Arrangement and method for measuring the respective concentration of three gas components in a gas sample

Abstract

The invention relates to a sensor arrangement and a measuring method for measuring the respective concentrations of three gas components in a gas sample (Gp). One gas component is a paramagnetic gas. The gas sample (Gp) is passed through a measuring chamber (2). A magnetic field with an oscillating magnetic field strength is applied to the measuring chamber (2). The thermal conductivity of the gas sample (Gp) and the magnetically modulated thermal conductivity of the gas sample in the measuring chamber (2) are measured. The three concentrations of the three gas components are determined using predetermined densities of the three gas components, as well as the measured thermal conductivity, the measured magnetically modulated thermal conductivity, and the measured density.

Description

[0001] The invention relates to a sensor arrangement and a measuring method for measuring the respective concentration of three gas components of a gas sample.

[0002] The task of measuring the respective concentrations of several gas components in a gas sample arises, for example, during artificial respiration of a patient. A ventilator delivers a gas mixture to a patient-side coupling unit, for example, a breathing mask or a tube, with the patient-side coupling unit connected to the patient. The gas mixture contains oxygen and, in one embodiment, at least one anesthetic (anesthetic gas).

[0003] A method and device for measuring the oxygen concentration and the anesthetic concentration are described in DE 10 2021 126 106 A1. A magnetic field with an oscillating magnetic field strength is generated in a measuring chamber. The thermal conductivity and the magnetically modulated thermal conductivity of the gas mixture are measured. The fact that oxygen is a paramagnetic gas is utilized.

[0004] The invention is based on the object of providing a sensor arrangement and a measuring method which are capable of measuring the respective concentration of three gas components of a gas sample, with a higher reliability than known sensor arrangements and measuring methods.

[0005] The object is achieved by a sensor arrangement having the features of claim 1 and by a measuring method having the features of claim 5. Advantageous embodiments of the sensor arrangement according to the invention are, where appropriate, also advantageous embodiments of the measuring method according to the invention, and vice versa.

[0006] The sensor arrangement and the measuring method according to the invention are capable of measuring the respective concentration of three gas components of a gas sample. "Concentration" is preferably understood to mean the respective proportion in vol%. The respective density and thermal conductivity of each of the three gas components are predetermined. For example, the sensor arrangement has at least temporary read access to a data storage device in which the densities and thermal conductivities are stored. One gas component of the gas sample is a paramagnetic gas, in particular oxygen.

[0007] The sensor arrangement comprises a measuring chamber, a thermal conductivity sensor, and a density sensor. The measuring chamber is capable of accommodating a gas sample. The thermal conductivity sensor is capable of measuring the thermal conductivity of the gas sample. The density sensor is capable of measuring the density of the gas sample. The measuring method according to the invention is carried out using such a sensor arrangement.

[0008] The measuring method according to the invention further comprises the following steps, and the sensor arrangement according to the invention is designed to carry out the following steps: - The gas sample is fed into the measuring chamber. - A magnetic field with an oscillating magnetic field strength is applied to the measuring chamber. - A measure of the magnetically modulated thermal conductivity of the gas sample in the measuring chamber is measured.

[0009] The "magnetically modulated thermal conductivity" of the gas sample refers to the portion of the thermal conductivity that oscillates depending on the magnetic field strength. This magnetically modulated thermal conductivity depends significantly, but usually not exclusively, on the concentration of the paramagnetic gas in the gas sample. It is possible that a measure of the thermal conductivity exhibited by the gas sample in the measuring chamber is measured as a measure of the (total) thermal conductivity of the gas sample. It is possible that the same thermal conductivity sensor measures both the thermal conductivity and the magnetically modulated thermal conductivity, thus providing two independent signals. It is also possible that two different thermal conductivity sensors are used.

[0010] The three gas component concentrations are determined using the following information: - the given densities of the three gas components, - the given thermal conductivities of the three gas components, - the measured thermal conductivity of the gas sample, - the measured magnetically modulated thermal conductivity of the gas sample and - the measured density of the gas sample, - optionally also the temperature of the gas sample, - optionally also the pressure under which the gas sample is.

[0011] According to the invention, three different properties of the gas sample are measured: thermal conductivity, magnetically modulated thermal conductivity, and density. These three properties of the gas sample generally depend on the concentrations of the three gas components in the gas sample, but are not dependent on each other. In particular, these three properties generally change independently of each other. Using these three independent properties, three unknowns can be determined: the three desired concentrations of the three gas components.

[0012] The invention does not require that the gas sample consist only of these three gas components. Rather, the gas sample may contain at least one additional gas component. To determine its concentration, the fact that the sum of the concentrations of the gas components, measured in vol% or wt%, is 100% can often be exploited.

[0013] In some applications, the concentration of the paramagnetic gas is primarily required, with the paramagnetic gas being oxygen in particular. Some known sensor arrangements and measurement methods are also capable of measuring the oxygen concentration in a gas sample, but exhibit a relatively high, undesirable cross-sensitivity to other components of the gas sample. The sensor arrangement and measurement method according to the invention, in contrast, are significantly less cross-sensitive, ideally not at all, to other gas components.

[0014] Thanks to the invention, in many cases it is not necessary to provide a reference gas with a known composition, while the sensor arrangement and the measuring method measure the gas component concentrations.

[0015] Electrochemical sensors have become well known. In an electrochemical sensor, a chemical process takes place that depends on the concentration of oxygen and / or another gas component in the gas sample. A detection quantity sensor of the electrochemical sensor measures an electrical detection quantity that correlates with the desired oxygen concentration. In some cases, such electrochemical sensors have the disadvantage of requiring a chemical, which is consumed over time and therefore must be replenished from time to time. The invention does not require a chemical and therefore avoids this disadvantage.

[0016] In one application, the paramagnetic gas component is oxygen. The two other gas components whose concentrations are measured according to the invention in this application are an anesthetic (an anesthetic gas) and argon. The noble gas argon occurs in the ambient air at a known concentration. However, the concentration of argon in the gas sample is in many cases higher than the known concentration of argon in the ambient air. This situation occurs particularly in the following application: The gas sample comes from a gas mixture that is used for artificial ventilation of a patient. The gas mixture is produced using ambient air, but has a higher oxygen content than ambient air. A so-called concentrator is used to generate the gas mixture.If a gas mixture with a higher oxygen content than ambient air is produced by means of a concentrator, the produced gas mixture usually also has a higher concentration of argon than the ambient air.

[0017] Preferably, the sensor arrangement is capable of simultaneously measuring both the thermal conductivity and the magnetically modulated thermal conductivity of a gas sample in the same measuring chamber. In one embodiment, the sensor arrangement comprises a heating element and is capable of heating the heating element, in particular by applying an electrical voltage to the heating element. When the heating element is heated, it supplies thermal energy to a gas sample in the measuring chamber. Preferably, this heating element does not react chemically with the gas sample in the measuring chamber.

[0018] According to the invention, a magnetic field with an oscillating magnetic field strength is applied to the measuring chamber. The thermal conductivity and the magnetically modulated thermal conductivity are measured in this measuring chamber. Preferably, an electrical detection variable is measured. This electrical detection variable correlates with the thermal conductivity of the gas sample in the measuring chamber. Electrical or electronic filtering of the electrical detection variable is performed. This filtering produces two signals: an oscillating signal and a further signal. The oscillating signal oscillates depending on the magnetic field strength. The temporal progression of the further signal does not depend on the oscillating magnetic field strength. The oscillating signal is used as the measure of, or as a measure of, the magnetically modulated thermal conductivity. The oscillating signal thus correlates with the concentration of the paramagnetic gas in the gas sample.The further signal is used as the or a measure of the thermal conductivity of the gas sample.

[0019] This design often results in a particularly compact sensor arrangement. In the same measuring chamber, two independent properties of the gas sample are measured using the same heated heating element: thermal conductivity and magnetically modulated thermal conductivity.

[0020] Various designs are possible for measuring the density of the gas sample. In one design, a mechanical or electronic flexural resonator is used. This flexural resonator comprises an oscillating body. In the case of a mechanical flexural resonator, this oscillating body is a movably mounted fluid guide unit. A "fluid guide unit" is understood to be a component that guides a fluid along a trajectory, whereby this trajectory is predetermined by the design and arrangement of the component. A corrugated hose, a smooth hose, and a tube are examples of a fluid guide unit. The fluid guide unit does not necessarily comprise a delivery unit. In the case of an electronic flexural resonator, this oscillating body is preferably a quartz crystal.

[0021] The gas sample is passed through the fluid guide unit of the oscillating U-tube or past the quartz crystal. The U-tube causes the oscillating body (fluid guide unit or quartz crystal) to oscillate while a portion of the gas sample remains in the fluid guide unit, is passed past the oscillating body, or surrounds the oscillating body. The natural frequency of the oscillating body is measured. This measured natural frequency correlates with the mass of the gas sample.

[0022] In the case of a mechanical flexural oscillator, the natural frequency correlates with the mass of the filled fluid guide unit. Typically, this mass is the sum of the mass of the empty fluid guide unit and the desired mass of the gas sample in the fluid guide unit. The mass of the empty fluid guide unit is known from the design of the flexural oscillator and does not change. The volume of the fluid guide unit is also known from the design and remains constant. The desired density of the gas sample can be derived from the measured natural frequency as well as the mass and volume of the empty fluid guide unit.

[0023] The principle of such a U-shaped oscillator has been known for a long time, and reliable U-shaped oscillators for density measurement are available.

[0024] In one embodiment, the concentration of at least a fourth gas component of the gas sample is measured directly. The respective concentration of the or each fourth gas component of the gas sample is used for the step of determining the respective concentration of the three gas components. This embodiment often increases the reliability with which the three concentrations of the three gas components are determined.

[0025] In one implementation of this embodiment, the concentration of the or at least one fourth gas component is measured by a sensor that applies the following well-known principle: - A radiation source emits electromagnetic radiation, or sound or ultrasound, into a measuring section or measuring chamber with a sufficiently broad bandwidth. The gas sample flows through this measuring section or is located in this measuring chamber. The measuring chamber can be the measuring chamber with the magnetic field strength just described or another measuring chamber located at a distance. - The electromagnetic radiation or sound penetrates the measuring section or the measuring chamber. - The gas sample in the measuring section or measuring chamber absorbs part of the radiation or sound. - A detector measures the intensity of the incident radiation or sound. This intensity correlates with the desired concentration of the fourth gas component. - The detector generates a signal depending on the measured intensity. This signal correlates with the intensity and therefore also with the concentration of the fourth gas component.

[0026] Many gases exhibit a characteristic spectral absorption curve, i.e. a characteristic dependence of the degree of absorption on the wavelength of the electromagnetic radiation or sound that penetrates this gas.

[0027] According to the invention, three properties of the gas sample are measured to determine values ​​for three unknowns, namely one value each for the three desired concentrations of the three gas components. In one embodiment, three functional relationships, three distance measures, and a target function are specified. Preferably, the sensor arrangement according to the invention has at least temporary read access to a data memory in which the target function, the distance measures, and the functional relationships are stored in a computer-analyzable form.

[0028] The first functional relationship describes the thermal conductivity as a function of the three gas component concentrations. The second functional relationship describes the magnetically modulated thermal conductivity as a function of the three gas component concentrations. The third functional relationship describes the density of the gas sample as a function of the three gas component concentrations. All three functional relationships therefore depend on the three unknown and desired gas component concentrations.

[0029] The first distance measure describes a measure of the distance between the measured thermal conductivity and the thermal conductivity derived using the first functional relationship. The second distance measure describes a measure of the distance between the measured magnetically modulated thermal conductivity and the magnetically modulated thermal conductivity derived using the second functional relationship. The third distance measure describes a measure of the distance between the measured density and the density derived using the third functional relationship. Preferably, each distance measure is the square of the respective difference, or alternatively, the absolute value of the difference.

[0030] The objective function is an aggregation of these three distance measures. Preferably, the objective function is a weighted average of the three distance measures. The weighting factors compensate, for example, for different magnitudes of the three properties: thermal conductivity, magnetically modulated thermal conductivity, and density. It is also possible for the weighting factors to additionally or instead take into account different accuracy requirements for the desired gas component concentrations.

[0031] The three measured values ​​for the gas sample—the measured thermal conductivity, the magnetically modulated thermal conductivity, and the density of the gas sample—are inserted into the objective function. After insertion, the objective function depends on three unknowns, namely the three desired gas component concentrations. The objective function is minimized numerically. This means that different triplet values ​​for the three gas component concentrations are used on a trial basis. Each triplet assigns a value to each of the three concentrations. The triplet or triplet values ​​that result in a minimum value of the objective function yields the three desired gas component concentrations. Ideally, the minimizing triplet yields the value zero for the objective function. In practice, there is always a discrepancy between the measured property and the property predicted based on the functional relationship.

[0032] It is possible that the objective function has several minima.

[0033] It is possible that the concentration of a fourth gas component also occurs in at least one functional context. In one implementation, a sensor directly measures the concentration of this fourth gas component, for example, using the measuring principle described above, comprising a radiation source and a detector. In another implementation, a standard value is specified for the concentration of the fourth gas component. It is possible that there is another, i.e., a fifth, gas component whose concentration is measured or for which a standard value is specified.

[0034] The invention further relates to a ventilation arrangement and a ventilation method for artificially respirating a patient. The ventilation arrangement comprises - a medical device, in particular a ventilator, - a patient-side coupling unit, - a ventilation control unit and - a sensor arrangement according to the invention.

[0035] The ventilation procedure is carried out using such a ventilation arrangement.

[0036] The patient is connected to the patient-side coupling unit or can be connected at least temporarily to a patient-side coupling unit. The patient-side coupling unit comprises, in particular, a breathing mask and / or a tube and / or a catheter. The ventilation arrangement is capable of conducting and / or conveying a gas mixture from the medical device to the patient-side coupling unit. The concentration of at least one gas component of the gas mixture, in particular that of oxygen, should be within a predetermined target range. It is possible for this target range to vary over time. It is also possible for a target range to be specified for at least two gas components.

[0037] The ventilation arrangement is designed to perform the following steps and the ventilation method comprises the following steps: - A gas sample is taken from the gas mixture that is delivered to the patient-side coupling unit. - The branched gas sample is directed to the sensor assembly. - The sensor arrangement measures the concentration of the or each gas component for which a target range is specified in the branched gas sample.

[0038] The ventilation control unit performs closed-loop or open-loop control. The controlled variable is the actual concentration of the gas component in the gas mixture supplied to the patient-side coupling unit. The control objective of the control or open-loop control is to ensure that the controlled variable, i.e., the actual gas component concentration, lies within the specified target range. For the control or open-loop control, the ventilation control unit uses the gas component concentration in the branched gas sample, which the sensor array has measured.

[0039] The invention is described below using an exemplary embodiment. Fig. 1 schematically shows a ventilation circuit for artificial ventilation of a patient; Fig. Figure 2 schematically shows a first embodiment of a sensor capable of measuring the concentration of oxygen and another gas; Fig. 3 schematically shows a second embodiment of such a sensor; Fig. 4 the measuring unit of the sensor of Fig. 3; Fig. 5 an exemplary evaluation circuit of the sensor of Fig. 2 and from Fig. 3; Fig. 6 a mechanical flexural oscillator used to measure the density of the gas sample; Fig. 7 an electronic flexural oscillator in the form of a quartz crystal, with which the density of the gas sample is measured; Fig. 8 shows the magnetically modulated thermal conductivity λ 2fof a gas mixture as a function of oxygen concentration.

[0040] In the exemplary embodiment, the sensor arrangement according to the invention is used for artificial respiration of a patient. The patient is supplied with a gas mixture comprising oxygen and at least one anesthetic. The patient is therefore anesthetized or at least sedated.

[0041] Fig. 1 schematically shows a ventilation arrangement 200 with a schematically shown ventilator 1, wherein the ventilation arrangement 200 is capable of artificially ventilating a patient P. Only the face of the patient P is shown schematically. The ventilator 1 maintains a ventilation circuit 40. In the example shown, the ventilator 1 is configured as an anesthesia device, and the patient P is anesthetized or at least sedated.

[0042] In the ventilation circuit 40, a gas mixture Gg is supplied to the patient P. In the exemplary embodiment, this gas mixture Gg comprises oxygen (O2), at least one anesthetic, and optionally a carrier gas for an anesthetic, e.g., nitrous oxide (N2O). An anesthetic vaporizer 31 generates a fluid stream 28 containing vaporous anesthetic. The fluid stream 28 is fed into the ventilation circuit 40. In addition, a fluid stream 27 of fresh air or other fresh gas is fed in. At least as long as there is no excessive overpressure in the ventilation circuit 40, the air exhaled by the patient P remains in the ventilation circuit 40, so that no anesthetic escapes into the environment.

[0043] The gas mixture Gg flowing through the ventilation circuit 40 inevitably contains carbon dioxide (CO2) exhaled by the patient P. A carbon dioxide absorber (CO2 absorber) 25a can absorb carbon dioxide from the ventilation circuit 40. In addition, this gas mixture Gg may contain other components that also occur in the ambient air, albeit possibly at a different concentration than in the ambient air.

[0044] A patient-side coupling unit 21, shown only schematically, such as a mouthpiece, a breathing mask, or a tube, connects the patient P to the ventilation circuit 40. The patient-side coupling unit 21 is connected to a Y-piece 22. The Y-piece 22 is connected to a breathing gas line 32 for inspiration and to a breathing gas line 33 for expiration.

[0045] A pump 24a draws in breathing gas and generates a permanent flow of breathing air through the inhalation breathing gas line 32 to the Y-piece 22 and to the patient-side coupling unit 21 and thus to the patient P. The ventilation circuit 40 is kept running by the pump 24a and optionally by a breathing bag 26, which can be operated manually.

[0046] A non-return valve 23a allows gas flow through the inhalation breathing gas line 32 toward the Y-piece 22 and blocks gas flow in the reverse direction. A non-return valve 23b allows gas flow through the exhalation breathing gas line 33 away from the Y-piece 22 and blocks gas flow in the reverse direction.

[0047] In the exemplary embodiment, the pump 24a continuously delivers the gas mixture Gg. A controllable PEEP valve 24b (PEEP = "positive end-expiratory pressure"), depending on its position, allows or blocks the air flow generated by the pump 24a, thereby contributing to the generation of the individual ventilation strokes and determining the amplitudes and frequencies of these ventilation strokes. The PEEP valve 24b also ensures that a sufficiently high air pressure is maintained in the lungs of the patient P, even at the end of exhalation or during a brief opening or interruption of the ventilation circuit 40. This reduces the risk of the patient P's lung collapsing due to insufficient pressure.

[0048] A pressure relief valve 29 is capable of reducing excess pressure in the ventilation circuit 40 by causing gas to escape from the ventilation circuit 40 if the pressure is too high. Preferably, the released gas is discharged into a line for anesthetic gas and enters a processor (not shown).

[0049] A signal-processing ventilation control unit 35, shown only schematically, receives a signal from a pressure sensor 58, which measures the air pressure P amb in the environment of the anesthesia machine 1 and thus of the ventilation circuit 40, and a signal from an optional temperature sensor 39, which measures the ambient temperature. Furthermore, the ventilation control unit 35 receives measured values ​​from a pressure sensor 36, which measures the current pressure in the ventilation circuit 40, for example, the ventilation pressure applied to the patient P (pressure in airway, P aw), in a configuration as differential pressure relative to the ambient pressure P amb The ventilation control unit 35 controls the pump 24a, the PEEP valve 24b, the anesthetic vaporizer 31, and other components of the ventilation circuit 40 in order to realize the desired artificial ventilation and anesthesia of the patient P.

[0050] It is often desired that the gas mixture Gg supplied to the patient P fulfill a specific property. In particular, the concentration of a component of the gas mixture Gg should be within a specified target range. In particular, the proportion of pure oxygen (O2) should often be within a specified target range, for example, between 40 vol% and 50 vol% or between 25 vol% and 30 vol%. Or the proportion of anesthetic should be within a specified range. In the following, the term "concentration" of a gas component in a gas mixture is used. A synonymous term is "proportion".

[0051] For this purpose, a sample of respiratory gas (hereinafter: a gas sample Gp) is taken (branched off) from the gas mixture Gg via a gas sample fluid guide unit in the form of a sampling tube 52 from the ventilation circuit 40, analyzed, and fed back into the ventilation circuit 40 via a discharge tube 56. The sampling tube 52 begins at a branching point 34 between the patient-side coupling unit 21 and the Y-piece 22. Thus, a gas mixture from line 22 and a gas mixture for line 33 temporarily enter the sampling tube 52. At the branching point 34 there is an optional valve (not shown), which in the closed position separates the sampling tube 52 from the ventilation circuit 40 and which can be controlled by the ventilation control unit 35. When the valve is fully open or omitted, the sampling tube 52 is in unrestricted fluid communication with the ventilation circuit 40.The discharge hose 56 leads to an inlet point 37 upstream of the carbon dioxide absorber 25a.

[0052] The sampling tube 52 guides the gas sample Gp to a sensor arrangement 50. This sensor arrangement 50 is spatially removed from the patient-side coupling unit 21 and from the lines 32 and 33 and also belongs, for example, to the schematically shown ventilator 1. In Fig.1, the sensor arrangement 50 is shown outside the ventilator 1 for clarity. In this exemplary embodiment, the sensor arrangement 50 comprises a pump 55, which sucks the gas sample Gp from the ventilation circuit 40 and draws it in through the extraction tube 52. The pump 55 preferably generates a permanent negative pressure on the side facing the extraction tube 52 and a permanent positive pressure on the side facing the discharge tube 56. The pump 55 is capable of generating a volume flow that is preferably constant over time and is, for example, 200 ml / min. A water trap 51 is arranged at the inlet of the sensor arrangement 50, wherein moisture is condensed and collected in the water trap 51. This reduces the water content in the gas sample Gp.

[0053] A sensor 54 is capable of generating signals, the signals correlating with the respective concentrations of CO2 and N2O in the extracted gas sample Gp. This sensor 54 preferably comprises an infrared measuring head that utilizes the dipole moment of molecules in the gas sample Gp and quantitatively evaluates the absorption of infrared-active gases to determine the respective concentration. Preferably, the sensor 54 comprises a radiation source that emits electromagnetic radiation and a detector that measures the intensity of incident electromagnetic radiation and generates a corresponding signal.

[0054] A sensor 53 is capable of generating a signal which correlates, among other things, with the concentration of O2 or another parametric component of the gas sample Gp. The sensor 53 is described below with reference to Fig. 2 to Fig. 5 described in more detail.

[0055] In addition, the sensor arrangement 50 comprises a pressure sensor 57 which measures the pressure P cell of the gas sample Gp at the inlet of the sensor arrangement 50. This pressure P cell is temporally variable because the pressure in the ventilation circuit 40 varies and because the sampling tube 52 is in fluid communication with the ventilation circuit 40 when there is no valve at the branch point 34 or as long as the optional valve at the branch point 34 is open. If the valve is missing or open, the pressure in the ventilation circuit 40 propagates to the sensor assembly 50 at approximately the speed of sound.

[0056] A density sensor 59, 60 measures a measure of the density of the gas sample Gp flowing through the sensor assembly 50. This density sensor 59, 60 is described below with reference to Fig. 6 and Fig. 7. In the example of Fig. 1, the density sensor 59, 60 is arranged parallel to the sensors 53, 54, 57.

[0057] It is also possible that the sensors 53, 54, 57 are arranged in series with the density sensor 59, 60 and the branched gas sample Gp flows through all four sensors.

[0058] The sensor assembly 50, the water trap 51, the signal processing unit 30, and the tubes 52 and 56 together belong to a measuring system 100, which extracts the gas sample from the ventilation circuit 40, examines it, and feeds it back into the ventilation circuit 40. The measuring system 100 belongs to the ventilation assembly 200.

[0059] Fig. Figure 2 shows, by way of example, a sensor 53 capable of measuring the respective concentrations of oxygen (O2) and another gas in the gas sample Gp. This sensor 53 exploits the fact that oxygen is a paramagnetic gas.

[0060] Two pole pieces 6, 7 and two field coils 4, 5 generate a magnetic field. An air gap 3 exists between the two pole pieces 6, 7, which functions as a measuring chamber 2. This measuring chamber 2 is defined by the two pole pieces 6, 7 and a wall 9. An inlet 10 and an outlet 11 are embedded in the wall 9.

[0061] A thermocouple 8 is attached to two support wires 15, 16 at two junctions 12 and 14, wherein the two support wires 15, 16 are passed through the lower pole piece 7 and are in thermal contact with the lower pole piece 7. The thermocouple 8 comprises two wires 17, 18 that are connected to one another at a junction 13. A voltage source 20 applies an alternating voltage to the two support wires 15, 16 and thus to the thermocouple 8. This heats the thermocouple 8 to a working temperature that is greater than the temperature of the gas sample Gp in the measuring chamber 2. A voltage U is measured across a measuring resistor 19. This voltage U contains an alternating voltage component and a direct voltage component.

[0062] The current operating temperature of thermocouple 8 is measured at junction 13. This temperature depends, on the one hand, on the voltage U that occurs between support wires 15, 16, and, on the other hand, on the thermal conductivity of the gas sample Gp in measuring chamber 2. Closed-loop control is implemented with the goal of maintaining the operating temperature of thermocouple 8 at a constant value. The manipulated variable is the time-varying voltage U that voltage source 20 applies to support wires 15, 16. Because the temperature of thermocouple 8 ideally remains constant, an electrical detection variable of thermocouple 8 correlates with the thermal conductivity of the gas sample Gp in measuring chamber 2.

[0063] One implementation for measuring the detection quantity is as follows: The time-varying electrical power supplied to the thermocouple 8 is measured as the detection quantity. The two support wires 15 and 16 are electrically connected to each other by the electrical measuring resistor 19. The electrical voltage U occurring across this measuring resistor 19 is measured. In addition, a measure of the strength of the electrical current flowing through the thermocouple 8 is measured. As is well known, electrical power depends on the voltage and the current. It is also possible to use the electrical voltage U as the detection quantity.

[0064] A voltage source 43 is connected to one field coil 5 via a power amplifier 42, and the other field coil 4 is connected to electrical ground. The voltage source 43 outputs a sinusoidal electrical voltage. This voltage generates a sinusoidally varying magnetic field in the measuring chamber 2. The thermocouple 8, which is heated to a constant temperature, releases a quantity of heat per unit time to the gas sample Gp in the measuring chamber 2. This released quantity of heat per unit time correlates with the measured electrical power supplied to the thermocouple 8. Because the field strength of the magnetic field in the measuring chamber 2 oscillates periodically, the released quantity of heat per unit time also oscillates—assuming a paramagnetic gas is present in the measuring chamber 2 as part of the gas sample Gp. The detection quantity correlates with the thermal conductivity λ of the gas sample Gp.Using the detection variable, a signal oscillating depending on the oscillation of the magnetic field, for example, an alternating voltage, and a signal that does not oscillate or oscillates less, for example, a direct voltage, are generated. The oscillating signal correlates with the thermal conductivity of the paramagnetic part of the gas sample Gp and thus with the O2 concentration. This thermal conductivity is also referred to as the magnetically modulated thermal conductivity λ. 2f The other signal correlates with the (total) thermal conductivity λ of the entire gas sample Gp.

[0065] Fig. 3, Fig. 4 and Fig. 5 show a further embodiment of the sensor 53. The same reference numerals have the same meaning as in Fig. 2. The circuit of Fig. 5 can also be applied accordingly to the design according to Fig. 2 apply.

[0066] An electromagnet 62 with an electric coil 63 generates a time-varying magnetic field in the air gap 3, cf. Fig. 3. The gas sample Gp to be analyzed reaches this air gap 3. The temporal progression of the strength of the generated magnetic field is determined by controlling the coil 63. The strength of the magnetic field preferably has a sinusoidal progression. A measuring unit 64 is arranged in the air gap 3. This measuring unit is implemented as a chip, preferably as a semiconductor chip, manufactured, for example, using doped silicon.

[0067] Fig.Figure 4 shows the measuring unit 64 in detail. The measuring unit 64 comprises an electrically controllable heat conduction measuring element 65, an electrically controllable heating unit 66, and a membrane 67 in a frame 69. A gas sample Gp can reach the elements 65, 66 through holes in the membrane 67 or around the membrane 67. The heating unit 66 can be an electrically conductive resistance structure deposited on the membrane 67 or configured as a heating wire. Two heating elements of the heating unit 66 are shown, which are electrically connected to one another by a connecting element 68. The heat conduction measuring element 65 and the heating unit 66 can also be configured as a single-piece element having a temperature-dependent electrical resistance.

[0068] The heating unit 66 heats the measuring element 65 to a working temperature that is greater than the temperature of a gas sample Gp in the measuring chamber 2. The heated measuring element 65 measures the temperature at the measuring position 77. In the illustrated implementation, the measuring element 65 measures a thermoelectric voltage and utilizes the Seebeck effect. The thermal conductivity of the gas sample Gp at the measuring position 77 changes synchronously with the time-varying magnetic field generated by the electromagnet 62, provided that the gas sample Gp at the measuring position 77 contains a sufficiently high concentration of a paramagnetic gas. A higher thermal conductivity leads to better dissipation of the heat energy. This, in turn, results in a lower temperature, which in turn results in a lower thermoelectric voltage.

[0069] Fig. 5 shows an example of an evaluation circuit with the following components: - an amplifier 70 connected as an impedance converter, - a voltage divider 71 with variable tap, - a DC voltage source 72, - a low-pass filter 73 and - a high-pass filter 74 connected in parallel to the low-pass filter 73.

[0070] The heating unit 66 is connected to the DC voltage source 72 via the amplifier 70 and the voltage divider 71. The output signal of the heat conduction measuring element 65 is passed through the low-pass filter 73 and the high-pass filter 74. At the output of the high-pass filter 74, a signal 75 is present, which oscillates depending on the oscillation of the magnetic field. The signal 75 correlates with the magnetically modulated thermal conductivity λ. 2fand thus with the concentration of the paramagnetic gas, for example, the concentration of oxygen, in the gas sample Gp. At the output of the low-pass filter 73, a signal 76 is present that does not oscillate at all, or at least not synchronously, with the magnetic field oscillation. The signal 76 correlates with the thermal conductivity λ of the entire gas sample Gp.

[0071] Because the magnetic field strength oscillates, the amount of heat supplied per unit of time comprises a superposition of a temporally constant component and a periodically fluctuating component. The periodically fluctuating component correlates with the thermal conductivity and thus with the oxygen concentration in the measuring chamber 2. The constant component, i.e., the component that does not oscillate depending on the strength of the magnetic field, correlates with the thermal conductivity of the entire gas sample Gp in the measuring chamber 2. The thermal conductivity of the oxygen and the respective thermal conductivity of each other component of the gas sample Gp contribute to this thermal conductivity of the gas sample Gp. Both components are measured. Sensor 53 therefore delivers two signals: - a signal oscillating depending on the magnetic field strength, here periodically fluctuating, which is a measure of the concentration of oxygen or another paramagnetic gas in the measuring chamber 2 (periodically fluctuating component, alternating voltage), and - a signal for the thermal conductivity of the gas sample Gp in the measuring chamber 2, whereby this signal does not oscillate or at least does not oscillate depending on the magnetic field strength (constant component, DC voltage).

[0072] Optionally, a measured value for the concentration of a component and / or for the thermal conductivity λ is displayed on a display device 44, cf. Fig. 2.

[0073] According to the invention, a measure of the density of the gas sample Gp is ​​also measured. Fig. 6 shows schematically an embodiment of a density sensor 59 in the form of a mechanical flexural oscillator, Fig.7 shows an embodiment of a flexural oscillator 60, which is implemented as a quartz crystal. In one embodiment, the density sensor 59, 60 is connected in parallel with the sensor 53, which measures the thermal conductivity and the magnetically modulated thermal conductivity and which was described above with reference to Fig. 2 to Fig. 5. It is possible that the sensor 53 is implemented as a chip and the density sensor 60 is mounted on this chip and is supplied with electrical voltage by this chip.

[0074] The principle described below has been known for a long time, but not for the application described here. In the exemplary embodiment, the density sensor 59, 60 measures a measure of the density p of the gas sample Gp flowing through the sensor arrangement 50.

[0075] First, a mechanical flexural oscillator is designed with reference to Fig.6. The gas sample Gp, whose density p is to be measured, is passed through a U-shaped tube 80 with two legs 80.1, 80.2. The tube 80 is located in a housing 83 and is made of a material that can chemically withstand the components of the gas sample Gp, for example, glass or steel. The two legs 80.1, 80.2 of the tube 80 form the spring elements of a U-shaped oscillator. This principle is similar to that of a tuning fork. The two legs 80.1, 80.2 are clamped at a mounting point 81. A region B of the tube 80 can be set into vibration. This region B is also U-shaped, comprises a segment of each leg 80.1, 80.2, and is delimited by the mounting point 81.

[0076] In one implementation, tube 80 can be temporarily closed for the purpose of a measurement. In another implementation, the gas sample Gp flows through tube 80 even during the measurement.

[0077] A schematically shown actuator excites this flexural oscillator to undamped oscillations. In the illustrated embodiment, the actuator is implemented by two transducers 82.1, 82.2. Each transducer 82.1, 82.2 comprises a coil 83.1, 83.2 and a magnet 84.1, 84.2. In one mode, an alternating electrical voltage is applied to each transducer 82.1, 82.2. The transducer 82.1, 82.2 generates mechanical oscillations, and these mechanical oscillations are transmitted to the tube 80, preferably through a mechanical connection between the magnet 84.1, 84.2 and the tube 80.

[0078] The two legs 80.1, 80.2 span a plane. The two directions of the oscillations generated by the excitation are orthogonal to this plane. Region B is set into oscillation. Actuator 84 is then switched off. After this, region B continues to oscillate, namely after a transient phase at its natural frequency.

[0079] Region B of tube 80 and that portion of the gas sample Gp located within this region B participate in the oscillation. This oscillating system has a mass, which is the sum of the mass of region B and the mass of the gas sample portion in region B. The mass of region B is predetermined by the design and remains constant. The volume that region B provides for the gas sample Gp also remains constant. As a rule, the mass of that portion of the gas sample Gp located in region B can be considered constant during a measurement. The desired density p is then proportional to the mass of the gas sample portion.

[0080] Subsequently, the two converters 82.1, 82.2 are switched off. The system just described now oscillates at a natural frequency τ. This natural frequency τ depends on the mass of the system and is measured. In the implementation shown, the two converters 82.1, 82.2 function in a different mode after switching off and convert the mechanical vibrations of area B into an alternating voltage. The frequency of this alternating voltage is equal to the natural frequency τ of area B. An amplifier 85 amplifies this alternating voltage. An evaluation unit 86 receives a signal from amplifier 85 and provides the desired density p.

[0081] The desired density p is related to the measured natural frequency τ as follows: ρ=A*τ2−B.

[0082] A and B are two constants of the density sensor (flexural oscillator) 59. These two constants A and B are determined empirically in a previous calibration. For this purpose, two different gases with known and differing densities are passed through the density sensor 59, and the respective resulting natural frequency is measured.

[0083] Fig. Figure 7 schematically shows a flexural oscillator 60 in the form of a quartz crystal. This quartz crystal is shaped like a tuning fork with two legs 61.1 and 61.2. Fig. Figure 7A shows a schematic of this quartz oscillator. Electrodes are connected to this flexural oscillator 60 in such a way that two opposing fields occur in the x-direction. This forces a bending in the z-direction. Fig.Figure 7B illustrates the oscillations of these two legs 61.1 and 61.2, with the x-direction and z-direction in the plane of the drawing. A feedback effect ensures that the forced frequency is equal to the natural frequency τ.

[0084] Such a U-shaped oscillator 60 is described, for example, in Th. Voglhuber-Brunnmeier et al.: Fluid Sensing Using Quartz Tuning Forks - Measurement Technology and Applications, Sensors, Vol. 19 (2019) No. 10.

[0085] In one embodiment, the following relationship is used: ρ=[−B2A+(B2A)2+(τ−CA)2]2

[0086] Again, A, B, and C are device-specific constants that are determined in advance through calibration. Because three constants need to be determined, three different gases with known and differing densities are used for calibration.

[0087] As already explained, the sensor arrangement 50 is intended to measure the respective concentration (proportion) in vol% of oxygen and anesthetic (anesthetic gas) in the branched gas sample Gp. This gas sample Gp may contain other components that, without a suitable countermeasure, can distort this measurement. In particular, the noble gas argon (Ar) in the gas sample Gp can distort the measurement. As is known, the proportion of argon in the ambient air is approximately 0.93 vol%. However, the concentration of argon in the gas sample Gp can be significantly higher than that of argon in the ambient air.This situation occurs in particular when the concentration of oxygen in the breathing circuit 40 and therefore in the gas sample Gp is ​​greater than the concentration of oxygen in the ambient air, in particular when the gas mixture Gg is generated from ambient air and the oxygen concentration has been increased by means of a so-called oxygen concentrator.

[0088] In some situations, the measured argon concentration is also used by another sensor or other component of the anesthesia machine 1. For example, the measured argon concentration is compared with an upper limit. As soon as this upper limit for the argon concentration is reached, the ventilation circuit 40 is purged.

[0089] In the example, the gas sample Gp n contains various components, including nitrogen (N2), pure oxygen (O2), carbon dioxide (CO2), an anesthetic gas (A-gas), nitrous oxide (N2O), water (H2O), and argon (Ar). The respective density ρ(x i ) (i=1,...,n) and the respective thermal conductivity λ(x i ) of these components are known. Preferably, the sensor arrangement 50 has at least temporary read access to a data storage device in which the densities and thermal conductivities are stored. The following table shows, by way of example, the respective densities and thermal conductivities of components that occur or may occur in the gas sample Gp, wherein the density and thermal conductivity refer to an ambient temperature of 15 degrees C and an ambient pressure of 1 bar. Table 1 Thermal conductivity and density of various gas components Gas x i Density ρ(x i ) [g / dm 3 ] Thermal conductivity λ(x i ) [W / mK] Oxygen (O2) 1,336 0,02615 Nitrogen (N2) 1,169 0,02566 Carbon dioxide (CO2) 1,8474 0,01643 dry ambient air 1,209 0,02603 Water vapor 1 0,0199 Isofluran 7,701 0,00942 Nitrous oxide (N2O) 1,848 0,0173 Argon (Ar) 1,669 0,01782

[0090] The gas components have different densities. It can be seen that the anesthetic isoflurane, cited as an example, has a density several times greater than that of the other gas components.

[0091] As already explained, an optional pressure sensor 36 measures the pressure in the ventilation circuit 40. The optional pressure sensor 58 measures the pressure P amb in the environment, the optional temperature sensor 39 the ambient temperature, an optional pressure sensor 57 the pressure P cell the gas sample Gp at the inlet of the sensor arrangement 50. Optionally, the signal processing unit 30 uses signals from the sensors 36, 58 and / or 39 to derive the actual thermal conductivity and the actual density at the actual ambient temperature and the actual ambient pressure.

[0092] We are looking for the respective concentration ξ(x i ), i.e. the proportion in vol-% of each component x i (i=1,...,n).

[0093] In many cases it is true with sufficient accuracy that the density p of the gas sample Gp is ​​a weighted average of the respective densities ρ(x i ) of the n components, so that: ρ=ξ(x1)*ρ(x1)+…+ξ(xn)*ρ(xn).

[0094] The desired concentrations ξ(x1), ..., ξ(x n ) of the gas components x1, ..., x n act as the weighting factors.

[0095] Above, with reference to Fig. 2 to Fig. 5 a sensor 53 which measures a detection quantity that correlates with the thermal conductivity λ of the gas sample Gp. In the example of Fig. 2 this is a detection quantity of the thermocouple 8, in the example of Fig. 5 the signal 76. In many cases it is true with sufficient accuracy that the thermal conductivity λ of the gas sample Gp is ​​a weighted average of the respective thermal conductivities λ(x i ) of the components is: λ=ξ(x1)*λ(x1)+…+ξ(xn)*λ(xn).

[0096] The concentrations ξ(x1), ..., ξ(x n ) of the gas components x1, ..., x n act as the weighting factors.

[0097] It is also possible to use the following functional dependency: λ=∑i=1nλ(xi)1+∑k=1k#inG(i,k)ξ(xk)ξ(xi)

[0098] The factors G(i,k) (i=1,...,n; k=1,...,n) can be determined empirically in advance.

[0099] The sensor 53 is also capable of measuring the magnetically modulated thermal conductivity λ 2f of the gas sample Gp, for example using the periodic component of the detection variable of the embodiment according to Fig. 2 or using the oscillating signal 75 of the circuit of Fig. 5. Because O2 is a paramagnetic gas, λ 2f depends significantly on the O2 concentration ξ(O2). In general, the following functional dependence f can be applied: λ2f=f[ξ(O2),ξ(N2O),ξ(CO2),ξ(H2O),ξ(Ar),Temp,Pcell]

[0100] The functional dependence f is given. Temp denotes the ambient temperature, which is measured, for example, by temperature sensor 39. Typically, the temperature of the gas sample Gp does not differ significantly from the ambient temperature. The O2 concentration is approximately linear. The pressure P cell is measured, for example, by sensor 57.

[0101] Fig. Figure 8 shows an example of the magnetically modulated thermal conductivity λ 2f of a gas mixture as a function of the O2 concentration ξ(O2). In this case, the gas mixture consists only of oxygen and N2O. The x-axis represents the oxygen concentration ξ(O2) in the gas mixture in vol%, and the y-axis represents the magnetically modulated thermal conductivity λ 2f . It can be seen that the relationship λ 2f = λ 2f [ξ(O2)] is approximately linear, but not ideally linear.

[0102] Sensor 54 measures the CO2 concentration ξ(CO2) and the N2O concentration ξ(N2O). Pressure sensor 57 measures the pressure P cell A capacitive sensor (not shown) measures the H2O concentration ξ(H2O), i.e. the concentration of water vapor in the gas sample Gp. The density sensor 59, 60, described above with reference to Fig. 6 and Fig. 7, measures the density ρ of the gas sample Gp.

[0103] The CO2 concentration ξ(CO2), the N2O concentration ξ(N2O), and the water vapor concentration ξ(H2O) are measured directly. This leaves three unknowns: the O2 concentration ξ(O2), the anesthetic concentration ξ(A-gas), and the argon concentration ξ(Ar). To determine these three unknowns, the three equations (3), (4), and (6) are used. Together, a system of equations with three unknowns, namely ξ(O2), ξ(A-gas), and ξ(Ar), and three equations, namely (3), (4), and (6), are used.

[0104] In one implementation, three values ​​ξ(x1), ξ(x2) and ξ(x3) are calculated for the three unknowns ξ(O2), ξ(A-Gas) and ξ(Ar) in such a way that an objective function Z with Z[ξ(x1),ξ(x2),ξ(x3)]=α1*{ρmeas−ρ[ξ(x1),ξ(x2),ξ(x3)]}2+α2*{λmea s−λ[ξ(x1),ξ(x2),ξ(x3)]}2+α3*{λ2f,meas−λ2f[ξ(x1),ξ(x2),ξ(x3)]}2+ is minimized. Here, ρ meas the measured density, λ meas the measured thermal conductivity and λ 2f,meas the measured magnetically modulated thermal conductivity. ρ[ξ(x1),ξ(x2),ξ(x3)] denotes the density that occurs according to equation (3), λ[ξ(x1),ξ(x2),ξ(x3)] the thermal conductivity according to equation (4) or (5) and A 2f[ξ(x1),ξ(x2),ξ(x3)] is the magnetically modulated thermal conductivity according to equation (6). The three factors α1, α2, α3 are chosen so that all three summands of the objective function Z have the same order of magnitude and / or different accuracy requirements for the measurement of the three concentrations ξ(x1),ξ(x2),ξ(x3) are met. The sum of the three factors α1, α2, α3 is 1.

[0105] Obviously, the sum of the gas component shares is 1, so ξ(x1)+…+ξ(xn)=1.

[0106] Using equation (8) the N2 concentration ξ(N2) can be derived. List of reference symbols 1 anesthesia machine, part of the ventilation system 200 2 Measuring chamber of the sensor 53, formed in the air gap 3 3 Air gap, provides the measuring chamber 2 4, 5 field coils, together with the pole pieces 6, 7, generate a magnetic field in the measuring chamber 2 6, 7 pole pieces, together with the field coils 4, 5, generate a magnetic field in the measuring chamber 2 8 Thermocouple, includes wires 17, 18 and support wires 15, 16 9 Wall of the measuring chamber 2 10 Inlet to measuring chamber 2 11 Outlet from measuring chamber 2 12 Connection point between the support wire 15 and the wire 17 13 Connection point between wires 17 and 18 14 Connection point between the support wire 16 and the wire 18 15, 16 Support wires for the thermocouple 8 17, 18 wires of the thermocouple 8 are connected to each other in the junction 13 19 Measuring resistance of the thermocouple 8 20 Voltage source 21 Patient-side coupling unit in the form of a mouthpiece or a breathing mask, connected to the Y-piece 22 22 Y-piece, which connects the patient-side coupling unit 21 with a supply line for the supply of gas (inhalation, inspiration) and a discharge line for the discharge of gas (exhalation, expiration) 23a Check valve which allows a gas flow in the inhalation line 32 towards the patient P and blocks it in the opposite direction 23b Check valve that allows gas flow in the exhalation line 33 away from the patient P and blocks it in the direction of the patient P 24a Blower, which generates a volume flow towards the patient P 24b PEEP valve, which maintains pressure in the lungs of patient P 25a Carbon dioxide absorber, absorbs 40 carbon dioxide from the ventilation circuit 26 breathing bag, through which the ventilation circuit 40 can be driven 27 Fluid flow of fresh air or other fresh gas to the ventilation circuit 40 28 Fluid flow of vaporous anesthetic to the ventilation circuit 40, generated by the anesthetic vaporizer 31 29 adjustable pressure relief valve, which can release gas from the ventilation circuit 40 30 Signal processing unit for the sensor arrangement 50, evaluates signals from the sensors 53, 54, 57 and 58 31 Anesthetic vaporizer, generates the anesthetic stream 28 32 Breathing gas line for inhalation, connected to the Y-piece 22, has the check valve 23a 33 Breathing gas line for exhalation, connected to the Y-piece 22, has the check valve 23b 34 Branching point of the extraction hose 52 35 Ventilation control unit, controls the pump 24a and the anesthetic vaporizer 31, receives signals about the respective gas concentration and messages from the signal processing unit 30 36 Pressure sensor in the ventilation circuit 40, preferably measures the pressure P applied to the patient P aw 37 Junction point at which the discharge tube 56 opens into the ventilation circuit 40, arranged upstream of the carbon dioxide absorber 25a 39 Temperature sensor, measures the temperature in the environment of the anesthesia machine 1 40 Ventilation circuit through which patient P is artificially ventilated comprises the patient-side coupling unit 21, the Y-piece 22, the inhalation line 32 and the exhalation line 33 42 Power amplifier between the voltage source 43 and the field coil 5 43 Voltage source, outputs a sinusoidal electrical voltage 44 optional display device of the sensor 53 50 Sensor arrangement, includes the sensors 53, 54, 57, the pressure sensor 59, 60 and the pump 55 51 Water trap upstream of the sensor array 50 52 Sampling tube, through which the gas sample Gp is ​​taken from the ventilation circuit 40, begins at a branch point 34 between the patient-side coupling unit 21 and the Y-piece 22 and leads to the water trap 51 53 Oxygen concentration sensor 54 Sensor for the concentration of CO2, H2O and anesthetic in the gas sample Gp 55 Pump which sucks a gas sample Gp into the sampling tube 52 56 Drainage tube, connect the sensor assembly 50 to the ventilation circuit 40 57 Pressure sensor of the sensor arrangement 50, measures the pressure 58 Ambient pressure sensor P amb 59 mechanical flexural oscillator, which measures the density of the gas sample Gp, comprises the housing 83, the tube 80 with the legs 80.1, 80.2, the fastening point 81, the electromagnetic converter 82.1, 82.2, the actuator 84, the amplifier 85 and the evaluation unit 86 60 U-shaped quartz oscillators, comprising legs 61.1, 61.2 62 Electromagnet, generates a time-varying magnetic field in the air gap 3, includes the coil 63 63 electric coil of the electromagnet 62 64 Measuring unit, implemented as a chip, includes the heat conduction measuring element 65, the heating unit 66 and the membrane 67 65 electrically controllable heat conduction measuring element of the measuring unit 64 66 electrically controllable heating unit of the measuring unit 64 67 Membrane of the measuring unit 64 68 electrically conductive connecting element between the two heating elements of the heating unit 66 69 Frame of the measuring unit 64 70 amplifiers 71 voltage divider 72 DC voltage source 73 Low-pass filter, delivers the signal 76 at its output 74 High-pass filter, delivers the signal 75 at its output 75 Signal at the output of the high-pass filter 74, correlated with the concentration ξ(O2) of oxygen 76 Signal at the output of the low-pass filter 73, correlated with the thermal conductivity λ of the gas sample Gp 77 Measuring position of the measuring unit 64 80 U-shaped tube, has the two legs 80.1, 80.2, takes the gas sample Gp, is excited to oscillate 80.1, 80.2 Legs of the U-shaped tube 80 81 Fastening point at which the two legs 80.1, 80.2 are clamped 82.1, 82.2 electromagnetic converters, convert in one mode electrical alternating voltage into mechanical oscillations and in another mode mechanical oscillations into electrical alternating voltage, comprise the coils 83.1, 83.2 and the magnets 84.1, 84.2 83.1, 83.2 Coil of the converter 82.1, 82.2 84.1, 84.2 Magnet of the converter 82.1, 82.2 85 Density sensor amplifier 59 86 Evaluation unit of the density sensor 59 83 Housing of the density sensor 59, accommodates the tube 80 100 measuring system, comprises the sensor arrangement 50, the water trap 51, the signal processing unit 30 and the hoses 52 and 56 200 ventilation arrangement, includes the anesthesia machine 1, the measuring system 100, the patient-side coupling unit 21 and the breathing gas lines 32 and 33 G(i,k) empirically determined weight factors Gg Gas mixture which the anesthesia machine 1 delivers to the patient-side coupling unit 21 Gp gas sample is branched off from the ventilation circuit 40, passed through the sampling tube 52 to the sensor arrangement 50 and fed back into the ventilation circuit 40 through the discharge tube 56 λ Thermal conductivity of the gas sample Gp λ(x i ) Thermal conductivity of the gas component x i (i=1,...,n) of the gas sample Gp λ 2fmagnetically modulated thermal conductivity, is a measure of the oxygen concentration in the gas sample Gp λ2f(x i ) magnetically modulated thermal conductivity of the gas component x i (i=1,...,n) of the gas sample Gp n Number of gas components in the gas sample Gp P Patient who is artificially ventilated and is connected to the patient-side coupling unit 21 P amb Pressure in the vicinity of the ventilation arrangement 200, measured by the pressure sensor 58 P aw Pressure in the breathing gas line 32, measured by the pressure sensor 58 P cell Pressure of the gas sample Gp at the inlet of the sensor arrangement 50, measured by the pressure sensor 57 ρ Density of the gas sample Gp ρ(x i ) Density of the gas component x i (i=1,...,n) of the gas sample Gp ξ(x i ) Concentration in vol-% of the gas component x i (i=1,...,n) of the gas sample Gp x1, ..., xn Gas components of the gas sample Gp QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This 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

[0000] DE 10 2021 126 106 A1

[0003] Cited non-patent literature

[0000] Th. Voglhuber-Brunnmeier et al.: Fluid Sensing Using Quartz Tuning Forks - Measurement Technology and Applications, Sensors, Vol. 19 (2019) No. 10

[0084]

Claims

[1] Sensor arrangement (50) for measuring the respective concentration of three gas components of a gas sample (Gp), where the respective density and thermal conductivity of each gas component are specified, where one gas component (O2) is a paramagnetic gas, wherein the sensor arrangement (50) - a measuring chamber (2), - a thermal conductivity sensor (53) and - a density sensor (59, 60) includes, wherein the thermal conductivity sensor (53) is designed to measure a measure of the thermal conductivity (λ) of the gas sample (Gp), wherein the sensor arrangement (50) is designed to - to direct the gas sample (Gp) into the measuring chamber (2), - to apply a magnetic field with an oscillating magnetic field strength to the measuring chamber (2) and - a measure of the magnetically modulated thermal conductivity (λ 2f) of the gas sample (Gp) in the measuring chamber (2), where the magnetically modulated thermal conductivity (λ 2f ) is the part of the thermal conductivity of the gas sample (Gp) that oscillates depending on the magnetic field strength, wherein the density sensor (59, 60) is designed to measure a measure of the density (ρ) of the gas sample (Gp), and wherein the sensor arrangement (50) is designed to the three gas component concentrations using - the specified densities of the gas components, - the specified thermal conductivities of the gas components, - the measured thermal conductivity (λ), - the measured magnetically modulated thermal conductivity (λ 2f ) and - the measured density (ρ) to determine. [2] Sensor arrangement (50) according to claim 1, characterized by , that the sensor arrangement (50) comprises a heating unit (8, 66), wherein the heating unit (8, 66) is designed to supply heat energy to a gas sample (Gp) in the measuring chamber (2), wherein the sensor arrangement (50) is designed to - to measure an electrical detection quantity (U) which correlates with the thermal conductivity (λ) of the gas sample (Gp), and - by filtering the electrical detection quantity (U) to derive an oscillating signal (75) which oscillates depending on the magnetic field strength and a further signal (76) whose temporal course does not depend on the oscillating magnetic field strength, and wherein the sensor arrangement (50) is further configured to - the oscillating signal (75) as the measure of the magnetically modulated thermal conductivity (λ 2f ) and - use the further signal (76) as the measure of the thermal conductivity (λ). [3] Sensor arrangement (50) according to one of the preceding claims, characterized by , that the density sensor comprises a bending oscillator (59, 60) with an oscillating body (80, 61.1, 61.2), wherein the sensor arrangement (50) is designed to guide the gas sample (Gp) through or along the oscillating body (80, 61.1, 61.2), wherein the flexural oscillator (59, 60) is designed to - to set the oscillating bodies (80, 61.1, 61.2) into oscillation and - to measure a measure of the natural frequency of the oscillating body (80, 61.1, 61.2), and wherein the sensor arrangement (50) is designed to determine the density (ρ) of the gas sample (Gp) as a function of the measured natural frequency of the oscillating body (80, 61.1, 61.2). [4] Ventilation arrangement (200) for artificially respiration of a patient (P), wherein the ventilation arrangement (200) - a medical device (1), in particular a ventilator, - a patient-side coupling unit (21), - a ventilation control unit (35) and - comprises a sensor arrangement (50) according to one of the preceding claims, wherein the patient-side coupling unit (21) is connected to the patient (B) or at least temporarily connectable, wherein the ventilation arrangement (200) is designed to convey a gas mixture (Gg) from the medical device (1) to the patient-side coupling unit (21), wherein a target range for the concentration [ξ(O2)] of a gas component (O2) in the gas mixture (Gg) is specified, wherein the ventilation arrangement (200) is designed to - to branch off a gas sample (Gp) from the gas mixture (Gg) which is conveyed to the patient-side coupling unit (21) and - to guide the branched gas sample (Gp) to the sensor arrangement (50), wherein the sensor arrangement (50) is designed to measure the actual concentration [ξ(O2)] of the gas component (O2) for which the target range is specified in the branched gas sample (Gp), wherein the ventilation control device (35) is designed to - to regulate the concentration [ξ(O2)] of the gas component (O2) in the gas mixture (Gg) which is conveyed to the patient-side coupling unit (21), and - to use the measured gas component concentration [ξ(O2)] for the control, and where one control objective is that the actual gas component concentration [ξ(O2)] in the gas mixture (Gg) remains within the specified target range. [5] Measuring method for measuring the respective concentration of three gas components of a gas sample (Gp), where the respective density and thermal conductivity of each gas component are specified, where one gas component (O2) is a paramagnetic gas and wherein the measuring method comprises the steps of - a measure of the thermal conductivity of the gas sample (Gp) is measured and - a measure of the density of the gas sample (Gp) is measured, wherein the measuring method comprises the further steps of - the gas sample (Gp) is passed into a measuring chamber (2), - a magnetic field with an oscillating magnetic field strength is applied to the measuring chamber (2), - a measure of the magnetically modulated thermal conductivity (λ 2f ) of the gas sample (Gp) is measured in the measuring chamber (2) and where the magnetically modulated thermal conductivity (λ 2f ) is the part of the thermal conductivity of the gas sample (Gp) that oscillates depending on the magnetic field strength, and where the further step is carried out that the three gas component concentrations using - the specified densities of the gas components, - the specified thermal conductivities of the gas components, - the measured thermal conductivity (λ), - the measured magnetically modulated thermal conductivity (λ 2f ) and - the measured density (ρ) be determined. [6] Measuring method according to claim 5, characterized by , that as the thermal conductivity (λ) the thermal conductivity of the gas sample (Gp) is measured in the measuring chamber (2) and the measuring procedure includes the further steps that - a heating unit (8, 66) is heated, - the heated heating unit (8, 66) supplies heat energy to the gas sample (Gp) in the measuring chamber (2), - an electrical detection quantity (U) of the heated heating unit (8, 66) is measured, where the detection quantity (U) correlates with the thermal conductivity (λ) of the gas sample (Gp), and - by filtering the electrical detection quantity (U), an oscillating signal (75) which oscillates depending on the magnetic field strength and a further signal (76) whose temporal course does not depend on the oscillating magnetic field strength are derived, where - the oscillating signal (75) as the measure of the magnetically modulated thermal conductivity (λ 2f ) is used and - the further signal (76) is used as the measure of the thermal conductivity (λ). [7] Measuring method according to claim 5 or claim 6, characterized by , that the measuring procedure includes the further steps that - the gas sample (Gp) is passed through or along an oscillating body (80, 61.1, 62.2) of a flexural oscillator (59, 60), - the oscillating body (80, 61.1, 62.2) is set into oscillation and - the natural frequency of the oscillating body (80, 61.1, 62.2) is measured, wherein the density of the gas sample (Gp) is determined depending on the measured natural frequency of the oscillating body (80, 61.1, 61.2). [8] Measuring method according to one of claims 5 to 7, characterized by , that the thermal conductivity, the magnetically modulated thermal conductivity and / or the density of the gas sample (Gp) additionally depends on the concentration of a fourth gas component, wherein the density of the fourth gas component is predetermined and wherein the measuring method comprises the further steps that - a measure of the concentration of the fourth gas component is measured and - in the step of determining the respective concentration of the three gas components, the measured concentration of the fourth gas component is also used. [9] Measuring method according to claim 8, characterized by , that the step of measuring the concentration of the fourth gas component comprises the steps of - a radiation source emits electromagnetic radiation or sound, - the emitted electromagnetic radiation or sound penetrates the gas sample (Gp) and hits a detector, - the detector measures a measure of the intensity of the incident electromagnetic radiation or sound and - the detector generates a signal depending on the measured intensity, whereby the signal generated by the detector is used as the measure of the concentration of the fourth gas component. [10] Measuring method according to one of claims 5 to 9, characterized by , that three functional relationships, three distance measures and a target function are specified, where the first functional relationship describes the thermal conductivity (λ) as a function of the three gas component concentrations, where the second functional relationship is the magnetically modulated thermal conductivity (λ 2f ) as a function of the three gas component concentrations, where the third functional relationship describes the density (ρ) of the gas sample (Gp) as a function of the three gas component concentrations, where the first distance measure describes a measure of a distance between the measured thermal conductivity (λ) and the thermal conductivity derived using the first functional relationship, wherein the second distance measure is a measure of a distance between the measured magnetically modulated thermal conductivity (λ 2f ) and the magnetically modulated thermal conductivity, which is derived using the second functional relationship, where the third distance measure describes a measure of a distance between the measured density (ρ) of the gas sample (Gp) and the density derived using the third functional relationship, where the objective function is an aggregation, in particular a weighted mean, of the three distance measures and wherein the measuring method comprises the further steps of - the three measured values ​​for thermal conductivity (λ), magnetically modulated thermal conductivity (λ 2f ) and the gas sample density (ρ) are inserted into the objective function and - a triplet of values ​​for the three gas component concentrations is calculated in such a way that the objective function is minimized. [11] Measuring method according to one of claims 5 to 10, characterized by , that The three gas components whose concentrations are measured in the branched gas sample (Gp) are oxygen (O2), an anesthetic and argon. [12] Ventilation method for artificial ventilation of a patient (P), wherein the patient (P) is or is connected to a patient-side coupling unit (21) and wherein the ventilation method comprises the automatically performed steps of - a gas mixture (Gg) is conveyed from a medical device (1), in particular from a ventilator, to the patient-side coupling unit (21), - a target range for the concentration [ξ(O2)] of a gas component (O2) in the gas mixture (Gg) is specified, - a gas sample (Gp) is branched off from the gas mixture (Gg) which is conveyed to the patient-side coupling unit (21), - the actual concentration [ξ(O2)] of the gas component (O2) for which the target range is specified is measured, wherein a measuring method according to one of claims 5 to 11 is used for measuring the actual gas component concentration [ξ(O2)], and - the actual concentration [ξ(O2)] of the gas component (O2) in the gas mixture (Gg) is controlled with the control objective that the actual oxygen concentration lies within the specified target range, whereby the measured actual gas component concentration [ξ(O2)] in the branched gas sample (Gp) is used for the control. [13] Ventilation method according to claim 12, characterized by , that the gas mixture (Gg) is generated using ambient air, wherein the oxygen concentration is increased during the generation of the gas mixture (Gg) and where the three gas components whose concentrations are measured in the branched gas sample (Gp) Oxygen (O2), an anesthetic and argon. [14] Ventilation method according to claim 12 or claim 13, characterized by , that the gas mixture (Gg) is conveyed through a fluid guide unit (32) from the medical device (1) to the patient-side coupling unit (21) and the detection of the event that at least one gas component in the pumped gas mixture (Gg) is outside the target range specified for this gas component, triggers the step of flushing the fluid guide unit (32).

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