Gas detection device and gas detection method with sensor component and with oxidation component

Abstract

To provide a gas detection device and method for monitoring an area for a combustible target gas.SOLUTION: A gas sample (G) is introduced into a measuring chamber (9) from a monitoring target area. A semiconductor sensor (1) includes an electrically conductive sensor component (10). The electrically conductive sensor component has an electrical detection variable according to the concentration of the combustible target gas in the measuring chamber. An oxidation component (2) can oxidize the combustible target gas in the measuring chamber. The detection variable is measured at a detection time, and the oxidation component is in a switched-on state or is switched on. The oxidation component oxidizes at least a part of the combustible target gas in the measuring chamber up to a reference time. The detection variable is measured again at the reference time. A difference between the measured value at the reference time and the measured value at the detection time is an indicator for the concentration of the combustible target gas in the measuring chamber.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a gas detection device and method for monitoring a spatial region for a combustible target gas.

[0002] In one application, the present invention is used to detect the presence of a target gas even when the concentration of a combustible target gas, such as methane (CH4), is low, for example, below 10 ppm.

[0003] The present invention is based on the problem of providing a gas detection device and a gas detection method that can detect a target gas with high reliability even when the combustible target gas is present at a relatively low concentration and / or changes in environmental conditions can have a significant impact on the measurement.

[0004] This problem is solved by a gas detection device having the features of claim 1 and a gas detection method having the features of claim 13. Advantageous configurations of the gas detection device according to the present invention are also, as far as reasonable, advantageous configurations of the gas detection method according to the present invention, and vice versa.

[0005] The gas detection device according to the present invention and the gas detection method according to the present invention can monitor a spatial region for at least one combustible target gas, such as methane (CH4). The method according to the present invention is implemented using the gas detection device according to the present invention. The spatial region is, for example, a region of a production factory or mine, or the interior of a building, vehicle, or aircraft.

[0006] The following describes the "flammable target gas". The gas sample in the measurement chamber may contain multiple flammable target gases simultaneously. The term "flammable target gas" is also intended to indicate a situation where different flammable target gases are present in the measurement chamber. The term "detection of the target gas" used below includes the process of detecting the presence of at least one target gas. In one configuration form, which flammable target gas is detected is preset. In another application, all flammable target gases in the spatial region are detected.

[0007] The gas detection device includes a measurement chamber. The gas detection device is configured such that the gas sample flows continuously or at least temporarily from the monitored area to the measurement chamber, for example, by suction and / or diffusion, and the method includes such steps.

[0008] A conductive sensor component and an oxidation component are arranged inside or adjacent to the measurement chamber. The sensor component has a measurable electrical detection variable and contacts the gas sample in the measurement chamber at the surface. This contact affects the measurable electrical detection variable of the sensor component, particularly the electrical resistance, as follows: In the first implementation form, the lower the concentration of the flammable target gas in the gas sample in the measurement chamber, the larger the value of the detection variable of the sensor component. In the second implementation form, the lower the concentration of the flammable target gas in the gas sample in the measurement chamber, the smaller the value of this detection variable. In both implementation forms, the detection variable correlates with the target gas concentration in the gas sample. Naturally, it is also possible that the gas sample contains no target gas at all, and thus the detection variable is not affected much or does not change compared to the reference state without the target gas.

[0009] The oxidation component can be switched on for use and can optionally be switched on and off during use. The switched-on oxidation component can oxidize the flammable gas in the measurement chamber, provided, of course, that there is flammable gas in the measurement chamber.

[0010] Note: The terms "switch on" and "switch off" as used above and below may mean a rapid transition from a switched-off state to a fully switched-on state, or may mean a gradual transition.

[0011] The gas detection device further comprises a detection sensor. The detection sensor is capable of measuring the magnitude of the detection variable of the sensor component, and for example, is capable of measuring the actual electrical resistance or voltage magnitude applied to the sensor component, or the intensity magnitude of the current flowing through the sensor component, or the magnitude of the total charge.

[0012] Furthermore, the gas detection device comprises a signal processing and evaluation unit capable of receiving and processing signals from the detection sensor. In one configuration, the gas detection device comprises a housing, and the other components described above are inside this housing. In another configuration, the evaluation unit is arranged outside the housing, and the signal of the detection sensor is preferably transmitted wirelessly to this spatially separated evaluation unit.

[0013] The gas detection device is configured to perform the following steps, and the method according to the present invention includes the following steps: - Switch on the oxidation component, or the oxidation component is switched on. During the oxidation period, the switched-on oxidation component completely or at least partially oxidizes the combustible target gas or all combustible target gases in the measurement chamber. By the step of oxidizing the combustible target gas by the oxidation component, the amount of the combustible target gas in the measurement chamber decreases, and in some cases, but not necessarily, all combustible target gases in the measurement chamber are eliminated. Naturally, especially when there is no combustible target gas in the monitoring target area at present, it is possible that there was no combustible target gas in the measurement chamber at the start of the oxidation period. - At the detection time point and the reference time point, the detection sensor measures the detection variable of the sensor component, more precisely the magnitude of the detection variable at each time point. The detection time point is before or even after the reference time point. By measuring the magnitudes at two different time points, there are two measured values of the detection variable (more precisely, two measured values for the magnitude of the detection variable), where both measured values relate to two different time points. - Operate the gas detection device such that the following situations occur: When a combustible target gas is present in the monitored area, at the detection time point, the combustible target gas is also present in the measurement chamber. The concentration of the target gas in the measurement chamber can be exactly the same as or lower than that in the monitored area. At the reference time point, due to oxidation by the oxidation component, the combustible target gas present in the measurement chamber is less than at the detection time point, or even, even if a combustible target gas is present in the area, there is no combustible target gas at all. When a combustible target gas is present in the monitored area, due to oxidation, at the reference time point, in the measurement chamber, there is a lower concentration of the combustible target gas than in the monitored area and also lower than in the measurement chamber at the detection time point, or even, even if a combustible target gas is present in the monitored area, there is no combustible target gas at all. - At least during the oxidation period, the oxidation component is switched on and is capable of oxidizing the combustible target gas in the measurement chamber. In a first alternative form, the detection time point is at or before the start of the oxidation period, and the reference time point is at or after the end of the oxidation period. In a second alternative form, conversely, the reference time point is at or before the start of the oxidation period, and the detection time point is at or after the end of the oxidation period. When the oxidation component is continuously switched on, the period from the earlier to the later of the two time points is used as the oxidation period. - The evaluation unit calculates the difference between the measured value of the detection variable of the sensor component measured by the detection sensor at the detection time point and the measured value of the detection variable measured by the detection sensor at the reference time point. When a combustible target gas is generated in the monitored area, at the detection time point, the combustible target gas is present in the measurement chamber. At the reference time point, there is less combustible target gas or none at all. - In a first alternative form, the evaluation unit automatically determines whether a combustible target gas is present in the gas sample according to the difference in this measured value. This determination further depends on whether the detection variable increases or decreases as the concentration of the target gas increases, and / or on the absolute value of the difference, i.e., │dist│. In a second alternative form, the evaluation unit automatically determines at least approximately the concentration of the combustible target gas in the gas sample according to the difference in the measured values. Preferably, the evaluation unit in the second alternative form applies a stored relationship between the difference in the measured values and the target gas concentration to the calculated difference. At least in the second alternative form, preferably, the oxidation component is switched off at the time of detection. - These two alternative forms of detecting a combustible target gas and determining its concentration can be combined.

[0014] According to a first embodiment, the lower the concentration of the target gas in the measurement chamber, the greater the detection variable of the sensor component. Therefore, the fact that the measured value of the detection variable at the reference time point is greater than the measured value of the detection variable at the detection time point presupposes that the combustible target gas is present in the monitored area and thus also in the measurement chamber. Therefore, according to a second embodiment, the measured value of the detection variable at the reference time point is smaller than the measured value of the detection variable at the detection time point.

[0015] When there is no combustible target gas in the monitoring target area and thus also not in the measurement chamber, the two measured values of the detection variable measured at both times are, ideally, equal. In reality, when there is no combustible target gas in the monitoring target area and thus also no combustible target gas in the measurement chamber at the time of detection, there may be a non-zero difference due to differences in environmental conditions. However, when the target gas is absent, this difference between the two measured values is usually, in terms of the absolute value │dist│, smaller than the difference caused by the presence of combustible target gas in the measurement chamber at the time of detection and the oxidation component oxidizing at least a part of the combustible target gas in this measurement chamber during the oxidation period. Even when the oxidation component oxidizes only a part of the combustible gas in the measurement chamber and not all of it, the difference is usually larger than when there is no combustible target gas in the area and thus also not in the measurement chamber. Therefore, the fact that the difference is non-zero or outside the preset tolerance range is a relatively reliable indicator that the combustible target gas is present in the monitoring target area and thus also in the measurement chamber at the time of detection.

[0016] Even when the combustible target gas is present in the measurement chamber only at a low concentration, the detection variable of the sensor component often changes in a measurable form due to contact with the combustible target gas. However, the detection variable usually depends not only on the concentration of the combustible target gas but also on environmental conditions, particularly environmental temperature and environmental humidity, and optionally environmental pressure. The value taken by the detection variable when there is no combustible target gas in the measurement chamber is often also referred to as the zero value (reference value). Gas detection devices known from the prior art equipped with sensor components having a detection variable that reacts to the concentration of the combustible target gas often have the following drawbacks: the zero point strongly depends on environmental conditions and is usually unknown. Alternatively, a sensor for the corresponding environmental conditions is required, i.e., an additional sensor is required.

[0017] The present invention solves this problem by having an oxidation component oxidize a combustible target gas in a measurement chamber during an oxidation period, and thus measuring, at a reference time point, substantially the actual zero point of the detection variable of the sensor component. The designation "actual zero point" indicates that the zero point generally depends on, and thus can vary with, changes in environmental conditions. Since the time interval between the two time points is usually very short, the environmental conditions do not change significantly during this time interval, and thus, despite the time interval, the measured value at the reference time point can be used as the zero point for the measurement at the detection time point. The difference calculated according to the present invention sufficiently accurately coincides with the difference between the measured value at the detection time point and the (actual) zero point at the detection time point.

[0018] The present invention avoids the need to readjust the gas detection device before each use in order to find the actual zero point. As explained above, the zero point is at least approximately automatically obtained by measurement at the reference time point. In many cases, the present invention also eliminates the need for the gas detection device to be equipped with a sensor for environmental conditions.

[0019] According to the present invention, the need to calibrate the gas detection device during use is also eliminated in order to adapt the gas detection device to possible zero - point changes. When the environmental conditions change relatively rapidly or when the concentration of the target gas changes rapidly, the calibration result, that is, the zero - point change, may already be outdated again, so the gas detection device provides incorrect results. On the other hand, the gas detection device according to the present invention can select the interval between the two time points to be sufficiently short, and since the measurement and evaluation results depend only on the difference rather than a predetermined zero - point, it often provides reliable results even when the environmental conditions change rapidly or when the concentration of the target gas changes rapidly. The interval between the two time points can be set to be as large as necessary on the one hand, that is, it can be set so that at least a part of the combustible target gas is oxidized at the reference time point, and on the other hand, it can be set to be as small as possible. Since the presence of the target gas is determined based on the difference between two actual measurement values, even for very low - concentration target gases, it can often be reliably detected and false alarms are often avoided. In many cases, detection that depends on an accurate knowledge of the correct zero - point can only be unreliable.

[0020] According to the present invention, the sensor component has an electrical detection variable that becomes larger in the first embodiment and smaller in the second embodiment as the concentration of the target gas is lower. This detection variable is, in particular, electrical resistance in one configuration, electrical capacitance in another configuration, and electric potential in a third configuration. The sensor component includes, for example, the following: - A semiconductor whose electrical resistance depends on the concentration of the target gas, or - A heat - flow sensor whose temperature depends on the concentration of the target gas, or - A photo - electric sensor that generates an electrical signal according to the intensity of incident electromagnetic radiation, where the target gas attenuates this electromagnetic radiation. - A photo - ionization detector that generates an electrical signal according to ionization. - A photo - acoustic sensor that generates an electrical signal according to an acoustic effect that depends on the concentration of the target gas, or - An electro - chemical sensor that generates a current of strength and / or voltage according to the concentration of the target gas.

[0021] According to the present invention, the oxidation component oxidizes at least a part of the combustible target gas in the measurement chamber during the oxidation period. This oxidized portion is preferably at least 30%, particularly preferably at least 50%, especially at least 80% of the amount of the combustible target gas present in the measurement chamber at the start of the oxidation period. In one configuration, the oxidation component oxidizes all of the combustible target gas in the measurement chamber during the oxidation period.

[0022] In one configuration, the gas detection device further comprises a heating element. This heating element can heat the gas sample in the measurement chamber. The heating element can be switched on and switched off again, and thus can be selectively operated in the switched-on state and the switched-off state. According to this configuration, the oxidation component can also be switched on and off, and thus can be selectively operated in the switched-on state or the switched-off state. According to the configuration in which the heating element is used, the method further includes the following steps, and the gas detection device is configured to perform the following additional steps: - At the start of the heating period, switch on the heating element. At the end of the heating period, switch off the heating element again. - The switched-on heating element heats up. - During the heating period, the switched-on heating element heats the gas in the measurement chamber. - During the heating period, the oxidation component is in the switched-off state. Conversely, the heating element is in the switched-off state at least during the oxidation period. Preferably, at any time, either the oxidation component or the heating element is in its respective switched-on state, but the two components are not in their respective switched-on states simultaneously.

[0023] According to the present invention, the required target gas concentration affects the detection variables of the sensor component. The detection variables usually further depend on the temperature of the sensor component. This temperature is affected by the switched-on oxidation component and the process of switching the oxidation component on and off. In the configured form where a heating element is used, by inputting more thermal energy in the switched-on state than in the switched-off state, the influence of the oxidation component on the sensor component is reduced. By reducing this influence, the reliability of the detection result is enhanced. Ideally, the switched-on heating element and the switched-on oxidation component generate the same amount of thermal energy input per unit time within or on the sensor component.

[0024] According to the configured form described above, the heating element is switched on during the heating period and is preferably switched off during the oxidation period, preferably throughout the oxidation period. The oxidation component is switched on during the oxidation period and is switched off during at least a part of the heating period, preferably throughout the heating period. Thus, preferably, the oxidation period and the heating period do not overlap at all or overlap only at a certain point. It is also possible that neither the oxidation component nor the heating element is switched on during a further period.

[0025] In one implementation form, the end of the heating period coincides with the start of the oxidation period. Alternatively, the end of the oxidation period coincides with the start of the heating period. These two configured forms reduce the influence of the temperature of the oxidation component on the sensor component compared to the configured form where the heating element is switched off and then, after a certain time interval has elapsed, the oxidation component is finally switched on or vice versa. Compared to the configured form where both the heating element and the oxidation component are temporarily switched on, this implementation form saves electrical energy. Furthermore, it becomes easier to keep the amount of thermal energy input per unit time to the sensor component constant.

[0026] Preferably, the gas detection device is always in exactly one of the following states during use: - The oxidation component is switched on and the heating element is switched off. - The heating element is switched on and the oxidation component is switched off. - The measurement chamber is purged or a gas sample flows into the measurement chamber. Preferably, both the heating element and the oxidation component are switched off.

[0027] When not in use, the gas detection device may be switched off, i.e., it can be in an idle state.

[0028] As already explained, both the switched-on oxidation component and the switched-on heating element act on the sensor component with thermal energy. Preferably, the amount of thermal energy input per unit time generated by the switched-on heating element is exactly the same as the amount of thermal energy input per unit time by the switched-on oxidation component. This description corresponds to a state where there is no combustible target gas in the measurement chamber.

[0029] The amount of thermal energy input per unit time generated by the oxidation component depends on the geometric shape of the oxidation component, particularly the surface, and the temperature, as well as the distance between the oxidation component and the sensor component. When the amount of thermal energy input per unit time is the same and there is no combustible target gas in the measurement chamber, ideally the value of the detection variable is also the same. More precisely, when the oxidation component is switched on and the heating element is switched off, the detection variable ideally takes the same value as when the oxidation component is switched off and the heating element is switched on. This only applies optionally after the transient phase that occurs when the oxidation component or the heating element is switched on or off.

[0030] The embodiments of the heating element described herein often eliminate the need to control the temperature of the detection sensor, oxidation component, or heating element, particularly to a constant value.

[0031] According to the present invention, the oxidation component is switched on at least during the oxidation period. In one configuration, the oxidation component is switched off at least during the inhalation period. Thus, the oxidation component is switched on and / or off during continuous operation.

[0032] During at least the inhalation period, a fluid communication is established between the measurement chamber and the environment, and the gas sample flows into the measurement chamber from the monitored spatial region, for example, by diffusion or suction. This inhalation period is before the oxidation period and ideally does not overlap with the oxidation period or only overlaps at a certain point. The detection time is outside the oxidation period, preferably within the inhalation period, particularly preferably at the start of the inhalation period. Since the oxidation component is continuously or at least predominantly switched off during the inhalation period, the oxidation component does not oxidize or only oxidizes a negligible amount of the combustible target gas during the inhalation period. Thus, assuming that the monitored region contains the combustible target gas, the combustible target gas accumulates in the measurement chamber during the inhalation period.

[0033] The configuration in which the oxidation component is switched on and / or off during continuous operation often allows the measurement chamber to be in continuous fluid communication with the monitored region. There is no need to open and close the closure for inhalation to the measurement chamber during continuous operation. Especially when the concentration of the combustible target gas is relatively low, the switched-on oxidation component oxidizes the combustible target gas in the measurement chamber very rapidly, so the fluid communication does not lead to falsification that is worth mentioning in the measurement result.

[0034] In one configuration, the detection time is at the start of the oxidation period. In a preferred configuration, a time interval occurs between the inhalation period and the oxidation period. A heating period exists within this time interval. Preferably, any heating element is switched on at the end of the inhalation period and switched off again at the end of the inhalation period, i.e., before or at the start of the oxidation period.

[0035] According to the present invention, the oxidation component is switched on at least during the oxidation period to oxidize the combustible target gas in the measurement chamber. The configurations described below can be combined with an oxidation component that can be switched on and off. However, the configurations described below eliminate the need to switch the oxidation component on and / or off during continuous operation. The oxidation component may be continuously switched on during continuous use. According to this alternative configuration, the measurement chamber can be selectively operated in an open or closed state. When the measurement chamber is in the open state, the gas sample can flow from the monitored area into the measurement chamber. Thus, in the open state, a fluid communication is established between the measurement chamber and the monitored area. In the closed state, the measurement chamber is fluid-tightly sealed against the area. "Fluid-tight" means excluding inevitable gaps and clearances. Preferably, in the idle state, the gas detection device is switched off and is fluid-tightly separated from the environment.

[0036] In this configuration, the gas detection device comprises a closable opening, for example a valve, or a slot having a flap or aperture for the opening. When this opening is open, the gas sample can flow from the environment into the measurement chamber. When the opening is closed, the measurement chamber is sealed against the environment, so that the gas sample cannot flow into the measurement chamber. Preferably, the opening is closed during the oxidation period and is at least temporarily open before and / or after the oxidation period. However, it is also possible for gas to flow into the measurement chamber during the oxidation period. Usually, the amount of the target gas flowing into the measurement chamber when the closing part is open during the oxidation period is less than the amount oxidized by the oxidation component during the oxidation period.

[0037] During the inhalation period, the measurement chamber is in the open state. Preferably, this inhalation period includes the detection time point or the inhalation period exists before the detection time point. At the reference time point, preferably, the measurement chamber is in the closed state.

[0038] During at least the oxidation period, the measurement chamber is in a closed state, and the oxidation component oxidizes the combustible target gas in the measurement chamber, ideally all of the combustible target gases. Since the measurement chamber is in a closed state, the combustible target gas cannot flow into the measurement chamber from the area. During the inhalation period described above, the measurement chamber is in an open state. During this inhalation period, assuming that the combustible target gas is present in the monitored area, the combustible target gas accumulates in the measurement chamber.

[0039] These two configurations can be combined, for example, as follows: During the oxidation period, the oxidation component is switched on and the measurement chamber is in a closed state. During the inhalation period, the oxidation component is switched off and the measurement chamber is in an open state. By combining these two configurations, it is often possible to detect the target gas with even higher reliability, even when the target gas is present in the monitored area only at a relatively low concentration. Optionally, there is a heating period between the inhalation period and the oxidation period.

[0040] In a first alternative form of the invention, the detection time is before the reference time. The gas sample has flowed into the measurement chamber at least by the detection time. The oxidation period starts at or after the detection time and ends before or at the reference time. Preferably, the oxidation component is switched on between the detection time and the reference time, and / or the measurement chamber is fluid-tightly separated from the monitored area.

[0041] Conversely, in a second alternative form of the invention, the reference time is before the detection time. The oxidation period starts at or after the reference time and ends before or at the detection time. In one configuration, the measurement chamber is fluid-tightly separated from the area at least during the oxidation period. By the reference time, the oxidation component has oxidized the combustible target gas in the measurement chamber. After the reference time and at least until the detection time, and optionally also thereafter, the gas sample flows into the measurement chamber. Preferably, the oxidation component is switched off between the reference time and the detection time, and / or fluid communication is established between the measurement chamber and the area.

[0042] A plurality of consecutive oxidation periods occur, and a gap occurs between two consecutive oxidation periods. The gas detection device can be operated so that the oxidation component oxidizes the target gas in the measurement chamber at least during each oxidation period. For each oxidation period, the magnitude of the detection variable is measured at the detection time point and the reference time point respectively, and the evaluation according to the present invention is carried out again for each oxidation period. Thereby, in many cases, the combustible target gas can be detected relatively quickly.

[0043] In the configuration described below, it is preferably possible to switch on and off the oxidation component. In the first configuration, the time interval of oxidation is set in advance to be constant. The oxidation period or the duration of each oxidation period is equal to this time interval of oxidation. The time interval of oxidation, and thus each oxidation period, is made as long as necessary on the one hand and as short as possible on the other hand. "As long as necessary" has the following meaning: Even when the predicted concentration of the combustible target gas in the measurement chamber is the highest, the oxidation component oxidizes the combustible target gas in the measurement chamber during the oxidation period, so that the measurement chamber does not contain the combustible target gas at the end of the oxidation period.

[0044] In the second configuration, the oxidation period or the duration of at least one oxidation period, that is, the time during which the oxidation component is switched on, depends on the concentration of the combustible target gas in the measurement chamber. This second configuration eliminates the need to set the time interval of oxidation in advance. According to the second configuration, the gas detection device is further configured to perform the following steps, and the method further includes the following steps: Perform the slope calculation sequence at least once. One or all of the slope calculation sequences include the following steps: - Measure the magnitude of the detection variable at at least two time points, where these time points are temporally separated from each other. Both time points are within the oxidation period. Preferably, measure the magnitude of the detection variable at the detection time point and at least one additional time point that is temporally after this detection time point. Preferably, preset the sampling rate for measuring the detection variable, and this sampling rate determines the time interval between two directly consecutive measurement time points. - Approximately determine the temporal progression of the detection variable during oxidation by measurement. When a combustible target gas is present in the measurement chamber, according to a first implementation form of the sensor component, the detection variable increases with time until all of the target gas is oxidized. Therefore, the slope of the temporal progression of the detection variable is positive until all of the target gas is oxidized. According to a second implementation form, the detection variable decreases until all of the target gas is oxidized, and the slope is negative. When no combustible target gas is present in the measurement chamber, the detection variable remains substantially constant during the oxidation period in both implementation forms. - Depending on the measured value of the detection variable, calculate the magnitude of the slope of the detection variable, that is, the magnitude for the derivation of the temporal progression of the detection variable over time, preferably by an evaluation unit. In the simplest case, this magnitude of the slope is the difference between two measured values of the detection variable measured at the two time points that are the latest in time. The calculated slope can change over time.

[0045] When the slope of the temporal progression of the detection variable falls below a preset limit value in terms of the absolute value, the measurement of the detection variable is terminated. The time point that is the latest in time is used as the reference time point. The measured value at the time point that is the latest in time is used as the measured value at the reference time point. The limit value can be zero or greater than zero. When the slope falls below the preset limit value, substantially all of the target gas in the measurement chamber has been oxidized.

[0046] In the second configuration mode, usually, the higher the concentration of the combustible target gas in the measurement chamber, the longer the oxidation period. When there is no combustible target gas in the monitored area and thus in the measurement chamber, this second configuration mode often provides particularly rapid detection results. In this case, the slope is only affected by environmental conditions and usually remains below a preset limit value. On the other hand, this second configuration mode provides reliable measurement results even when there is a very high concentration of the combustible target gas. Usually, in this case, all the combustible target gas in the measurement chamber is oxidized, so in this case too, the measured value at the second point (the latest point in time) surely functions as a zero value.

[0047] In the third configuration mode, a correlation based on a function that describes the temporal evolution of the detection variable during the oxidation period is defined. This correlation based on the function includes at least one model parameter. Often, this correlation based on the function is in the form of an exponential function, i.e., f(t)=A - C*exp(-α*t), or f(t)=A*[1 - C*exp(-α*t)] where A, C, and α are model parameters.

[0048] During the oxidation period, the detection variable (more precisely, the magnitude of the detection variable) is measured multiple times to collect random samples. Using these random samples, the values of the model parameters are automatically calculated. Often, by extrapolation, the measured value at the second point can be predicted with sufficient reliability. The third configuration mode often provides reliable measurement results quickly, whether the target gas concentration is low or high.

[0049] Also, in the third configuration mode, it is not necessary to preset a fixed oxidation time interval. However, it is also possible to preset a fixed number N>1 with respect to the measured values of the random samples, i.e., the number of random sample elements, and end the oxidation period when N measured values of the random samples are obtained.

[0050] The second configuration and the third configuration can be combined with each other.

[0051] In one implementation, the oxidation component comprises a conductive sensor component. When the oxidation component is switched on, current flows through the sensor component. When the oxidation component is switched off, no current flows through the sensor component. For example, the oxidation component is configured as a so-called varistor and includes a heating element, which functions as the sensor component. The oxidation component further includes a ceramic coating provided around the heating element and a catalyst coating provided on the ceramic coating or a catalyst mixture provided within the ceramic coating. The heating element functions as the sensor component. The detection sensor measures a detection variable of the heating element.

[0052] In another implementation, the oxidation component and the sensor component are separated from each other. A voltage can be applied to the sensor component, and as a result, current flows through the sensor component regardless of whether the oxidation component is switched on or off. According to this another implementation, the oxidation component is used only for oxidizing a combustible target gas that may be present in the measurement chamber, but is not used for detecting this target gas. The detection sensor preferably does not measure the size of the oxidation component. In this another implementation as well, the oxidation component may be configured as a varistor.

[0053] In one application, the monitored space area is directly adjacent to the gas detection device, and the gas sample can flow into the measurement chamber through the inlet. In another application, there is a gap between the monitored space area and the gas detection device. The gas sample can flow from the space area to the measurement chamber through the inlet only through the fluid guide unit, and it is not possible to bypass this fluid guide unit. Due to the spatial gap, the gas detection device is well protected from the environmental influence of the monitored area. The fluid guide unit can particularly have the shape of a tube or a pipe. Preferably, the gas detection device sucks in the gas sample from the monitored area through the fluid guide unit.

[0054] In one configuration, the fluid transport unit is fluid-tightly connected to the adapter. The adapter can be attached to and removed from the gas detection device again. When the adapter is attached, the gas sample can only flow into the measurement chamber through the fluid guide unit, and when the adapter is removed, it can flow directly from the space region into the measurement chamber.

[0055] The gas detection device according to the present invention may be configured as a portable device, and the user can carry this portable device. Preferably, this portable device is provided with a dedicated power supply unit. The gas detection device according to the present invention may also be configured as a stationary device and may be at least temporarily connected to a stationary power supply network. The gas detection device according to the present invention can be provided with an output unit, and in that case, an alarm or a determined concentration is output to this output unit.

[0056] Hereinafter, the present invention will be described with reference to exemplary embodiments.

Brief Description of the Drawings

[0057]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

[0058] FIG. 1 schematically shows a first embodiment of a gas detection device 100 according to the present invention, and FIG. 2 shows a second embodiment.

[0059] The gas detection device 100 is used for the purpose of monitoring a spatial area for the presence of a combustible gas and / or determining the concentration of the combustible gas. This combustible gas is hereinafter referred to as the "target gas". The spatial area is, for example, a refinery or other production plant, the interior of a building, a mine, a vehicle or an aircraft. The combustible gas is, for example, methane (CH4).

[0060] In another application, the gas detection device 100 is used to perform an alcohol test on a subject. As is well known, when a subject ingests alcohol and as a result, alcohol is still present in the subject's blood and / or oral cavity, the subject's exhaled breath contains breath alcohol. In this application, the gas detection device 100 is provided with a mouthpiece. The subject blows air into this mouthpiece, and at least a part of the sent exhaled breath sample reaches the inside of the gas detection device 100. Therefore, in this application, the gaseous breath alcohol becomes the combustible target gas.

[0061] In one embodiment, the gas detection device 100 is a portable device that can be held in one hand by a person or attached to clothing or protective gear and is provided with a dedicated power supply unit. For example, the user carries such a gas detection device 100 while in an area where there may be at least one combustible target gas. Alternatively, the subject holds the gas detection device 100 in one hand and sends an exhaled breath sample to the mouthpiece. The gas detection device 100 may be configured as a stationary device that can be connected to a stationary power supply network and does not necessarily need to be provided with a dedicated power supply unit.

[0062] The gas detection device 100 includes a housing 5 that fluid-tightly surrounds the measurement chamber 9, except for the openings described below and except for inevitable gaps and slits.

[0063] In the first embodiment, the inlet E of the housing 5 communicates with the measurement chamber 9 from the environment, and the outlet A of the housing 5 communicates from the measurement chamber 9 to the environment. The controllable valve 6 can selectively open and close the inlet E. The controllable valve 7 can selectively open and close the outlet A. When the valve 6 is open, the gas sample G can flow into the measurement chamber 9 from the environment, i.e., the monitored area, through the inlet E. When the valve 7 is open, the gas sample G can flow out from the measurement chamber 9 to the environment. The signal processing control unit 12 equipped with the system clock 14 can automatically control the valves 6 and 7 and other components described later.

[0064] Optionally, the control unit 12 can control the pump 13, and the pump 13 controlled and thereby operated sucks the gas sample G into the interior of the gas detection device 100 through the open inlet E. When the outlet A is open, the gas flows out from the measurement chamber 9 simultaneously. Also, it is possible for the gas sample G to diffuse into the interior of the gas detection device 100 through the inlet E.

[0065] Also, an implementation form is possible in which the pump 13, the inlet E, and the outlet A exist but the valves 6 and 7 do not. The inlet E and the outlet A can be continuously open. Also, the valve 6 can be replaced with another form of closure, for example, an orifice aperture having an orifice pattern, the orifice pattern having at least one orifice, and the orifice aperture being movable with respect to the housing 5. Depending on the position of the orifice aperture with respect to the housing 5, the orifice of the orifice pattern overlaps the inlet E and the inlet E is open, or the orifice aperture closes the inlet E.

[0066] The pump 13 may be continuously driven during the operation of the gas detection device 100, or may be alternately switched on or off. The configuration in which the pump 13 is continuously switched on can be combined with a movable orifice aperture. The configuration in which the pump 13 is switched on and off avoids the need to provide an orifice aperture or other closure.

[0067] In the second embodiment (FIG. 2), since the gas permeable membrane 8 separates the measurement chamber 9 from the environment, the gas sample G can flow from the environment through the membrane 8 into the measurement chamber 9 and again flow out of the measurement chamber 9 through the membrane 8. In the illustrated second embodiment, the membrane 8 serves as an alternative to the inlet E and outlet A of the first embodiment (FIG. 1). Also in the second embodiment, a pump 13 (not shown in FIG. 2) can suck in the gas sample G through the membrane 8. Preferably, a flame guard, for example a metal grid (not shown), prevents a flame from spreading from the measurement chamber 9 through the membrane 8 to the environment.

[0068] Also in the second embodiment, an orifice aperture (not shown) can be movable relative to the housing 5 and can fluid-tightly separate or open the measurement chamber 9 from the environment depending on its position.

[0069] Unless otherwise specified, the following description relates to both embodiments.

[0070] Inside the measurement chamber 9, a semiconductor sensor 1 is arranged. The semiconductor sensor 1 comprises a semiconductor component 10 and a heating element 11. The semiconductor component 10 functions as a sensor component in the sense of the claims. The semiconductor component 10 has conductivity and is preferably composed of a metal oxide, particularly preferably a semiconductor, for example tin dioxide (SnO2). In FIGS. 1 and 2, the semiconductor component 10 is shown as a wire, which should be understood as a symbol in an equivalent circuit diagram and is only one of several possible embodiments. Electrical contacts are shown for the semiconductor component 10 and further components of the gas detection device 100 described below.

[0071] The gas sample G in the measurement chamber 9 reaches the semiconductor component 10. The gas sample G acts on the semiconductor component 10 and affects its electrical resistance R. In this embodiment, the detected variable that is affected and measurable is this electrical resistance R. In this embodiment, the chemical action is such that the higher the concentration of the combustible target gas in the gas sample G and thus in the measurement chamber 9, the lower the electrical resistance R of the semiconductor component 10. One of the reasons is that the combustible target gas often has a higher thermal conductivity value than exhaled breath, and thus the combustible target gas in the measurement chamber 9 cools the semiconductor component 10.

[0072] Hereinafter, taking tin dioxide (SnO2) as an example of the material of the semiconductor component 10, a preferred functional mode of the semiconductor component 10 will be described: The conductivity, and thus the electrical resistance R, depends on the number of free electrons (charge carriers) in the semiconductor component 10. Since there are O2 vacancies on the surface of the SnO2 crystal, there is no partner for the electrons supplied from the adjacent Sn atoms. These electrons can move freely. The number of freely moving electrons affects the conductivity of the semiconductor component 10 and thus the electrical resistance R. The semiconductor component 10 adsorbs oxygen from the environment on its surface. As a result, at least a part of the O2 vacancies is occupied by the adsorption of environmental oxygen, and the electrons that were free until then are bound. The semiconductor component 10 is heated and operated, for example, by a heating element 11. The combustible target gas is oxidized on the surface of the semiconductor component 10, and at this time, the adsorbed oxygen is desorbed again as described above. Therefore, the density of the charge carriers in the form of free electrons increases again. The higher the proportion of oxygen in the environment of the semiconductor component 10, the more free electrons combine with oxygen and the greater the electrical resistance R. Therefore, the oxidation of the combustible target gas reduces the amount of oxygen that the semiconductor component 10 can adsorb. Therefore, when the environmental conditions are the same in other respects, the higher the concentration of the combustible target gas in the measurement chamber 9, the lower the electrical resistance R of the semiconductor component 10. According to the present invention, this characteristic is utilized.

[0073] At each sampling time of the sampling times of a preset sequence, the magnitude of the actual electrical resistance R of the semiconductor component 10 is measured again. For example, the voltage sensor 25 measures the voltage U applied to the semiconductor component 10. The current intensity sensor 24 measures the current intensity I flowing through the semiconductor component 10. From the voltage U and the current intensity I, the electrical resistance R = U / I is derived. As described above, this electrical resistance R is correlated with the concentration of the target gas in the measurement chamber 9 and further depends on the environmental conditions, particularly the temperature in the measurement chamber 9.

[0074] In the exemplary embodiment, the heating element 11 takes the form of an electrical resistor and is in thermal contact with the semiconductor component 10, so the temperature of the heating element 11 sufficiently accurately matches the temperature of the semiconductor component 10. As described above, by heating the semiconductor component 10, the combustible target gas is oxidized and oxygen is desorbed.

[0075] Fluctuations in environmental conditions, particularly temperature, humidity, and atmospheric pressure, also similarly affect the conductivity of the semiconductor component 10. One of the reasons is that it is conceivable that the surface temperature of the semiconductor component 10, for example, the outer surface temperature of the semiconductor sensor 1, can change due to environmental conditions.

[0076] Hereinafter, a method for compensating to some extent the influence of such environmental conditions on the electrical resistance R by calculation will be described. In order for this influence to be compensated, the measured value of the electrical resistance R - generally the detection variable - can be used to determine the target gas concentration to be obtained.

[0077] In a preferred implementation form of the present invention, the temperature of the semiconductor component 10 is kept constant at a temperature above any possible environmental temperature during use. Thereby, the influence of the environmental temperature on the electrical resistance R of the semiconductor component 10 is reduced.

[0078] Preferably, the control unit 12 controls the temperature of the heating element 11 with the control objective of keeping the temperature of the heating element 11 constant even when the environmental conditions change, and thus the amount of heat energy input per unit time exerted by the heating element 11 on the semiconductor component 10 also remains constant even when the environmental temperature changes. In order to change the heat energy released by the heating element 11 as needed, in one configuration, the control unit 12 changes the voltage U applied to the heating element 11. In another configuration, the control unit 12 changes the current intensity I flowing through the heating element 11. These two configurations can be combined with each other. Since it is desirable for the temperature of the semiconductor component 10 to be higher than the environmental temperature, this one-sided temperature control with the heating element 11 as the actuator is sufficient. Although it is possible to cool while controlling the heating element 11, it is usually not necessary.

[0079] The electrical resistance of the semiconductor component 10 depends on the environmental conditions, particularly the oxygen content in the environment, and sometimes also on the humidity, even at a substantially constant temperature. Therefore, the electrical resistance R of the semiconductor component 10 is measured at least at a first sampling time point t1 and a subsequent second sampling time point t2. Referring to FIG. 3, a measurement period Z3 starts at the first sampling time point t1 and ends at the second sampling time point t2. Furthermore, it is possible to measure the electrical resistance R at least once at a sampling time point t_x between these two sampling time points t1 and t2. In this exemplary embodiment, this measurement period Z3 coincides with the oxidation period described later. Not only the measurement period but also the oxidation period starts at the first time point t1 and ends at the second time point t2. Therefore, the reference sign Z3 is also used for the oxidation period. In the exemplary embodiment, the first time point t1 functions as a detection time point, and the second time point t2 functions as a reference time point.

[0080] In the graph of FIG. 3, time t is plotted on the x-axis, and the measured resistance R of the semiconductor component 10 is plotted on the y-axis. At the first sampling time (detection time) t1, the concentration of the combustible target gas in the gas sample G and thus in the measurement chamber 9 is in good agreement with the environment of the gas detection device 100, i.e., the target gas concentration in the monitored area. Since the existing target gas was oxidized during the period Z3, at the second sampling time (reference time) t2, there is substantially no combustible target gas in the measurement chamber 9. Therefore, the measurement at the second sampling time t2 functions as a reference measurement or a zero-point measurement.

[0081] In order to be able to perform such a reference measurement at the second sampling time t2, the combustible target gas in the measurement chamber 9 is removed during the oxidation period Z3, so that there is no combustible target gas in the measurement chamber 9 at the second time t2. This removal is carried out by the oxidation component 2 oxidizing the combustible target gas present as a component of the gas sample G in the measurement chamber 9. Of course, there may be no combustible target gas in the monitored area, and thus no combustible target gas may already be present in the measurement chamber 9 at the first time t1.

[0082] Preferably, the concentration limit value is preset as the upper limit value of the expected concentration of the target gas in the monitored area. This concentration limit value and the volume of the measurement chamber 9 related to the structure determine the possible maximum amount of the combustible target gas in the measurement chamber 9. This possible maximum amount of the target gas is so small that there is enough oxygen in the measurement chamber 9 to oxidize all of the target gas in the measurement chamber 9.

[0083] On the one hand, the oxidation period Z3 is long enough for all of the combustible target gas in the measurement chamber 9 to be oxidized during the process of the oxidation period Z3, on the premise that the concentration of the target gas is below the concentration limit value. On the other hand, the oxidation period Z3 is preferably as short as possible so that the steps of oxidizing the combustible target gas and measuring the electrical resistance R of the semiconductor component 10 twice can be repeated as frequently as possible.

[0084] In the deviation, the concentration limit value is not necessarily preset. The measurement period and the oxidation period Z3 end when the result that the electrical resistance R does not change is obtained by measurement, or more precisely, when the slope of the change of the electrical resistance R over time remains below a preset limit value. This indicates that all the combustible target gases or at least a preset proportion of the target gases in the measurement chamber 9 have been oxidized.

[0085] The combustible target gas in the measurement chamber 9 is oxidized by the oxidation component 2. FIG. 4 shows a preferred configuration of the oxidation component 2. In this example, the combustible target gas is methane (CH4). By the oxidation component 2, a chemical reaction [Chemical formula] occurs.

[0086] This chemical reaction is shown in FIG. 4. Certainly, oxygen binds during the oxidation of the target gas. However, an arbitrary concentration limit value is preset so that the decrease in the content of O2 molecules in the measurement chamber 9 due to oxidation is small and the electrical resistance R of the semiconductor component 10 changes only negligibly.

[0087] In the preferred configuration shown in FIG. 4, the oxidation component 2 is configured as a peristaltic element and includes the following: - A helical heating segment 20, - A preferably spherical coating 21 provided around the heating segment 20, - Two electrical contacts 22, and - A plate 23.

[0088] A voltage is applied to the heating segment 20. Thereby, the heating segment 20 is heated to an operating temperature of 300°C to 700°C, preferably 400°C to 550°C. Since the heating segment 20 is in thermal contact with the coating 21, the coating 21 is also heated.

[0089] However, this temperature alone may not be sufficient to oxidize the combustible target gas to a sufficient extent. If the temperature is high, a large amount of electrical energy is consumed, and there is a high risk that the target gas in the measurement chamber 9 will burn rapidly or even explode. Even if the temperature is preferably less than 550°C, a catalyst material, such as platinum or platinum oxide, is fitted into the coating 21 to oxidize all the combustible target gas in the measurement chamber 9. Preferably, since the coating 21 is porous, the thermally effective surface area of the coating 21 is larger than when the surface is smooth.

[0090] As schematically shown in FIGS. 1 and 2, a heat barrier 4 is disposed between the semiconductor sensor 1 and the oxidation component 2. This heat barrier 4 reduces the thermal influence of the oxidation component 2 on the semiconductor sensor 1, and thus reduces the risk that the electrical resistance R of the semiconductor component 10 will change significantly due to the heated oxidation component 2 and / or due to the switching on and off of the oxidation component 2, leading to incorrect measurements. However, at least one opening, preferably a peripheral opening, is provided between the housing 5 and the heat barrier 4 so that the gas sample G can flow through the entire measurement chamber 9. This is desirable so that the oxidation component 2 can oxidize all the target gas in the measurement chamber 9, including the target gas behind the heat barrier 4, and the measured electrical resistance R of the semiconductor component 10 can be used as an indicator of the required target gas concentration.

[0091] The control unit 12 can switch the oxidation component 2 on and off. In the first configuration of the present invention, the control unit 12 switches the oxidation component 2 on during each oxidation period Z3 and switches it off outside the oxidation period Z3. Since the oxidation component 2 has a relatively low thermal mass, it quickly reaches an operating temperature of 300°C to 700°C after being switched on and rapidly cools down to the temperature of the measurement chamber 9 after being switched off. This intentionally significant and usually fluctuating temperature change will usually inevitably result in a change in the amount of thermal energy input per unit time to the outer surface of the semiconductor sensor 1 through the oxidation component 2. This temperature fluctuation usually changes the electrical resistance R of the semiconductor component 10 and thus may lead to incorrect measurements.

[0092] In the first configuration, the oxidation component 2 with fluctuating temperature may have an undesirable thermal effect on the semiconductor component 10. To reduce this thermal effect in the measurement chamber 9, a controllable heating element 3 is additionally arranged in the measurement chamber 9, particularly on the side of the same thermal barrier 4 as the oxidation component 2.

[0093] According to the first configuration, the control unit 12 can switch the heating element 3 on and off as well as the oxidation component 2. Ideally, the switched-on heating element 3 generates the same amount of thermal energy input to the semiconductor component 10 per unit time as the switched-on oxidation component 2. Effect: The oxidation component 2 has the same thermal effect on the semiconductor component 10 as the heating element 3. The risk that the actual temperature of the oxidation component 2 falsifies the measurement result of the semiconductor sensor 1 is reduced.

[0094] In one configuration, the heating element 3 includes a helical heating segment 20, a coating 21, and electrical contacts 22, similar to the oxidation component 2, but the coating 21 does not have a catalyst material. Therefore, even when the heating segment 20 is heated, the switched-on heating element 3 cannot oxidize the combustible target gas in the measurement chamber 9.

[0095] Before or after the acidification period (=measurement period) Z3 in terms of time, there is an inhalation period Z1. At least during this inhalation period Z1, the gas sample G can flow into the measurement chamber 9 from that area, in particular by being sucked in by the pump 13 and / or diffusing into the measurement chamber 9. In a first configuration form, a heating period Z2 is arranged between the inhalation period Z1 and the acidification period Z3. See Figure 3.

[0096] During each acidification period Z3, the acidification component 2 is switched on and the heating element 3 is switched off. During the heating period Z2, the heating element 3 is switched on and the acidification component 2 is switched off. The heating element 3 heats the gas sample G in the measurement chamber 9 so that a rapid temperature change does not occur in the measurement chamber 9 when transitioning from the heating period Z2 to the acidification period (=measurement period Z3). Due to the heating element 3, the amount of heat energy input per unit time to the semiconductor component 10 during the heating period Z2 is approximately equal to the amount of input during the measurement period Z3. In particular, the amount of heat energy input to the semiconductor sensor 1 has less change over time compared to the state without the heating element 3. During the inhalation period Z1, preferably both the acidification component 2 and the heating element 3 are switched off.

[0097] In one configuration, an adjustment for determining the set operating temperature Temp_Soll(3) of the heating element 3 is carried out in advance. The heating element 3 reaches this set operating temperature Temp_Soll(3) after being switched on. The purpose of the adjustment is to equalize the amount of thermal energy input per unit time to the semiconductor sensor 1 by the switched-on heating element 3 and the amount of thermal energy input per unit time by the switched-on oxidation component 2. In addition to the set operating temperature Temp_Soll(3), the distance dist(3) between the heating element 3 and the semiconductor sensor 1 and the distance dist(2) between the oxidation component 2 and the semiconductor sensor 1 can also be changed. For the adjustment, a state where there is no combustible target gas in the measurement chamber 9 is established. The set operating temperature Temp_Soll(3) and the distance are adjusted so that the detection variable of the semiconductor component 10, here the electrical resistance R, is the same when the oxidation component 2 is switched on and the heating element 3 is switched off and when the oxidation component 2 is switched off and the heating element 3 is switched on.

[0098] Figure 3 shows an exemplary time course during the operation of the gas detection device 100. Time t is plotted on the x-axis and the electrical resistance R of the semiconductor component 10 is plotted on the y-axis. The following description relates to the first embodiment according to FIG. 1.

[0099] A sequence consisting of an inhalation period Z1, a subsequent heating period Z2, and a subsequent measurement period (= oxidation period Z3) is carried out at least once. Preferably, this sequence having the three periods Z1, Z2, Z3 is repeatedly carried out using the gas detection device 100. Figure 5 shows an exemplary flowchart regarding such a sequence during the operation of the gas detection device 100.

[0100] During the inhalation period Z1, it starts at time point ta. During the inhalation period Z1, valves 6 and 7 are open, and any pump 13 is switched on. The measurement chamber 9 is flushed and filled with a new gas sample G. That is, the gas sample G already present in the measurement chamber 9 flows out of the measurement chamber 9 through the outlet A, and now the gas sample G to be inspected flows into the measurement chamber 9 from the monitored area through the inlet E. In one configuration, any pump 13 is switched on to transport the gas sample G from the environment to the measurement chamber 9. Also, it is possible for the gas sample G to be inspected to diffuse from this area into the measurement chamber 9.

[0101] In Figure 5, ta:S1 means the step of opening valves 6 and 7, switching on pump 13, and flushing the measurement chamber 9 at time point ta. The heating element 3 and the oxidation component 2 are switched off.

[0102] The inhalation period Z1 is of such a length that after the end of the inhalation period Z1, the concentration of the combustible target gas in the measurement chamber 9 is approximately equal to the concentration of the target gas in the environment and thus in the monitored area. In particular, the inhalation period Z1 is of such a length that when no combustible target gas is detected in the measurement chamber 9, it is certain that no combustible target gas above the detection limit exists in the environment. In one configuration, the duration of the inhalation period Z1 is set to be constant in advance.

[0103] During the inhalation period Z1, the oxidation component 2 is switched off. In one implementation, the heating element 3 is also switched off during the inhalation period Z1, thereby saving electrical energy. In another implementation, the heating element is switched on or switched on during the inhalation period Z1, which often makes it possible to shorten the heating period Z2, thereby saving time.

[0104] At time t0, the inhalation period Z1 has ended and the subsequent heating period Z2 begins. During the heating period Z2, the oxidation component 2 remains switched off. The control unit 12 triggers the following events at time t0: - Close valves 6 and 7 to isolate the measurement chamber 9 from the environment. - Switch off any pump 13. - Switch on the heating element 3.

[0105] In Figure 5, t0:S2 means the step of closing valves 6 and 7 and switching off pump 13 at time t0. t0:S3 means the step of switching on the heating element 3 at time t0. The oxidation component 2 remains switched off.

[0106] The heating period Z2 during which the heating element 3 is switched on is of such a length that the heating element 3 is heated to the set operating temperature Temp_Soll(3) during the heating period Z2. The set operating temperature Temp_Soll(3) was determined in a previous adjustment as described above and generates the same amount of heat energy input per unit time as the subsequently switched-on oxidation component 2.

[0107] In one configuration, the set operating temperature Temp_Soll(3) of the heating element 3 is preset. The actual temperature Temp(3) of the heating element 3 is measured. For example, the actual electrical resistance of the heating element 3 is measured. As is well known, the electrical resistance of a metal is correlated with its temperature, so the resistance serves as an indicator of temperature.

[0108] In Figure 5, E1? indicates a determination of whether the heating period Z2 has already passed, i.e., whether the heating element 3 has reached the set operating temperature Temp_Soll(3).

[0109] At time t1 (detection time), the heating period Z2 has ended and the measurement period Z3 begins. The control unit 12 triggers the following events at time t1: - Measure the electrical resistance R of the semiconductor component 10. Denote the electrical resistance value measured at t1 as r1. - Switch off the heating element 3. - Switch on the oxidation component 2.

[0110] During the measurement period Z3, the heating element 3 remains switched off. The valves 6 and 7 remain closed, and the pump 13 remains switched off. The oxidation component 2, which is switched on during the oxidation period (= measurement period) Z3, oxidizes the combustible target gas or each combustible gas in the measurement chamber 9. Naturally, there may be no combustible target gas in the area to be monitored and thus also in the measurement chamber 9, so the heated oxidation component 2 may not perform oxidation.

[0111] In one embodiment, the first time point t1 is both the end of the heating period Z2 and the start of the measurement period (= oxidation period) Z3. In FIG. 5, t1:S4 means the step of switching off the heating element 3 and switching on the oxidation component 2 at time point t1. S5(t) means that the electrical resistance R of the semiconductor component 10 is measured at time point t. Initially, the time point t is set to t1. By the measurement S5(t1) at the first time point t1, the resistance value r1 is obtained.

[0112] At the time point t2 (reference time point), the measurement period Z3, and thus the sequence consisting of the periods Z1, Z2, Z3, is ended.

[0113] The control unit 12 triggers the following events at time point t2: - Measure the electrical resistance R of the semiconductor component 10 again. By the measurement S5(t2) at the second time point t2, the value of the electrical resistance R denoted as r2 is obtained. - Switch off the oxidation component 2.

[0114] In the exemplary flowchart, the oxidation period Z3 between t1 and t2 is not set to be constant in advance. The electrical resistance R is measured at time points t1, t1 + Δt, t1 + 2*Δt, ..., where Δt is an interval set to be constant in advance. Since the oxidation component 2 burns the combustible target gas in the measurement chamber 9, the electrical resistance R becomes larger and larger. The resistance value at time t is denoted as r(t). The difference between the resistance values at two directly consecutive time points t - Δt and t, that is, the difference r(t) - r(t - Δt) is calculated.

[0115] In the example shown, during the measurement period Z3, the combustible target gas cannot reach the inside of the measurement chamber 9 from the outside. When the difference r(t) - r(t - Δt) is smaller than a preset limit value ΔR_min, substantially all of the combustible target gas in the measurement chamber 9 has been oxidized. The time point t when this is determined is used as the time point t2 when the measurement period Z3 ends. The last measured resistance value r(t) is used as the value r2 = r(t2).

[0116] In the example shown, the difference r(t) - r(t - Δt) between the two most recent resistance values is used. Generally, the slope of the electrical resistance R is calculated as a function of time, and for this purpose, the time series r(t1), r(t1 + Δt), r(t1 + 2*Δt),... is used. When this slope falls below a preset limit value, the time point of the most recent measurement is used as the second time point t2.

[0117] In FIG. 5, t2:S6 means that the oxidation component 2 is switched off at time point t2.

[0118] A subsequent sequence is started. In FIG. 3, the inhalation period Z1 of the subsequent sequence is shown. Optionally, at the second time point t2, the valves 6 and 7 are opened again, and the pump 13 is switched on again.

[0119] In the first configuration described above, the oxidation component 2 is switched on only during the oxidation period Z3 and is switched off otherwise. An alternative second configuration will be described below. In this second configuration, the oxidation component 2 is switched on not only during the oxidation period Z3 but also at least during the inhalation period Z1. Optionally, the oxidation component 2 remains switched on during the entire operation of the gas detection device 100 and is switched off only in the idle state of the gas detection device 100. In many cases, the configuration of keeping the oxidation component 2 switched on eliminates the heating element 3. Since the oxidation period Z3 can directly follow the inhalation period Z1, the heating period Z2 becomes unnecessary. However, the second configuration can also be used in combination with the heating element 3, thereby compensating to some extent for possible variations in the amount of thermal energy input generated by the oxidation component 2 in the semiconductor component 10.

[0120] In the second configuration, since the measurement chamber 9 is open during the inhalation period Z1, the gas sample G can flow from the monitored area into the measurement chamber 9. During the oxidation period Z3, the measurement chamber 9 is closed and thus fluid-tightly closed with respect to the monitored area. Therefore, during the oxidation period Z3, even if a combustible target gas is present in the area, the target gas cannot flow into the measurement chamber 9.

[0121] The process of opening and closing the measurement chamber 9 and thereby operating it selectively in an open or closed state can be realized, for example, in any of the following manners: - Switch the pump 13 on and off. In particular, the pump 13 is switched on during the inhalation period Z1 and switched off during the oxidation period Z3. - Open and close the valve 6 at the inlet E. The valve 6 is open during the inhalation period Z1 and closed during the oxidation period Z3. - Move the orifice aperture or even the flap relative to the housing 5 so that the orifice aperture 5 or the flap opens the inlet E during the inhalation period Z1 and closes the inlet E during the oxidation period Z3.

[0122] These two configuration forms can be combined with each other, which often enhances the reliability of the gas detection device 100. According to this combination, during the inhalation period Z1, the inlet E is open, and the oxidation component 2 and any heating element 3 are switched off. During the oxidation period Z3, the inlet E is closed, the oxidation component 2 is switched on, and any heating element 3 is switched off. During any heating period Z2, preferably, the inlet E is closed.

[0123] The following description relates to the configuration according to FIG. 1 and both of the two configuration forms, that is, the configuration form in which the oxidation component 2 is switched on and off, and the configuration form in which the measurement chamber 9 is opened and closed.

[0124] Two measured values r1 and r2 regarding the electrical resistance R, and optionally further measured values, are transmitted to the signal processing and evaluation unit 15, and the evaluation unit 15 is a component of the control unit 12 in the illustrated embodiment. As already explained, in this exemplary embodiment, the greater the proportion (concentration) of the combustible target gas in the measurement chamber 9, the smaller the electrical resistance R of the semiconductor component 10. The electrical resistance R further depends on the environmental conditions. According to the present invention, the difference Δr = r2 - r1 is calculated and evaluated by the evaluation unit 15. This difference Δr depends substantially only on the determined combustible target gas concentration in the measurement chamber 9, and the environmental conditions have substantially the same influence on the electrical resistance R at the two measurement times t1 and t2. "Substantially" means that the influence of the environmental conditions on the difference Δr is so small that it can be ignored. In this way, the influence of the environmental conditions is compensated by the calculation.

[0125] In one configuration, the gas detection device 100 is used to determine whether at least one combustible target gas is present in the monitored area. During use, sequences Z1, Z2, Z3 are repeatedly performed. After the sequence ends, if the measured difference Δr exceeds the difference limit value, the combustible target gas is detected. Otherwise, although it is certain that there is actually no combustible target gas, of course, this is on the premise that the gas detection device 100 is not damaged. The inventors have found that in internal tests using specific combustible target gases, the gas detection device 100 according to the present invention can reliably detect this target gas at concentrations below 10 ppm, often even below 2 ppm.

[0126] Preferably, the gas detection device 100 is calibrated in advance. In this calibration, various concentrations con(1), con(2),... of the target gas to be detected are continuously established in the environment of the gas detection device 100. For each concentration con(i), the difference Δr(i) is measured at least once. Preferably, a plurality of sequences Z1, Z2, Z3 are performed and an average is taken for the measured differences. By this calibration, an empirically determined functional relationship Con = f(ΔR) is obtained. This empirically determined functional relationship is stored in a computer-evaluable form in the data memory of the evaluation unit 15. Note: Con represents a quantity, and con represents a specific measured value of this quantity.

[0127] Preferably, during this adjustment, the heating element 3 is also set as described above so that the amount of input energy per unit time by the heating element 3 is equal to the amount of input energy per unit time by the oxidation component 2.

[0128] When the gas detection device 100 is used, the sequences Z1, Z2, Z3 are repeatedly performed. The stored functional relationship f is applied to the measured difference Δr, and the obtained actual target gas concentration con = f(Δr) is obtained.

[0129] According to the present invention, the electrical resistance R of the semiconductor component 10 is measured at least at two time points t1 and t2. In one configuration, the electrical resistance R is further measured at at least one intermediate time point t_x between the time points t1 and t2. In a preferred development, the time-dependent change in the electrical resistance R is measured during the measurement period Z3. For example, by appropriate numerical processing such as smoothing, outliers and other measurement errors are compensated to some extent by calculation.

[0130] In the second embodiment according to FIG. 2, the gas detection device 100 does not include an inlet E and an outlet A. In one configuration, a movable aperture or another suitable closure can selectively open or close the fluid communication between the measurement chamber 9 and the environment. In this configuration, at least one sequence having an inhalation period Z1, a heating period Z2, and a measurement period Z3 is similarly implemented, where the fluid communication between the measurement chamber 9 and the environment is open during the inhalation period Z1 and blocked during the heating period Z2 and the measurement period Z3. The configuration according to FIG. 2 with a movable closure can be combined with an implementation in which the oxidation component 2 is continuously switched on and the heating element 3 may or may not be present.

[0131] On the other hand, when fluid communication is continuously established between the measurement chamber 9 and the environment through the membrane 8, a sequence consisting only of the heating period Z2 and the subsequent measurement period Z3 is preferably carried out at least once, where the control unit 12 triggers the steps described above for both these periods Z2 and Z3. In this configuration, the heating period Z2 functions simultaneously as the inhalation period Z1.

Explanation of reference numerals

[0132] 1 Semiconductor sensor comprising a semiconductor component 10 and a heating element 11 2 Controllable oxidation component 2 comprising a heating wire 20, a ceramic and catalyst coating 21, electrical contacts 22, and a plate 23, configured as a catalytic peristor 3 Controllable heating element in the measurement chamber 9 4 Thermal barrier between the oxidation component 2 and, on the one hand, the heating element 3 and, on the other hand, the semiconductor sensor 1 5 Housing of the gas detection device 100 surrounding the measurement chamber 9 6 Valve at the inlet E 7 Valve at the outlet A 8 Gas permeable membrane connecting the measurement chamber 9 and the environment 9 Measurement chamber of the gas detection device 100 surrounded by the housing 5 and containing the semiconductor sensor 1, the oxidation component 2, the heating element 3, and the thermal barrier 4 10 Semiconductor component of the semiconductor sensor 1 whose electrical resistance R is measured and which functions as a sensor component 11 Heating element of the semiconductor sensor 1 for heating the semiconductor component 10 12 Signal processing control unit having an evaluation unit 15 for controlling the heating element 11 of the semiconductor sensor 1, the oxidation component 2, the heating element 3, any valves 6 and 7, and any pump 13 13 Controllable pump for sucking in the gas sample G from the environment and feeding it into the measurement chamber 9 through the inlet E 14 System clock of the control unit 12 15 Signal processing and evaluation unit which determines the concentration of the combustible target gas and is a component of the control unit 12 20 Heating wire of the oxidation component 2 21 Ceramic and catalyst coating of the oxidation component 2 22 Electrical contact of the oxidation component 2 23 Plate of the oxidation component 2 24 Current intensity sensor for measuring the current intensity I flowing through the semiconductor component 10 25 Voltage sensor for measuring the voltage U applied to the semiconductor component 10 100 Gas detection device comprising the measurement chamber 9 in the housing 5, the semiconductor sensor 1, the oxidation component 2, the heating element 3, the thermal barrier 4, an inlet E optionally provided with a valve 6 and an outlet A optionally provided with a valve 7, optionally a membrane 8, and optionally a pump 13 A Outlet from the measurement chamber 9 provided with a valve 7 dist(2) Distance between the oxidation component 2 and the semiconductor sensor 1 distance between the heating element 3 and the semiconductor sensor 1 Inlet to the measurement chamber 9 equipped with an E valve 6 E1? Decision: Has the heating period Z2 passed? Gas sample G from the monitored area that flows into the measurement chamber 9 through the inlet E or the membrane 8 and is analyzed there Electrical resistance of the semiconductor component 10 determined based on the measured values of sensors 24 and 25 Measured value r1 of the electrical resistance R at time point t1 Measured value r2 of the electrical resistance R at time point t2 Measured value r(t) of the electrical resistance R at time point t ΔR_min Predetermined limit value for the change in the electrical resistance R Step S1: Open valves 6 and 7 at time point ta, switch on the pump 13, and flush the measurement chamber 9 Step S2: Close valves 6 and 7 at time point t0, and switch on the pump 13 Step S3: Switch on the heating element 3 at time point t0 Step S4: Switch off the heating element 3 at time point t1 and switch on the oxidation component 2 t0 Start of the heating period Z2 t1 First time point at which the detection variable is measured and functions as the detection time point - at this first time point, there may be a combustible target gas in the measurement chamber 9 t2 Second time point at which the detection variable is measured and functions as the reference time point - at this second time point, there is no combustible target gas in the measurement chamber 9 due to oxidation ta Start of the inhalation period Z1 Z1 Inhalation period during which the gas sample G flows into the measurement chamber 9 and the heating element 3 is switched off Z2 Heating period starting at time point t0, during which the heating element 3 is switched on and the oxidation component 2 is switched off Z3 Oxidation period from the first time point t1 to the second time point t2, during which the oxidation component 2 is switched on and the heating element 3 is switched off

Claims

1. A gas detection device (100) for monitoring a spatial region for a combustible target gas (CH ４ ), comprising: The gas detection device (100) comprises: - a measurement chamber (9); - conductive sensor components (10, 20); - an oxidation component (2); - detection sensors (24, 25); - a signal processing and evaluation unit (15) and is configured such that: The gas detection device (100) is configured such that: - at least temporarily, a gas sample (G) flows from the area into the measurement chamber (9); - the sensor components (10, 20) come into contact with the gas sample (G) in the measurement chamber (9); The detection sensors (24, 25) are configured to measure the magnitude of the detection variable (R) of the sensor components (10, 20). The sensor components (10, 20) are such that the measurable electrical detection variable, particularly the electrical resistance (R), of the combustible target gas (CH ４ ) in the gas sample (G) in the measurement chamber (9) becomes larger in the first embodiment and smaller in the second embodiment as the concentration of the combustible target gas becomes lower. The gas detection device (100) is configured such that: The oxidation component (2) is configured to oxidize a combustible target gas (CH ４ ) contained in the gas sample (G) in the measurement chamber (9). the detection sensors (24, 25) measure the magnitude of the detection variable (R) of the sensor components (10, 20) not only at the detection time (t1) but also at a reference time (t2). The oxidation component (2) completely or at least partially oxidizes the combustible target gas (CH ４ ) in the gas sample (G) in the measurement chamber (9) during the oxidation period (Z3). The oxidation period (Z3) starts at the earlier of the two times (t1, t2), i.e., at time (t1), or after time (t1), and ends before or at the later of the two times (t1, t2), i.e., at time (t2). The gas detection device (100) is further configured such that: The evaluation unit (15) calculates the difference (Δr) between the measured value (r2) at the reference time (t2) and the measured value (r1) at the detection time (t1) for the detection variable (R), and, depending on the difference (Δr), is configured as such a gas detection device (100). When a combustible target gas (CH ４ ) exists within the monitored target area, - At the time of detection (t1), the combustible target gas (CH ４ ) also exists in the measurement chamber (9), - At the reference time point (t2), due to the oxidation during the oxidation period (Z3), the combustible target gas (CH ４ ) present in the measurement chamber (9) is less than at the detection time point (t1), and in particular, there is no combustible target gas present at all

2. The oxidation component (2) can be switched on and off. The gas detection device (100) further comprises a heating element (3) that can be switched on and off. The heating element (3) is configured to heat the gas sample (G) in the measurement chamber (9) when in the switched-on state. The gas detection device (100) is configured such that: - during the heating period (Z2), the heating element (3) is in the switched-on state and the oxidation component (2) is in the switched-off state; - during the oxidation period (Z3), the oxidation component (2) is in the switched-on state and the heating element (3) is in the switched-off state. - Automatically determine whether or not a combustible target gas (CH ４ ) exists in the gas sample (G), and / or - Automatically determine the concentration of the combustible target gas (CH ４ ) in the gas sample (G) The gas detection device (100) according to claim 1 is configured as such.

3. The oxidation component (2), when in the switched-on state, generates a quantity of thermal energy input to the sensor components (10, 20). ​ ​ ​ ​ ​ ​ ​ ​ The heating element (3) similarly generates an amount of thermal energy input to the sensor components (10, 20) in the switched-on state. The gas detection device (100) according to claim 2, wherein the amount of thermal energy input per unit time by the switched-on heating element (3) is the same as the amount of thermal energy input per unit time by the switched-on oxidation component (2).

4. The gas detection device (100) is configured such that, under the same environmental conditions, if the gas sample (G) in the measurement chamber (9) does not contain a flammable target gas, the detection variable (R) of the sensor components (10, 20) is the same as that when the oxidation component (2) is switched on and the heating element (3) is switched off and when the oxidation component (2) is switched off and the heating element (3) is switched on. takes the same value The gas detection device (100) according to claim 2 or 3.

5. The gas detection device (100) is configured such that the heating period (Z2) is temporally before the oxidation period (Z3), preferably, the end (t1) of the heating period (Z2) is the same as the start (t1) of the oxidation period (Z3). The gas detection device (100) according to any one of claims 2 to 4.

6. The oxidation component (2) - can be switched on and off, - is switched on during the oxidation period (Z3) and switched off outside the oxidation period (Z3). The gas detection device (100) according to any one of claims 1 to 5.

7. The gas detection device (100) is configured to perform at least one inclination calculation sequence, wherein the one or all inclination calculation sequences - the detection sensors (24, 25) measure the magnitude of the detection variable (R) of the sensor components (10, 20) at at least two time points (t1, t_x), wherein the two time points (t1, t_x) are within the oxidation period (Z3) and are temporally separated from each other, - the evaluation unit (15) calculates the magnitude of the inclination of the detection variable (R) over time according to the measurement value or at least two measurement values of the detection variable (R), including the step of The evaluation unit (15) if the inclination calculated in the inclination calculation sequence is below a preset limit value (ΔR_min), - Using the most recent time point in terms of time at which the magnitude of the detection variable (R) was measured as the reference time point (t2), - Using the measured value at the most recent time point as the measured value (r2) at the reference time point (t2) The gas detection device (100) according to any one of claims 1 to 6, configured as such.

8. The oxidation component (2) - Can be switched on and off, - Is switched on during the oxidation period (Z3) and switched off at least during the inhalation period (Z1), The gas detection device (100) according to any one of claims 1 to 7, wherein the gas sample (G) is configured to flow from the space region into the measurement chamber (9) at least during the inhalation period (Z1).

9. The gas detection device (100) The gas sample (G) also flows from the space region into the measurement chamber (9), preferably continuously, during the oxidation period (Z3) The gas detection device (100) according to claim 8, configured as such.

10. The measurement chamber (9) can be operated selectively in an open state and a closed state, The gas detection device (100) - In the open state, the gas sample (G) flows into the measurement chamber (9), - In the closed state, the measurement chamber (9) is fluid-tightly sealed with respect to the space region Configured as such, The gas detection device (100) The measurement chamber (9) - Is in an open state during the inhalation period (Z1) that includes the detection time point (t1) or is before the detection time point (t1), - Is in a closed state at the reference time point (t2) The gas detection device (100) according to any one of claims 1 to 9, configured as such.

11. The gas detection device (100) The oxidation component (2) is switched on also during the inhalation period (Z1), Preferably, it is continuously switched on during the operation of the gas detection device (100) The gas detection device (100) according to claim 10, configured as such.

12. An electric current flows through the sensor components (10, 20) at least when the oxidation component (2) is switched on. The gas detection device (100) according to any one of claims 1 to 11.

13. A method for monitoring a spatial region for a combustible target gas (CH ４ ) using a gas detection device (100), wherein the gas detection device (100) is - The measurement chamber (9), and - Conductive sensor components (10, 20), - Detection sensors (24, 25), - Oxidation component (2) are provided, The method is At least temporarily, a gas sample (G) flows from the region into the measurement chamber (9), The sensor components (10, 20) are in contact with the gas sample (G) in the measurement chamber (9), Said contact affects the sensor components (10, 20), and the effect is such that a measurable sensed variable of the sensor components (10, 20), in particular the electrical resistance (R), is larger in a first embodiment and smaller in a second embodiment as the concentration of the combustible target gas (CH ４ ) in the gas sample (G) in the measurement chamber (9) is lower. The oxidation component (2) oxidizes a combustible target gas (CH ４ ) contained in the gas sample (G) in the measurement chamber (9) at least during the oxidation period (Z3). The detection sensors (24, 25) measure the magnitude of the detection variable (R) of the sensor components (10, 20) not only at the detection time point (t1) but also at a reference time point (t2), The oxidation period (Z3) starts at the earlier of the two time points (t1, t2), or after the time point (t1), and ends before or at the later of the two time points (t1, t2), When a combustible target gas (CH ４ ) exists within the monitoring target area, - At the time of detection (t1), the combustible target gas (CH ４ ) also exists in the measurement chamber (9), - At the reference time point (t2), due to the oxidation during the oxidation period (Z3), the combustible target gas (CH ４ ) present in the measurement chamber (9) is less than at the detection time point (t1), and in particular, there is no combustible target gas present, Calculate the difference (Δr) between the measured value (r2) at the reference time point (t2) and the measured value (r1) at the detection time point (t1), According to the difference (Δr), - Automatically determine whether or not a combustible target gas (CH ４ ) is present in the gas sample (G), and / or - Automatically determine the concentration of the combustible target gas (CH ４ ) in the gas sample (G) including steps that enable or cause that. A method.

14. The gas detection device (100) further includes a heating element (3) that can be switched on and switched off again, Similarly, the oxidation component (2) can be switched on and switched off again, The method is - Switch on the oxidation component (2) at the start of the oxidation period (Z3) and switch it off at the end of the oxidation period (Z3), - Switch on the heating element (3) at the start of a heating period (Z2) outside the oxidation period (Z3) and switch it off again at the end of the heating period (Z2), - The switched-on heating element (3) heats the gas sample (G) in the measurement chamber (9), - At this time, preferably, the heat input per unit time of the switched-on heating element (3) to the sensor components (10, 20) is the same as the heat input per unit time of the switched-on oxidation component (2) to the sensor components (10, 20) including the step described in claim 13.

15. Perform at least one slope calculation sequence, The one or all slope calculation sequences are - The detection sensors (24, 25) measure the magnitude of the detection variable (R) of the sensor components (10, 20) at at least two time points (t1, t_x), At this time, the two time points (t1, t_x) are during the oxidation period (Z3) and are temporally separated from each other, - Calculate the magnitude of the slope of the detection variable (R) over time according to the measurement value or at least two measurement values of the detection variable (R); If the calculated slope is less than a preset limit value (ΔR_min), - Use the most recent time point at which the magnitude of the detection variable (R) was measured as the reference time point (t2), - Use the measurement value at the most recent time point as the measurement value (r2) at the reference time point (t2). The method according to claim 13 or 14, comprising the steps described above.

16. Implement the first sequence and / or the second sequence, The first sequence is - The oxidation component (2) is switched off during the inhalation period (Z1), and the inhalation period (Z1) preferably includes or is before the detection time point (t1), - The gas sample (G) flows into the measurement chamber (9) at least during the inhalation period (Z1). The method includes the steps described above. The second sequence is - Operate the measurement chamber (9) in an open state during the inhalation period (Z1), in which state the gas sample (G) flows from the monitored space region into the measurement chamber (9), - Operate the measurement chamber (9) in a closed state, in which state the measurement chamber (9) is fluid-tightly sealed with respect to the region, Preferably, the measurement chamber (9) is operated in an open state or shifted from a closed state to an open state at the detection time point (t1), - When the measurement chamber (9) is operated in a closed state, the oxidation component (2) is at least switched on. The method according to any one of claims 13 to 15, comprising the steps described above.

Images