WO2013045572A1

WO2013045572A1 - Fluid level gauge for a respiratory humidifier

Info

Publication number: WO2013045572A1
Application number: PCT/EP2012/069120
Authority: WO
Inventors: Rudolf BÜCHI; Marc MAEDER
Original assignee: Hamilton Bonaduz Ag
Priority date: 2011-10-01
Filing date: 2012-09-27
Publication date: 2013-04-04
Also published as: DE102011054133A1

Abstract

The invention relates to a fluid level gauge for a respiratory humidifier which comprises a liquid container (3) having a base plate (11) and a housing (2) having a heating plate (8). In order to heat the liquid in the liquid container (3), the heating plate (8) can be heated and the base plate (11) can be brought in contact with the heating plate (8). The fluid level gauge is characterized by comprising a first electrode (11) and a second electrode (13), each connected to an AC voltage source (20), and a measuring unit which is suitable to measure the capacitance between the first electrode (11) and the second electrode (13), for the capacitive measurement of the liquid level of the liquid in the liquid container (3). The housing (2) has a first wall (27) which substantially adjoins a second wall (15) of the liquid container (3), the base plate (11) being provided as the first electrode (11) and the second electrode (13) being arranged on the first wall (27) such that it is opposite the second wall (15) of the liquid container (3).

Description

Level measuring device for humidifier

The present invention relates to a level measuring device for breathing humidifier when breathing patients with breathing gas, and more particularly to a humidifier with a capacitive level measuring device.

During mechanical ventilation of patients, for example, in an intensive care unit, the patient to be ventilated is pneumatically connected to the ventilator using a breathing circuit. Since the respiratory gas supplied to the patient must be adjusted in temperature and humidity to the physiological requirements of the patient, a humidifier is placed in the inspiratory or inspiratory tube which warms and moistens the respiratory gas. The humidifier has a liquid container filled with distilled water, through which the inhaled gas is passed and enriched with moisture.

The heating of the liquid in the liquid container via a heating plate in the lower portion of the housing of the humidifier, wherein the heat is thermally transferred from the heating plate to the heat-conductive bottom of the liquid container. So that the liquid container does not run dry, the level in the liquid container is monitored. For refilling liquid from an external reservoir, for example, in the prior art, a hose is passed from above into the liquid container, to the lowest permissible level. On this hose there is a float valve, which opens the valve seat when a liquid level falls below a certain level and releases the supply of liquid from the external reservoir until a maximum permissible level is reached. Then the float valve blocks the further supply of liquid from the external reservoir.

Such monitoring and refilling can be problematic if the external reservoir itself is idle or about to run empty. In addition, the exact level of the humidifier can not be measured with it, because only the two extreme values are processed as events. Furthermore, it is only possible with the known monitoring function to initiate refilling. It is not possible to issue a warning signal to the user. The contactless capacitive level measurement in vessels is known in principle, for. Example from WO 2006/000378 A1. In this case, electrodes are applied from the outside to a vessel made of non-electrically conductive material, for example, glued or produced by applying by means of a conductive plastic. High-frequency alternating voltage is supplied via one or more transmitting electrodes, which causes capacitive currents in at least one further electrode designed as a receiving electrode. Among other things, the electric field reaches through the vessel wall and the medium in the vessel. Since most media have a dielectric constant different from 1, the filling of the vessel leads to an increase in the capacitance between the electrodes and thus to a proportional increase in the current amplitude, which can be evaluated as a measurement signal.

The GB 2 358 789 A discloses a non-contact level measurement in a kettle or kettle, in which two parallel electrodes are mounted in the fill level outside on a Kunststoffbeh older. The measuring signal is passed to a control device which controls the function of the kettle accordingly.

Further examples of the contactless capacitive level measurement are described in US Pat. No. 5,017,909 and DE 10 2006 033 204 A1.

An important requirement for a liquid container in a humidifier is that it must be particularly easy and inexpensive to produce as a disposable medical / disposable article. The construction of a level measuring device must therefore not be complex and should include as few components as possible.

It is therefore an object of the present invention to provide a level measuring device for a humidifier, which can accurately measure the level in the liquid container at any time, can provide the measured value immediately for evaluation and display ready and manages without additional components in the liquid container.

This object is solved by the features of claim 1. Advantageous embodiments and embodiments are described in the subclaims. According to the invention, a level measuring device for a humidifier is provided, the humidifier having a liquid container with a bottom plate and a housing with a heating plate, wherein for heating the liquid in the liquid container, the heating plate can be heated and the bottom plate can be brought into contact with the heating plate. The level measuring device is characterized in that, for capacitive measurement of the liquid level in the liquid container, it has a first electrode and a second electrode, each connected to an AC voltage source, and a measuring device adapted to measure the capacitance between the first electrode and the first electrode second housing, wherein the housing has a first wall which is substantially adjacent to a second wall of the liquid container, wherein the bottom plate is provided as a first electrode and the second electrode is arranged on the first wall, that it the second Wall of the liquid container opposite. Because the bottom plate of the liquid container usually made of very good electrically and thermally conductive metal such. As aluminum is formed, it can serve as a first electrode in the capacitive measurement of the level without an additional components would be required. Although an additional function for the humidifier is provided with the level measuring device according to the invention, a change in the structure of the liquid container is not necessary. Furthermore, the current level can be transmitted at any time to a control device of the humidifier, there displayed and evaluated. Since the bottom plate as the first electrode has a very large area, it is possible that the second electrode may extend on the first wall over a relatively large area. This also allows a large area for the second electrode, whereby the capacity and with it also the measuring range of the capacity between the filled and empty liquid container relatively large. This allows more accurate measurement results.

The second electrode is preferably arranged on the first wall in such a way that it extends over the height of all fill levels to be expected in the liquid container. Alternatively, the level measuring device may comprise a plurality of second electrodes, which are arranged on the first wall such that the plurality of second electrodes are distributed over the height of all to be expected in the liquid container levels. In both cases, the arrangement increases the accuracy of the measurement.

Preferably, the first wall and the second wall are arranged substantially parallel to each other. This simplifies the measurement and calibration of the level gauges. since the numbers of electrons of the materials of the first wall, the second wall and the gap are constant over the entire area of the second electrode. Decisive therefore is essentially only the level of the liquid. It is advantageous if the first wall and the second wall are arranged substantially perpendicular to the bottom plate. This results in a simple construction.

With particular advantage, the bottom plate is grounded. This is used for interference immunity by high-frequency interference signals. Since the bottom plate is firmly pressed in the operating state of the humidifier on the heating plate of the housing and is formed of electrically conductive material, it is at the same potential as the heating plate and thereby the grounding of the bottom plate can be effected by the grounding of the heating plate. This can be used on existing components for grounding the bottom plate. Particularly effective is the heating effect when the bottom plate and the heating plate are flat and each having a substantially equal contact surface. It is preferred that the bottom plate made of aluminum and the second electrode are formed of copper. It is further preferred that the second electrode extends substantially across the width of the liquid container. As already mentioned above, it is desirable for the purpose of a larger measuring range to form the area of the second electrode as large as possible. Furthermore, according to the invention, a humidifier with a housing, a liquid container and a level measuring device as defined above, wherein the humidifier has a control device, in which the measuring device is integrated and which is adapted to determine the level in the liquid container from the measured capacitance. The control device can then at any time transmit the fill level measurement signal, for example, to a user interface which displays a corresponding fill level value on a display device. It is also advantageous that the control device is suitable for outputting an optical or acoustic signal for the user at certain level values. The invention will now be described by way of example with reference to the accompanying figures, in which:

Fig. 1 shows a perspective view of a housing of a humidifier with a preferred embodiment of the level measuring device according to the invention;

FIG. 2 shows a perspective view of a liquid container of a respiratory humidifier with a fill level measuring device according to the invention of the preferred embodiment; FIG.

Fig. 3 is a schematic side view of a liquid container;

FIG. 4 shows a schematic representation of the functional principle of the present invention; FIG. and

5 shows a perspective cross-sectional view of a portion of a humidifier according to a preferred embodiment of the present invention.

1 shows a perspective view of the housing 2 of a humidifier having a filling level measuring device according to the invention according to a preferred embodiment. The housing 2 has a substantially L-shape with a horizontal leg 4 and a vertical leg 6. On the horizontal leg 4, a heating plate 8 is arranged, which is oriented substantially horizontally and covers almost the entire surface of the horizontal leg 4. From the upper end of the vertical leg 6 extends approximately in the center of a projection-like portion 10, the inclined surface comprises a user interface 12. The user interface 12 has a display device 14 and operating elements 16, by means of which and a control device (not shown) the respiratory humidifier can be monitored and controlled. On the side of the projection-like section 10, electrical contact elements 18 are respectively arranged at the upper end of the vertical leg 6 and can be brought into electrical contact with corresponding connecting pieces of a ventilation hose system. The arrow in FIG. 1 indicates the insertion direction for the liquid container, which has a shape which is substantially complementary to the projection-like section 10 of the housing 2 is. The liquid container will now be described with reference to FIG.

2 shows a perspective view of a liquid container 3 of the humidifier, which has a preferred embodiment of the level measuring device according to the invention. In the upper area, the liquid container 3 each have a connection element 5, which is designed as a pipe socket with a circular cross-section for pneumatic connection to a breathing circuit. Between the two connection elements 5, the liquid container 3 has a recess or a cutout 7. Furthermore, a refill hose 10 can be connected to the cover surface of the liquid container 3.

Fig. 3 shows a schematic side view of the liquid container 3 with the elements of the level measuring device according to the invention. The bottom plate 11 of the liquid container 3 is designed as a first electrode, and a second electrode 13 is here arranged schematically perpendicular to the bottom plate 11. It should be noted that in the present invention, the second electrode 13 is not disposed directly on the first wall 15 of the liquid container 3 as shown in FIG. 3, but on the second wall 27 of the housing 2 (not shown in FIG. 3). The illustration in FIG. 3 therefore has a purely illustrative character.

Within the liquid container 3 is in the operating state, a liquid 17, for example, normal or distilled water, which extends to a marked with the wavy line 19 level 21. The dashed line 23 is the lower course of the section 7 shown in Fig. 2 again and determines the maximum level height 25 for the liquid 17. As soon as the maximum level height 25 is reached, the respiratory gas flow in operation no longer wets the maximum surface of the liquid 17th and therefore the function of the humidifier is further limited. The respiratory gas flow is then no longer the largest possible liquid surface available for moisture absorption.

In Fig. 4, the functional principle of the capacitive level measurement is shown schematically in the level measuring device according to the invention. The standing with the heating plate 8 in complete electrical contact bottom plate 11 forms the first electrode. An AC voltage source 20 is connected to this first electrode via a line 22, and the other end of the lead 22 is connected to the second electrode 13. Similar to Fig. 3, in Fig. 4, the first and second walls are not shown for the sake of simplicity. The first electrode 11 is supplied by the AC voltage source 20 via the line 22, a high-frequency AC voltage, which causes capacitive currents in the second electrode 13, which can be detected for example by a measuring device in the line 22. The magnitude of the capacitive currents in the second electrode 13 is determined by the electrical properties, in particular the dielectric constant, of the substances that are physically present between the first electrode 1 1 and second electrode 13 and are detected by the high-frequency alternating electric field. The capacity 24 is representative of the capacity of the substances between the electrodes.

The liquid 17 extends in the liquid container 3 to the filling level 21, and because, for example, water 17 has a different dielectric constant than liquid 17, a higher filling level 21 leads to an increase in the capacitance 24 between the two electrodes 8, 13 and thus to one proportional increase in the measurable amplitude of the capacitive currents. In an analogous manner, a lower fill level leads to a smaller capacity 24 and thus to a drop in the measurable current amplitude.

5 shows a perspective cross-sectional view of a respiratory humidifier with a preferred embodiment of the level measuring device according to the invention. In a housing 2, the liquid container 3 is completely inserted, as indicated by the arrow in Fig. 1. As a result, the bottom plate or first electrode 11 rests completely on the heating plate 8 of the housing 2 and is in complete thermal and electrical contact with it. The base plate 11 adjoins the second wall 15 of the liquid container 3 in the area shown on the right in FIG. 5, and this second wall 15 is flat and parallel to the first wall 27 of the housing 2 over a larger portion. In the operating state of the humidifier, the first wall 27 and the second wall 15 face each other so close to each other that only a thinnest possible air gap is formed therebetween, the dielectric properties of which are taken into account in the level measurement.

The second electrode 13 is arranged on the surface of the first wall 27, which is directed into the interior of the housing 2 and is perpendicular to the heating plate 8, in such a way that it likewise acts in the direction of the wall. sentlichen and parallel to the second wall 15 of the liquid container 3 extends. The width of the electrode 13 extends substantially over the height of all in the liquid container expected levels up to the maximum level height 25. Thus, each level value can be continuously measured.

The electronic components of the filling level measuring device according to the invention, in particular the alternating voltage source and the measuring device which measures the induced high-frequency capacitance currents, are for example integrated in the control device, preferably on the same printed circuit board. As a result, essentially no additional volume or additional installation space is required. The measuring device may preferably be an application-specific integrated circuit (ASIC) which is arranged on the main circuit board of the control device. Such ASICs are mass-produced and therefore cost-effective, simple and flexible. In the preferred embodiment of the present invention, the humidifier also includes a controller to which the level gauge continuously supplies the values of its measurements. The control device is suitable for displaying the measured values on the user interface 12 or the display device 14 and outputting acoustic or optical signals when the limit values fall below or exceed predetermined limits.

With the object of the present invention, a level measuring device for a humidifier has been provided, which can accurately measure the level in the liquid container at any time, can provide the measured value immediately for evaluation and display and manages without additional components in the liquid container.

Claims

claims

Level measuring device for a humidifier, which has a liquid container (3) with a bottom plate (1 1) and a housing (2) with a heating plate (8), wherein for heating the liquid in the liquid container (3) the heating plate (8) can be heated and the Bottom plate (1 1) in contact with the heating plate (8) can be brought, characterized in that the level measuring device for capacitive measurement of the liquid level in the liquid container (3) has a first electrode (1 1) and a second electrode (13) are each connected to an AC voltage source (20), and having a measuring device which is adapted to measure the capacitance between the first electrode (1 1) and the second electrode (13), wherein the housing (2) has a first wall (27 ), which is substantially adjacent to a second wall (15) of the liquid container (3), wherein the bottom plate (1 1) is provided as a first electrode (1 1) and the second E The electrode (13) is arranged on the first wall (27) such that it lies opposite the second wall (15) of the liquid container (3).

Level measuring device according to claim 1, characterized in that the second electrode (13) on the first wall (27) is arranged so that it extends over the height of all in the liquid container (3) expected levels (21).

Level measuring device according to claim 1, characterized in that it comprises a plurality of second electrodes (13) which are arranged on the first wall (27), that the plurality of second electrodes (13) on the height of all in the liquid container (3) to be expected levels (21) are distributed. Level measuring device according to one of the preceding claims, characterized in that the first wall (27) and the second wall (15) are arranged substantially parallel to each other.

Level measuring device according to one of the preceding claims, characterized in that the first wall (27) and the second wall (15) are arranged substantially perpendicular to the bottom plate (1 1).

Level measuring device according to one of the preceding claims, characterized in that the bottom plate (1 1) is grounded.

Level measuring device according to one of the preceding claims, characterized in that the bottom plate (1 1) and the heating plate (8) are flat and each having a substantially equal contact surface.

Level measuring device according to one of the preceding claims, characterized in that the bottom plate (1 1) made of aluminum and the second electrode (13) is formed of copper.

Level measuring device according to one of the preceding claims, characterized in that the second electrode (13) extends substantially over the width of the liquid container (3).

Humidifier with a housing (2), a liquid container (3) and a level measuring device according to one of the preceding claims, characterized in that the humidifier has a control device, in which the measuring device is integrated and which is suitable from the measured capacitance, the level in to determine the liquid container (3).

Breathing air humidifier according to claim 10, characterized in that the control device is adapted to output a visual or audible signal for the user at certain level values.