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MEASURING SYSTEM FOR DETERMINING GAS CONCENTRATIONS

20230114548 · 2023-04-13

    Inventors

    Cpc classification

    International classification

    Abstract

    A measurement system (100) determines gas concentrations in a gas mixture of a gas sample by utilizing thermal conductivities and paramagnetic effects of thermal conductivities in the gas mixture involving data sets (203). A circuit arrangement provides measured values with an AC signal component and with a DC signal component to a calculation and control unit (200). An oxygen concentration in the gas mixture of the gas sample is determined based on the standardized AC signal components and a concentration of another gas in the gas mixture of the gas sample is determined based on the standardized DC voltage signal components. Output signals are generated by the calculation and control unit, which indicate the determined oxygen concentration and the determined concentration of another gas in the gas mixture of the gas sample.

    Claims

    1. A measuring system for determining gas concentrations in a gas mixture, the measuring system comprising: a measuring device comprising: a measuring element in a measuring chamber; an electromagnet; and a coil, wherein the measuring element includes a membrane with a heating structure; a gas supply configured to supply a quantity of a gas mixture of a gas sample to the measuring element; a gas outlet; a circuit arrangement cooperating with the measuring device to heat the heating structure on the membrane of the measuring element and cooperating with the electromagnet and the coil of the measuring device to generate a magnetic field acting on the measuring element, wherein the circuit arrangement is configured to operate the measuring device with the measuring element and the electromagnet and the coil and is configured to provide measured values with an alternating voltage signal component and with a DC signal component to the calculation and control unit; a calculation and control unit configured to consider or compensate for environmental conditions and configured to provide a standardization of the AC voltage signal component and a standardization of the DC voltage signal component to a reference value to provide standardized AC voltage signal components and standardized DC signal components and is configured to determine an oxygen concentration in the gas mixture of the gas sample based on the standardized alternating voltage signal components and to determine a concentration of another gas in the gas mixture of the gas sample based on the standardized DC voltage signal components and is configured to generate output signals, which indicate the determined oxygen concentration and the determined concentration of another gas in the gas mixture of the gas sample.

    2. A measuring system according to claim 1, wherein the calculation and control unit is configured to determine the oxygen concentration, or determine the concentration of the further gas in the gas mixture of the gas sample, or both determine the oxygen concentration and determine the concentration of the further gas in the gas mixture of the gas sample based further on data sets previously determined in measurements, which represent a correlation of the signal curves to concentrations of the further gas and oxygen in the gas mixture of the gas sample.

    3. A measuring system according to claim 2, wherein the data sets are stored in the form of a data field or several data fields or are stored in the form of a function or assignment rule.

    4. A measuring system according to claim 1, wherein the calculation and control unit is configured to determine the oxygen concentration, or determine the concentration of the further gas in the gas mixture of the gas sample, or both determine the oxygen concentration and determine the concentration of the further gas in the gas mixture of the gas sample based further on a measured value of a pressure sensor, which indicates a pressure level in the gas mixture of the gas sample or based further on provided pressure level information with regard to a pressure level in the gas mixture of the gas sample or based further on both a measured value of a pressure sensor, which indicates a pressure level in the gas mixture of the gas sample and provided pressure level information with regard to a pressure level in the gas mixture of the gas sample.

    5. A measuring system according to claim 1, wherein the measuring device or the calculation and control unit or both the measuring device and the calculation and control unit is configured to heat the measuring chamber or the gas supply or both the measuring chamber and the gas supply.

    6. A measuring system according to claim 1, wherein the calculation and control unit is configured to determine the oxygen concentration, or determine the concentration of the further gas in the gas mixture of the gas sample, or both determine the oxygen concentration and determine the concentration of the further gas in the gas mixture of the gas sample based further on a measured value of a moisture sensor, which indicates a moisture situation in the gas mixture of the gas sample or based further on provided information with regard to moisture in the gas mixture of the gas sample or based further on a measured value of a temperature sensor, which indicates a temperature situation in the gas mixture of the gas sample or based further on provided information regarding a temperature in the gas mixture of the gas sample or based further on any combination of a measured value of a moisture sensor, which indicates a moisture situation in the gas mixture of the gas sample and provided information with regard to moisture in the gas mixture of the gas sample and a measured value of a temperature sensor, which indicates a temperature situation in the gas mixture of the gas sample and provided information regarding a temperature in the gas mixture of the gas sample.

    7. A measuring system according to claim 6, wherein the moisture sensor is arranged in a purge chamber of the measuring device.

    8. A measuring system according to claim 6, wherein: the moisture sensor comprises a reference temperature sensor; and the calculation and control unit is configured to standardize the measured value of the moisture sensor using the reference temperature sensor.

    9. A measuring system according to claim 7, wherein the purge chamber is arranged in a gas flow and in the measuring device at the measuring element or in relation to the measuring element and in relation to the gas flow such that the flowing gas mixture of the gas sample flows into and through the purge chamber after flowing around/over a surface of the membrane of the measuring element.

    10. A measuring system according to claim 7, wherein: at least one resistance measuring element is arranged in the purge chamber in a gas flow and another resistance measuring element is arranged behind a shadow element; and the calculation and control unit is configured to determine a flow condition based on the measured values of at least one resistance measuring element or both resistance measuring elements.

    11. A measuring system according to claim 4, wherein a sensor measuring unit is provided and is associated with the calculation and control unit to detect at least one of the measured values of the moisture sensor and is configured to provide the acquired measured values or data derived from measured values to the calculation and control unit.

    12. A measurement system according to claim 10, wherein the calculation and control unit is configured to determine, based on the data from the resistance measurement elements, whether a condition is present with a flow through the purge chamber with the gas mixture of the gas sample.

    13. A measuring system according to claim 12, wherein the calculation and control unit is configured to determine the oxygen concentration, or determine the concentration of the further gas in the gas mixture of the gas sample, or both determine the oxygen concentration and determine the concentration of the further gas in the gas mixture of the gas sample based on provided information regarding a gas composition of the gas mixture of the gas sample.

    14. A measuring system according to claim 1, wherein the calculation and control unit is configured to determine the oxygen concentration, or determine the concentration of the further gas in the gas mixture of the gas sample, or both determine the oxygen concentration and determine the concentration of the further gas in the gas mixture of the gas sample based further on information provided regarding a dosing state of a dosing system, information provided in relation to respiratory phases, information provided regarding operating conditions of an anesthesia device or ventilator.

    15. A measuring system according to claim 1, wherein: the measuring system is supplied with a gas sample of a gas mixture by means of a gas supply; the gas sample is: an expiratory gas sample from an expiratory feed line, or an inspiratory gas sample from an inspiratory feed line, or a near-patient gas sample from a near-patient connecting element (Y-piece) or an internal gas sample from a sampling point of the gas line; and the calculation and control unit is configured to determine gas concentrations of oxygen and of a further gas in the gas samples.

    16. A process for determining gas concentrations in a gas mixture of a gas sample using measured values with an alternating voltage signal component and with a direct voltage signal component, the process comprising the steps of: separating thermo-voltage signals into a DC voltage signal component and an AC voltage signal component; standardizing the AC voltage signal components and the DC voltage signal components to reference values converted into standardized AC voltage signal components and DC voltage signal components; pressure compensating the standardized alternating voltage signal components based on measured values of a pressure sensor or information indicating current pressure level in the gas mixture of the gas sample; determining an oxygen concentration in the gas mixture of the gas sample based on the AC signal components; determining an anesthetic gas concentration in the gas mixture of the gas sample based on the DC signal components; and providing an output signal, which indicates a concentration of a further gas and the oxygen concentration in the gas mixture of the gas sample.

    17. A process according to claim 16, wherein in one of the steps or in a further step a moisture compensation of the AC signal components and/or DC signal components is performed by including measured values of a moisture sensor or information indicating a moisture content in the gas mixture of the gas sample.

    18. A process according to claim 16, wherein in one of the steps or in a further step, a matching of heat-conducting and heat-dissipating properties of the measuring element is carried out.

    19. A process according to claim 16, wherein in a further step a pressure compensation of the DC signal components or of the standardized DC signal components is performed by including measured values of a pressure sensor or information indicating the current pressure level in the gas mixture of the gas sample.

    20. A process according to claim 16, wherein in a further step moisture and/or temperature compensation of the AC voltage signal components or of the standardized AC voltage signal components and/or of the DC voltage signal components or of the standardized DC voltage signal components is carried out.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0106] In the drawings:

    [0107] FIG. 1 is a schematic view showing a measuring device with an electromagnet having an air gap with a measuring element arranged therein;

    [0108] FIG. 2 is a schematic view showing a representation of the measuring element according to FIG. 1;

    [0109] FIG. 3a is a schematic view showing a first variant of an electronic circuit for controlling the measuring point of FIG. 2 with the supply of a constant electrical voltage;

    [0110] FIG. 3b is a schematic view showing a variant of an electronic circuit for controlling the measuring point with the supply of a constant electric current;

    [0111] FIG. 3c is a schematic view showing a variant of an electronic circuit for controlling the measuring point with the supply of a constant electrical power;

    [0112] FIG. 3d is a schematic view showing a variant of an electronic circuit in which the heating power is used for temperature control;

    [0113] FIG. 3e is a schematic view showing a variant of an electronic circuit in which the heating current is used for temperature control;

    [0114] FIG. 3f is a schematic view showing a variant of an electronic circuit in which the heating voltage is used for temperature control;

    [0115] FIG. 3g is a schematic view showing a variant of an electronic circuit in which the heating power is used as a heat conduction signal;

    [0116] FIG. 3h is a schematic view showing a variant of an electronic circuit in which the heating current is used as a heat conduction signal;

    [0117] FIG. 3i is a schematic view showing a variant of an electronic circuit in which the heating voltage is used as a heat conduction signal;

    [0118] FIG. 4 is a schematic view showing a variant of the electronic circuit according to FIG. 3a with further components for operating the measuring device according to FIG. 1 and FIG. 2 with elements for signal evaluation, calculation and for determining the concentration;

    [0119] FIG. 5 is a view showing diagrams of thermo-voltage signals with DC voltage signal components and AC voltage signal components;

    [0120] FIG. 6 is a schematic view showing how the measuring device can be supplemented with further sensor technology and how the measuring device is arranged in the measuring system with measuring chamber, purge chamber, gas guide, gas supply and gas outlet for gas flow, flowing over or around the measuring element;

    [0121] FIG. 7 is a flow diagram showing an exemplary procedure for operating the measuring system.

    DESCRIPTION OF PREFERRED EMBODIMENTS

    [0122] Referring to the drawings, FIG. 1 shows a measuring device 1 with an electromagnet 4 with an air gap 3, in which a measuring element 2 is arranged. The measuring device (or sensor) 1 is intended and suitably configured for the metrological detection of an oxygen concentration or the concentration of another paramagnetic gas in a gas sample.

    [0123] The gas guidance within the measuring device 1, for example in the form of designs of cuvettes or caverns (pockets), and also the gas guidance towards and away from the measuring device 1 is not shown in FIGS. 1 to 4 for reasons of clarity of the drawings. The measuring device 1 has a measuring element 2 which, in the case shown, is arranged in the air gap 3 of an electromagnet 4 provided with a coil 5, so that an electrically controllable magnetic field can be applied to the measuring point of the measuring element 2. Instead of the coil 5, in an alternative embodiment a permanent magnet (not shown) can also be provided, with the aid of which a constant magnetic field can be generated. The measuring device 1 is further configured to allow the gas to be analyzed to flow as a gas sample through the air gap 3 and past the measuring element 2.

    [0124] In FIG. 2 it is shown that the measuring element 2 has a measuring point with a heat conduction measuring unit 6, which is configured as a thermocouple (thermopile). The measuring element 2 may comprise one or more heat conduction measuring units 6. The measuring element 2 may comprise an at least partially perforated membrane 7 for the gas sample to enter from the upper side and/or the lower side. Preferably, however, a closed membrane 7 is used, the support frame of which has been removed, for example by etching, to the extent that the sample gas can pass under the membrane through the resulting gap. In order to allow access of the measuring gas to be analyzed to both sides of the measuring point 9, either the membrane 7 can be partially removed by etching, or the measuring element 2 is partially etched thinly in such a way that the gas access from the front is possible. Preferably, the magnetic field generated by the coil 5 is implemented as a pure alternating field with a time course symmetrical to the zero point. The time course is preferably sinusoidal, but may also have other shapes (for example triangular or stepped rectangular shape). The magnetic field may alternatively or additionally be controlled in amplitude. The amplitude control of the alternating magnetic field results in the advantage of being able to simultaneously reduce the electrical power for the measuring points at higher oxygen signal levels with the magnetization. However, a magnetization with a DC component is also conceivable, in which the modulated field component can be shifted on the magnetization characteristic. In order to keep the energy input for the magnetization low, the magnetic field may be generated at least partially with a permanent magnet. As can further be seen in FIG. 2, the measuring element 2 has an electrically controllable heating structure 8, which can be configured, for example, as an electrically conductive resistance structure arranged on the membrane or as a heating wire. Preferably, the heating structure 8 is configured to heat the membrane 7 of the measuring element 2 to a desired temperature. It should be noted that the thermal conduction measuring unit 6 and the heating structure 8 may be integrally configured, i.e. a resistive heating/measuring element in which temperature measurement is enabled using the temperature coefficient of the resistive material. Examples of such heating structures 8 may comprise heating wires or similar heating means with a temperature-dependent resistivity. Consequently, if technically feasible, the measuring units 6 and the associated heating structures 8 can also be replaced by integrated temperature-dependent structures.

    [0125] In the figures, for reasons of clarity, these temperature-dependent heating structures 8 are shown separately and simplified as a heat conduction measuring unit 6 and a heating structure 8, respectively. The aspects described in the following description of the figures regarding operation and signal evaluation predominantly refer to arrangements with one measuring point and one measuring unit 6 arranged on one measuring element 2, unless otherwise mentioned, these aspects are thereby also transferable to arrangements with more than one measuring point and more than one measuring unit 6 arranged on one measuring element 2. In the following, operation and control of the heating structures 8 on the measuring element 2 will be described. In the type of control as shown in FIGS. 3a, 3b, 3c, the measuring point 9 is operated with a constant heating voltage (FIG. 3a), with a constant heating current (FIG. 3b) or with a constant heating power (FIG. 3c), which are adapted to the respective thermal operating point of the heating structure 8, the required values being determined once in a reference gas, e.g. oxygen or air, and then kept constant (calibration). The measured values for the thermal conduction 20 of the gas flowing past the measuring point 9 and the resulting periodic oxygen signals 21 can be found here in the voltages of the thermal conduction measuring unit 6.

    [0126] FIGS. 3a to 3i show variants of the measuring device 1 with different circuit arrangements 101, 102, 103, 104, 105, 106, 107, 108, 109 for operating the measuring device 1. Identical elements in FIGS. 1, 2 and in FIGS. 3a, 3b, 3c, 3d, 3f, 3g 3h, 3i are designated by the same reference numerals in FIGS. 1, 2, 3a, 3b, 3c, 3d, 3f, 3g 3h, 3i.

    [0127] FIG. 3a shows a schematic representation of an electronic circuit arrangement 101 for an operation of the measuring element 2 according to FIG. 2. In the circuit arrangement 101, the magnetizing device is not shown for simplification of the representation, and also the connection of the measuring points, of the heating structure 8, of the measuring element 2 and of the heat conduction measuring unit 6 is only shown simplified and schematically. On the one hand, the operation of the measuring element 2 comprises the configuration of the way of heating the measuring element 2. The heating of the measuring element 2 can be carried out with a constant heating voltage, with a constant heating current or with a constant heating power. By way of example, a control system with constant heating voltage is described with reference to this FIG. 3a. The heating structure 8 is connected to a DC voltage source 12 via an amplifier 10 connected as an impedance converter and a voltage divider 11 with variable tap. The elements 10, 11, 12 together form a constant voltage source. The measured value of the thermal conductivity measuring unit 6 is passed for evaluation through a low-pass arrangement 13 and through a high-pass arrangement 14. An alternating voltage signal component 21 is provided at the output of the high-pass arrangement 14. A direct voltage signal component 20 is provided at the output of the low-pass arrangement 13. The AC signal component 21 in the measured value represents an oxygen concentration in the gas composition of the gas sample. The DC signal component 20 in the measured value represents a thermal conductivity of the gas composition of the gas sample. Simple filtering devices can be used to remove fluctuations in the oxygen concentration that occur periodically in the gas sample from the measured value. With such simple filter circuits, signal components superimposed on the measured value, which are caused by electromagnetic radiation, for example from the 230V AC/50 Hz supply voltage network, can also be eliminated. To determine the oxygen concentration, the resulting periodic alternating voltage signal component and the non-periodic direct voltage signal component are related to each other and evaluated; the process of evaluation is further described in the description of FIGS. 4 and 5.

    [0128] FIGS. 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i each show in schematic form further alternative embodiments 102, 103, 104, 105, 106, 107, 108, 109 of the electronic circuit arrangement 101 for operation of the measuring element 2 according to FIG. 2. Identical elements in FIGS. 1, 2 and in FIGS. 3a, 3b, 3c, 3d, 3f, 3g 3h, 3i are designated by the same reference numerals in FIGS. 1, 2, 3a, 3b, 3c, 3d, 3f, 3g 3h, 3i.

    [0129] The circuit configuration 102 of FIG. 3b, constant current control, differs from the configuration of FIG. 3a only in that the amplifier 10 is connected as a non-inverting amplifier, a portion of the output voltage of the amplifier being fed back to the inverting input of the amplifier through a voltage divider consisting of heater structure 8 and shunt 15. In the constant power control circuit 103 of FIG. 3c, the output (voltage) of the amplifier 10 connected to the first contact of the heating structure 8 is coupled to the first input of a multiplier 16, the second input (current) of which is connected to the second contact of the heating structure 8 via an inverting amplifier 17 and two series resistors. The output of the multiplier 16 is coupled to the inverting input of the amplifier 10. In the constant temperature control circuit 104 of FIG. 3d, the output (voltage) of the amplifier 10 connected to the first contact of the heating structure 8 is coupled to the first input of a multiplier 16, the second input (current) of which is connected to the second contact of the heating structure 8 via an inverting amplifier 17 and two series resistors. The output of the multiplier 16 is coupled to the low pass arrangement 13 and the high pass arrangement 14, which provide the DC and AC output signals. As shown in FIGS. 3d, 3e and 3f, during actuation the respective thermal operating points are controlled by circuit arrangements 104, 105, 106 to constant values independent of the gas composition. In this case, the output voltages of the heat conduction measuring unit 6 are used as controlled variables and heating voltages, heating currents, or heating powers are tracked. In this case, the carriers of the measured values are the required heating voltages 24, heating currents 23 and heating powers 22, respectively. FIGS. 3g, 3h, 3i show further possibilities of control with circuit arrangements 107, 108, 109, which represent combinations and variations of the aforementioned processes and circuit arrangements 101, 102, 103,104, 105,106 and combine the advantages of operation at constant temperature levels with comparatively simple (because slow) temperature control. Here, the output voltage of the heat conduction measuring unit 6 is used as the control variables, and the heating voltage, heating current, or heating power are tracked in such a way that the working temperatures are constant as a time average. The constant temperature averages produce stable measuring conditions, independent of the type of gas mixture, while the rapidly changing, modulation-related signals 25 (oxygen) remain directly measurable as temperature fluctuations without causing significant operating point shifts due to their lower amplitude. The control signals are conditioned using electronic low-pass arrangements in such a way that the temperature changes caused by the gas mixture (which are slower) are compensated without disturbing the faster periodic thermal conductivity changes (oxygen measured values) caused by the magnetic field.

    [0130] In FIG. 4, the circuit arrangement 101 according to FIG. 3a is included as an example in an embodiment of the measuring device 1 to form a measuring system 100 which is suitably configured for determining a concentration of oxygen in a respiratory gas mixture and at least one further gas, in particular a volatile anesthetic gas. Identical elements in FIGS. 1, 2, 3a, 3b, 3c, 3d, 3f, 3g 3h, 3i and in FIG. 4 are designated by the same reference numerals in FIGS. 1, 2, 3a, 3b, 3c, 3d, 3f, 3g 3h, 3i and in FIG. 4. A dashed demarcation line graphically separates the components known from FIG. 3a from other components. A calculation and control unit 200 is provided, in particular in the form of a multifunctional calculation and control unit 200, which can also have, in addition to a calculation module 207 with data memory 207 (RAM, ROM), further modules, such as magnetic field control 204, signal processing 205 with amplifier elements, filter circuits and analogue-to-digital converters and also a data interface 206. The calculation and control unit 200 is configured for measured value and signal acquisition 310, 320, 255, 20, 21, 25, with a sensor measuring unit 300 or is connected to a sensor measuring unit 300.

    [0131] The calculation and control unit 200 may include a magnetic field controller 204, which is responsible for driving the electromagnet 4 via control lines 244 and thus for generating a magnetic field as an alternating magnetic field with an excitation frequency if in the range of 1 Hz to 100 Hz. Exemplary excitation frequencies are about 7 Hz or even 15 Hz. The measured value of the heat conduction measuring unit 6 is passed for evaluation via a low-pass arrangement 13 and via a high-pass arrangement 14. An AC signal component 21 is provided at the output of the high-pass arrangement 14. At the output of the low-pass arrangement 13 a DC signal component 20 is provided. The AC signal component 21 in the measured value represents an oxygen concentration in the gas composition of the gas sample. The DC voltage signal component 20 in the measured value represents a thermal conductivity of the gas composition of the gas sample. The calculation and control unit 200 receives from the circuit arrangement 101 according to FIG. 1a, —or also from the circuit arrangements 101, 102, 103, 104, 105, 106, 107, 108, 109 (FIGS. 3a-3i) by means of signal lines 255 the direct voltage signal component U.sub.X=20 and the alternating voltage signal component U.sub.X˜ 21 for further data processing. In the measuring signals of the measuring element 2, or of the heat conduction measuring unit 6, twice the frequency 2f of the excitation frequency can be seen as the AC voltage signal component 21. This can be explained by the fact that the alignment of the oxygen molecules in the magnetic field, which reduces a degree of freedom of the mobility of the oxygen molecules in the gas mixture of the gas sample, is independent of the polarity of the excitation of the magnetic field and in this respect the alignment of the oxygen molecules during a period 1T of the excitation frequency if is twofold, i.e. with the frequency 2f. i.e. with the frequency 2f and then also becomes visible in the alternating voltage signal components U.sub.X1˜ 502, U.sub.X2˜ 602, U.sub.X3˜ 702, U.sub.X4˜ 802, U.sub.X1F˜ 506, U.sub.X2F˜ 606, U.sub.X3F˜ 706, U.sub.X4F˜ 806 (FIG. 5) of the thermoelectric voltage signals in the diagrams 201, 202 (FIG. 5).

    [0132] The calculation and control unit 200 performs a standardization of the DC voltage signal components 20 and AC voltage signal components 21. This standardization of the signal components 20, 21 is carried out by the calculation and control unit 200 to a reference value 400. The reference value 400 is assumed to be a measured value of the thermoelectric voltage signals (FIG. 5) for a state in which a dry gas mixture with a gas concentration of 100% oxygen is supplied to the measuring device 1 with the gas sample and thus the measuring element 2 is also surrounded by a gas concentration of 100% oxygen.

    [0133] For dry gas mixtures X1 500, X2 600, X3 700, X4 800 (FIG. 5) this results in standardized voltage signals with standardized alternating voltage signal components U.sub.Y˜ and standardized direct voltage signal components U.sub.Y=. For humid gas mixtures X1F 508, X2F 608, X3F 708, X4F 808 (FIG. 5) this results in standardized voltage signals with standardized alternating voltage signal components U.sub.YF˜ and standardized direct voltage signal components U.sub.YF=. The calculation and control unit 200 is configured to pressure compensate the standardized AC signal components U.sub.Y˜, U.sub.YF˜ into pressure compensated standardized AC signal components U.sub.Z˜, U.sub.ZF˜. The calculation and control unit 200 is configured to determine an oxygen concentration in the gas sample based on the standardized AC signal components U.sub.Y˜, U.sub.YF˜, U.sub.Z˜, U.sub.ZF˜.

    [0134] The calculation and control unit 200 is configured to determine a concentration of another gas in the gas sample based on the standardized DC signal components U.sub.Y=, U.sub.YF=. Information or data regarding moisture in the gas sample may be provided to the calculation and control unit 200 via the data interface 206 or by means of a moisture sensor 320 connected to the calculation and control unit 200 or connected to the measurement system 100 via signal lines 255. The moisture sensor 320 is in metrological contact with the gas mixture of the gas sample.

    [0135] Information or data about the temperature in the gas sample may be provided to the calculation and control unit 200 via the data interface 206 or by means of a temperature sensor 330 connected to the calculation and control unit 200 or connected to the measurement system 100 via signal lines 255. The temperature sensor 330 is in metrological contact with the gas mixture of the gas sample.

    [0136] Information or data on the pressure level of the gas sample may be provided to the calculation and control unit 200 via the data interface 206 or by means of a pressure sensor 310 connected to the calculation and control unit 200 or connected to the measurement system 100 via signal lines 255. The pressure sensor 310 is in a metrological contact with the gas mixture of the gas sample.

    [0137] In the data memory 207 of the computing module 207, both in embodiments as volatile (RAM) or non-volatile (ROM) memory modules and in embodiments in the form of data carriers (hard disks, memory cards), data records 203 are stored in the form of tables or multi-dimensional data fields, on the basis of which it is possible for the calculation and control unit 200 to determine an oxygen concentration in the gas mixture of the gas sample by processing the alternating voltage signal components U.sub.X˜, U.sub.XF˜ In addition, it is possible for the calculation and control unit 200 to determine a concentration of a further gas in the gas mixture of the gas sample, preferably a concentration of a volatile anesthetic gas, such as desflurane, on the basis of the data sets 203 stored in the form of tables or multi-dimensional data fields and processing of the DC signal components U.sub.X=, U.sub.XF=. Anesthetic gases whose concentration can be determined based on the data and from the DC signal components by the calculation and control unit 200 are, for example, halothane, sevoflurane, enflurane, isoflurane or desflurane. The data records (data sets) 203, which are stored in the form of data fields or tables in the data memory 207, comprise information or correlations on signal characteristics which result for the DC signal components U.sub.X=, U.sub.XF= under a wide variety of conditions with respect to the content of moisture, the pressure level and the temperature level. The data records 203, which are stored in the form of data fields or tables in the data memory 207, comprise information or correlations on signal characteristics which result for the AC voltage signal components U.sub.X˜, U.sub.XF˜ under a wide variety of conditions with regard to the moisture content, the pressure level and the temperature level. The information or correlations can be stored, for example, in the form of a table with measured values or pairs of values standardized to a dry gas mixture with a content of 100% oxygen, which were determined, for example, in a series of measurements with precise adjustment of the concentrations of oxygen, nitrogen and an anesthetic gas in the gas mixture. For example, the following concentration ranges of oxygen, nitrogen and at least one anesthetic gas may have been applied (data in % by volume): [0138] Oxygen: 15%-100%, [0139] Nitrogen: 0%-85%, [0140] Anesthetic gas desflurane: 0%-20%, [0141] Anesthetic gas isoflurane: 0%-12%, [0142] Anesthetic gas sevoflurane: 0%-12%, [0143] Anesthetic gas halothane: 0%-12%, [0144] Anesthetic gas enflurane: 0%-12%, [0145] Moisture range of the sample gas: 0%-95%, ATPS (Ambient Temperature Pressure Saturated).

    [0146] Typical and common environmental conditions during implementation include: [0147] Ambient pressure range: 400 hPa-1100 hPa, [0148] Temperature range of the temperature-controlled measuring system: 55° C.-65° C., [0149] Ambient temperature range 10° C.-50° C.
    This information or values may be stored as discrete data values in the data memory 207, the calculation and control unit 200 is configured in such a case, in the signal acquisition of the AC voltage signal components U.sub.X1˜ 502, U.sub.X2˜ 602, U.sub.X3˜ 702, U.sub.X4˜ 802, U.sub.X1F˜ 506, U.sub.X2F˜ 606, U.sub.X3F˜706, U.sub.X4F˜ 806 (FIG. 5) and DC voltage signal components U.sub.X1= 503, U.sub.X2= 603, U.sub.X3= 703, U.sub.X4= 803, U.sub.X1F= 507, U.sub.X2F= 607, U.sub.X3F= 707, U.sub.X4F= 807 (FIG. 5) occurring during operation of the measuring system 100 by interpolation, for example via an at least section-wise linear, quadratic, cubic, polynomial or spline interpolation, in order to map the assignment relationship more finely or at a finer level.

    [0150] The information or correlations can alternatively or partially also be formed with the aid of calculation formulas determined from the measurement data, for example in the form of functions, similar to those shown in general form in the formulas 1 to 5 listed below. The functions can thereby represent, for example, as polynomial functions, in each case ranges of the concentration ranges of oxygen, nitrogen and at least one anesthetic gas under the influence of temperature, pressure level and moisture. The correlations in the data sets 203 (FIG. 4) can also include special features, such as signals superimposed on the signals 20, 21 (FIG. 4) or offset voltages of the electronic components (amplifiers, A/D converters, filter circuits) caused by the operation of the measuring device 1 (FIG. 4) and/or the measuring system 100 (FIG. 4) using the circuit arrangements 101, 102, 103, 104, 105, 106, 107, 108, 109 (FIGS. 3c to 3i). In this context, such correlations of assignment can also include the effects which act in the measuring device 1 on the heat balance at the measuring element 2 and the diaphragm 7 and thus also have an effect on the AC voltage signal components U.sub.X1˜ 502, U.sub.X2˜ 602, U.sub.X3˜ 702, U.sub.X4˜ 802, U.sub.X1F˜ 506, U.sub.X2F˜ 606, U.sub.X3F˜ 706, U.sub.X4F˜ 806 (FIG. 5) and direct voltage signal components U.sub.X1= 503, U.sub.X2= 603, U.sub.X3= 703, U.sub.X4= 803, U.sub.X1F= 507, U.sub.X2F= 607, U.sub.X3F= 707, U.sub.X4F= 807 (FIG. 5) during operation of the measuring system 100. In particular, effects can also be included in the assignment correlations 203 (FIG. 4) or data sets 203 (FIG. 4) that are due to the difference in the configurations of the circuit arrangements 101, 102, 103, 104, 105, 106, 107, 108, 109 (FIGS. 3c to 3i) with regard to the operation with temperature control of the measuring element 2 (FIG. 1, FIG. 2, FIG. 4, FIGS. 3c to 3i) and the type of control with open-loop and/or closed-loop control of the temperature control of the measuring element 2 (FIG. 1, FIG. 2, FIG. 4, FIGS. 3c to 3i) are conditioned, such as the operation with constant temperature of the heating structure, constant electric power, constant electric voltage, constant electric current by the circuit arrangements 101, 102, 103, 104, 105, 106, 107, 108, 109 (FIGS. 3c to 3i). The calculation and control unit 200 is further adapted to include in the determination of the oxygen concentration and/or in the determination of the further gas concentration, measured values of the pressure sensor 310 indicating a pressure level in the gas mixture of the gas sample and/or information provided by means of the data interface 206 regarding a pressure level in the gas mixture of the gas sample. The calculation and control unit 200 is further configured to include in the determination of the oxygen concentration and/or in the determination of the further gas concentration, measured values of the moisture sensor 320, which indicates a moisture situation in the gas mixture of the gas sample and/or information provided by means of the data interface 206 regarding a moisture in the gas mixture of the gas sample. The calculation and control unit 200 may further be configured to include, in the determination of the oxygen concentration and/or in the determination of the further gas concentration, measured values of the temperature sensor 330 which indicates a temperature level in the gas mixture of the gas sample and/or information provided by means of the data interface 206 regarding a temperature level in the gas mixture of the gas sample. The calculation and control unit 200 is further configured to include, when standardizing the measurement signals U.sub.X=20, U.sub.X˜ 21 into standardized AC signal components U.sub.Y˜, U.sub.YF˜ and DC signal components U.sub.Y=, U.sub.YF=, measured values of the moisture sensor 320, measured values of the pressure sensor 310, measured values of the temperature sensor 330 and/or information provided by means of the data interface 206 regarding temperature, pressure level or moisture in the gas mixture of the gas sample. In the following, a process for operating the measurement system 100 for a determination of gas concentrations in a gas mixture of a gas sample is described on the basis of FIG. 4—partly with reference to FIG. 5. The process allows the determination of an oxygen concentration and an anesthetic gas concentration. The calculation and control unit 200—or another unit suitable for carrying out a process for the determination of the gas concentration of the further gas and the determination of the oxygen concentration of the measuring system 100 after the provision of the thermoelectric voltage signals 20, 21 by the heat conduction measuring unit 6 on the measuring element 2 and signal processing 205, the following process steps are carried out by the computing module 207 and further components 13, 14, 205 of the measuring system 100:

    [0151] a. Signal Separation: [0152] A separation (AC← .fwdarw.DC-separation) of the thermo-voltage signals into a DC-signal component (DC-component) 20 and an AC-signal component (2f-component) 21 takes place. Since the AC signal component (2f component) 21 is several orders of magnitude smaller than the DC signal component 20, this 2f component 21 must be amplified to a correspondingly significantly higher level than the DC signal component 20 prior to the subsequent analog-to-digital conversion 205. Such signal amplification of the AC signal components 21 can typically be performed with an amplification factor in the range of 20 to 750. The amplitude of the 2f signal is determined by the calculation and control unit 200 and calculation module 207, for example in a digital manner, using a lock-in process. [0153] Prior to separation (AC← .fwdarw.DC-separation) of the thermo-voltage signals into a DC-signal portion (DC-portion) 20 and an AC-signal portion (2f-portion) 21, a signal amplification of the thermo-voltage signals (DC- and AC-signal portion) may be provided. Such signal amplification can typically be performed with an amplification factor in the range of 5 to 20. Overall, the amplification of the AC voltage signal components 21 then results in a typical amplification value above 200.

    [0154] b. Moisture Compensation: [0155] In an optional manner, a compensation of the alternating voltage signal components (2f-component) 21 and/or of the direct voltage signal components 20 can take place, so that signals 20′, 21′ (FIG. 7) with a DC-component and a 2f-component result, as they would have been recorded without a water vapor component—i.e. for a dry gas mixture, so that values result which correspond to dry gas. For this purpose, measured values of the moisture sensor 320 or information indicating a moisture content in the gas mixture of the gas sample are used.

    [0156] c. Standardization/Calibration: [0157] i. Standardization of the AC signal components: [0158] The AC signal component 21 is standardized to a reference signal 502 (FIG. 5), which corresponds to an AC signal component without any influence of moisture or moisture content in the gas mixture of the gas sample with a volume content of 100% oxygen. This reference signal 502 has previously been obtained by means of measurement experiments. [0159] This results in standardized alternating voltage signal components U.sub.Y˜, U.sub.YF˜. [0160] ii. Standardization of the DC voltage signal components: [0161] The DC voltage signal component 20 is standardized to a reference signal 503, 400 (FIG. 5), which corresponds to a DC voltage signal component without a moisture influence or proportion of moisture in the gas mixture of the gas sample with a volume proportion of 100% oxygen. This reference signal 503, 400 has previously been obtained by means of measurement experiments. [0162] This results in standardized DC voltage signal components U.sub.Y=, U.sub.YF=.

    [0163] d. Pressure Compensation: [0164] Pressure compensation of the standardized alternating voltage signal components U.sub.Y˜, U.sub.YF˜ takes place so that pressure-compensated, standardized signals U.sub.Z˜, U.sub.ZF˜ with a 2f component result, as they would have been recorded at a reference pressure of, for example, 1013 hPa for a dry gas mixture, so that a value results which corresponds to dry gas at standard pressure. For this purpose, measured values of the pressure sensor 310 or information indicating the current pressure level in the gas mixture of the gas sample are used.

    [0165] e. Calculation of the Oxygen Concentration. [0166] The pressure-compensated standardized AC signal components U.sub.Z˜, U.sub.ZF˜ are used to determine the oxygen concentration in the gas mixture of the gas concentration and to determine therefrom an output signal which indicates the oxygen concentration in the gas mixture of the gas concentration. [0167] f. Calculation of the concentration of the further gas in the gas mixture of the gas concentration, in particular an anesthetic gas concentration in the gas mixture of the gas concentration. The standardized DC signal components U.sub.Y=, U.sub.Y= are used to determine the concentration of the further gas, in particular the anesthetic gas concentration, and to determine therefrom an output signal which indicates the concentration of the further gas, in particular the anesthetic gas concentration, in the gas mixture.
    The described steps a)-f) can also be carried out in a varied sequence of steps in the sense of the present invention, for example the sequence of standardization and compensation of pressure, or moisture can be carried out in a different order, depending on the preparation and design of the data sets 203 and reference signals 400, 502, 503, which have been obtained beforehand with the aid of measurement experiments.

    [0168] In one of the steps of the process or in a further step, for example in one of steps b), c) or d), an adjustment of the heat-conducting and heat-dissipating properties of the measuring element may be carried out. Such an adjustment with respect to the differences between different measuring elements due to the series dispersion of the measuring elements with respect to the heat-conducting and heat-dissipating properties may be performed, for example, as outlined below: [0169] Test gas supply and operation of the measuring element at the standard operating point [0170] Acquisition of the DC voltage signal components U.sub.X=, U.sub.X˜, [0171] optional repetition of the previous steps with other gases [0172] Comparisons of the signal components with standard values or with reference values [0173] Determination of correction values

    [0174] In one of the steps of the process or in a further step, preferably in step d), a pressure compensation of the DC signal components U.sub.X= or of the standardized DC signal components U.sub.Y= can be carried out. The pressure compensation makes it possible to compensate for differences in the density and thus in the thermal conductivity of the gas mixture of the gas sample. Differences in density arise, for example, in the case of an application at high altitudes, such as altitudes of more than 2500 meters, for example, in mountains or in aircraft.

    [0175] In one of the steps of the process or in a further step, preferably in one of the steps b) or c), a temperature compensation of the DC voltage signal components can be performed. In one of the steps of the process or in a further step, preferably in one of the steps b) or c), a temperature compensation of the AC voltage signal components can be performed.

    [0176] In one of the steps of the process or in a further step, preferably in one of the steps b) or c), a moisture compensation of the DC signal components can be performed. In one of the steps of the process or in a further step, preferably in one of the steps b) or c), a moisture compensation of the AC voltage signal components can be performed.

    [0177] The calculation and control unit 200 may provide output signals 266, 267 based on the determined gas concentration of the further gas concentration and/or the determined oxygen concentration in the gas mixture of the gas sample, which comprises and/or indexes the oxygen concentration and the concentration of at least one further gas. The output signal 266, 267 may be used to provide a numeric, alphanumeric or a graphical output on an output unit 220 to inform a user of the results of the gas concentration measurement. The output signal 266, 267 may also be used to provide the determined gas concentration of the further gas concentration and/or the determined oxygen concentration in the gas mixture of the gas sample to a data network 900 via the data interface 206. In an optional embodiment, the data interface 206 may also be bidirectional to provide externally provided information from the data network 900 to the calculation and control unit 200. Such externally provided information may include, for example, information regarding a dosing state of a dosing (metering) system configured to dose the further gas, for example desflurane and/or to dose oxygen. Such a dosing system may be a dosing device for gases with a valve arrangement or an anesthetic vaporizer (vapor) for a dosage of volatile anesthetics (desflurane, halothane, sevoflurane, enflurane, isoflurane). Such externally provided information may also include information regarding a gas composition of the gas mixture of the gas sample, which is for example acquired and provided by another external system, for example by an anesthetic gas monitor for a determination of anesthetic gases in a gas mixture.

    [0178] FIG. 5 shows diagrams 201, 202. With assignment to an ordinate (x-axis) 399, voltage signals are plotted in the diagrams 201, 202 on the abscissa (y-axis) 499 for four different gas compositions 500, 600, 700, 800, respectively, by way of example. Identical elements in FIGS. 1, 2, 3a, 3b, 3c, 3d, 3f, 3g 3h, 3i, 4 and in FIG. 5 are designated by the same reference numerals in FIGS. 1, 2, 3a, 3b, 3c, 3d, 3f, 3g 3h, 3i, 4 and FIG. 5. In diagram 201 the thermoelectric voltage signals U.sub.X1 501, U.sub.X2 601, U.sub.X3 701, U.sub.X4 801 resulting at the measuring element 2 (FIG. 1, FIG. 2, FIG. 4) as output signals of the measuring elements 2 (FIG. 2) according to the embodiments of the measuring device 1 as measuring system 100 according to FIG. 4, are shown standardized for the four exemplary gas compositions X1 500, X2 600, X3 700, X4 800 without an influence of moisture in the gas sample. In diagram 202 the thermoelectric voltage signals U.sub.X1F 505, U.sub.X2F 605, U.sub.X3F 705, U.sub.X4F 805 resulting at the measuring element 2 (FIG. 1, FIG. 2, FIG. 4) as output signals of the measuring elements 2 (FIG. 2) according to the configurations of the measuring device 1 as measuring system 100 according to FIG. 4 are shown standardized for four further exemplary gas compositions X1F 508, X2F 608, X3F 708, X4F 808 under the influence of moisture in the gas sample.

    [0179] The signal characteristics of the thermoelectric voltage signals U.sub.X1 501, U.sub.X2 601, U.sub.X3 701, U.sub.X4 801 in diagram 201 and U.sub.X1F 505, U.sub.X2F 605, U.sub.X3F 705, U.sub.X4F 805 in diagram 202 were recorded in the measurement test under usual ambient conditions of ambient temperature, temperature of the gas mixture of the gas sample and air pressure. One can assume a temperature range of approximately 12° C. to 28° C. for the ambient temperature and the temperature of the gas mixture of the gas sample and a pressure range of approximately 1000 hPa to 1025 hPa. The standardization is based on the thermoelectric voltage signal U.sub.X3 503, 400 which is the output signal of a heated measuring element 2, 8 (FIG. 1, FIG. 2) when a dry gas mixture with a gas concentration of 100% oxygen is supplied to the measuring device 1 (FIG. 1; FIG. 2) and thus the measuring element 2 (FIG. 1; FIG. 2) is also surrounded by a gas concentration of 100% oxygen.

    [0180] The four exemplary gas compositions 500, 600, 700, 800 are composed as follows, as different compositions of air, or oxygen with an exemplary selected volatile anesthetic gas—in the embodiments of this FIG. 5, the agent sevoflurane is selected for this purpose:

    Gas composition X1 500: 100% oxygen,
    Gas composition X2 600: 100% air (oxygen content 21%),
    Gas composition X3 700: 97% oxygen, 3% sevoflurane,
    Gas composition X4 800: 97% air, 3% sevoflurane.

    [0181] For these four gas compositions X1 500, X2 600, X3 700, X4 800, the time courses of standardized thermoelectric voltage signals U.sub.X1 501, U.sub.X2 601, U.sub.X3 701, U.sub.X4 801 are assigned and displayed on the abscissa 499. Thereby for each gas composition X1 500, X2 600, X3 700, X4 800 in each case a direct voltage signal component and an associated superimposed sinusoidal alternating voltage signal component are shown in the time courses of the standardized thermoelectric voltage signals U.sub.X1 501, U.sub.X2 601, U.sub.X3 701, U.sub.X4 801. The separation of DC voltage components and AC voltage components can be achieved—as shown in FIG. 4 in the measuring system 100 (FIG. 4)—by using suitable signal filtering with low-pass arrangements 13 (FIG. 1) and high-pass arrangements 14 (FIG. 4), respectively, in such a way that DC voltage signal components and AC voltage signal components result for the different gas compositions. These DC and AC voltage signal components are provided by the measuring device 1 (FIG. 1, FIG. 2, FIG. 4) for further evaluation with regard to the gas composition.

    [0182] The further evaluation with regard to the gas composition can be carried out by means of a calculation and control unit 200 (FIG. 4) arranged in the measuring system 100 (FIG. 4). In this case, the thermoelectric voltage signals U.sub.X1 501, U.sub.X2 601, U.sub.X3 701, U.sub.X4 801 are evaluated with the direct voltage signal components and alternating voltage signal components previously standardized to 100% dry oxygen in such a way that the then resulting standardized periodic alternating voltage signal component and the non-periodic direct voltage signal component are related to each other and evaluated in order to determine an oxygen concentration in the gas sample of the gas mixture with high accuracy. With reference to the signal characteristics of the standardized thermoelectric voltage signals U.sub.X1 501, U.sub.X2 601, U.sub.X3 701, U.sub.X4 801, this means, for example, that the standardized alternating voltage signal components U.sub.X1˜ 502, U.sub.X2˜ 602, U.sub.X3˜ 702, U.sub.X4˜ 802 can be set in relation to the standardized direct voltage signal components U.sub.X1= 503, U.sub.X2= 603, U.sub.X3= 703, U.sub.X4= 803 and can be compared with one another and the oxygen concentration in the gas mixture of the gas sample can be determined from the ratio formed in this way or on the basis of the comparison.

    [0183] In addition to the determination of the oxygen concentration in the gas sample of a gas mixture, a determination of a further gas concentration takes place within the scope of the evaluation by the calculation and control unit 200 (FIG. 4). Such a further gas concentration is, for example, the volatile anesthetic agent sevoflurane, the effects of which on the measured values have also been selected for illustration in the exemplary representations of the thermoelectric voltage signals U.sub.X3 701, U.sub.X4 801.

    [0184] Measurement experiments have shown that the amplitude of the alternating voltage signal components U.sub.X1˜ 502, U.sub.X2˜ 602, U.sub.X3˜ 702, U.sub.X4˜ 802, under certain and known boundary conditions (magnetic field operating point) and taking into account or compensating for environmental influences (pressure, moisture) in gas mixtures of any gas mixtures of oxygen and air, or oxygen and nitrogen with a proportion of a volatile anesthetic agent, for example sevoflurane (3% in the alternating voltage signal components U 702, U 802) has an almost linear dependence. Oxygen and nitrogen with a proportion of a volatile anesthetic agent, for example sevoflurane (3% in the alternating voltage signal components U.sub.X3˜ 702, U.sub.X4˜ 802) has an almost linear dependence on the oxygen concentration in the gas mixture of the gas sample.


    .Math..sub.Xn˜=f(c.sub.O2)  Formula 1

    In addition, the amplitude of the AC signal components U.sub.X1˜ 502, U.sub.X2˜ 602, U.sub.X3˜ 702, U.sub.X4˜ 802 is dependent on the proportion of the concentration of volatile anesthetic gas (AGas) as anesthetic agent, for example sevoflurane in the gas mixture of the gas sample.


    .Math..sub.Xn˜=f(c.sub.AGas)  Formula 2


    .Math..sub.Xn˜=f(c.sub.Sevofluran)  Formula 2.1

    The level of the standardized DC signal components U.sub.X1= 503, U.sub.X2= 603, U.sub.X3= 703, U.sub.X4= 803 depends on the thermal conductivity of the gas mixture of the gas sample, i.e. on the proportional composition of oxygen, air, moisture, nitrogen, and volatile Anesthetic gas (AGas) as an anesthetic agent, for example sevoflurane in the gas mixture of the gas sample. The higher the concentration of volatile anesthetic agent in the gas mixture of the gas sample, the lower the total thermal conductivity of the gas mixture, and accordingly the DC signal component U.sub.Xn= standardized to a signal U.sub.X1= 503, 400 with a dry gas with 100% oxygen increases in relation to this standardization signal U.sub.X1= 503, 400.


    U.sub.Xn==f(c.sub.AGas,c.sub.Air,c.sub.O2,c.sub.cN2,Humidity)  Formula 4

    The lower the concentration of oxygen in the gas mixture of the gas sample, the lower the paramagnetic effect on the total thermal conductivity of the gas mixture, accordingly the amplitude of the AC signal component .Math..sub.Xn˜ standardized to a signal .Math..sub.X1˜ 502, 400 with a dry gas containing 100% oxygen decreases compared to this standardization signal .Math..sub.X1˜ 502, 400.


    .Math..sub.Xn˜=f(c.sub.AGas,c.sub.Air,c.sub.O2,c.sub.N2,Humidity)  Formula 5

    This is illustrated by the signal characteristics of the thermoelectric voltage signals U.sub.X1 501, U.sub.X2 601, U.sub.X3 701, U.sub.X4 801 in diagram 201 with the DC voltage signal components U.sub.X1= 503, U.sub.X2= 603, U.sub.X3= 703, U.sub.X4= 803 and the AC voltage signal components U.sub.X1˜ 502, U.sub.X2˜ 602, U.sub.X3˜ 702, U.sub.X4˜ 802. The influence of the moisture in the gas sample on the DC voltage signal component and the AC voltage signal component is exemplified in diagram 202 by the signal characteristics of the thermoelectric voltage signals U.sub.X1F 505, U.sub.X2F 605, U.sub.X3F 705, U.sub.X4F 805 with the DC voltage signal components U.sub.X1F= 507, U.sub.X2F= 607, U.sub.X3F= 707, U.sub.X4F= 807 and the AC voltage signal components U.sub.X1F˜ 506, U.sub.X2F˜ 606, U.sub.X3F˜ 706, U 806.sub.X4F˜.

    [0185] Since in the operation of the measuring device 1 (FIGS. 1, 2, 4) by means of the heating structure 8 (FIGS. 1, 2, 4) a supply and/or tracking of heating energy in the form of electrical energy for the measuring element 2 (FIGS. 1, 2, 4) on the membrane 7 (FIGS. 1, 2, 4) a constant electrical energy, electrical power, electrical voltage, electrical current or temperature, resp. excess temperature in relation to a reference temperature is set, i.e. adjusted, controlled or regulated, even in the event of changes in the gas composition in the gas sample—and thus resulting changes in the overall thermal conductivity of the gas mixture in this gas sample—the thermovoltage signals and changes in the thermovoltage signals represent a measure of changes in the setting and tracking of the heating energy which can be caused by changes in the thermal conductivity in the gas mixture of the gas sample.

    [0186] Basically, physics shows that most liquids have higher thermal conductivities than gases or gas mixtures. If one considers thermal conductivities of different gases—in this diagram 201, for example, in a gas sample 500 of air (λ=0.02603 W/mK), or of essentially approximately 78% nitrogen in a mixture with 21% oxygen in comparison with a gas sample 600 of 100% oxygen (λ=0.02615 W/mK)—, an increase in the DC signal components U.sub.X1= 503, U.sub.X2= 603 can be seen with a decrease in the total thermal conductivity of the gas mixture in the gas sample. This can be explained by the fact that with a reduced thermal conductivity less electrical energy has to be supplied to the measuring element 2 (FIG. 4) as heating energy in order to set a certain defined temperature level on the measuring element 2, since due to a reduced thermal conductivity of the gas mixture less energy is carried away by the gas and transferred from the measuring element 2 (FIG. 4) to the gas mixture. An increase in the total thermal conductivity of the gas mixture, however, is accompanied by a decrease in the temperature on the measuring element 2 (FIG. 4) and, associated with this, a decrease in the thermoelectric voltage signals in the gas sample.

    [0187] In Diagram 202, instead of the four exemplary dry gas compositions in Diagram 201, there are now shown four moist gas compositions X1F 508, X2F 608, X3F 708, X4F 808, which are composed as follows as different compositions of air, or oxygen with an exemplary selected volatile anesthetic gas—in the representations of this FIG. 5, the agent sevoflurane is selected—and a content of water vapor (H.sub.2O) with 100% saturated vapor:

    Gas composition X1F 508: 100% oxygen, 3% H.sub.2O,
    Gas composition X2F 608: 100% air (oxygen content 21%), 3% H.sub.2O,
    Gas composition X3F 708: 97% oxygen, 3% sevoflurane, 3% H.sub.2O,
    Gas composition X4F 808: 97% air, 3% sevoflurane, 3% H.sub.2O.
    The 100% saturated vapor of water (H.sub.2O) corresponds—according to vapor pressure tables—in this diagram 202 to a gas concentration of approximately 3% H.sub.2O in the gas mixture of the gas sample at the temperature of 24° C. The influence of the moisture in the gas sample on the DC signal component and the AC signal component is shown in diagram 202 by the signal characteristics of the thermoelectric voltage signals U.sub.X1F 505, U.sub.X2F 605, U.sub.X3F 705, U.sub.X4F 805 with the DC voltage signal components U.sub.X1F= 507, U.sub.X2F= 607, U.sub.X3F= 707, U.sub.X4F= 807 and the AC voltage signal components U.sub.X1F˜ 506, U.sub.X2F˜ 606, U.sub.X3F˜ 706, U.sub.X4F˜ 806.

    [0188] The voltage signals U.sub.X1F 505, U.sub.X2F 605, U.sub.X3F 705, U.sub.X4F 805 resulting at the measuring element 2 (FIG. 1, FIG. 2, FIG. 4) for four exemplary moist gas compositions 508, 608, 708, 808 are shown in diagram 202. The standardization is carried out on the thermoelectric voltage signal U.sub.X1 501, which is obtained as the time courses of the output signal of a heated measuring element 2, 8 (FIG. 1, FIG. 2), when a dry gas mixture with a gas concentration of 100% oxygen is supplied to the measuring device 100 (FIG. 1; FIG. 2) and thus the measuring element 2 is also surrounded by a gas concentration of 100% oxygen. In diagram 202, changes in the thermo-voltage signals U.sub.X1F 505, U.sub.X2F 605, U.sub.X3F 705, U.sub.X4F 805 under the influence of moisture are apparent. In particular, the DC voltage signal components U.sub.X1F= 507, U.sub.X2F= 607, U.sub.X3F= 707, U.sub.X4F= 807 are lower in the moist gas mixture of the gas sample than the DC voltage signal components U.sub.X1= 503, U.sub.X2= 603, U.sub.X3= 703, U.sub.X4= 803 in the dry gas mixture according to diagram 201, while the AC voltage signal components U.sub.X1F˜ 506, U.sub.X2F˜ 606, U.sub.X3F˜706, U.sub.X4F˜ 806 in this schematic representation according to diagrams 201, 202 do not differ significantly from one another within the scope of the measurement accuracies provided for this measurement test. Since for obtaining the thermo-voltage signals U.sub.X1 501, U.sub.X2 601, U.sub.X3 701, U.sub.X4 801 the measuring elements 2 (FIG. 2) have been operated for temperature control with a circuit arrangement 101 (FIG. 3a) with a substantially constant supply of energy, it can be concluded from such a reduction in the thermo-voltage signals that the temperature of the measuring element 2 (FIG. 2) has reduced overall under the influence of moisture. This means that a portion of the constant energy supplied was conducted away from the measuring element 2 (FIG. 2) into the gas mixture and thus could not contribute to a temperature control of the measuring element 2 (FIG. 2). Water vapor forms—especially in the case of saturated vapor—molecular clusters in the gas mixture of the gas sample. The DC voltage signal components U.sub.X1F= 507, U.sub.X2F= 607, U.sub.X3F= 707, U.sub.X4F= 807 of the thermoelectric voltage signals decrease in comparison with dry gas mixtures in the case of a moist gas mixture, since part of the energy supplied is required to release the water vapor molecules from the molecular arrangement in the molecular clusters. As a result of this effect, in operation of the measuring system 100 (FIG. 4) under the influence of moisture, there is a reduction in the DC voltage signal components U.sub.X1F= 507, U.sub.X2F= 607, U.sub.X3F= 707, U.sub.X4F= 807 of the thermoelectric voltage signals, although on the basis of the thermal conductivity of water vapor (λ=0.0199 W/mK), a decrease in the total thermal conductivity of the gas mixture in the gas sample—and thus also an increase in the DC voltage signal components U.sub.X1F= 507, U.sub.X2F= 607, U.sub.X3F= 707, U.sub.X4F= 807 of the thermoelectric voltage signals—would be expected. From this it can be concluded that in this configuration of a resulting heat balance for the measuring element 2 (FIG. 4) with effects of heat flow, heat conduction, heat radiation, there is an increased energy requirement to release the water vapor molecules from the molecular clusters, than would result as expected from the reduction of the total thermal conductivity by the proportion of water vapor (λ=0.0199 W/mK) in the gas sample compared with the reference value 400, 503.

    [0189] Since the measuring device 1 is essentially not a measuring device for determining thermal conductivities in gases, but a measuring device 1 for determining gas concentrations in gas mixtures by utilizing paramagnetism of certain gases, in particular oxygen in combination with thermal conductivity effects, which act on a state of the measuring element 2 (FIGS. 1, 2, 4) and on the operation of the measuring element 2 (FIGS. 1, 2, 4), the differences in the signal courses of the thermoelectric voltage signals U.sub.X1F 505, U.sub.X2F 605, U.sub.X3F 705, U.sub.X4F 805 with the DC voltage signal components U.sub.X1F= 507, U.sub.X2F= 607, U.sub.X3F= 707, U.sub.X4F= 807 and the AC voltage signal components U.sub.X1F˜ 506, U.sub.X2F˜ 606, U.sub.X3F˜ 706, U.sub.X4F˜ 806, which are associated with a moist gas mixture, to the signal characteristics U.sub.X1 501, U.sub.X2 601, U.sub.X3 701, U.sub.X4 801 in diagram 201 with the DC voltage signal components U.sub.X1= 503, U.sub.X2=603, U.sub.X3=703, U.sub.X4=803 and the alternating voltage signal components U.sub.X1˜ 502, U.sub.X2˜ 602, U.sub.X3˜ 702, U.sub.X4˜ 802, which belong to a dry gas mixture, are based on a combination of different effects. These effects result from changes in the gas compositions with resulting changes in the thermal conductivity and the heat balance in the measuring device 1 (FIGS. 1, 2, 4) and their changes and effects on the heat balance at the measuring element 2 (FIG. 4). The heat balance at the measuring element 2 (FIG. 4) results during operation of the measuring system 100 (FIG. 4) from effects of heat transport, such as heat dissipation to the environment by thermal radiation, effects of heat flow (convection) into the gas sample, effects of heat dissipation by thermal conduction within the measuring device 1 or to the outside of the measuring device 1 (FIGS. 1, 2, 3, 4), effects of heat conduction within the membrane 7 (FIGS. 1, 2, 3, 4) and to the surrounding structures of the measuring device (FIG. 4), as well as effects caused by heat dissipation by heat conduction through the electrical contacting of the measuring device 1 (FIGS. 1, 2, 4).

    [0190] FIG. 6 shows the measuring device 1 schematically integrated in a gas duct 398 with a pressure sensor 310, moisture sensor 320, temperature sensor 330, a further reference temperature sensor 340, a first thermistor 345, a second thermistor 346 with arrangement of measuring chamber 380, measuring element 2, purge chamber 390 in the measuring device 1 with gas supply 385 and gas outlet 395. Identical elements in FIGS. 1, 2, 3a, 3b, 3c, 3d, 3f, 3g 3h, 3i, 4, 5 and in FIG. 6 are designated with the same reference numerals in FIGS. 1, 2, 3a, 3b, 3c, 3d, 3f, 3g 3h, 3i, 4, 5 and FIG. 6. The measured values of the sensors 310, 320, 330, 340, 345, 346 are supplied and made available to a sensor measuring unit 300 suitable for this purpose and associated with the calculation and control unit 200. The sensor measuring unit 300 may be an independent measuring module or a sub-module of the calculation and control unit 200 (FIG. 4). In an optional embodiment, the moisture sensor 320 may include a reference temperature sensor 340. The calculation and control unit 200 may be configured to standardize the measured value of the moisture sensor 320 using the reference temperature sensor 340. The calculation and control unit 200 may determine the absolute from the relative humidity using knowledge of ambient and gas temperatures, pressure levels, and thus convert the ambient conditions of the sample gas that are current at the time of measurement into standardized conditions accordingly for the corrections required in determining the gas concentration of the further gas and in determining the oxygen concentration. As standardized conditions can be mentioned for example:

    ATPS (Ambient Temperature Pressure Saturated), 20° C., 1013 hPa, saturated with moisture,
    BTPS (Body Temperature Pressure Saturated), 37° C., 1013 hPa, saturated with moisture,
    STPD (Standard Temperature Pressure Dry), 0° C., 1013 hPa, without moisture in the gas mixture.

    [0191] With the gas guide 398, measuring gas in the measuring device 1 can reach the measuring chamber 380 via a gas supply 385. In the measuring chamber 380, the measuring gas flows around the measuring element 2 and the temperature sensor 330 and exits again via a gas outlet 395. In the area of the gas outlet 395, the first thermistor (NTC) 345, the second thermistor (NTC) 346, the pressure sensor 310, and the moisture sensor 320 with the optional reference temperature sensor 340 are arranged in a purge chamber 390. The second thermistor (NTC) is located in the gas outlet 395 in the flow shadow of a shadow element 347. The calculation and control unit 200 is configured to determine, on the basis of the measured values of the first thermistor 345 and the second thermistor 346, whether a flow 398 is present in the gas outlet 395 and to provide an output signal 268 which indicates a flow situation in the purge chamber 390—and thus indirectly also in the measurement chamber 380, in the gas outlet 395, and in the gas supply 385. The output signal 268 may be used, for example, to cause an indication relating to the flow situation to be provided on the output unit 220 or to be provided to a data network 900.

    [0192] FIG. 7 shows an exemplary sequence 1100 of the process for operating the measuring system 100 (FIG. 4) for a determination of gas concentrations in a gas mixture of a gas sample in a flow chart with an exemplary step sequence of several steps. FIG. 7 is to be read in addition to, or in conjunction with, the figure description for FIG. 4. Identical elements in FIGS. 1, 2, 3a, 3b, 3c, 3d, 3f, 3g 3h, 3i, 4, 5, 6 and in FIG. 7 are designated by the same reference numerals in FIGS. 1, 2, 3a, 3b, 3c, 3d, 3f, 3g 3h, 3i, 4, 5, 6 and FIG. 7. The sequence 1100 of steps of a basic process for operating the measuring system 100 (FIG. 4) comprising steps 1001, 1002, 1003, 1004, 1005, 1006, 1007, 1008 and 1009 comprises the following process steps after a start 1001 to an end 1009: [0193] a. Signal separation 1002 with division of the thermoelectric voltage signals into a direct voltage signal component (DC component) 20 and an alternating voltage signal component 21. [0194] b. Optional moisture compensation 1003 of the AC voltage signal components 21 and/or optional moisture compensation of the DC voltage signal components 20. Optional signals are then AC voltage signal components 21′ and/or DC voltage signal components 20′ compensated for moisture. [0195] c. Standardization 1004 of the AC voltage signal components 21, or the moisture compensated AC voltage signal components 21′ to a reference signal 502. This results in standardized AC voltage signal components U.sub.Y˜. [0196] Standardization 1005 of the DC voltage signal components 20, or of the moisture-compensated DC voltage signal components 20′ to a reference signal 503. This results in standardized DC voltage signal components U.sub.Y=. [0197] d. Pressure compensation 1006 of the AC signal components 21 using information indicative of the current pressure level 310 in the gas mixture of the gas sample. [0198] e. Calculating 1007 the oxygen concentration and providing an output signal 266 indicative of the oxygen concentration in the gas mixture of the gas concentration. [0199] f. calculating 1008 the concentration of the further gas and providing an output signal 267 indicating the concentration of the further gas, in particular the anesthetic gas concentration, in the gas mixture.
    After calculation and output of oxygen concentration and concentration of the further gas, a return 1011 is performed to the start 1001 and the sequence 1100 and is performed continuously. In a further optional step 1010, in this exemplary sequence 1100 according to this FIG. 7, an adjustment of the heat conductive and heat dissipative properties 1012 of the measuring element can be performed.

    [0200] In the further optional step 1010, in the exemplary sequence 1100 of this FIG. 7, a pressure compensation of the DC signal components 20 can take place.

    [0201] In this FIG. 7, the optional moisture compensation 1003 is also made clear pictorially by dashed line form in the steps 1003, 1004, 1005, so that according to the FIG. 7 it is to be represented in the sequence 1100 that, for example, also no moisture compensation must take place, in such a case a standardization of the alternating voltage signal components 21 to the reference signal 502 takes place in the step 1004 and a standardization of the direct voltage signal components 20 to the reference signal 503 takes place in the step 1005. However, FIG. 7 also depicts the following further options for steps 1004, 1005 with: [0202] Step 1004: Standardization of the AC voltage signal components 21 to the reference signal 502, [0203] Step 1005: Standardization of the moisture compensated DC signal components 20′ to the reference signal 503. [0204] Step 1004: standardization of the moisture compensated AC signal components 21′ to the reference signal 502, [0205] Step 1005: Standardization of the moisture compensated DC voltage signal components 20′ to the reference signal 503. [0206] Step 1004: standardization of the moisture compensated AC signal components 21′ to the reference signal 502, [0207] Step 1005: standardization of the DC signal components 20 to the reference signal 503.

    [0208] In all cases, the steps 1004, 1005 are followed by a pressure compensation 1006 of the AC voltage signal components 21. In an optional embodiment of the sequence 1100, a pressure compensation of the DC voltage signal components 20 can also be performed, for example in the further optional step 1010.

    [0209] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

    LIST OF REFERENCE NUMBERS

    [0210] 1 Measuring device [0211] 2 Measuring element [0212] 3 Air gap [0213] 4 Electromagnet [0214] 5 Coil [0215] 6 Heat conduction measuring unit [0216] 7 Membrane [0217] 8 Heating structure [0218] 9 Measuring point [0219] Amplifier [0220] 11 Voltage divider [0221] 12 DC voltage source [0222] 13 Low Pass Arrangements, Low Pass Filter, Low Pass [0223] 14 High Pass Arrangements, High Pass Filter, High Pass [0224] 15 Shunt [0225] 16 Multiplier [0226] 17 inverting amplifier [0227] 20, 20′ DC voltage signal component (thermal conduction signal) U.sub.X˜, U.sub.XF= [0228] 21, 21′ AC voltage signal component (oxygen signal) U.sub.X=, U.sub.XF˜ [0229] 22 Heating capacity [0230] 23 Heating current [0231] 24 Heating voltage [0232] 25 Modulation-related signals (oxygen) [0233] 100 Measuring system [0234] 101-109 Circuit arrangements [0235] 200 Calculation and control unit [0236] 201, 202 Diagrams [0237] 203 Records, association, table, data field (array) [0238] 204 Magnetic field control [0239] 205 Signal processing [0240] 206 Data interface [0241] 207 Data memory, calculation module, μC, RAM, ROM [0242] 220 Output unit [0243] 244 Control lines to the solenoid [0244] 255 Signal lines from measuring element [0245] 266, 267 Output signals [0246] 300 Sensor measuring unit [0247] 310 Pressure sensor, pressure reading, pressure measurement signal information or data on the pressure level in the gas sample [0248] 320 Moisture sensor, moisture measured value, moisture measurement signal Information or data on moisture in the gas sample [0249] 330 Temperature sensor, temperature measured value, temperature measurement signal information or data on the temperature in the gas sample [0250] 340 Reference temperature sensor [0251] 345, 346 Thermistors (NTC's) [0252] 347 Shadow element [0253] 380 Measuring chamber [0254] 385 Gas supply [0255] 390 Purge chamber [0256] 395 Gas outlet [0257] 398 Gas guide [0258] 399 Ordinate (x-axis) [0259] 400, 450 Scaling values, reference values, standardization values [0260] 499 Abscissa (y-axis) [0261] 500, 600, 700, 800 Gas compositions (dry), gas samples [0262] 501, 601, 701, 801 Thermoelectric voltage signals of dry gas compositions [0263] 502, 602, 702, 802 Thermo-voltage signals (AC voltage signal component) [0264] 503, 603, 703, 803 Thermo-voltage signals (DC signal component) [0265] 502, 503 Reference values for standardization [0266] 505, 605, 705, 805 Thermoelectric voltage signals of the humid gas mixtures [0267] 506, 606, 706, 806 Thermo voltage signals (AC voltage signal component) [0268] 507, 607, 707, 807 Thermo-voltage signals (DC signal component) [0269] 508, 608, 708, 808 Gas compositions (wet) [0270] 900 Data network [0271] 1000 Demarcation line [0272] 1001-1011 Step sequence for operating the measuring system [0273] 1012 heat conducting/heat dissipating properties of the measuring element [0274] 1100 Flowchart