DE102011054133A1 - Level measuring device for humidifier - Google Patents

Abstract

A level measuring device for a humidifier is provided which has a liquid container (3) with a bottom plate (11) and a housing (2) with a heating plate (8), the heating plate (8) being heated to heat the liquid in the liquid container (3). can be heated and the bottom plate (11) 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 (11) and a second electrode (13), each connected to an AC voltage source (20) and having a measuring device adapted to measure the capacitance between the first electrode (11) and the second electrode (13), the housing (2) having a first wall (27 ) substantially adjacent to a second wall (15) of the liquid container (3), the bottom plate (11) being provided as a first electrode (11) and the second electrode (13) is disposed on the first wall (27) so as to face the second wall (15) of the liquid container (3).

Description

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 needs to be adjusted in temperature and humidity to the physiological needs of the patient, a humidifier is placed in the inspiratory or inspiratory tube which heats and humidifies 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. B. from the 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 in the fill direction are mounted on the outside of a plastic container. The measuring signal is passed to a control device which controls the function of the kettle accordingly.

Another example of the contactless capacitive level measurement is in the US 5,017,909 described.

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 it for capacitive measurement of the liquid level in the liquid container, a first electrode and a second electrode, each connected to an AC voltage source and having a measuring device adapted to measure the capacitance between the first electrode and the second electrode, the housing having a first wall substantially to a second wall of the liquid container adjacent, wherein the bottom plate is provided as a first electrode and the second electrode is arranged on the first wall, that it faces the second wall of the liquid container. 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 gauge because the electricity counts 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 suitable 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:

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

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

3 a schematic side view of a liquid container shows;

4 a schematic representation of the principle of operation of the present invention shows; and

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

1 shows a perspective view of the housing 2 a humidifier having a 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 is a hot plate 8th arranged, which is oriented substantially horizontally and almost the entire surface of the horizontal leg 4 covered. From the top of the vertical leg 6 extends approximately in the middle of a projection-like section 10 whose sloping surface is a user interface 12 includes. The user interface 12 has a display device 14 and controls 16 by means of which and a (not shown) control device, the humidifier can be monitored and controlled. Laterally of the projection-like section 10 are at the top of the vertical leg 6 each electrical contact elements 18 arranged, which can be brought into electrical contact with corresponding connecting pieces of a breathing circuit. The arrow in 1 indicates the insertion direction for the liquid container having a shape substantially complementary to the projection-like portion 10 of the housing 2 is. The liquid container will now be with reference to 2 described.

2 shows a perspective view of a liquid container 3 the humidifier, which has a preferred embodiment of the level measuring device according to the invention. In the upper area, the liquid container 3 one connection element each 5 on, 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 points the liquid container 3 a recess or a cutout 7 on. Furthermore, on the lid surface of the liquid container 3 a refill hose 10 connected.

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 formed as a first electrode, and a second electrode 13 is here schematically perpendicular to the bottom plate 11 arranged. It should be noted that in the present invention, the second electrode 13 not like in 3 displayed directly on the first wall 15 of the liquid container 3 but at the (in 3 not shown) second wall 27 of the housing 2 is arranged. The representation in 3 has therefore purely illustrative character.

Inside the liquid container 3 is a liquid in the operating state 17 For example, normal or distilled water that is up to one with the wavy line 19 marked level height 21 enough. The dashed line 23 gives the lower course of the 2 section shown 7 again and determines the maximum level 25 for the liquid 17 , As soon as the maximum level height 25 is reached, the respiratory gas flow during operation no longer wets the maximum surface of the liquid 17 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 4 schematically shows the principle of operation of the capacitive level measurement in the level measuring device according to the invention. The with the heating plate 8th in complete electrical contact floor plate 11 forms the first electrode. At this first electrode is an AC voltage source 20 over a line 22 connected, and the other end of the line 22 is with the second electrode 13 connected. Similar to in 3 are in 4 the first and second walls are not shown for the sake of simplicity.

The first electrode 11 is from the AC source 20 over the line 22 a high frequency alternating voltage supplied in the second electrode 13 causes capacitive currents, for example, by a measuring device in the line 22 can be detected. The height 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 between the first electrode 11 and second electrode 13 are physically present and are detected by the high-frequency alternating electric field. The capacity is representative of the capacity of the substances between the electrodes 24 ,

The liquid 17 is enough in the liquid container 3 up to the filling level 21 , and because, for example, water as a liquid 17 one of 1 has different dielectric constant, leads to a higher filling level 21 to an increase in capacity 24 between the two electrodes 8th . 13 and thus a proportional increase in the measurable amplitude of the capacitive currents. In an analogous manner, a lower level leads to a lower level capacity 24 and thus a drop in the measurable current amplitude.

5 shows a perspective cross-sectional view of a humidifier with a preferred embodiment of the level measuring device according to the invention. In a housing 2 is the liquid container 3 pushed in completely, just like the arrow in 1 suggests. This is the bottom plate or first electrode 11 completely on the hot plate 8th of the housing 2 and is in complete thermal and electrical contact with her. The bottom plate 11 is bordering in 5 right side to the second wall 15 of the liquid container 3 on, and this second wall 15 is flat over a larger section and parallel to the first wall 27 of the housing 2 educated. In the operating state of the humidifier are the first wall 27 and the second wall 15 so close to each other opposite, that in between only a thinnest possible air gap is formed, whose dielectric properties are taken into account in the level measurement.

The second electrode 13 is on the inside of the case 2 directed, to the heating plate 8th vertical surface of the first wall 27 arranged so that they are also substantially planar and parallel to the second wall 15 of the liquid container 3 runs. The width of the electrode 13 extends essentially over the height of all in the liquid container expected levels up to the maximum level height 25 , This allows each level value to 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 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, the measured values on the user interface 12 or the display device 14 to display and output when exceeding or exceeding predetermined limits acoustic or optical signals.

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

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely 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.

Cited patent literature

• WO 2006/000378 A1 [0006]
• GB 2358789 A [0007]
• US 5017909 [0008]

Claims (11)

Level measuring device for a humidifier, comprising a liquid container ( 3 ) with a bottom plate ( 11 ) and a housing ( 2 ) with a heating plate ( 8th ), wherein for heating the liquid in the liquid container ( 3 ) the heating plate ( 8th ) and the bottom plate ( 11 ) in contact with the heating plate ( 8th ), characterized in that the level measuring device for capacitive measurement of the liquid level in the liquid container ( 3 ) a first electrode ( 11 ) and a second electrode ( 13 ), each with an AC source ( 20 ) and having a measuring device which is suitable for reducing the capacitance between the first electrode ( 11 ) and the second electrode ( 13 ), the housing ( 2 ) a first wall ( 27 ) substantially to a second wall ( 15 ) of the liquid container ( 3 ), wherein the bottom plate ( 11 ) as the first electrode ( 11 ) and the second electrode ( 13 ) on the first wall ( 27 ) is arranged that they the second wall ( 15 ) of the liquid container ( 3 ) is opposite. Level measuring device according to claim 1, characterized in that the second electrode ( 13 ) on the first wall ( 27 ) is arranged so that they are above 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 in such a way on the first wall ( 27 ) are arranged such that the plurality of second electrodes ( 13 ) about the height of all in the liquid container ( 3 ) 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 ) substantially perpendicular to the bottom plate ( 11 ) are arranged. Level measuring device according to one of the preceding claims, characterized in that the bottom plate ( 11 ) is grounded. Level measuring device according to one of the preceding claims, characterized in that the bottom plate ( 11 ) and the heating plate ( 8th ) 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 ( 11 ) 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 ) substantially across 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 the liquid container ( 3 ) to investigate. 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.

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