DE102018131355A1 - Total gas measuring device with molded body - Google Patents

Abstract

Measuring device for determining the total pressure of gases dissolved in a liquid, comprising a gas-filled measuring volume (2), which is separated from the liquid by a flat, semi-permeable, i.e. liquid-tight but gas-permeable membrane (3), and a pressure determining means (4), in particular a pressure sensor (41) arranged in the measuring volume (2) with connected evaluation electronics (42), the semi-permeable membrane (3) spanning an upper side (51) of a molded body (5) and the upper side having a cavity (50), so that the measuring volume (2) is limited by inner surfaces of the cavity (50) and sections of the membrane (3) not touching the molded body (5).

Description

The present invention relates to a measuring device for determining the total pressure of gases dissolved in a liquid, comprising a gas-filled measuring volume, which is separated from the liquid by a flat, semi-permeable membrane, and a pressure determining means, in particular a pressure sensor arranged in the measuring volume with connected evaluation electronics, and a manufacturing method and use of such a measuring device.

The measurement or analysis of the gases dissolved in a liquid is relevant in a variety of technical or physiological situations. Examples of this are the oxygen content or the oxygen saturation of the blood, for divers also the nitrogen content of the blood, 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, that is to say a gas analysis. 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, the basic presence of damage can also be seen from the total partial pressure of the dissolved gases.

Situations in which the total content of dissolved gases in itself is the relevant quantity 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 important in the field of printing, be it conventional, two-dimensional printing or 3D printing, which is becoming increasingly important today, since an excessive content of dissolved gases, usually air, forms gas bubbles in can lead to the printer nozzles, which reduces the print image and print quality. Problems already occur with an air partial pressure in the pressure fluid (printer ink or binder fluid) well below the atmospheric pressure of approx. 1 bar, which is why care must be taken to ensure adequate air or gas-tight sealing when processing and storing pressure fluids.

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 , cannot be penetrated in the liquid phase, 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 sensor, so that a pressure is established there that corresponds to the partial pressure of all dissolved gases in the liquid. A measurement of the pressure occurring in the measurement volume by means of a pressure sensor thus provides information about the proportion or the total pressure of all gases dissolved in the liquid.

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.

From the publications US 2006/0070525 A1 and US 2008/0289396 A1 Total gas measuring devices are known which propose a tubular configuration of the semi-permeable membrane and here the reaction time, i.e. the time until a change in the total gas partial pressure is registered by the sensor, as well as the measuring time, i.e. the time until an assumed step-shaped Pressure change the new equilibrium value is displayed, improve by increasing the membrane surface per sensor volume and at the same time reducing the measuring volume by inserting displacers, for example wire bundles laid inside the membrane tube. Also the DE 19705195 A1 shows a measuring device with a tubular membrane, but no measures have been taken to reduce the measuring volume.
The fundamental disadvantage of measuring devices with a tubular membrane is the comparatively large space requirement, the complex manufacture and the high mechanical sensitivity of the tubular membrane.

A simple, can-shaped TDG sensor with a flat membrane is in the patent CH 679 890 A5 disclosed. A major disadvantage of this sensor is that it is comparatively large Measurement volume, which has an adverse effect on both response and measurement time.

Against this background, the present invention has for its object to find a measuring device for determining the total gas content of a liquid, which combines a short reaction time with a compact design and simple and inexpensive manufacture.

This object is achieved by a device according to claim 1, an associated manufacturing method according to claim 10 and use of the device in a printing press or a printer, in particular a 3D printer, according to claim 11.

An essential element of the total gas pressure measuring device according to the invention is the molded body, which forms the basis or the basic structure of the device to a certain extent. On at least one side, which is defined as the upper side, this molded body has a cavity, that is to say an indentation or concave cavity. To create the gas-filled measuring volume, the membrane is now placed over this cavity and fastened to the molded body in such a way that the cavity is completely spanned and the membrane is fully gas-tightly connected to the edge of the cavity.
The gas pressure in the measuring volume is monitored with the aid of the pressure determination means. For this purpose, at least one pressure sensor of the pressure determination means is arranged in or adjacent to the measurement volume.

In order to achieve short reaction and measurement times, a molded body should be selected that has a flat cavity with the smallest possible volume. The cavity should be flat, that is, have a lateral extension that is far larger than its vertical extension in order to obtain the largest possible ratio of membrane area to measurement volume.

In its most general form, the production according to the invention comprises the provision of the components membrane, pressure determination means and molded body, which are then assembled in subsequent steps. The sequence of the connection between the shaped body and the pressure determining means or shaped body and membrane is basically arbitrary. In practice, however, it may be advantageous to first place the pressure determination means, or a pressure sensor belonging to it, in or adjacent to the measurement volume that may no longer be accessible after the membrane has been attached.

The use of a prefabricated molded body, over which only the membrane has to be stretched and the pressure determination means has to be used, enables the measuring device according to the invention to be manufactured cost-effectively. When using a molded body with a suitable design, the mechanical robustness and compact design are guaranteed at the same time.

According to the invention, the compact and robust measuring device proposed here is used in a printer or a printing press to measure the total gas content of the printing fluids used therein, that is to say the liquids consumed and output by the printer to produce a desired printing result.

Because of its small design and its robustness, it can also be integrated into moving parts, in particular the print head or print heads of the printing press or the printer.

This is economically feasible even in printing machines with a large number of print heads, since the measuring device according to the invention is simple in construction and can be produced economically.

The measuring device according to the invention is used here in such a way that it replaces part of the side wall of a rigid line or a measuring chamber which is switched into the (pressure) liquid flow. For this purpose, the measuring device is inserted into an opening in a side wall in such a way that the membrane projects completely into the interior filled with (pressure) liquid. The lower part of the measuring device according to the invention, including an evaluation unit of the pressure determination means, however, remains outside the line or the measuring chamber and thus outside the liquid. The seal between the side wall and the measuring device, more precisely the outer surface of the shaped body of the measuring device, can be ensured by positive locking (pressing in with or without a sealing ring) or material locking (gluing).

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.

In preferred embodiments of the present invention, the ratio of the vertical extent, that is to say the height, of the cavity of the shaped body to its lateral extent, in particular in the case of a round cavity, its diameter is less than 1: 4, particularly preferably less than 1:10.

In order to be sufficiently robust, the molded body should not be made too thin-walled compared to its dimensions. In particular, the total height of the molded body, ie its extent in a direction parallel to a normal to the top, at least three times the height, that is to say vertical extent, of the cavity.

In some embodiments of the present invention, support structures are introduced and / or integrally formed on the shaped body in the interior of the cavity on the upper side of the shaped body, which extend as far as the membrane, so that this at least when there is a pressure difference between the liquid in the outer space and the measurement volume on the The top of the support structures rests and is thus supported.
The floor plan of these support structures is largely arbitrary within the scope of the present invention, as long as there are only enough to adequately fulfill their support function. Another function of the support structures, however, is to minimize the volume of the cavity and thus the measurement volume in order to increase the response time of the measuring device according to the invention. With regard to the arrangement of the support structures, care must be taken that a rapid gas exchange can take place between all partial volumes of the measurement volume.
In particularly preferred refinements, the support structures can be columns, in particular curved or radiating ribs, wedges or other structures which are arranged around a center.

The molded body of the measuring device, which is preferably prefabricated from plastic, metal, ceramic, glass or wood, preferably has a round outline and an approximately rectangular cross section, which is widened in the lower region in the manner of a base or plug and on the outside below which the membrane supporting edge area can have a circumferential groove.
The widening serves as a stop when mounting the measuring device in an opening of a wall of a container filled with the liquid to be measured, such as a tank, reservoir, pipe or also a measuring chamber interposed in a pipe or a line, which prevents the device is accidentally pushed too far or not enough into the inside of the container. Furthermore, the widening also increases the space available for this in the embodiments of the present invention with an evaluation unit of the pressure determination means integrated in the molded body.
The groove mainly serves as a seat for a sealing ring, by means of which the seal between a wall and the outer surface of the molded body is ensured. In addition, it also enables a securely seated membrane stretched over the molded body, provided that its collar extends into the area of the groove and thus slightly engages behind the edge region of the molded body surrounding the cavity.

In some configurations of the molded body, the latter has an opening which is continuous from the top to an opposite underside and which opens into the cavity and which is preferably arranged at a point of symmetry of the cavity, in the case of a circular cavity approximately at the center. A pressure sensor of the pressure determination means can be accommodated in this opening by inserting it in a gas-tight manner, in particular pressing it in or gluing it in.

The flat membrane is preferably fastened to the shaped body in that it is clamped onto the shaped body by a collar of the membrane engaging around the edge of the upper side of the shaped body. The collar of the membrane particularly preferably engages behind the edge structure by means of a circumferential fillet present under the edge structure in the outside of the molded body. Alternatively or additionally, the membrane is glued to the edge area and or the support structures in order to guarantee a firmer grip or a better seal. However, this makes it difficult to change the membrane in the event of damage or loss of function due to age. Since the pressure in the measuring volume is usually significantly lower than in the liquid, tensioning is usually completely sufficient.

In one embodiment of the manufacturing method according to the invention, a suitable molded body is produced in a previous step by pouring a liquefied material into a negative mold, by molding it out of a block of suitable material by means of a machining shaping method or by an additive manufacturing method (3D printing).

If the shaped body provided or produced in this way does not have a suitable accommodation option for a pressure determination means, this can be created in a step preceding the assembly, for example by appropriately, for example by means of a drilling process, an opening in the cavity from the upper side as defined up to an opposite underside through opening is created, in which the pressure sensor of the pressure determining means can be used gas-tight. In order to keep the additional dead volume of the sensor created thereby, that is to say the effective enlargement of the measuring volume, as low as possible, it is proposed to insert the pressure sensor as far as possible within this opening.

Further properties, features and advantages of the present invention result from those presented below with reference to the figures Embodiments. 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: perspektivische Ansichten einer bevorzugten Ausführungsform eines Formkörpers einer erfindungsgemäßen Messvorrichtung
• 2: in zwei Teilfiguren, Querschnitte durch eine den Formkörper aus 1 verwendende, sowie eine leicht abgewandelte erfindungsgemäße Messvorrichtung
• 3: in zwei Teilfiguren, Draufsichten auf weitere Ausgestaltungen des Formkörpers einer erfindungsgemäßen Messvorrichtung

Show it:

• 1 : Perspective views of a preferred embodiment of a shaped body of a measuring device according to the invention
• 2nd : in two sub-figures, cross sections through one of the molded body 1 using, as well as a slightly modified measuring device according to the invention
• 3rd : in two partial figures, plan views of further configurations of the molded body of a measuring device according to the invention

In 1 perspective views of a preferred embodiment of a shaped body of a measuring device according to the invention are shown.

Sub-figure A shows a view obliquely from above. The molded body 5 as well as the cavity 50 on its top 51 have a circular floor plan. The cavity 50 is circumferential from an edge 55 limited and has arch-shaped ribs in its interior 52 to support a membrane (not shown) drawn over the molded body. The support ribs 52 have a semicircular cross-section, and are each quarter-circle segments that are at the center of the cavity 50 mouth opening 59 surround. Between the support ribs 52 The same circle is gaps to allow gas exchange between the spaces defined by adjacent rings and the opening 59 available. In this version with four-fold rotational symmetry around the vertical axis, there are a total of four gaps per circular ring. Other configurations with fewer, for example only 2 or 3 or even more, for example 5, 6 or 8 gaps, which are arranged symmetrically or not, would also be conceivable.
The latter is, as from partial figure B, which shows a perspective bottom view, from the top 51 to the bottom 53 consistent and allows the use of a pressure sensor.
The molded body knows to improve the hold of a flat membrane stretched over the cavity 5 below the edge 55 a circumferential throat 56 on. Due to the widened base in the manner of a pedestal 57 a more stable connection with a structure carrying the measuring device is possible.

2nd shows a cross section through the molded body 1 using measuring device 1 (Part figure A) and a slightly modified form (part figure B).
In both embodiments is over the top of the molded body 5 the membrane 3rd curious; excited. It has a collar 31 on the molded body in the area of the edge 55 fits and up to the area of the throat 56 is enough for the membrane 3rd on the molded body 5 attached and one from the inside surface of the cavity 50 and the membrane 3rd limited measuring volume 2nd is created. Ribs 52 support the membrane 3rd against a pressure difference between the liquid 100 and the measurement volume 2nd from.
In the variant according to sub-figure A, the support structures are sufficient 52 with their respective top, attached to the membrane 3rd adjacent ends up to the convex shell of the molded body 5 without the support structures 52 approach, while in the variant according to sub-figure B they also extend. Accordingly, the membrane 3rd in sub-figure A plan or even, while in sub-figure B it is convex upwards.

The cavity faces in both variants 50 on the top 51 of the shaped body 5 a lateral extension, here a diameter, d, which is significantly larger than its vertical extension H . On the one hand, this serves the relationship between the membrane area, more precisely that available for gas exchange, not on the molded body 5 adjacent part of the membrane 3rd , and the measurement volume 2nd to maximize and also helps with the design of the molded body 5 and thus the measuring device 1 keep compact without compromising mechanical robustness.
Inside the through opening 59 is the pressure sensor 41 of the pressure determining means 4th used and to the evaluation unit 42 connected, which in both shown embodiments in a, approximately cylindrical or cuboid, expansion of the opening 59 used in its lower area and thus in the molded body 5 is sunk. Alternatively, an expansion and the evaluation unit can also be dispensed with 42 be arranged outside the molded body. This is particularly advantageous for a space-saving design of the measuring device according to the invention.

Part B also indicates how the measuring device can be used by inserting it into an opening in a wall 6 used and so far in the liquid 100 is pushed in until the thickened lower area 57 of the molded body on the wall 6 triggers. The seal between the wall 6 and the measuring device 1 or their shaped body 5 is here through the sealing ring 61 ensured which in the circumferential groove 56 of the molded body sits.

3rd presents plan views of two further possible configurations of the molded body in two partial figures 5 , or its top 51 , the total gas measuring device according to the invention.
In sub-figure A are the support structures for supporting the upper side in the complete measuring device 51 spanning membrane radiating ribs 52 and wedges 52 ' , which is different from the center of the circular cavity 50 arranged opening 59 starting to the edge 55 extend. Wedge-shaped support structures help the dead space, i.e. the volume of the cavity 50 , to minimize.
In the alternative embodiment shown in sub-figure B are columnar support structures 52 " shown, which to minimize dead space in a regular hexagonal pattern around the central opening 59 are arranged. Alternative arrangements and the use of columns of different diameters to further minimize dead space would also be possible.

Reference symbol list

1

Measuring device

2nd

Measuring volume

3rd

membrane

31

collar

4th

Pressure determining means

41

Pressure sensor

42

Evaluation unit

5

Molded body

50

cavity

51

Top

52, 52 ', 52 "

Support structures

53

bottom

55

edge

56

Throat

57

Broadening

59

opening

6

wall

61

Sealing ring

100

Fluid space

H

vertical extension of the cavity 50

d

lateral extension of the cavity 50

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 2006/0070525 A1 [0007]
• US 2008/0289396 A1 [0007]
• DE 19705195 A1 [0007]
• CH 679890 A5 [0008]

Claims (13)

Measuring device for determining the total pressure of gases dissolved in a liquid, comprising: - a gas-filled measuring volume (2), which is separated from the liquid by - a flat, semi-permeable, i.e. liquid-tight but gas-permeable, membrane (3), and - a pressure determining means (4), in particular a pressure sensor (41) arranged in the measuring volume (2) with a connected evaluation electronics (42), characterized in that - the semi-permeable membrane (3) spans an upper side (51) of a molded body (5), the upper side having a cavity (50) so that the measurement volume (2) is limited by inner surfaces of the cavity (50) and sections of the membrane (3) not touching the molded body (5). Device after Claim 1 , characterized in that the ratio of vertical extent (h) to lateral extent (d) of the cavity (50) is less than 1: 4, in particular less than 1:10. Device after Claim 1 or 2nd , characterized in that column-like and / or rib-like and / or wedge-shaped support structures (52) are present within the cavity (50) of the shaped body (5) and in particular are integrally formed from the material of the shaped body. Device after Claim 3 , characterized in that the support structures (52) extend in a vertical direction, essentially parallel to a surface normal to the upper side (51) of the molded body (5), beyond a convex envelope which the molded body (5) does without the support structures would have, so that the membrane (3) supported on the support structures (52) is curved outwards relative to the convex envelope. Device after Claim 3 , characterized in that the support structures are arranged around a center point within the cavity (50) and here are - ribs (52) which represent arcuate segments of concentric circles around the center point, and / or - as radial ribs (52) and / or Wedges (52 ') extend from the center point to an edge (55) of the cavity (50). Device according to one of the preceding claims, characterized in that the shaped body (5) and / or the cavity (50) have a round plan and / or a rectangular cross section. Device according to one of the preceding claims, characterized in that the molded body (5) consists of plastic, metal, glass, ceramic and / or wood, is in particular in one piece and has an enlarged base area at a lower end. Device according to one of the preceding claims, characterized in that the membrane (3) is fastened to the shaped body by adhesive bonding and / or clamping, the membrane (3) having a collar (31) in particular for better fastening in the event of clamping which it spans an outside of an edge region (55). Device according to one of the preceding claims, characterized in that the molded body has an opening (59) which opens into the cavity (50) and is continuous from the top (51) to the underside of the molded body (5) and into which a pressure sensor (41 ) of the pressure determining means (4), the opening (51) is inserted in a gas-tight manner, in particular pressed or glued in or sealed by means of a sealing ring. Device according to the Claims 5 and 9 , characterized in that the through opening (53) is arranged in the center. Method for producing a device according to one of the preceding claims, characterized by the steps: providing a flat semipermeable membrane (3), a pressure determination means (4) and a molded body (5) with an upper side (51) having a cavity (50), - Attaching the membrane (3) on the upper side (51) of the shaped body (5), in particular by gluing with or clamping onto an edge (55) of the upper side (51), whereby one through inner surfaces of the cavity (50) and not the shaped body (5) contacting sections of the membrane (3) limited measuring volume (2) is created, - inserting the pressure determining means (4), in particular by inserting a pressure sensor (41) of the pressure determining means (4) into or adjacent to the measuring volume (2). Use of a device according to one of the Claims 1 - 8th in a printing press or a printer, in particular a 3D printer, for measuring the total gas content of a printer ink or a binder liquid of the printing press or the printer, in particular a 3D printer. Use after Claim 11 , characterized in that the device in a Printing process moving part, in particular a print head, is integrated.

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