the hollow fibers of the membrane fiber bundle. For this purpose, the fibers are connected at each of their two ends to one of two distributor structures. Each of the two distributor structures is assigned to an opening in the housing, the interior of the distributor structures being in fluid communication with the respective opening. A liquid-tight subdivision of the interior of the housing into a partial volume complementary to the hollow fiber bundle and the distributor structures and a partial volume comprising the interior spaces of the hollow fibers and distributor structures is thus achieved. The liquid stream to be measured is now first led through a first opening into the interior of the first distributor structure, where it branches onto the individual hollow fibers. In the second distributor structure, the partial flows reunite and finally leave the housing through the second opening.
In this embodiment, the gas-filled measurement volume is formed by the volume which is complementary to the hollow fiber bundle and the distributor structures. The pressure determining means thus measures the gas pressure which arises in this partial volume, in particular a pressure sensor of the pressure determining means is arranged in this partial volume or adjacent thereto, for example integrated into the housing wall.

In particular, by means of the flow-through embodiments of the measuring device according to the present invention, use on moving parts of a printing press or a (3D) printer, in particular on or in the vicinity of the print head, is possible. In order to be able to recognize in real time the danger of gas bubbles forming and the resulting deterioration of the print image, it is proposed according to the invention to determine the total gas content of the printer ink or the binder liquid in 3D printers by means of the TDG measuring device according to the invention. Only the device according to the invention allows a sufficiently precise and responsive device to be designed in the compactness that is essential for this application.

The term “printer ink” here is intended to encompass in general all of the liquid media used in printers or printing presses for the creation of a specific print image and usually supplied via lines from a reservoir to one or more print heads.
In the present case, the term “binder liquid” is intended to encompass all liquids used in 3D printing to produce a printed object, regardless of whether with or without solid particles present therein.

The reaction rate is further increased if the measuring method according to the invention is used for pressure determination. In this case, an extrapolation value is calculated from a measured actual course over time of the total gas pressure, with which the actually present gas pressure value is to be approximated better and which corresponds to an expected equilibrium pressure value with an assumed step-like pressure change. The measurement time, defined as the minimum time that the device requires from a step-like pressure change in order to determine the new pressure value within the given measurement accuracy, can be more than halved in most cases.

The extrapolation formula which is preferably used in the measurement method according to the invention is given by: $$p_{ex}\left(t\right)=p_m\left(t\right)+\left(p_m\left(t\right)-p_m\left(t_0\right)\right)\times \{\begin{array}{c}{F}_1:p_m\left(t\right)>p_m\left(t_0\right)\\ F_{\mathrm{2nd}}:p_m\left(t\right)\le p_m\left(t_0\right)\end{array}$$

Here is p _ex (f) the extrapolation value output at a time t, p _m (t) is the pressure measured in the measuring volume at this time t, p _m (t ₀ ) is the measured pressure at an earlier time to, at which the pressure p _m (t) determined rate of change dp _m / dt of the measured pressure was below a certain, empirically determined threshold value for the last time and F ₁ respectively. F ₂ are also empirically determined constants.

Advantageous developments of the present invention are presented below. They can be implemented individually or in combination, as long as they are not mutually exclusive.

The distributor structure, which enables fluid communication between the interior spaces of the individual hollow membrane fibers of the fiber bundle, can also be formed by gluing the hollow fibers placed next to each other in parallel at their open ends and closing the graft-like end of the hollow fiber bundle thus created with a liquid and gas-tight cap becomes. The pressure determination means can then be arranged in the interior of this cap or in the wall thereof.

In order to achieve the fastest possible reaction to a change in the total gas pressure in the liquid to be measured, it is proposed to minimize the measurement volume. In the case of the flow-through designs of the measuring device according to the invention, in which the inside of the hollow fibers together with the inside of a possibly existing distributor structure form the gas-filled measuring volume, the use of fibers with a minimum inside diameter for the given outside diameter is recommended for this purpose. This minimizes the internal volume of the hollow fibers.

In the case of the flow-through embodiments in which the liquid is passed through the interior of the hollow fibers and the partial volume of the interior of the housing which is complementary to the hollow fiber bundle forms the measurement volume, it is proposed to minimize the latter by the hollow fiber bundle filling the interior of the housing as completely as possible.
For this purpose, the hollow fibers should first be arranged and run parallel to the inside of the housing. Hollow fibers of different diameters can also be used. Since hollow fibers below a certain (outer) diameter cannot be produced for manufacturing reasons, only the larger fibers of the hollow fiber membrane bundle can be designed as hollow fibers, while the fibers with a smaller diameter are solid. As a result, although the liquid cannot flow through them, they advantageously contribute to reducing the measurement volume.
In addition to the usual circular outline of the hollow fiber cross section, an outline can also be selected in a surface-filling geometry, for example in the form of a regular hexagon, triangle or square. The advantage of the hexagon here is that it is even closer to the circular shape and therefore undesired increases in the measurement volume due to fibers that are not laid exactly parallel are smaller compared to the square or triangular shape.

Furthermore, the complementary volume is also minimized if the shape and size of the interior of the housing is adapted to the hollow fiber bundle. In particular, it is proposed to subdivide the housing, or at least the interior of the housing, into three sections, two end sections with an intermediate middle section. The middle section should have a constant cross section, the end sections, in contrast, have a cross section tapering from the middle section to a vertex. In particular, the three-dimensional shape of the central section should have that of a (hollow) cylinder or a (hollow) hexagon prism, that of the end sections corresponding to that of a cone or a hemisphere or a hexagonal pyramid, possibly with curved sides.

A distributor structure arranged in the interior of the housing and connected to the housing can preferably have a hemispherical outer surface for connecting the hollow fibers, the radius of this hemisphere being approximately a quarter of the diameter of the hollow fiber bundle and thus likewise preferably approximately a quarter of the inner diameter of the central section of the housing corresponds.
Other embodiments of the present invention have an overall cylindrical hollow fiber membrane bundle, in which all fibers are laid with the same length, as parallel as possible to one another, and are glued together at both ends in such a way that a gas-tight plug is formed by the hardened adhesive matrix. In this embodiment, the interior of the housing can have a simple cylindrical shape, except for any adaptation to the fine structure of the outer surface of the hollow fiber bundle. A distributor structure in the sense of a separate structure suitable for connecting the hollow fibers is not necessary here, or this is formed by the glued hollow fiber ends and the adhesive matrix itself.
Since the hollow fibers must not touch at the ends in order to guarantee a complete covering of the end with adhesive and thus a gas-tight seal, the use of hollow fibers with a cross section that is constant over their length leads to a thickening at the ends of the hollow fiber bundle. In order to avoid a disadvantageous increase in the measurement volume, it is proposed to either shape the interior of the housing in such a way that that it clings to the cross section of the hollow fiber bundle, that is to say has a smaller inner diameter in a central region than at the ends. Alternatively, hollow fibers with a smaller outer diameter in the area of the ends can also be used, so that the cross section of the hollow fiber bundle is essentially cylindrical even after the fiber ends have been glued.

If only hollow fibers which are open on one side and which are glued to their respective open ends as described are used, embodiments without a housing are also possible. In these, fluid communication between the hollow fiber interiors, with the liquid being closed, would be achieved in that a gas- and liquid-tight sealing cap is pushed over the plug-like, glued end of the hollow fiber bundle. The tightness on the contact surface between the inside of the cap and the outside of the plug-like hollow fiber bundle end can optionally be ensured by using a sealing ring. The pressure determining means in the form of a pressure sensor could be embedded in the wall of the cap, for example in the case of a cap with a round outline, in the center thereof.

The measurement volume preferably has a degassing opening. This is closed by a valve during the measurement. which, however, can be opened to reduce the pressure in the measuring volume, either by letting the gas escape from the measuring volume into an outside space of lower pressure or by actively pumping it out. As a result, the measuring device according to the invention can fulfill a double function as a degassing device, for example for printer ink or binder liquid of a 3D printer. As soon as the exceeding of a limit value is determined during a total gas pressure measurement, the degassing valve is opened for a certain time, this time being able to be selected on the basis of the threshold exceeding, approximately proportional to it. To prevent bubbles from forming in the printhead due to pressure differences in the system, the ink must be far from gas saturation.

Under normal conditions there is always a lower pressure in the measuring volume than in the liquid to be measured. With completely degassed water this is only the steam pressure of the water, at room temperature approx. 25 mbar absolute. Because of these low pressures, the measurement volume is usually degassed by connecting the degassing opening to a vacuum.

Embodiments of the present invention have, in addition to the means for determining the (gas) pressure in the measurement volume, at least one further pressure determination means with which a pressure of the liquid to be measured can be determined. In particular, it is proposed to provide embodiments of the present invention with a housing with a pressure sensor in the (liquid) volume complementary to the measurement volume. This makes it possible to determine the relative gas pressure in the liquid. If two (liquid) pressure sensors are used in a flow-through embodiment of the measuring device of the present invention, one of which is arranged in each case in the area of the inflow or outflow opening, the pressure drop caused by the flow resistance of the interior of the housing can also be determined in addition to the relative gas pressure.

Further properties, features and advantages of the present invention result from the exemplary embodiments presented below with reference to the figures. These are only intended to illustrate the present invention and in no way limit the general principle of the invention set out in the independent claims.

• 1: In drei Teilfiguren Längsschnitte dreier verschiedener Varianten einer ersten, gehäuselosen Ausführungsform der Messvorrichtung vorliegender Erfindung
• 2: in zwei Teilfiguren Längsschnitte durch eine zweite und eine dritte Ausführungsform, jeweils mit einem Gehäuse, bei welchen das Messvolumen durch die Hohlfaserinnenräume gebildet ist
• 3: Einen Längsschnitt durch eine vierte Ausführungsform mit einem Gehäuse, bei welcher das Messvolumen durch das zum Innenraum der Hohlfasern komplementäre Teilvolumen des Gehäuseinneren gebildet ist
• 4: In vier Teilfiguren Querschnitte durch verschiedene Ausführungsformen der erfindungsgemäßen Messvorrichtung mit unterschiedlichen Hohlfaserquerschnitten
• 5: In drei Teilfiguren, Längsschnitte durch drei verschiedene, vorteilhaft geformte Gehäuse
• 6: Einen beispielhaften zeitlichen Verlauf des gemessenen und des nach dem erfindungsgemäßen Messverfahren extrapolierten Drucks bei einer angenommenen stufenförmigen Druckänderung

Show it:

• 1 : In three partial figures, longitudinal sections of three different variants of a first, housing-free embodiment of the measuring device of the present invention
• 2nd : in two partial figures, longitudinal sections through a second and a third embodiment, each with a housing in which the measurement volume is formed by the hollow fiber interior
• 3rd : A longitudinal section through a fourth embodiment with a housing, in which the measurement volume is formed by the partial volume of the interior of the housing which is complementary to the interior of the hollow fibers
• 4th : In four partial figures, cross sections through different embodiments of the measuring device according to the invention with different hollow fiber cross sections
• 5 : In three partial figures, longitudinal sections through three different, advantageously shaped housings
• 6 : An exemplary time course of the measured and of the pressure extrapolated according to the measuring method according to the invention with an assumed step-like pressure change

In 1 Three variants of a first, housingless embodiment of the gas pressure measuring device of the present invention are shown in longitudinal section.
The measuring device according to the invention 1 according to variant A this first embodiment comprises a bundle 3rd from a variety of one-sided closed hollow fibers 31 made of a semi-permeable membrane, each with its open end via a hollow distributor structure 23 are connected to each other so that the interior of the hollow fibers are in fluid communication and the measurement volume as a whole 2A form. At the union point 23 the hollow fiber is a pressure sensor 41 , for example a piezoresistive pressure sensor, which is connected to the connected evaluation electronics 42 the pressure determining means 4th this embodiment forms.
The variant shown in sub-figures B and C differ from the one shown in sub-figure A in that the fluid communication of the interiors of the hollow fibers is realized 31 of the hollow fiber membrane bundle 3rd . In both variants, this is such that the fibers, which are only open at one end, are placed parallel next to one another and placed in a cylindrical container filled with an adhesive or resin, which ideally has a diameter only slightly larger than the bundle 3rd having. The capillary action draws the adhesive or resin into both the open hollow fiber ends and the hollow fiber interstices. To ensure that the ascent height inside the fibers remains lower than in the intermediate spaces, care must be taken that the fiber ends do not touch each other, but that a certain distance remains. After hardening, the bundle can be removed from the vessel, which serves as a kind of casting mold. The end of the hollow fiber bundle, which is now provided with a graft-like end, has to be ground on the face side so far that the hollow fiber ends are open again. In order to obtain a measuring device according to the invention, this is done using the adhesive or resin matrix 24th held together end of the hollow fiber bundle 3rd a cap 25th with the pressure determining means 4th from sensor 41 and evaluation unit 42 fitted gas-tight. With both variants B and C. an outer cylindrical cap is used. They differ in how communication between the hollow fiber interiors is made possible. In the variant B is that due to the adhesive matrix 24th Graft-glued end of the hollow fiber bundle ground flat. To prevent that after attaching the cap 25th the ends of the hollow fibers are closed by the inside of the cap, this is concave, with the pressure sensor 41 is positioned in the apex. Instead of the conical cavity shown, a U-shaped curvature or another concave shape could in principle also be selected, but a conical cavity can be very easily realized in terms of production technology.
The one in variant C. uses a cap 25th with flat inner face. Here is the fluid communication of the hollow fibers 31 the end face of the hollow fiber bundle must be guaranteed 3rd and the adhesive matrix 24th ground concave, for example, as shown here, tapered concave.

The first embodiment in all its variants represents an implementation of the principle on which the invention is based, in which only the basic components of hollow fiber bundles and pressure determination means are used. It is particularly suitable for measuring total gas pressure in comparatively large volumes of little-moving liquids without potentially damaging hollow fibers, which float around in the liquid. It is preferably attached to a float in a free-floating manner or attached in a suitable manner in the liquid volume, for example a tank or a basin.

2nd shows in two partial figures a longitudinal section through a second and a third embodiment with a housing. In both embodiments, the measurement volume is essentially formed by the hollow fiber interior.

In the second embodiment shown in sub-figure A, the difference from the first embodiment consists 1 in that the hollow fiber bundle 3rd inside a case 5 , in the representation of a rectangular cross-section, in three dimensions cuboid or cylindrical, is arranged, the union or distributor structure 23 , in which the membrane hollow fibers open on one side converge, are attached to an inner wall of the housing or are integrally formed. This will make the interior 50 of the housing 5 in a first, the interconnected interiors of the hollow fibers 31 as well as the distribution structure 23 extensive partial volume 51 and a second, complementary part volume 59 divided. The measurement volume 2A is identical to the partial volume in this embodiment 51 . The housing has several openings. A first opening 52 , 55 is the distribution structure 23 assigned and is in fluid communication with it. It is by means of a valve 56 closed and serves as a degassing opening or for connecting a further, external pressure determination means. A second opening 58 the complementary partial volume connects in a side wall of the housing 59 of the housing interior 50 with the external outside space 100 and allows the transfer and exchange of the liquid to be measured between the interior of the housing 50 and outside space 100 .
One way of fluid exchange with the outside 100 To improve still further consists of part or all of the housing, with the exception of the distribution structure 23 to execute as a lattice structure In the embodiment according to sub-figure A, this is the distributor structure 23 opposite end face 5g is designed as such a lattice structure and therefore, as can be seen, has a multiplicity of openings 58 on.
The pressure determining means 4th consists of one in the area of the distribution structure 23 pressure sensor embedded in the housing wall 41 , and an evaluation unit 42 , which is advantageously attached to the outside of the housing here.
The second embodiment, in the form of the housing, provides protection for the comparatively sensitive hollow fibers of the bundle and is therefore also suitable for use in strongly moving liquid volumes and / or in the presence of objects floating in the liquid which could damage the measuring device according to the invention. The measuring device is also mechanically protected by the housing during transport and assembly.

The housing also serves this purpose 5 the third embodiment of the present invention shown in partial figure B. The difference from the second embodiment is that the housing has two openings 58a and 58b for liquid exchange between the complementary partial volume 59 and the outside space 100 having. This makes it possible to implement a liquid flow through the housing, in which, as indicated by arrows in the figure, one of the openings 58a as an opening and the other opening 58b serves as an exit. In order to realize a favorable, low-resistance flow course inside the housing, the housing is 5 divided into three sections and has an upper end section 5a a lower end portion 5b and a middle section 5 m , with the end sections tapering from the central section to a vertex. The openings 58a and 58b now lie in the area of the vertex of the section to which they are assigned.
The hollow fibers 31 of the fiber bundle 3rd unite in a distribution structure 23 which is the entrance opening 58a concentrically surrounds and with, also in the area of the apex of the upper end section 5a arranged and by a valve 56 Degassing opening closed during a measuring process 55 is in fluid communication. The hollow fibers shown here 31 the third embodiment, as in the two previous ones, is closed at its end facing away from the distributor structure. However, it would also be possible to use hollow fibers that are open on both sides and are connected to distribution structures on both sides. This could be done, for example, in the lower end section 5b of the housing 5 a second, in particular corresponding to the first toroidally around the outlet opening 58b arranged distributor structure can be provided. This would make both ends of the hollow membrane fibers 31 fixes what would reduce the movement of the fibers under the influence of a turbulent flow inside the housing. This would come from the flow resistance or through the measuring device 1 caused pressure drop. In addition, the symmetry thus created would allow the flow direction to be reversed without or with only a slight increase in the flow resistance or pressure drop.

The pressure sensor 41 of the pressure determining means 4th is, as in the first two embodiments, also integrated into the housing wall in such a way that it enters the interior of the distributor structure 23 protrudes. The evaluation electronics can be connected by wire or, via a transmitter (not shown), also wirelessly. In any case, the positioning of the evaluation electronics is essentially independent and the attachment to the wall of the housing indicated here in the illustration 5 just an example.

The third embodiment is suitable for interposition in a hose or a tube in which the liquid to be measured flows, for example in the context of a real-time measurement of the total gas content of the ink or the binder of a (3D) printer or a printing machine. Particularly advantageously, the measuring device according to the invention, due to its small size, thanks to the high surface density of the membrane hollow fiber bundle, enables a gas pressure measurement of sufficient accuracy at or shortly before the print head.

3rd represents a fourth embodiment of the present invention, in which the measuring volume, in contrast to the previous ones, is not formed by the partial volume of the interior of the housing formed by the interior spaces of the hollow fibers, but by the partial volume complementary to this.
The device 1 includes the housing 5 in which similar to the third embodiment from a central section 5 m between two yourself from the middle section 5 m starting from tapering end sections 5a and 5b consists. At the vertices of the sections 5a and 5b are openings 52a and 52b which flow in or out of the liquid to be measured into the interior of the housing 50 enable. Each of the two openings 52a and 52b is a distribution structure inside the housing 23a respectively. 23b assigned. The interiors of the distribution structures 23a and 23b are in direct fluid communication with both the associated opening 52a respectively. 52b as well as the inside of the hollow membrane fibers 31 of the hollow fiber bundle, which is located between the distributor structures 23a and 23b extend and with their ends on both sides to one of the distributor structures 23a , 23b are connected. Overall, this enables the liquid to be measured through one of the openings, as shown here 52a , inside the housing 50 occurs, first in the distributor structure directly behind in the direction of flow, here 23a , arrives and from there into the hollow fibers radiating from the distributor structure 31 occurs after flowing through the hollow fibers 31 yourself in the second distribution structure, here 23b , reunited and finally the inside of the case through the second opening, here 52b , leaves again. The direction of flow of the liquid is drawn by arrows in the inlet and outlet openings 52a , 52b and inside the hollow fibers 31 indicated. Since the device is constructed essentially symmetrically, and in particular the hollow membrane fibers 31 are fixed with both ends, the flow direction can be easily reversed without the measuring device 1 damage and without changing the pressure drop caused by the device.
The gas-filled measuring volume 2 B is in this embodiment by the interior of the hollow fibers 31 of the hollow fiber bundle and the distribution structures 23a and 23b complementary partial volumes 59 of the housing interior 50 educated. This requires that, unlike the first three embodiments, the housing 5 is not only liquid-tight but also gas-tight.

It is proposed, as shown, the pressure sensor 41 and the evaluation electronics 42 on a common board 43 arrange and the pressure sensor 41 in the side wall of the housing 5 let in, for example, by closing it gas-tight in a part of the complementary volume 59 communicating opening is inserted or pressed or glued. The controllable valve 56 is above the vent 55 in the side wall of the housing 5 arranged and here on that of the pressure sensor 41 opposite side shown. However, in an alternative embodiment it is proposed to use an electronically switchable valve and to arrange this, together with the degassing opening, on the same side of the housing as the pressure sensor, so that it becomes possible to place the valve directly on the circuit board 43 to integrate.
The vent opening 55 extends the range of applications and versatility of the device according to the invention. The valve is during the gas pressure measurement 56 closed by a pressure equilibrium between the total gas pressure in the liquid and in the measuring volume 2 B and thus enable an accurate measurement. If the valve is opened, the gas can be removed from the measuring volume if necessary 2 B escape or be suctioned off. Depending on the application, this may be desired, for example, if an excessively high total gas pressure in the measuring liquid was determined during a previous gas pressure measurement. This advantageously eliminates the need to provide a dedicated degassing device further downstream of the measuring device according to the invention. In addition, a second, external pressure determination means can also be applied to the opening 55 be connected. Then the valve should 56 remain open even during the measurement process.
Basically, it could also lead to the in 1 shown, simplest embodiment of the present invention, a degassing opening can be added.

The hollow fibers 31 of the membrane hollow fiber bundle 3rd fill the inside if possible 50 of the housing 5 as far as possible from the dead space of the sensor, so here the complementary partial volume 59 which with the measurement volume 2 B is identical to minimize if possible. As a result, the reaction speed of the sensor, that is the time interval between a change in the total gas pressure in the liquid and the visibility of this change in the measurement signal of the pressure determining means 4th accelerated. The hollow fibers are measures to minimize the dead space 31 laid as cleanly as possible parallel to each other. In addition, the inner housing shape in the end sections is at the cross section of that of the manifold structures 23a and 23b from radiating hollow fiber bundles 3rd customized. In addition, it is suggested the hollow fibers

The diameter of the hollow fibers is a compromise between the surface density of the membrane, ie the surface of the hollow fibers 30th which is the interface between measurement volume 2 B and the liquid and the flow behavior of the liquid to be measured. On the one hand, for a given sensor volume, the hollow fiber diameter should be as small as possible in order to maximize the surface density and thus the response time and the accuracy of the sensor. On the other hand, an excessively small fiber cross section also results in a high flow resistance of the liquid flowing through the fiber interior in this fourth embodiment, in particular in applications for measuring a liquid which has a high viscosity. Likewise, possible contamination of the liquid with particles must be taken into account when dimensioning the hollow fiber (inner) cross section. The (inner) cross section of the hollow fibers 31 It should therefore be chosen at least so large that particle sizes that are usually to be expected can pass through the fiber in order to avoid or at least delay the clogging of the fibers and the cleaning that is therefore necessary.

This could include the use of a hollow fiber bundle 3rd with hollow fibers 31 of different diameters. Two, three or even a range of different diameters could be used. This would have two advantages. On the one hand, with a corresponding alternating arrangement of the hollow fibers of different sizes, a higher packing density of the hollow fibers can be achieved than would be the case with a hollow fiber bundle with only identical hollow fibers. On the other hand, with a given measuring speed and accuracy, reliability is guaranteed of the total gas pressure measuring device according to the invention with regard to the particle contaminations mentioned, or the maintenance intervals are extended, because while the hollow fibers of smaller diameter increase the surface density, the larger hollow fibers, which can also be passed through by larger particles, ensure that the measuring device does not clog as quickly.
Although, strictly speaking, these considerations only concern the inside cross-section and / or diameter, this essentially corresponds to the outside cross-section and, in addition to the thickness of the more or less uniformly strong membrane surface of the hollow fibers, also to the outside diameter.

4th shows in four partial figures schematic cross sections through possible configurations of the third and in particular the fourth embodiment of the measuring device according to the invention. For the better visibility and comprehensibility of the illustrated principle, the hollow fibers shown here have a much larger diameter compared to the diameter of the housing than would be the case in practical embodiments of the device according to the invention, in which the hollow fiber bundle comprises hundreds or thousands of hollow fibers.

In part figure A is a simple version with a hollow fiber bundle 3rd consisting of round hollow fibers 31 shown, which all have the same round cross-section and diameter. Here too, the fibers can be laid as parallel as possible inside the housing 5 already a very small complementary volume 59 to reach.

erhöht sich die theoretisch mögliche Packungsdichte im Bündelquerschnitt - unter Vernachlässigung der in der Praxis unvermeidlichen und in den Darstellungen angedeuteten elastischen Verformung der Fasern - von $\pi /2\sqrt{3}\approx \mathrm{0,91}\text{ auf }\pi \left(17-8\sqrt{3}\right)/6\sqrt{3}\approx \mathrm{0,95.}$

Wird statt der dargestellten hexagonalen Anordnung der dickeren Fasern 31 eine Anordnung auf einem quadratischen Gitter gewählt ist das Verhältnis der Durchmesser $\text{D2}/\text{D1}=\sqrt{2}-1\approx \mathrm{0,41}$

und die maximal mögliche Packungsdichte im Bündelquerschnitt erhöht sich von π/4 ≈ 0,79 auf $\pi \left(2-\sqrt{2}\right)/2\approx \mathrm{0,92.}$

Durch Hinzufügen weiterer, noch kleinerer Fasern könnte die Packungsdichte entsprechend weiter an 1 bzw. 100% angenähert werden. Fast noch wichtiger als die bessere Packungsdichte im Inneren des Bündels ist bei der Verwendung von Hohlfasern verschiedenen Querschnitts aber die bessere Packungsdichte im Randbereich des Hohlfaserbündels, also am Übergang zwischen Hohlfaserbündel und Gehäuseinnenwand. Anstatt, wie gezeigt, durchweg hohle Membranfasern einzusetzen könnten insbesondere die Fasern 31' mit dem geringeren Durchmesser D2 auch massiv ausgeführt sein. Bei sehr geringen Faserdurchmessern D2 ist dies fertigungstechnisch simpler.This is further improved if hollow fibers of different diameters are used and, in particular, as shown in sub-figure B, are arranged alternately. Sub-figure B shows hollow fibers 31 and 31 ' two different outer diameters D1 and D2 . With the chosen ratio of $\text{D2}/\text{D1}=\left(\mathrm{2nd}-\sqrt{\mathrm{3rd}}\right)/\sqrt{\mathrm{3rd}}\approx 0.15$

the theoretically possible packing density in the bundle cross-section increases - neglecting the elastic deformation of the fibers, which is inevitable in practice and indicated in the illustrations - from $\pi /\mathrm{2nd}\sqrt{\mathrm{3rd}}\approx 0.91\text{on}\pi \left(\mathrm{17th}-\mathrm{8th}\sqrt{\mathrm{3rd}}\right)/6\sqrt{\mathrm{3rd}}\approx \mathrm{0.95.}$

Will instead of the hexagonal arrangement of the thicker fibers shown 31 An arrangement chosen on a square grid is the ratio of the diameters $\text{D2}/\text{D1}=\sqrt{\mathrm{2nd}}-1\approx 0.41$

and the maximum possible packing density in the bundle cross section increases from π / 4 ≈ 0.79 $\pi \left(\mathrm{2nd}-\sqrt{\mathrm{2nd}}\right)/\mathrm{2nd}\approx \mathrm{0.92.}$

By adding further, even smaller fibers, the packing density could be further approximated to 1 or 100%. Almost more important than the better packing density inside the bundle is the use of hollow fibers of different cross-section but the better packing density in the edge area of the hollow fiber bundle, i.e. at the transition between the hollow fiber bundle and the inner wall of the housing. Instead of using consistently hollow membrane fibers, as shown, in particular the fibers 31 ' with the smaller diameter D2 also be solid. With very small fiber diameters D2 this is simpler in terms of production technology.

Another way to increase the packing density is in C. shown and relates to the choice of the fiber cross-section, more precisely the outline of the outer cross-section, in such a way as a completely area-filling shape. This would allow a packing density of theoretically 100% even when using similar fibers. Since this value can hardly ever be achieved in practice for various reasons, which are listed below, the problem that this packing density would lead to a disappearing measurement volume and thus to a suppression of gas exchange never occurs in practice. Because even if the inner surface of the housing were shaped in such a way that it adapts to the outline of the hollow fiber bundle and the theoretical packing density would also be achieved at the edge, it is very difficult to lay all of the flexible hollow fibers completely parallel, so that actually in cross section there is a perfect grid. For this reason, the use of the hexagonal hollow fibers shown is recommended. Since this shape comes closest to the usual circular shape, the enlargement of the fiber interstices and thus of the complementary volume caused by improper laying of the fibers, for example a slight twisting 59 less than for example rectangular or triangular fibers. Due to a certain flexibility or resilience of the membrane wall of the hollow fibers, the cross-section of the fibers adapt to the available space, which, as in C. shown, especially at the edge leads to a deformation of the fiber cross section.

To the complementary volume 59 when using hollow fibers 31 can further decrease, as in D shown, a housing with an inner cross-section can be used, which is rigidly adapted to the outline of the fiber bundle or adjusts elastically. In order to achieve the latter, it is proposed to manufacture at least the inside of the housing from a rubber-like elastic material.

The complementary volume to the hollow fiber bundle in the interior of the housing can by means of the in the partial figures of the 5 Refinements of the Housing of the third and fourth embodiment of the present invention can be further minimized.

Both show a housing in longitudinal section 5 , which is divided into three sections, the end sections 5a and 5b and the middle section in between 5 m is divided. The central section has a constant cross-section and can, what in connection with 4th can be seen to be a hollow cylinder or a hollow hexagonal prism. The end sections 5a and 5b tapering from their respective connection to the central section towards a vertex. Part A shows a linear change in cross-section, so that the end regions have the shape of a cone or a hexagon pyramid in three dimensions. Sub-figure B, on the other hand, shows a non-linear change in cross-section according to which the end regions have approximately the shape of a hemisphere in three dimensions. In the form shown in sub-figure B, the connection of the hollow fibers (not shown) to the distributor structure 23 advantageously relieved. In the case of intermediate forms, for example with elongated oval or elliptical end regions, this would also be the case compared to the embodiment shown in partial figure A.

In both cases, distribution structures are shown at both ends, only the structure is shown 23 in the section 5a of the housing, with an at least approximately hemispherical outer surface, the outer radius R of the distributor structures to the inner diameter d of the middle section 5 m of the housing 5 are roughly in the relation R = d / 4. This ensures that the hollow fibers (not shown) are connected to the distributor structure 23 an area is available that corresponds to the cross-sectional area of the hollow fiber bundle in the middle section of the housing 5 m corresponds. In order to keep the volume of the interior of the distributor structure small, the wall thickness of the distributor structure can 23 be chosen accordingly high and / or alternatively or additionally, as shown in sub-figure B, around the openings 52a and 52b Thickenings or inner beads 54 on the inside case 5 provided which of the hemispherical distribution structure 23 Fill the enclosed volume for the most part.

The minimization of the complementary partial volume 59 stands out particularly in the fourth embodiment 3rd in the foreground, in which the partial volume 59 the measurement volume 2 B forms. The third embodiment ( 2 B) , where by the partial volume 59 The liquid to be measured flows to minimize the measuring volume there 2A , which passes through the interior of the hollow fibers 31 and the distribution structure (s) 23 , to the smallest possible hollow fiber cross section. The packing density of the hollow fibers in the interior of the housing is also important in the third embodiment, for a given size of the housing 5 to maximize the membrane surface, however, it must be taken into account here that a very high packing density increases the flow resistance of the liquid flowing through the device according to the third embodiment, especially since the flow there tends to be less laminar and more turbulent than in the fourth embodiment. However, the resulting increased flow resistance or pressure drop across the measuring device is offset by the increased reliability, as a more turbulent flow and the lack of fixed diameters and courses of the flow channels (the hollow fibers around which the liquid flows are flexible and can move against each other, which also causes movement change the flow paths) make clogging of the device by particle contamination much less likely.

In order to improve the clogging probability or time in the fourth embodiment, the space available inside the distributor structures could also be used to accommodate the branches of the hollow fibers cleaning, flow-driven impellers.

und ist in der Figur in seinem zeitlichen Verlauf p_ex (t) mittels der gestrichelten Linie dargestellt. Hierbei ist p_m(t₀) ist der gemessene Druck zu einem früheren Zeitpunkt to, an dem die anhand des Verlaufs p_m(t) bestimmte Änderungsrate dp_m/dt des gemessenen Drucks letztmalig unter einem gewissen, empirisch bestimmten Schwellwert lag und F₁ bzw. F₂ sind ebenfalls empirisch bestimmte Konstanten. Vorliegend entspricht p_m(t₀) näherungsweise dem anfänglichen Gleichgewichtsdruck p₀ . Die Messzeit T₂ liegt beim gemäß dem erfindungsgemäßen Verfahren extrapolierten Wert p_Ex deutlich unter der Messzeit T₁ ohne Extrapolation.In 6 a diagram with graphs of possible temporal profiles of the total gas pressure and the measurement and extrapolation values output by the pressure determination means of the device according to the invention is shown.
The dotted line represents the assumed course of the actual total gas pressure p _a in the liquid for the entry of a measuring device according to the invention through which the liquid flows (third or fourth embodiment). As can be seen, there is a jump in the actual total gas pressure at time t = 0 p _a of a lower value here p ₀ to a higher value here p ₁ instead of.
The solid line is the time course of the value p _m (t) actually measured by the pressure determining means. Due to the finite rate of diffusion of the gas particles through the membrane surfaces of the hollow fibers, the finite time due to the finite flow velocity until the signal to be measured, i.e. the jump in total gas pressure, is actually present in the entire measuring device and the finite size of the measuring volume is the answer to the pressure change delayed in the measurement signal. Only after a time t _{1 can} it be recognized that a pressure change has actually taken place, namely when the pressure change in the measurement volume exceeds the sensitivity threshold dp of the pressure determining means. Until the new equilibrium measurement of the total gas pressure p ₁ has set approximately, the significantly longer measurement time passes T ₁ . By means of the measuring method according to the invention using extrapolation, the measuring time, here understood as the time after which the displayed one Pressure value corresponds to the actual one down to the measuring accuracy dp (p _meas = p ₁ ± dp), sometimes significantly reduced. The extrapolated value p _ex is calculated using the formula: $$p_{ex}\left(t\right)=p_m\left(t\right)+\left(p_m\left(t\right)-p_m\left(t_0\right)\right)\times \{\begin{array}{c}{F}_1:p_m\left(t\right)>p_m\left(t_0\right)\\ F_{\mathrm{2nd}}:p_m\left(t\right)\le p_m\left(t_0\right)\end{array}$$

and is in the figure in its temporal course p _ex (t) represented by the dashed line. Here, p _m (t ₀ ) is the measured pressure at an earlier point in time at which the rate of change dp _m / dt of the measured pressure determined on the basis of the curve p _m (t) was below a certain, empirically determined threshold value for the last time F ₁ respectively. F ₂ are also empirically determined constants. In the present case, p _m (t ₀ ) approximately corresponds to the initial equilibrium pressure p ₀ . The measurement time T ₂ is the value extrapolated according to the method according to the invention p _Ex well below the measurement time T ₁ without extrapolation.

Reference symbol list

1

Measuring device

2A, 2B

Measuring volume

23

Distribution structure

24th

Adhesive matrix

25th

cap

3rd

Membrane hollow fiber bundle

31, 31 '

Membrane hollow fiber

4th

Pressure determining means

41

Pressure sensor

42

Evaluation unit

43

circuit board

5

casing

5a, 5b

Housing end sections

5 m

Housing middle section

5g

Housing wall in lattice structure

50

Interior of the housing

51

partial volume formed by hollow fibers and distributor structure 50

52, 52a, 52b

with partial volume 51 communicating openings

54

thickening

55

Degassing opening

56

Valve

58, 58a, 58b

with partial volume 59 communicating openings

59

to the hollow fiber bundle and the distributor structures complementary part volume of 50

100

(liquid-filled) outdoor space

D1, D2

Hollow fiber diameter

d

Housing inside diameter

R

Radius of a hemispherical version of 23

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 5763762 [0006]

Claims (17)

Device for determining a total gas content dissolved in a liquid, comprising: a gas-filled measuring volume (2A, 2B) which is separated from the liquid to be measured by a semi-permeable, i.e. liquid-tight but gas-permeable membrane (3), and - a Pressure determination means (4) for determining a gas pressure in the measurement volume (2A, 2B), in particular a pressure sensor (41) with a connected evaluation electronics (42), characterized in that - the semi-permeable membrane as a bundle (3) from a multitude of Hollow fibers (31) is formed, each of the hollow fibers having an inner space (30) and - the inner spaces (30) of the hollow fibers (31) of the hollow fiber bundle (3) are in fluid communication with one another. Device after Claim 1 , characterized in that the interiors of the hollow fibers are in fluid communication via at least one distributor structure (23) to which each of the hollow fibers (31) is connected with an open end (32), the distributor structure (23) being in particular by a Adhesive matrix (24) holding the ends of the hollow fibers (31) together is formed in connection with a gas-tight cap (25). Device after Claim 2 , characterized in that the measurement volume (2A) is formed by the totality of the interior spaces (30) of the hollow fibers (31) and an interior space of the distributor structure (23). Device according to one of the Claims 2 or 3rd , characterized in that the device comprises a housing (5) which has an interior (50) in which the hollow fiber bundle (3) is arranged, so that the interior (50) into a through the total of the interior of the hollow fibers (30 ) and the distributor structure (23) formed volume (51) and a complementary volume (59), and the housing (5) further has at least one opening (52, 55, 58). Device after Claim 3 and 4th , characterized in that the opening (58) of the housing (5) enables fluid communication between the complementary partial volume (59) of the housing interior (50) and an exterior space (100) outside the housing (5), in particular a large number of such openings are present, for example in that one side of the housing (5) has a lattice structure or the housing is a lattice cage. Device after Claim 5 , characterized by at least two openings (58a, 58b) in fluid communication with the complementary volume (59). Device after Claim 4 characterized by at least two openings (52a, 52b) in the housing (5) and two distributor structures (23a, 23b) to which the hollow fibers (30) are connected at one end, each of the distributor structures (23a, 23b) being precise one of the openings (52a, 52b) is assigned and is in exclusive fluid communication with it, and the measurement volume (2B) corresponds to the complementary partial volume (59) of the interior (50). Device after Claim 3 , characterized in that the measurement volume (2A) is minimized for a given total surface area of the hollow fiber bundle (3) by selecting hollow fibers with a small inner diameter, that is to say a correspondingly higher wall thickness. Device after Claim 7 , characterized in that the measurement volume (2B) is minimized for a given total surface area of the hollow fiber bundle (3) by - hollow fibers (31) having a small outer diameter being selected, - the hollow fiber bundle (3) hollow fibers (31, 31 ') various outer diameters, - the hollow fiber bundle (3) also includes non-hollow fibers with a diameter that is smaller than the diameter of the hollow fibers (31, 31 '), - the hollow fibers pack the housing as tightly as possible and completely, in particular by filling the fibers (30) of the bundle (3) are as parallel as possible to one another, - the hollow fiber bundle has a cylindrical shape with fibers not glued at the ends and / or - an inner wall of the housing 5 is caused by the finite diameter of the hollow fibers (31) unevenness of an outer surface of the hollow fiber bundle (3) is adjusted or actively adjusts due to an elasticity of the inner wall material. Device according to one of the preceding claims, characterized in that an outline of a cross section of the hollow fibers (31) has essentially the shape of a circle, a hexagon, a square or a triangle. Device according to one of the Claims 4 - 10th , characterized in that the housing (5) has a degassing opening (55) in fluid communication with the measurement volume (2A, 2B), the degassing opening (55) being closed by means of a controllable valve (56). Device according to one of the Claims 4 - 11 , characterized in that the housing (5) consists of an upper end section (5a) and a lower end section (5b) and an intermediate middle section (5m), wherein: the middle section (5m) is a hollow cylinder or a hollow hexagonal tube, - The end sections (5a, 5b) taper starting from the middle section (5m), in particular conically or in the form of a hexagonal pyramid, and / or - in each end section (5a, 5b) and / or in the middle section at least one opening, in particular one with one Hose or pipe connection possibility, for example a hollow cylindrical connector, provided opening, is available. Device according to one of the preceding claims, characterized by at least one further pressure determination means with which a pressure of the liquid can be measured, in particular two additional pressure determination means, one in each case in the area of an inlet opening (52a, 58a) through which liquid into the housing interior (50) flows in, and one is arranged in the region of an outlet opening (52b, 58b) through which liquid flows out of the housing interior (50). Printer or printing machine, in particular 3D printer, with a device according to one of the Claims 1 - 13 , characterized in that a total gas content of a printer ink or binder liquid used by the printer or the printing machine can be measured by means of the device. Printer or press Claim 14 , characterized in that a device according to Claim 6 or 7 is used, which is flowed through by the printer ink or binder liquid used in the printer or the printing press. Printer or printing machine according to one of the Claims 14 or 15 , characterized in that the gas pressure measuring device is arranged in a movable part of the machine, in particular in or on the print head. Method for rapidly determining a total content of a gas or gas mixture dissolved in a liquid using an apparatus according to one of the Claims 1 - 13 , characterized in that - a time profile p _m (t) of the gas pressure in the measurement volume (2A, 2B) is measured over time, and - by extrapolation according to the formula $$p_{ex}\left(t\right)=p_m\left(t\right)+\left(p_m\left(t\right)-p_m\left(t_0\right)\right)\times \{\begin{array}{c}{F}_1:p_m\left(t\right)>p_m\left(t_0\right)\\ F_{\mathrm{2nd}}:p_m\left(t\right)\le p_m\left(t_0\right)\end{array}$$

an extrapolation value p _ex (t), which better represents the actual gas pressure p _a (t), is calculated and output, where F ₁ and F _{2 are} empirically determined constants and p _m (t ₀ ) is the pressure measured at a time t ₀ in which a rate of change of the measured pressure was below an empirically determined threshold.

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