Gas measuring device and gas measuring method for measuring high target gas concentration

Abstract

The present invention relates to a gas measurement device and a gas measurement method capable of measuring the concentration of a combustible target gas. During operation in the oxidation measurement mode, the detector and the compensator are heated. The heated detector oxidizes the combustible target gas, and the oxidation continues to heat the detector. The heated compensator compensates for the influence of environmental conditions on the detector. A total detection variable (U10-U11) dependent on the detector temperature and the compensator temperature is measured, and the target gas concentration is ascertained on the basis of the measured total detection variable (U10-U11). While operating in a thermal conduction measurement mode, the compensator is heated and the combustible target gas cools the compensator more strongly than ambient air. A compensator detection variable (U11) dependent on the temperature of the compensator is measured, and the target gas concentration is ascertained on the basis of the measured compensator detection variable (U11). The compensator is heated more strongly when operating in the thermal conduction measurement mode than when operating in the oxidation measurement mode.

Description

Technical Field

[0001] The present invention relates to a gas measuring device and a gas measuring method that can reliably measure the concentration of a target gas even when the target gas is present at a high concentration. Background Technology

[0002] A gas measuring device is known, comprising a detector and a compensator. A conductive section of the detector is heated, oxidizing a combustible target gas in a gas sample, only if the gas sample contains a sufficient amount of the target gas. The oxidation of the target gas releases heat, further heating the detector section. Therefore, the temperature of the detector section is related to the concentration of the target gas being sought and measured. A metric is used to measure the temperature of the detector section.

[0003] The compensator allows for at least partial compensation for the effects of environmental conditions on the detector, particularly the corresponding effects of ambient temperature, ambient pressure, and ambient humidity. It is possible, but not necessary, to measure at least one or even every relevant environmental condition due to the compensator. Ideally, the compensator does not oxidize the target gas, but responds to environmental conditions and the detector. Such gas measuring devices are also known as "thermal effect sensors" or "catalytic sensors." This invention also utilizes this principle. Not only the detector but also the compensator is often constructed as a so-called catalytic combustion sensor.

[0004] The inventors have internally recognized the following problem: the temperature of the detector segment is only relevant to the concentration of the target gas if the detector segment can oxidize the combustible target gas. For high target gas concentrations, a situation may arise where, although the combustible target gas is present inside the gas measuring device, there is insufficient oxygen to oxidize it. If the determination of the target gas concentration in this case is also based on the total detection parameters and thus on the temperature of the detector segment, the gas measuring device may provide erroneous results. In particular, there is a risk of failing to detect high concentrations of the combustible target gas. Summary of the Invention

[0005] The objective of this invention is to provide a gas measuring device and a gas measuring method that can reliably determine the concentration of a combustible target gas even when the target gas is present at a relatively high concentration.

[0006] This task is accomplished by a gas measuring device having the features of claim 1 and a gas measuring method having the features of claim 13. Advantageous designs are given in the dependent claims. Any advantageous design of the gas measuring device according to the invention, if meaningful, is also an advantageous design of the gas measuring method according to the invention, and vice versa.

[0007] The gas measuring device and method according to the invention are capable of measuring the concentration of a combustible target gas, which is present or may be present in a space region to be monitored. The target gas is, for example, methane (CH4) or hydrogen (H2). Typically, the gas measuring device and method according to the invention provide an estimate of the actual target gas concentration, which may deviate from the actual value.

[0008] It is possible that multiple flammable target gases may be present simultaneously in the space region. In this case, it is preferable to measure the sum of the concentrations of these flammable target gases. Hereinafter, we will refer to it simply as "target gas concentration," even if multiple flammable target gases are present and the sum of their concentrations is measured.

[0009] The gas measuring device can operate in oxidation measurement mode and, in addition, in heat conduction measurement mode. These two modes will be described in more detail below. Optionally, the gas measuring device can also operate in a static state.

[0010] The gas measuring device includes a detector and a compensator. The detector includes a conductive detector segment. The compensator includes a conductive compensator segment. The gas measuring device is configured to apply voltage to the detector and the compensator, respectively. In both modes, a voltage is applied to the compensator, and a voltage is applied to the detector, at least in oxidation measurement mode and optionally, but not necessarily, in thermal conduction measurement mode. The voltage applied to the compensator can always be the same as the voltage applied to the detector. Alternatively, the two applied voltages may be different from each other, at least temporarily and / or in thermal conduction measurement mode. The voltage applied to the detector and / or the voltage applied to the compensator can be constant over time or can vary over time. It is preferable to apply the voltage in a pulsed manner to save energy. It is preferable that no voltage is applied to either the detector or the compensator in an optional static state.

[0011] The gas sample flows into the interior of the gas measuring device, at least temporarily, from the space to be monitored, for example, because the gas measuring device draws in the gas sample and / or because the gas sample diffuses into the interior. At least a portion of the gas sample reaches the detector, and at least a portion of the gas sample reaches the compensator.

[0012] As long as voltage is applied to the detector, current flows through the detector segment. This heats the detector segment. Heating the detector segment causes the combustible target gas to be oxidized within the gas measuring device. Oxidation releases heat energy. This heat energy raises the temperature of the detector segment through which the current flows. This effect occurs if the gas sample contains a sufficient amount of combustible target gas and if there is sufficient oxygen for oxidation. Otherwise, it is possible that although combustible target gas is present, the detector fails to oxidize the target gas due to a lack of oxygen and therefore does not release heat energy.

[0013] As long as voltage is applied to the compensator, current flows through its segments. This heats the compensator segments. The gas measuring device is configured such that, ideally, even when the compensator segments are heated, the compensator does not oxidize the combustible target gas inside the measuring device. For some combustible target gases, especially hydrogen, this target is only roughly achieved.

[0014] The gas measuring device includes a total detection parameter sensor. This total detection parameter sensor is capable of measuring a total detection parameter. This total detection parameter depends not only on the temperature of the detector segment but also on the temperature of the compensator segment. In a first alternative, the higher the temperature of the detector segment, the larger the total detection parameter, and the higher the temperature of the compensator segment, the smaller the total detection parameter. Conversely, in a second alternative, the higher the temperature of the detector segment, the smaller the total detection parameter, and the higher the temperature of the compensator segment, the larger the total detection parameter. In one design, the total detection parameter sensor is capable of measuring the detector detection parameter dependent on the temperature of the detector segment and the compensator detection parameter dependent on the temperature of the compensator segment, and deriving the total detection parameter from them, for example, as a difference.

[0015] Note: If we discuss below that a sensor can measure physical parameters, then this means that the sensor directly measures the physical parameter or other parameters related to the physical parameter to be measured and is therefore a measure of the physical quantity to be measured.

[0016] Environmental conditions, especially ambient temperature, humidity, and pressure, affect not only the detector but also the compensator. The ideal state in which the compensator responds to environmental conditions just like the detector is usually only approximated. Therefore, the total detection parameter is typically influenced not only by the target gas concentration but also by environmental conditions. If sufficient oxygen is present, the total detection parameter is generally a good measure of the concentration of the target gas being sought.

[0017] Provided sufficient oxygen remains within the gas measuring device, the detector segment can utilize this oxygen to oxidize the combustible target gas, thus relating the total detection parameter to the desired target gas concentration. In oxidation measurement mode, the gas measuring device can determine the target gas concentration based on the measured total detection parameter. For example, in oxidation measurement mode, the gas measuring device applies a pre-defined proportionality coefficient or other pre-defined functional relationship to at least one measured value of the total detection parameter. Optionally, the gas measuring device may additionally use measured environmental conditions, particularly ambient temperature.

[0018] The gas measuring device includes a compensator detection parameter sensor. This sensor measures the compensator detection parameter. The compensator detection parameter depends on the temperature of the compensator segment and is generally dependent to a small extent on environmental conditions, but less often and ideally, it depends none at all on the temperature of the detector segment. Preferably, the temperature of the detector segment has at most half, more preferably at most one-quarter, and especially at most one-tenth of the overall influence of the compensator segment temperature on the compensator detection parameter. The higher the temperature of the compensator segment, the larger the compensator detection parameter in one design and the smaller in another.

[0019] In heat conduction measurement mode, the gas measuring device determines the target gas concentration based on the measured compensator detection parameters, and preferably does not use the total detection parameters for this purpose. It applies a pre-defined functional relationship to the compensator detection parameters. Generally, the smaller the compensator detection parameters, the higher the measured target gas concentration. It is possible that the measured compensator detection parameters are additionally used to derive the total detection parameters in oxidation measurement mode and / or to check the detector.

[0020] Operating in heat conduction measurement mode utilizes the fact that many combustible target gases, especially methane and hydrogen, have higher thermal conductivity than ambient air. Thermal conductivity, also known as the thermal conductivity coefficient of a medium, describes the transport of heat without active mass transport and has, for example, a unit of measurement [W / m*K]. Typically, the individual thermal conductivity for each target gas under consideration is known. Due to the higher thermal conductivity, the heated compensator segment is cooled by a gas sample containing the combustible target gas compared to the case without a combustible target gas. Therefore, with the applied voltage and other ambient conditions remaining constant, for many target gases, the higher the concentration of the target gas in the gas sample, the lower the temperature of the compensator segment. Consequently, the temperature of the compensator segment, and thus the compensator detection parameters, are also related to the desired target gas concentration.

[0021] As already described, the gas measuring device can apply voltage to the compensator segment in two modes. The gas measuring device can apply voltage as follows: when operating in thermal conduction measurement mode, the compensator segment is heated more intensely by the applied voltage than when operating in oxidation measurement mode. Preferably, the temperature of the compensator segment is at least 15%, particularly preferably at least 30%, and especially at least 50% higher in thermal conduction measurement mode than in oxidation measurement mode. This applies to the same target gas concentration and the same environmental conditions. In one design, the temperature of the compensator segment is at least 50°C higher in thermal conduction measurement mode than in oxidation measurement mode, particularly preferably at least 100°C higher, and especially at least 200°C higher, for example, between 180°C and 220°C. This more intense heating is preferably achieved by the compensator segment consuming more electrical power, for example because the voltage and / or current intensity applied in thermal conduction measurement mode is greater than in oxidation measurement mode, or because if the voltage is applied in a pulsed manner, the pulse duration is longer and / or the interval between two pulse durations is shorter. If the voltage is applied in a pulse manner, the power consumed preferably refers to the power consumed on an average time basis.

[0022] As already explained, the fact that many combustible target gases cool the heated compensator sections more intensely than air is fully utilized when operating in heat conduction measurement mode. This cooling effect is related to the concentration of the target gas being measured. The inventors have discovered in internal testing that the more intensely the compensator sections are heated, the greater the cooling effect and this correlation generally are. On the other hand, more intense heating consumes more electrical energy. Therefore, the compensator sections are heated more intensely when operating in heat conduction measurement mode than when operating in oxidation measurement mode.

[0023] When operating in oxidation measurement mode, the compensator should respond to environmental conditions almost identically to the detector. Ideally, the compensator segment should not oxidize the combustible target gas. Generally, the more intensely the detector and compensator segments are heated, the more combustible target gas they oxidize. In oxidation measurement mode, the temperature of the compensator segment does not deviate significantly from that of the detector segment, thus the compensator and detector respond to environmental conditions roughly the same way. For the reasons mentioned above, it is meaningful that the compensator segment is heated less in oxidation measurement mode than in heat conduction measurement mode. This typically results in relatively better compensation for environmental conditions in oxidation measurement mode. In heat conduction measurement mode, the resulting cooling is relatively strongly dependent on the target gas concentration and the temperature of the compensator segment. Furthermore, energy savings are achieved compared to designs where the compensator segment is intensely heated in both modes. Energy conservation is particularly important if the gas measuring device is not or cannot be connected to a fixed voltage supply network during operation.

[0024] The following situation may occur: although oxygen is present inside the gas measuring device, the amount of oxygen is so small that only a small portion of the combustible target gas inside can be oxidized. In this case, especially when operating in heat conduction measurement mode, two opposing effects may occur on the temperature of the compensator segment, where these two effects depend on the target gas concentration: - The combustible target gas causes the heated compensator to be cooled in stages more intensely than ambient air or other gas mixtures that do not contain the combustible target gas; - It is generally not possible to completely prevent the heated compensator sections from oxidizing the combustible target gas. The heat energy released by oxidation further heats the compensator sections.

[0025] Ideally, the heated compensator segment should not oxidize the combustible target gas at all, and more precisely, preferably in both modes. The following describes a design that can, optionally in combination with other designs, at least approximately achieve this objective. In other words, the design described below improves the reliability that the temperature of the compensator segment depends far more strongly on the cooling effect of the combustible target gas than on the heating effect, which depends on oxidation.

[0026] According to this design, a passivating coating is applied to the compensator functional components of the compensator. The compensator functional components include conductive compensator segments that are heated by a flowing current, and preferably include electrically insulating portions surrounding the compensator segments. The compensator functional components may have, for example, a spherical, ellipsoidal, or plate shape and internally receive the conductive compensator segments.

[0027] A passivation coating surrounds the compensator functional component, forming its outer surface, and thus comes into contact with the gas sample inside the gas measuring device. Ideally, the passivation coating covers the entire compensator functional component, meaning there are no voids within it. The passivation coating separates the gas sample from the compensator functional component, or more precisely, ideally completely separates them. Thus, the passivation coating prevents physical or chemical contact between the compensator functional component and the gas sample, and ideally completely prevents the heated compensator segment from oxidizing the combustible target gas. Conversely, there is thermal contact between the gas sample and the compensator functional component, and therefore also between the gas sample and the heated compensator segment, allowing the changing thermal conductivity of the gas sample to be measurably applied to the compensator segment, and enabling the compensator sensing parameter sensor to measure the changing thermal conductivity.

[0028] The passivation coating comprises a compound. This compound preferably contains iodine (I), particularly iodides or iodates. The passivation coating may also contain other components, especially due to contamination that is often unavoidable. In weight percent (Gew.-%), the iodine-containing compound comprises at least 50%, preferably at least 80%, and particularly preferably at least 95% of the passivation coating.

[0029] In internal testing, the inventors have found that this compound and this passivation coating, expressed in weight percent, particularly effectively prevent the unwanted event of the heated compensator segment oxidizing the flammable target gas within the relevant range. This desired preventative effect is maintained during prolonged use of the gas measuring device, even if such use lasts for days, weeks, or even months. However, other possible compounds for the passivation coating do not achieve this desired preventative effect as reliably over extended periods. This desired effect also occurs in the case of hydrogen (H2) as a flammable target gas.

[0030] The passivation coating comprises at least 50% by weight of a compound, particularly preferably, an iodide or iodate of an alkali metal or alkaline earth metal, especially at least 80% by weight. The alkali metal or alkaline earth metal is preferably potassium. The compound is particularly preferably potassium iodide (KI) or potassium iodate (KIO3). These two compounds have been shown in internal tests to be particularly suitable for preventing the associated oxidation of flammable target gases over long periods of use. Internal tests have also shown that this desired effect is achieved for hydrogen, which is a flammable target gas. Alternatively, the compound may be a mixture of potassium iodide (KI) and potassium iodate (KIO3).

[0031] The following describes a preferred design of the invention, which can be implemented in combination with the passivation coating just described or with compensators configured differently.

[0032] According to the invention, when current flows through both segments, both the detector segment and the compensator segment are heated. Preferably, the detector segment is heated to a high temperature. This temperature is preferably between 450°C and 550°C to reliably oxidize all possible flammable target gases. If only hydrogen (H2) is likely to be detected as the flammable target gas and should be reliably oxidized, in many cases heating the detector segment to a temperature between 150°C and 250°C is sufficient. Preferably, the compensator segment is heated such that, when operating in oxidation measurement mode, the temperature deviation between the heated compensator segment and the detector segment is at most 150°C, preferably at most 100°C, and in one implementation, less than the temperature of the detector segment.

[0033] The gas measuring device applies voltage to both the detector segment and the compensator segment. According to the invention, the gas measuring device applies voltage to the compensator segment such that the compensator segment is heated more intensely when operating in thermal conduction measurement mode than when operating in oxidation measurement mode. In one design, the gas measuring device applies voltage to the detector segment such that the detector segment is heated equally in both modes.

[0034] Conversely, in a preferred design, the gas measuring device applies voltage to the detector segment such that, during oxidation measurement mode operation, the detector segment is heated to a greater extent, preferably at least twice, than during thermal conduction measurement mode operation. Particularly preferred is that no voltage is applied to the detector segment during thermal conduction measurement mode operation, and therefore ideally, the detector segment is not heated at all. This design, which involves less intense or no heating of the detector segment during thermal conduction measurement mode operation, has particular advantages for oxidation measurement mode: the risk of heated material depositing on the detector surface and the detector thus no longer reliably oxidizing the combustible target gas during oxidation measurement mode operation (detector "poisoning" or "coking") is reduced. Furthermore, less heating consumes less electrical energy.

[0035] According to the present invention, the gas measuring device applies voltage to a compensator, resulting in the compensator segments being heated more intensely when operating in thermal conduction measurement mode than when operating in oxidation measurement mode. Different design schemes for achieving this are described below. Several of these design schemes can be combined with each other.

[0036] In one design, an electrical bypass line is arranged in parallel with the compensator. A controllable switch can selectively release or block (interrupt) the bypass line. If the switch releases the bypass line, a parallel connection is established. Only a portion of the current flows through the compensator and heats its segments. The remaining portion of the current flows through the parallel bypass line and does not contribute to heating the compensator segments. It is known that the current intensity flowing through the compensator segments and the current intensity flowing through the bypass line depend on the resistance of the compensator segments and the resistance of the bypass line. If the switch blocks the bypass line, the bypass line has a theoretically infinite resistance, and all current flows through the compensator and heats its segments. The gas measuring device can control the switch as follows: when operating in thermal conduction measurement mode, the controlled switch blocks the bypass line; when operating in oxidation measurement mode, the switch releases the bypass line. Thus, the compensator segments are heated more intensely in thermal conduction measurement mode than in oxidation measurement mode.

[0037] In a variation or generalization of this design, a controllable resistive element is arranged in the bypass circuit. By manipulating this element, the signal processing control equipment of the gas measuring device can change the resistance of the resistive element. The greater the resistance of the element, the more intensely the compensator segment is heated. The resistive element is manipulated such that its resistance is greater when operating in thermal conduction measurement mode than when operating in oxidation measurement mode. The design with a switch just described can be considered a special case of variable resistance.

[0038] In an improved or alternative design with a bypass line in parallel with the compensator, another bypass line is arranged in parallel with the detector. Another controllable switch selectively releases or blocks (interrupts) the other bypass line. The gas measuring device can control the switch in such a way that the other bypass line is released when operating in thermal conduction measurement mode and blocked when operating in oxidation measurement mode. Consequently, the detector segment is heated less in thermal conduction measurement mode than in oxidation measurement mode. Alternatively, another controllable resistor with variable resistance can be arranged in the other bypass line instead of a separate switch.

[0039] In one design, the gas measuring device is configured such that the intensity of the current flowing through the detector segment deviates, at least temporarily, from the intensity of the current flowing through the compensator segment. For example, the compensator is arranged in parallel with the detector, and / or the detector and compensator are powered by two different current loops. In the case of pulsed voltage, the current intensity refers to the average current intensity.

[0040] In this design scheme, one implementation results in the following: the compensator segments are heated more intensely when operating in heat conduction measurement mode than when operating in oxidation measurement mode: - When operating in oxidation measurement mode, the voltage is continuously or pulsedly applied to the compensator segment as follows: if there is no combustible target gas inside the gas measuring device, the temperature of the compensator segment deviates from the temperature of the detector segment by at least a predetermined upper temperature limit. The upper limit is preferably at most 150°C, and particularly preferably at most 100°C; - When operating in thermal conduction measurement mode, voltage is applied and / or pulsed onto the compensator segment as follows: if there is no combustible target gas inside the gas measuring device, the temperature of the compensator segment is at least as large as a pre-defined lower temperature limit, and more precisely, this is independent of the temperature of the detector segment and also independent of the cooling effect of the combustible target gas. Preferably, the temperature of the compensator segment is greater than the temperature of the detector segment in thermal conduction measurement mode.

[0041] The gas measuring device preferably achieves this effect by adjusting the applied voltage or resistance component accordingly through appropriate manipulation.

[0042] According to the present invention, the gas measuring device can selectively operate in an oxidation measurement mode or a thermal conduction measurement mode. Preferably, the gas measuring device is configured to operate in oxidation measurement mode as long as sufficient oxygen is present so that the heated detector segment can oxidize the combustible target gas in the gas sample, i.e., all combustible target gases. Only when this prerequisite cannot be met with sufficient reliability does the gas measuring device automatically switch to thermal conduction measurement mode. The reason is as follows: generally, the concentration measurements achieved by the gas measuring device in oxidation measurement mode are more reliable and / or more accurate than those achieved in thermal conduction measurement mode, but only if sufficient oxygen is still present in the gas sample, i.e., inside the gas measuring device. In other words, the gas measuring device operates in oxidation measurement mode for as long as possible and only switches to thermal conduction measurement mode when oxidation measurement mode no longer provides sufficiently reliable measurements. This design, in many cases, results in more reliable detection of target gases with lower concentrations compared to another possible approach (which determines which mode to operate the gas measuring device in).

[0043] According to one implementation of this preferred design, an oxidation standard is pre-defined in a computer-measurable form. This pre-defined oxidation standard ensures that the oxidation standard is met as long as sufficient oxygen remains within the gas measuring device so that the heated detector segment can oxidize the combustible target gas within, and thus the entire detection parameter is suitable for reliably determining the target gas concentration.

[0044] In a preferred implementation, the oxidation criterion is at least satisfied if the target gas concentration, as determined by the gas measuring device in oxidation measurement mode, is less than a pre-defined first upper concentration limit. This first upper concentration limit is pre-defined such that when the target gas concentration is less than this upper concentration limit, there is always sufficient oxygen present. Preferably, in this preferred implementation, the interior of the gas measuring device is permanently fluidly connected to the space to be monitored, allowing oxygen to continuously flow into the interior.

[0045] According to this design, when the target gas concentration determined by the total detection parameters is above the first upper concentration limit, the gas measuring device automatically switches to the heat conduction measurement mode.

[0046] Upon activation, i.e., at startup, the gas measuring device preferably operates initially in oxidation measurement mode. However, it is also possible that the gas measuring device initially operates in heat conduction measurement mode. The gas measuring device preferably remains in oxidation measurement mode and determines the target gas concentration based on the total detection parameters as long as sufficient oxygen is present. Typically, it can also reliably detect combustible target gases with relatively low concentrations. Once the gas measuring device automatically detects that the oxidation conditions are no longer met, it automatically switches to heat conduction measurement mode and measures the target gas concentration based on the compensator detection parameters. Once the gas measuring device has detected that the oxidation standard has been met again, it preferably automatically switches back to oxidation measurement mode.

[0047] Preferably, the first upper concentration limit of the oxidation standard is determined in advance based on experience, and more precisely, it is determined according to the following pre-defined rule: as long as the target gas concentration has not reached or exceeded the first upper concentration limit, the detector segment can reliably oxidize all other target gases because oxygen is available to a sufficient extent. Once the target gas concentration reaches or exceeds the first upper concentration limit, an undesirable situation arises, namely, there is no longer enough oxygen available. In this case, the total detection parameter is no longer a reliable measure of the target gas concentration. When the target gas concentration, determined by means of the compensator detection parameter, falls below this first upper concentration limit or falls below another upper concentration limit, the gas measuring device preferably switches back to oxidation measurement mode.

[0048] In one design, if the gas measuring device operates in oxidation measurement mode, it can determine the target gas concentration not only based on the total detection parameters but also, additionally, on the compensator detection parameters. For example, the high thermal conductivity of the target gas can be utilized. Typically, two estimates of the actual target gas concentration obtained in these different ways will differ from each other.

[0049] Comparing these two estimates allows for checking in many cases whether the detector is still functioning flawlessly or has been severely poisoned. Detector "poisoning" refers to the process where harmful substances deposit on the surface of the heated detector segment, rendering the segment unable to oxidize the target flammable gas sufficiently, even in the presence of sufficient oxygen. Typically, the detector segment is heated more intensely than the compensator segment, and therefore the detector poisons more quickly than the compensator. In one design, the gas measuring device itself can automatically check for poisoning. In some cases, comparing these two estimates also allows the gas measuring device to automatically check whether sufficient oxygen is still present.

[0050] The above describes a design in which the gas measuring device automatically switches from oxidation measurement mode to heat conduction measurement mode when a pre-given oxidation criterion is no longer met. In one implementation, the oxidation criterion is not met at least when the target gas concentration, as determined by the total detection parameters, is above a pre-given first concentration limit, and more specifically, for at least one measurement and preferably for all measurements, for a duration at least as long as a pre-given minimum duration. Preferably, the minimum duration is pre-given so that at least the minimum duration is elapsed even when the concentration of the combustible target gas is high, until all the combustible target gas is oxidized inside the gas measuring device, and more specifically, even without oxygen replenishment flow.

[0051] In an improved implementation, a second upper concentration limit is predetermined. This second upper concentration limit is greater than the first upper concentration limit. This improved implementation utilizes the design just described, in which the gas measuring device, while operating in oxidation measurement mode, additionally determines the target gas concentration based on compensator detection parameters. The oxidation criterion is no longer satisfied, and the gas measuring device automatically switches to heat conduction measurement mode when the target gas concentration determined by the compensator detection parameters is above the predetermined second upper concentration limit. If the condition dependent on the compensator detection parameters is met, then preferably the gas measuring device switches to heat conduction measurement mode regardless, and more precisely, regardless of what target gas concentration the gas measuring device has already determined based on the total detection parameters.

[0052] This design is a possible remedy, particularly useful in situations where the concentration of the target gas in the monitored area fluctuates significantly, or at least is likely to fluctuate significantly, for example, because the user carries the gas measuring device to areas containing different target gases, or because the flammable target gas suddenly leaks or may leak (a sharp increase) or the leak point (from which the flammable target gas leaks) is sealed (a sharp decrease). Even if a large amount of flammable target gas is present inside a sealed container rather than outside the container, the target gas concentration may rise sharply and draw the probe of the gas measuring device from the outside into the container. The step of determining the target gas concentration based on the total detection parameters necessarily requires a certain processing time. Therefore, in some cases, when operating in oxidation measurement mode, the gas measuring device cannot detect a sudden increase in target gas concentration quickly enough. The implementation with the second upper concentration limit described above reduces the risk that such a potentially dangerous event may go undetected and therefore no alarm may be issued. Typically, the cooling effect of a large number of flammable target gases can be determined quickly.

[0053] The preferred gas measuring device includes a detector chamber. The detector is located within the detector chamber. The detector chamber is situated inside the gas measuring device. At least a portion of the gas sample from the area to be monitored reaches the detector chamber and thus the surrounding environment of the detector. Preferably, a compensator is located outside the detector chamber and / or is thermally separated from the detector in other or additional ways.

[0054] In one design, the gas measuring device includes an oxygen sensor. The oxygen sensor is capable of measuring the oxygen content in a gas sample located inside the gas measuring device. The oxygen sensor can be arranged such that it measures the oxygen content of a gas sample in a detector chamber. In many cases, the oxygen sensor can additionally measure the oxygen content of another gas sample, which also originates from the space to be monitored and also arrives inside the gas measuring device, but which has not yet reached the detector chamber and therefore has not yet had oxygen oxidized. Typically, such oxygen sensors are already available as an integral part of the gas measuring device.

[0055] The gas measuring device is capable of using at least one measurement from an oxygen sensor, preferably a time-varying curve of the measured oxygen content, to check whether an oxidation criterion has been met. If the oxygen content in the detector chamber remains above a predetermined lower oxygen limit for a sufficiently long period, the oxidation criterion is met; otherwise, it is not. In one implementation, the lower limit for oxygen content is between 10% and 15% by volume, and particularly preferably 12% by volume. This lower oxygen limit applies at least if the oxygen sensor measures the oxygen content in other gas samples outside the detector chamber.

[0056] According to the present invention, the gas measuring device can operate in a thermal conduction measurement mode. In the thermal conduction measurement mode, the gas measuring device determines the concentration of the target gas based on the measured compensator detection parameters. In one design, if the gas measuring device operates in the thermal conduction measurement mode, no voltage is continuously or at least temporarily applied to the detector segments. This design has particular advantages over designs that also apply voltage to the detector segments in the thermal conduction measurement mode: - If the gas measuring device is operating in thermal conductivity measurement mode, the gas sample inside the gas measuring device and surrounding the detector typically has a high concentration of flammable target gas. If the detector segment also oxidizes the flammable target gas in this situation, the oxidation will release a particularly large amount of heat energy, and the detector segment may be heated very intensely. This can lead to undesirable deposits ("coking," "poisoning") on the detector segment and cause the detector to stop operating; - The intensely heated detector segments may also heat the compensator segments, which reduces the desired cooling effect on the combustible target gas to be detected. Furthermore, because there is typically insufficient oxygen inside the gas measuring device to oxidize all combustible target gases when operating in thermal conduction measurement mode, intense heating can cause the detector to chemically react with the heated and only partially oxidized target gas in an undesirable manner. For example, the target gas might extract oxygen from the detector's ceramic coating. This chemical reaction could damage the detector. The process of heating the detector segments by applying voltage inevitably consumes electrical energy. Typically, gas measuring devices are not, or at least not permanently connected to a fixed voltage supply network, but rather include their own voltage supply unit. Importantly, this results in relatively low energy consumption.

[0057] In one design, the gas measuring device includes an operating element that can be operated by a user. The operating element can be activated and deactivated. If the operating element is activated, the gas measuring device switches to and remains in a thermal conductivity measurement mode, and more precisely, this is independent of whether an oxidation criterion is met, the concentration of the target gas being measured, and the oxygen concentration. If the operating element is deactivated, the gas measuring device switches to an oxidation measurement mode or remains in a thermal conductivity measurement mode, as described above, and more precisely, this preferably depends on whether an oxidation criterion is met. Preferably, activation of the operating element additionally results in no voltage being applied to the detector segment, thus preventing it from being heated.

[0058] It may be particularly advantageous to pre-determine that the gas measuring device be operated in a heat conduction measurement mode: - The presence of a gas that substitutes for oxygen, such as an inert gas, particularly nitrogen, in the space area to be monitored. This situation can be intentionally induced to prevent ignition or other oxidation in the space area. In this case, there is often insufficient oxygen, and sometimes gas measuring devices cannot or cannot quickly detect this situation. This situation can also occur unintentionally; - A high concentration of at least one flammable target gas is present or may be present in the space region to be monitored. The detector is then heavily loaded when operating in oxidation measurement mode. High target gas concentrations are generally also reliably identified when operating in thermal conduction measurement mode.

[0059] In one application of the invention, a gas measuring device is used to determine the concentration of hydrogen as a target gas, or one of the combustible target gases. Hydrogen is expected to become increasingly important, and more precisely, particularly as a low-emission energy carrier for driving devices or generating electricity, or as a raw material in the chemical industry. In one implementation, the gas measuring device is capable of identifying a pre-defined requirement for the detection of hydrogen or other combustible target gases. As explained above, segmentally heating the detector to temperatures below 200°C is sufficient for the detection of hydrogen, while significantly higher temperatures are typically required for the detection of other combustible target gases.

[0060] In one design, the gas measuring device according to the invention has an output unit. Once the gas measuring device has determined a target gas concentration outside a predetermined numerical range, particularly above a predetermined limit value, the gas measuring device causes an alarm to be output on this output unit in at least one human-perceptible form. Alternatively or supplementarily, the gas measuring device causes the determined target gas concentration itself to be output. In particular, the output unit can output the alarm visually, acoustically, and / or tactilely (through vibration). Optionally, the gas measuring device additionally causes the output unit to output which mode the gas measuring device is currently operating in. The gas measuring device typically includes its own voltage supply unit, and in one design, the current charging state of the voltage supply unit is additionally output on the output unit.

[0061] Such a gas measuring device can be carried by a person who remains in an area where a flammable target gas may be present. Alternatively, the gas measuring device may be located in this area while at least one person is working there, and the gas measuring device may be fixed to a wall or ceiling or placed on the floor, for example.

[0062] In another design, the gas measuring device according to the invention has a communication unit, but not necessarily its own output unit, on which the measured target gas concentration is output. By means of this communication unit, the gas measuring device can transmit a message, including information about the identified target gas concentration, at least once, preferably repeatedly, to a spatially remote receiver. The receiver is located, for example, in an operations center that remotely monitors spatial areas where the flammable target gas may be present. Optionally, the message includes information about the current operating mode of the gas measuring device. The receiver's display unit can output the received message in at least one human-readable form. Such a gas measuring device can be fixedly (positionally) installed in or at the spatial area to be monitored. Preferably, multiple such gas measuring devices are installed in or at this area.

[0063] One possible application of this alternative design is as follows: The gas measuring device, or at least one receiver for the gas measuring device, is arranged in a completely or at least largely enclosed space, such as in a boiler, a pipe, a container, a space with combustion equipment, or a storage room belonging to a building or vehicle. Initially, access to the enclosed space is prevented. The receiver's display unit is located outside this enclosed space and outputs the identified numerical value for the target gas concentration visually and / or acoustically. If the identified target gas concentration is less than a pre-defined concentration limit and therefore not dangerous to humans, then the user or control device subsequently opens the entrance to the enclosed space. The enclosed space is then "measured open." For example, work that could result in sparks being launched is only permitted in the enclosed space if the target gas concentration is sufficiently low.

[0064] In one implementation, the gas measuring device is entirely located outside a sealed space. A hose or other fluid guiding unit connects the gas measuring device to the sealed space. A pump or other fluid delivery unit of the gas measuring device draws a gas sample from the sealed space through the fluid guiding unit. Alternatively, the gas sample diffuses to the gas measuring device through the fluid guiding unit.

[0065] In one design, the gas measuring device can control an alarm unit located spatially remotely. Once the measured concentration of the target gas falls outside the permissible range, the gas measuring device causes the alarm unit to output an alarm in at least one perceptible form, particularly acoustically. Attached Figure Description

[0066] The invention will now be described with reference to an embodiment. Here: Figure 1 The first design of the gas measuring device is schematically shown, in which the detector and compensator are arranged in a Wheatstone measuring bridge; Figure 2 It shows according to Figure 1 The two switches of the gas measuring device; Figure 3 An exemplary detector configured as a catalytic combustion sensor is shown; Figure 4 An example is shown of a detector constructed as a flat component; Figure 5 A second design scheme for the gas measuring device is schematically shown; Figure 6 An example is shown of the detection parameters used as a function of the target gas concentration. Detailed Implementation

[0067] The gas measuring device and method according to the invention are capable of monitoring a space region for the presence of at least one combustible target gas and / or at least approximately measuring the concentration of the combustible target gas in that region. The gas measuring device uses principles known from the prior art to examine gas samples from the space region for the presence and / or concentration of the combustible target gas.

[0068] The detector is located inside the housing of the gas measuring device. A gas mixture diffuses from the area to be monitored into or is delivered into the housing through an opening in the housing, for example, by a pump. In this embodiment, the interior of the housing is permanently fluidly connected to the area to be monitored during use, allowing a gas sample to continuously flow into the interior of the housing. Typically, this gas sample contains the target gas to be detected and oxygen, provided the target gas is present in the space area. Alternatively, the interior of the gas measuring device may only be fluidly connected to the space area during the process of delivering the gas sample into the interior.

[0069] The detector includes a conductive wire with heated segments, hereinafter referred to as detector segments. A detector segment is, for example, a coil forming a segment of the wire. The conductive material is, for example, platinum, rhodium, or tungsten, or an alloy of at least one of these metals. A voltage U is applied to this wire, causing a current I to flow through it. The flowing current heats the detector segment, and the heated detector segment dissipates heat. The dissipated heat causes at least one combustible target gas within the housing, typically each combustible target gas, to be oxidized, but only if the area and thus the interior contains at least one combustible target gas and if sufficient oxygen is available for oxidation.

[0070] In one application, methane (CH4) is the target combustible gas to be detected. With the supply of heat, methane reacts with oxygen to produce water and carbon dioxide. Thus, CH4 and 2 O2 are converted into 2 H2O and CO. 2。 In another application, the target gas is hydrogen (H2). It is well known that hydrogen reacts with oxygen to form water (H2O).

[0071] When the target gas oxidizes, heat energy is released inside the housing. This heat energy acts on the detector and raises the temperature of the detector segment through which the current flows. This temperature increase is related to the released heat energy and thus to the concentration of the target gas inside the housing. Gas measuring devices with such detectors are sometimes called "thermal effect sensors".

[0072] Increased temperature alters the measurable characteristics of the detector, which are related to the temperature of the detector segment. For example, increased temperature changes the resistance R of the detector segment through which current flows. For many conductive materials, it is known that the higher the temperature of the conductive material, the higher the resistance R. The gas measuring device measures at least one measurable parameter, which is affected by the characteristics and thus by the temperature of the detector segment, and this parameter is hereinafter referred to as a "detector-detected parameter." Detector-detected parameters are, for example, parameters directly related to temperature or the resistance R of the detector segment, such as the voltage U or current intensity I applied to the detector, or the electrical power P consumed by the detector segment.

[0073] Figure 1 and Figure 2 A first design of the gas measuring device 100 according to the invention is illustrated by way of example. The same reference numerals have the same meaning.

[0074] In this embodiment, detector 10 is arranged in detector chamber 8 and compensator 11 is arranged in compensator chamber 5, see [reference]. Figure 1 The detector chamber 8 with detector 10 and the compensator chamber 5 with compensator 11 are located within a stable housing 1. Due to the opening O, the stable housing 1 is fluidly connected to the area to be monitored, allowing the gas sample to reach the interior of the housing 1 from the monitored area and also from there to the interior of the detector chamber 8. A fire-resistant element 2, such as a metal grid, in the opening O reduces the risk of flames impinging outward from the interior of the stable housing 1. The stable housing 1 is surrounded by an outer housing 4, schematically shown, which preferably allows for good gripping and holding.

[0075] The voltage U10 applied to detector 10 causes current I to flow. The flowing current I heats detector segment 20 of detector 10 to its operating temperature. This temperature is typically between 450°C and 550°C if the heated detector segment 20 is to be able to oxidize all considered flammable target gases. For hydrogen as a flammable target gas, an operating temperature between 150°C and 250°C is usually sufficient. However, this operating temperature alone is generally insufficient to oxidize the flammable target gas within the inner casing 1. Higher operating temperatures are generally undesirable because they may lead to combustion or even explosion of the flammable target gas, which is generally undesirable and also consumes more electrical energy.

[0076] In order to oxidize combustible target gases even at operating temperatures below 550°C, or even below 250°C for hydrogen, the detector 10 includes a catalytic material that, in conjunction with the heated detector segment 20, oxidizes the target gas. Therefore, a gas measuring device having such a detector 10 is also referred to as a "catalytic sensor" or a "catalytically active sensor."

[0077] In a commonly used implementation, the detector segment 20 is surrounded by an electrically insulating portion, such as a ceramic sheath. This electrically insulating portion insulates the detector segment 20 and, in particular, prevents unwanted short circuits. The electrically insulating portion is thermally conductive, thereby allowing the detector segment 20 to dissipate heat energy to the surrounding environment of the detector 10, and conversely, heat energy from the surrounding environment can further heat the detector segment 20. A coating made of a catalytic material is applied to this electrically insulating portion. Alternatively, the catalytic material is embedded in the electrically insulating portion. This catalytic coating is in contact with the gas mixture in the inner housing 1 and thus also with the combustible target gas. Detectors 10 constructed in this way are often referred to as "catalytic combustion sensors."

[0078] Figure 3 A detector 10 configured as a catalytic combustion sensor is exemplarily shown, and the conversion of methane (CH4) to CO2 and H2O is schematically illustrated. The detector 10 includes... - A spirally wound and conductive wire 20, which functions as a detector segment and is made of, for example, platinum or tungsten. - A ceramic sheath 21 surrounds the detector segment 20 and has a global shape in the example shown. -A catalytic coating on the outer surface of the ceramic sheath 21, the catalytic coating on Figure 3 The middle part is drawn using circle 23. - Mounting plate 22 and - Electrical connection and mechanical retainer 36 for conductor 20.

[0079] The detector segment 20, ceramic sheath 21, mounting plate 22, and connecting parts and retainers 36 are functional components 50 of the detector 10. The catalytic coating 23 surrounds or is embedded in the detector functional component 50.

[0080] Platinum or palladium can be used as a catalyst material, for example. As an alternative to or supplement to the catalyst coating 23, the catalyst material 23 can also be embedded in the ceramic sheath 21.

[0081] In a preferred design, the detector 10 has a porous surface with a catalytic coating 23. In one design, this porous surface is fabricated as follows: a detector functional component 50, i.e., a detector 10 with a porous surface but without the catalytic coating, is provided. The catalytic coating 23 is applied to the porous surface, and a portion of the catalytic material is extruded into the interior of the detector 10. Alternatively, ceramic materials and catalytic substances may be mixed together and jointly coated onto the detector segment 20, for example, in an immersion bath.

[0082] Due to this porous surface, detector 10 has a larger surface area compared to a smooth surface. Because of this larger surface area, detector segment 20 is able to better oxidize the combustible target gas, especially because a larger amount of target gas is in contact with the catalytic material. Due to the porous surface, the gas can penetrate deeper into the detector 10.

[0083] Figure 4 A differentiated design is shown in which the detector 10 is constructed as a flat component. The detector segment 20 is part of a conductive printed conductor 30, which additionally has an electrical connection 46 and an electrical contact 34. The printed conductor 30 is applied to a support plate 31. A wafer substrate 33 supports the support plate 31. A protective layer 35 is applied to the printed conductor 30 having the detector segment 20. In one implementation, this protective layer 35 acts as a catalyst. In another implementation, a catalytic layer is applied to the protective layer 35, and more precisely, at least in the region of the detector segment 20. In a possible third implementation, the protective layer 35 is permeable to gases and covers the catalytic layer on the detector segment 20.

[0084] In one design, the fabrication of detector 10 includes the following steps: - Provide wires for detector segment 20 for detector 10.

[0085] - A liquid (coating suspension) is applied to coat the wires with a ceramic coating.

[0086] - Apply heating current to detector segment 20. This dries the liquid and causes it to calcine.

[0087] Liquids consist of the following three components: - Materials that become catalytically active after drying, such as palladium nitrate [Pd(NO3)2] or hexachloroplatinic acid (H2PtCl6). - Carrier materials, such as oxides of elements aluminum, silicon, cerium, and / or zirconium, and - Solvents, such as water.

[0088] The following description relates to two implementations of detector 10 as previously described. However, the temperature of detector 10 and consequently its detection parameters are affected not only by the released heat energy but also by the environmental conditions in the area to be monitored, particularly the ambient temperature, as well as air humidity, ambient pressure, and the concentration of non-flammable gases in the air, such as CO2 or rare gases. These environmental conditions can also alter the internal conditions of the inner housing 1. That is, these environmental conditions can also affect the detector temperature and thus the detector detection parameters, for example, because the thermal conductivity in the environment of detector 10 is altered. Ideally, the gas measuring device 100 should be able to reliably detect flammable target gases despite changes in environmental conditions, while generating fewer false alarms—that is, fewer instances where a target gas is assumed to be present even when it is not actually present—which is a flawed outcome.

[0089] In this embodiment, the gas measuring device 100 includes an optional temperature sensor 14, which measures the ambient temperature in the environment surrounding the gas measuring device 100. See [link to documentation]. Figure 1 The preferred temperature sensor 14 measures the difference between the ambient temperature and a pre-given reference temperature.

[0090] Conversely, the gas measuring device 100 of this embodiment does not include a sensor for ambient pressure or an ambient humidity sensor. The gas measuring device of this embodiment is also able to avoid processing signals from either the ambient pressure sensor or the ambient humidity sensor. More specifically, the gas measuring device 100 structurally and / or computationally compensates, to a certain extent, for the influence of indirectly measured environmental conditions on the detection parameters dependent on the temperature of the detector segment 20.

[0091] For this purpose, the gas measuring device 100 includes a compensator 11 in addition to the detector 10, see [link to relevant documentation]. Figure 1 The compensator 11 also includes conductors with compensator segments. A voltage U11 is also applied to the compensator 11, causing current to flow and the segments of the compensator 11 to be heated. The compensator 11 is also subjected to varying environmental conditions.

[0092] In a preferred embodiment, the compensator 11 also includes a helically wound and conductive wire that functions as a compensator segment and is indicated by reference numeral 38. The compensator 11 also includes a ceramic sheath, a mounting plate, an electrical connection, and a mechanical retainer. However, unlike the detector 10, the ceramic sheath of the compensator 11 does not have a catalytic coating. The compensator segment 38, the ceramic sheath, the mounting plate, the connection, and the retainer together constitute the compensator functional component 51, which can in particular have a spherical or plate shape, i.e., it can have... Figure 3 Detector 10 or Figure 4 The shape of detector 10.

[0093] Figure 1 , Figure 2 and Figure 5 The compensator 11 is shown in compensator chamber 5. Figure 1 As can be seen, detector 10 includes detector segment 20 and compensator 11 includes compensator segment 38. Figure 1 , Figure 2 and Figure 5 In the example, the compensator 11 is also constructed as a spherical or elliptical catalytic combustion sensor, but according to... Figure 3 The detector 10 does not include the catalytically active coating 23. The compensator 11 can also be constructed as a flat component, i.e., as in... Figure 4 Like the detector 10 shown in the figure.

[0094] exist Figure 1 and Figure 2 The following other components of the gas measuring device 100 can be seen in the image: -Its own voltage source 42, such as a rechargeable battery bank, -Wire 3 connects voltage source 42 to detector 10 and compensator 11. - Voltage sensor 40 (only) Figure 1 ), - Voltage sensor 12.2 (only) Figure 1 ), - Current intensity sensor 41 (only) Figure 1 ), - Two resistor components R100 and R110 with variable resistance, - Two resistor components R10 and R11 (only) Figure 2 ), - Two resistor components, R20 and R21, - Control element 17 (only) Figure 1 )and -Signal processing control unit 6 (only) Figure 1).

[0095] Optionally, a thermal barrier (not shown) inside the gas measuring device 100 thermally isolates the detector 10 from the compensator 11. The invention can also be implemented without such a thermal barrier.

[0096] according to Figure 1 and Figure 2 The gas measuring device 100 is configured as a Wheatstone bridge. The voltage sensor 40 measures the bridge voltage ΔU_B in the Wheatstone bridge. This bridge voltage ΔU_B is measured according to... Figure 1 and Figure 2 The total detection parameter plays a role in the design scheme. The total detection parameter is based on... Figure 1 and Figure 2 In the first design, the total detection parameter depends on the voltage U10 applied to detector 10 and the voltage U11 applied to compensator 11 as follows: the larger the detector voltage U10, the larger the total detection parameter; and the larger the compensator voltage U11, the smaller the total detection parameter. Voltage sensor 12.2 measures the voltage U11 applied to compensator 11. Current intensity sensor 41 measures the intensity I.3 ​​of the current flowing through wire 3.

[0097] Compensator 10 and detector 11 in Figure 1 and Figure 2 The resistors are connected in series. Resistor R100 is connected in parallel with detector 10, and resistor R110 is connected in parallel with compensator 11. Resistors R20 and R21 are connected in parallel with the series circuit of detector 10 and compensator 11.

[0098] exist Figure 1 and Figure 2 Outline -Voltage U42 of voltage source 42 - The voltage U10 applied to detector 10, and - Voltage U11 applied to compensator 11.

[0099] The measured values ​​from sensors 40, 41, 12, 2, and 14 are transmitted to and processed by control device 6. Signal processing and evaluation unit 9 derives an estimate for the concentration of the target gas, specifically, an estimate for the concentration of methane or hydrogen in the gas sample. In this embodiment, evaluation unit 9 is an integral part of control device 6.

[0100] exist Figure 1 and Figure 2In the example shown, the components form a Wheatstone measuring bridge. Detector 10 and compensator 11 are connected in series. The resistance of voltage sensor 40 is higher than that of components 10, 11, R10, R11, R20, and R21. In one design, voltage sensor 40 directly measures the so-called bridge voltage ΔU_B = (U10 - U11) / 2. The current intensity I.3 ​​is kept constant by adjustment (closed-loop control) so that the voltage U, especially the bridge voltage ΔU_B, is proportional to the resistance R and therefore related to the temperature of detector segment 20 and the target gas concentration. For this adjustment, the actual current intensity I.3 ​​is used, as measured by current intensity sensor 41.

[0101] In one implementation, a pulsed voltage is applied to save power. The adjustment target of keeping the current intensity I.3 ​​constant involves the current intensity during the electrical pulse. In another implementation, a voltage is continuously applied to the detector 10 and the compensator 11.

[0102] The corrected bridge voltage ΔU_B korr =ΔU_B – ΔU_B0 is related to the target gas concentration. Here, ΔU_B0 is the zero point, which is the bridge voltage ΔU_B that occurs when there is no flammable target gas in the area to be monitored and thus inside the gas measuring device 100. It is preferable to determine this zero point ΔU_B0 in advance based on experience. The correction performed with the zero point ΔU_B0 compensates for possible differences between the detector 10 and the compensator 11 caused by their structural types. It is possible to re-determine the zero point ΔU_B0 at least once by at least one second adjustment during the use of the gas measuring device 100.

[0103] In accordance with Figure 1 and Figure 2 In the design scheme, the corrected bridge voltage ΔU_B korr =ΔU_B–ΔU_B0 plays a role as the total detection parameter.

[0104] Figure 5 A second design of the gas measuring device 100 is shown. Consistent reference numerals are used in the accompanying drawings. Figure 1 and Figure 2 The reference numerals in the figures have the same meaning. Detector chamber 8 is fluidly connected to the monitored area B via opening O1, and compensator chamber 5 is fluidly connected to the monitored area via opening O2. The spacing between the catalytic coating 23 and the rest of detector 10, and the spacing between the passivation coating 24 and the rest of compensator 11 (described below), are shown exaggeratedly.

[0105] According to the second design, electrical energy is supplied to detector 10 and compensator 11 independently. A first current loop 1.1 connects detector 10 to a first voltage source 43, and a second current loop 3.2 connects compensator 11 to a second voltage source 44. An optional operable switch 28 can release or interrupt the current loop 3.1 between detector 10 and voltage source 43 depending on its position. Current loop 3.2 is preferably not interrupted.

[0106] Voltage sensor 12.1 measures the voltage U10 applied to detector 10. Current sensor 13.1 measures the current intensity I.1 flowing through the current loop 3.1 for detector 10. Voltage sensor 12.2 measures the voltage U11 applied to compensator 11. Current sensor 13.2 measures the current intensity I.2 flowing through the current loop 3.2 for compensator 11. Current intensities I.1 and I.2 are kept constant by adjustment.

[0107] In one implementation of the second design scheme, the total detection parameters are derived from the voltage difference ΔU = U10 – U11. Ideally, the voltage difference ΔU = U10 – U11 is zero when no flammable target gas is present, but in practice, it is not zero even when no flammable target gas is present. Therefore, the corrected voltage difference ΔU is calculated. korr =U10–U11-ΔU0 and used as the total detection parameter. This total detection parameter ΔU korr It is related to the target gas concentration. A zero value ΔU0 occurs when there is no flammable target gas, and this zero value compensates for the structural differences between detector 10 and compensator 11. Alternatively, the zero value ΔU0 can be reset by at least one readjustment during its service life.

[0108] The aforementioned method for measuring target gas concentration rests on the following premise: sufficient oxygen must be present in detector chamber 8 so that detector 10 can oxidize all combustible target gases. Only then can the heat released during oxidation be reliably used as a measure of target gas concentration. This premise may no longer be met in cases of high target gas concentrations. In particular, it is possible that while combustible target gases are present in detector chamber 8, oxygen for oxidation is absent. Oxygen may also be absent when another gas, not necessarily the target gas, has replaced it. This other gas is especially an inert gas, which should prevent undesirable oxidation in the space region. If, despite this, the target gas concentration is measured solely by the heat released during oxidation, there is a danger of measuring an excessively low target gas concentration, i.e., failing to detect a dangerously high concentration. This could endanger the user and is therefore undesirable.

[0109] Therefore, if the target gas concentration measured by the released heat energy has reached a predetermined upper concentration limit, it is preferable to use an alternative treatment method. The upper concentration limit is chosen such that, upon reaching or exceeding this upper concentration limit, there is a possibility that almost all combustible target gases in detector chamber 8 will be oxidized. In other words, as long as the upper concentration limit has not been reached, there is certainly sufficient oxygen in detector chamber 8 for oxidation.

[0110] In another processing method, when the target gas concentration has reached the upper concentration limit, the detection parameters related to the temperature of detector segment 20 are not used to determine the target gas concentration. Therefore, in this embodiment, the voltage U10 applied to detector 10 is not used in other processing methods. This other processing method utilizes the fact that hydrogen and many other flammable target gases to be detected have higher thermal conductivity than air. Therefore, these flammable target gases cool the heated compensator segment 38 of compensator 11 more intensely than ambient air.

[0111] In another approach, the temperature of compensator segment 38 is measured, more precisely, as a temperature measurement. The temperature of compensator segment 38 is related to the desired target gas concentration. More precisely, under otherwise identical conditions, the higher the desired target gas concentration, the lower the temperature, compared to a state without combustible target gas. In this embodiment, the current intensity I.3 ​​flowing through compensator 11 is... Figure 1 and Figure 2 ) or I.2 ( Figure 5 The voltage U11 applied to the compensator 11 is kept constant, and more precisely, kept constant through appropriate adjustments. The voltage U11 applied to the compensator 11 is related to the temperature of the compensator segment 38. The zero point, i.e., the voltage U110 applied to the compensator 11 when no flammable target gas is present, is determined empirically. In this embodiment, the corrected compensator voltage U11 is... korr =U11–U110 is used as a probe parameter for the compensator.

[0112] The gas measuring device 100 can operate in at least two different modes, optionally additionally in a static state. The control device 6 results in the gas measuring device 100 of this embodiment automatically switching from one mode to another, and more precisely, switching according to a pre-given oxidation standard. In this embodiment, the gas measuring device 100 can operate in the following modes: - In oxidation measurement mode, the gas measuring device 100 measures the gas according to the calibrated bridge voltage ΔU_B. korr (according to Figure 1 and Figure 2(Design scheme) or based on the corrected voltage difference ΔU korr (according to Figure 5 The design scheme), that is, to determine the concentration of the target gas based on the total detection parameters, or - In the heat conduction measurement mode, the gas measuring device 100 measures according to the corrected compensator voltage U11. korr =U11–U110, that is, the concentration of the target gas is determined based on the detection parameters of the compensator.

[0113] Therefore, in this embodiment, the corrected bridge voltage ΔU_B korr (according to Figure 1 and Figure 2 (Design scheme) or corrected voltage difference ΔU korr (according to Figure 5 The design scheme) functions as the total detection parameter, and the corrected compensator voltage U11 korr It functions as a probe parameter for the compensator.

[0114] As just explained, the gas measuring device 100 can operate in two different modes. It is preferable to use different zero values ​​in these two modes. The zero value ΔU_B0 of the bridge voltage ΔU_B or the zero value ΔU0 of the voltage difference ΔU = U10 – U11 is used in the oxidation measurement mode to calculate the total detection parameter. In the heat conduction measurement mode, the zero value U110 of the compensation voltage U11 is used to calculate the compensator detection parameter U11. korr Note: The compensator 11 is able to have a different zero value U110 when operating in oxidation measurement mode than when operating in heat conduction measurement mode, especially due to the different temperatures of the compensator segments 38.

[0115] When operating in oxidation measurement mode, evaluation unit 9 applies the first evaluation rule to the total detection parameter ΔU_B being measured. korr or ΔU korr Above, the first evaluation rule is pre-defined in a computer-measurable form. This first evaluation rule depends on the total detection parameter ΔU_B. korr or ΔU korr Furthermore, it optionally depends on the measured ambient temperature and optionally on another measured ambient condition. As explained above, the optional temperature sensor 14 can preferably measure the ambient temperature as the difference from a pre-given reference temperature. When operating in heat conduction measurement mode, the evaluation unit 9 applies the second evaluation rule to the measured compensator probe parameter U11. korr Above. The second evaluation rule depends on the compensator detection parameter U11. korr And optionally, it depends on the measured ambient temperature and / or another measured ambient condition.

[0116] In this embodiment, the two evaluation rules are determined in advance through a learning method using sampling. For example, two evaluation rules are given in advance, and each of these rules includes at least one model parameter. A preferred model parameter is the reciprocal of an empirically determined proportionality coefficient, where this proportionality coefficient describes the influence of the target gas concentration on the corresponding detection parameter used. An optional other model parameter is the reciprocal of another empirically determined proportionality coefficient, where this other proportionality coefficient describes the influence of the measured ambient temperature on the detection parameter used.

[0117] The oxidation criterion is predetermined such that at least this criterion is met when sufficient oxygen is present in detector chamber 8 to oxidize all combustible target gases. The preferred oxidation criterion depends on the measured concentration of the target gas. Different implementations of the oxidation criterion are possible.

[0118] The preferred gas measuring device 100 initially operates in oxidation measurement mode. The control device 6 repeatedly checks, preferably at a fixed sampling rate, whether the oxidation criteria are still met. For example, the evaluation unit 9 compares the target gas concentration identified in the oxidation measurement mode with a pre-defined first upper concentration limit. Alternatively, the evaluation unit 9 checks how long the identified target gas concentration remains above a pre-defined lower concentration limit.

[0119] Once the control device 6 detects that the oxidation standard is no longer met with sufficient reliability, the control device 6 causes the gas measuring device 100 to automatically switch to the heat conduction measuring mode. In one implementation, the control device 6 manipulates... Figure 2 Switch S10 or Figure 5 Switch 28 and cause no voltage to be applied to detector segment 20.

[0120] Preferred evaluation unit 9 is based on compensator detection parameter U11 during use. korr The estimated value for the target gas concentration is continuously determined, and more specifically, this estimated value is also determined when the gas measuring device 100 is operating in oxidation measurement mode. In one implementation, a second upper concentration limit larger than the first upper concentration limit is predetermined. If the evaluation unit 9 has detected the following event, the control device 6 causes the gas measuring device 100 to switch to heat conduction measurement mode: according to the compensator detection parameter U11 korr The identified target gas concentration is above the second upper concentration limit. Control device 6 preferably induces this conversion without depending on the target gas concentration already measured according to the total detection parameters.

[0121] As already explained, the oxidation criterion is met if there is sufficient oxygen in detector chamber 8 so that detector 10 can oxidize all combustible target gases present there. A design has been described above in which control device 6 determines whether the oxidation criterion has been met based on the measured concentration of the target gas. Alternatively, an optional oxygen sensor 15 may measure the oxygen content in the gas sample within detector chamber 8, and control device 6 may check whether the oxidation criterion has been met based on the measurement from oxygen sensor 15.

[0122] Preferably, if the pre-defined reverse criterion is met, the control device 6 causes the gas measuring device 100 to switch back to the oxidation measuring mode.

[0123] In a preferred implementation, when the evaluation unit 9 has detected the following event: in the heat conduction measurement mode, i.e., according to the compensator detection parameter U11 korr If the measured concentration of the target gas is less than a pre-defined upper concentration limit, then the reverse standard is satisfied. This upper concentration limit is preferably less than the first upper concentration limit mentioned above.

[0124] This describes a design in which the gas measuring device 100 automatically switches from one mode to another. Possibly, the gas measuring device 100 may additionally include a selection switch that the user can operate. By operating the selection switch accordingly, the user determines how the gas measuring device 100 should be operated. - The gas measuring device 100 is selectively operated in oxidation measurement mode or heat conduction measurement mode according to the oxidation standard; - The gas measuring device 100 operates in thermal conduction measurement mode without depending on the oxidation standard.

[0125] exist Figure 1 and Figure 5 The example shows a selection switch in the form of an actuating element 17.

[0126] It is also conceivable that the control device 6 has detected, for example, the following event based on the detected user input: the detector chamber 8 has been flushed with a gas sample containing sufficient oxygen. For example, the user has brought the gas measuring device 100 to an area with sufficient oxygen and no flammable target gas. For example, the user then manipulates the control element 17, making the oxidation measurement mode possible again.

[0127] Alternatively, the following design could be conceived: an optional oxygen sensor 15 has already measured a sufficiently high oxygen concentration in the detector chamber 8.

[0128] Figure 6 The diagram schematically illustrates how the detection parameters used depend on the target gas concentration. Results from internal experiments are shown. The concentration of the combustible target gas, methane (CH4), in [volume % (Vol%)] is plotted on the x-axis, and the corresponding values ​​in [mV] for the detection parameters used are plotted on the y-axis. Curve OxM relates to the oxidation measurement mode, in which the target gas concentration is determined based on the total detection parameters, which in this case is based on the calibrated bridge voltage ΔU_B. korr =ΔU_B–ΔU_B0 (according to Figure 1 and Figure 2 (Design scheme) or corrected voltage difference ΔU korr =U10-U11-ΔU0 (according to) Figure 5 (Design scheme). Curves WlM;eq and WlM;high relate to the heat conduction measurement mode, in which the compensator probe parameters are used, in this case, the calibrated compensator voltage U11. korr =U11-U110 Determine the concentration of the target gas.

[0129] exist Figure 6 In the example, methane is the flammable target gas. The Lower Explosive Level (LEL) is 4.4% by volume in this embodiment. If the gas measuring device 100 has measured a target gas concentration greater than α * UEG, it outputs an alarm or causes a remote receiver to output an alarm. This is independent of the mode in which the target gas concentration is measured. The factor α is between 0 and 0.6 and preferably less than 0.5. In one implementation, the gas measuring device 100 outputs a preliminary alarm when the target gas concentration is greater than α1 * UEG, and a main alarm when the target gas concentration is greater than α * UEG. Here, 0 < α1 < α <= 0.6. For example, α1 = 0.2 and α = 0.4.

[0130] As already described, in this embodiment, during the use of the gas measuring device 100, the detector chamber 8 is continuously in fluid connection with the space region B to be monitored, and the gas sample continuously flows into the detector chamber 8. Total detection parameter ΔU_B korr or ΔU korr The concentration reaches its maximum at 9.6% by volume of methane in the air, a so-called stoichiometric concentration, where all oxygen in detector chamber 8 is consumed. At higher target gas concentrations, the following two effects occur: -Because there is not enough oxygen in the detector chamber 8, the heated detector segment 20 oxidizes less of the combustible target gas, and the temperature of the detector segment 20 decreases again. - In addition, because methane has higher thermal conductivity than air, the gas sample in detector chamber 8 and the gas sample in compensator chamber 5 have even higher thermal conductivity.

[0131] For these two reasons, the total probe parameter (corrected bridge voltage ΔU_B) korr See Figure 1 and Figure 2 Or the corrected voltage difference ΔU korr See Figure 5 It gets smaller again.

[0132] As mentioned above, in a preferred design, when the target gas concentration identified in the oxidation measurement mode reaches or exceeds a pre-defined first upper concentration limit, the control device 6 causes the gas measuring device 100 to automatically switch to the heat conduction measurement mode. This first upper concentration limit is less than the stoichiometric concentration and, in the example shown, is 6% by volume.

[0133] Furthermore, as mentioned above, one design scheme is employed in which, when a pre-defined adverse criterion is met, the control device 6 causes the gas measuring device 100, operating in thermal conductivity measurement mode, to switch back to oxidation measurement mode. This adverse criterion is met when the target gas concentration identified in thermal conductivity measurement mode is less than a pre-defined adverse limit. In the example shown, this adverse limit is 3.8% by volume.

[0134] When the target gas concentration changes rapidly, the aforementioned 6 volume % limit may be insufficient in some cases when operating in oxidation measurement mode. For safety, a second upper concentration limit, preferably above the stoichiometric concentration, is pre-defined, for example, 11 volume % . The control device 6 switches the gas measuring device 100 from oxidation measurement mode to heat conduction measurement mode when the following event is detected: the evaluation unit 9 detects the compensator parameter U11. korr Determine the concentration of the target gas above the second upper concentration limit. Control device 6 determines the target gas concentration independently of which concentration is being determined in oxidation measurement mode, i.e., based on the total detection parameter ΔU_B. korr Or ΔU korr This leads to a shift to the heat conduction measurement mode.

[0135] When operating in oxidation measurement mode, compensator segment 38 must be heated to approximately the same temperature as detector segment 20 so that detector 10 and compensator 11 respond sufficiently similarly to environmental conditions, including those not directly measured, in order to at least approximately compensate for the impact of these environmental conditions on the total detection parameter ΔU_B. korr or ΔU korr The influence of these environmental conditions, especially ambient pressure, ambient humidity, and the chemical composition of ambient air. If the gas measuring device 100 does not have a temperature sensor 14, then ambient temperature is also considered an unmeasured environmental condition.

[0136] In this embodiment, however, the compensator 11 should not oxidize the combustible target gas, more specifically, it should not oxidize the combustible target gas when deriving the measured value for the target gas concentration based on the detector voltage U10 and the compensator voltage U11, nor should it oxidize the combustible target gas based solely on the compensator voltage U11. If the target gas concentration is calculated based on the increased thermal conductivity and thus based on the compensator voltage U11, the compensator 11 must especially not oxidize the combustible target gas within the relevant range. If the compensator 11 also oxidizes only a relatively small amount of the combustible target gas, this effect masks the increased thermal conductivity, i.e., the cooling effect, thus increasing the risk of providing erroneous measurements. It is even possible that the oxidation of the target gas by the compensator 11 offsets the increased thermal conductivity, causing the gas measuring device 100 to provide an erroneous result indicating the absence of the target gas.

[0137] In this embodiment, during the manufacture of the compensator 11, wires for the compensator segment 38 of the compensator 11 are provided. These wires are coated with ceramic, which does not contain any catalytically active material. In one implementation, alumina is used for this purpose.

[0138] As already described, the conductors of compensator segment 38 are coated with ceramic. Next, the ceramic is coated with a passivation coating 24. The passivation coating 24 is applied as follows: the conductors with the ceramic coating are immersed in a bath containing chemical components and a solvent, such as water. Subsequently, the coated conductors are removed from the bath and then dried. This causes the solvent to evaporate. When using the gas measuring device 100, the passivation coating 24 comes into contact with the gas sample in the compensator chamber 5. Ideally, the passivation coating 24 completely separates the ceramic and conductors of the compensator 11 from the gas sample.

[0139] In this embodiment, the passivation coating 24 is composed of at least 50% by weight, preferably at least 80% by weight, and particularly preferably at least 95% by weight, a compound containing iodine. Preferably, the passivation coating 24 is composed of at least 50% by weight, preferably at least 80% by weight, an iodide or iodate of an alkali metal or alkaline earth metal. This alkali metal or alkaline earth metal is preferably potassium. Particularly preferred are compounds of potassium iodide (KI) or potassium iodate (KIO3).

[0140] As already described, the gas measuring device 100 can selectively operate in either an oxidation measurement mode or a heat conduction measurement mode. In oxidation measurement mode, the gas measuring device 100 operates according to the total detection parameter ΔU_B. korr or ΔU korr In the heat conduction measurement mode, the compensator detection parameter U11 is used. korr To determine the concentration of the target gas. In oxidation measurement mode, compensator 11 compensates for the influence of environmental conditions. Therefore, in oxidation measurement mode, the deviation between the compensator temperature and the detector temperature is not too large, preferably a maximum of 150°C, and particularly preferably a maximum of 100°C. This boundary determination does not exist in heat conduction measurement mode because the compensator detection parameter U11... korr It depends solely on the temperature of the compensator.

[0141] The inventors have determined through internal experiments that, in the heat conduction measurement mode, the higher the temperature of the compensator, the higher the compensator detection parameter U11. korr The better the measurement is for the desired target gas concentration. Regarding background: It is known that most target gases have higher thermal conductivity than air; therefore, the higher the target gas concentration, the more intensely the compensator 11 is cooled. The inventors have internally determined that the higher the compensator temperature, the stronger the cooling effect. The compensator temperature refers to the temperature obtained by applying voltage to the compensator 11 and allowing current to flow through the wire 38.

[0142] exist Figure 6 The example illustrates the effect of two different temperatures on compensator segment 38. Curve WlM;eq shows the compensator probe parameter, here U11, in the following possible implementations. korr The correlation: As mentioned above, not only in the oxidation measurement mode but also in the thermal conduction measurement mode, the compensator temperature is thus generated such that it deviates from the detector temperature only slightly and is the same in both modes. Conversely, if the compensator temperature is induced to be higher in the thermal conduction measurement mode than in the oxidation measurement mode according to the invention, the curve WlM;high shows the compensator detection parameter U11 korr The correlation. In Figure 6 The curves shown are for illustrative purposes only.

[0143] The following technical theory according to the present invention arises from the principle just mentioned: The compensator temperature is higher in the heat conduction measurement mode than in the oxidation measurement mode. Therefore, when switching to the heat conduction measurement mode, the control device 6 increases the current intensities I.2 and I.3 flowing through the wire 38 of the compensator 11. Conversely, when switching to the oxidation measurement mode, the control device 6 decreases the current intensities I.2 and I.3.

[0144] As is achieved, different implementations are possible.

[0145] Figure 2 This illustrates one possible implementation method that can be applied to... Figure 1 On the Wheatstone measuring bridge, a bypass line L11, containing a resistor R11 and a switch S11, is arranged in parallel with the compensator 11. The resistor R11 and the switch S11 together constitute... Figure 1 One implementation of the resistive component R110. If switch S11 is closed, only a portion of the current I.3 flows through compensator 11 and heats compensator segment 38. Another portion of the current I.3 flows in parallel with compensator 11 through bypass line L11 with the closed switch S11. If switch S11 is open, all current I.3 flows through compensator 11. One result is that compensator segment 38 is heated more intensely when switch S11 is open than when switch S11 is closed. Switch S11 can be manipulated. Control device 6 manipulates switch S11 such that switch S11 is open when operating in thermal conduction measurement mode and closed when operating in oxidation measurement mode.

[0146] Another result is that the resistance of the circuit with compensator 11 and resistive member R11 is smaller when switch S11 is closed than when switch S11 is open. In one design, the voltage U11 applied to compensator 11 is adjusted such that the current intensity I.3 ​​remains constant regardless of the position of switch S11—naturally, it remains constant after the start-up time.

[0147] In another design, the compensator voltage U11 is kept constant by adjustment.

[0148] Optionally, a bypass line L10, comprising a resistor R10 and a switch S10, is connected in parallel with the detector 10. The resistor R10 and the switch S10 together constitute... Figure 1One implementation of the resistive component R100. When switch S10 is closed, only a portion of the current I.3 flows through detector 10, and the other portion of the current I.3 flows through bypass line L10. When switch S10 is open, the total current I.3 flows through detector 10. Control device 6 manipulates switch S10 in such a way that switch S10 is open in oxidation measurement mode and closed when operating in thermal conduction measurement mode. This design particularly reduces the risk of damage to detector 10 when high target gas concentrations are present in detector chamber 8 and therefore gas measuring device 100 is operating in thermal conduction measurement mode.

[0149] Figure 5 It shows that when as in Figure 5 This is one implementation where the detector 10 and compensator 11 are powered independently, and therefore the current intensity I.1 flowing through the detector 10 can deviate from the current I.2 flowing through the compensator 11. The control device 6 can manipulate the voltage source 43, and preferably independently manipulates the voltage source 44. This manipulation results in the voltage U11 applied to the compensator 11 being larger in the thermal conductivity measurement mode than in the oxidation measurement mode. Conversely, the voltage U10 applied to the detector 10 is preferably larger in the oxidation measurement mode than in the thermal conductivity measurement mode. In one design, the resistance in current loop 3.1 and the resistance in current loop 3.2 are the same in both modes.

[0150] according to Figure 5 In the design scheme, a resistor element R110 with a variable resistance value is additionally arranged in the current loop 3.2 for the compensator 11. The control device 6 can manipulate the resistor element R110. The manipulation results in the following: when operating in oxidation measurement mode, the resistance of the resistor element R110 is larger, preferably at least twice as large, as when operating in thermal conduction measurement mode.

[0151] In an improved version of this design, a resistive element R100 with a variable resistance value is arranged in the current loop 3.1 for the detector 10. The control device 6 is capable of manipulating the resistive element R100. The manipulation results in the following: when operating in oxidation measurement mode, the resistance of the resistive element R100 is smaller, preferably at most half the size, than when operating in thermal conduction measurement mode.

[0152] In another design, control device 6 can manipulate voltage source 44 in current loop 3.2 and optionally additionally manipulate voltage source 43 in current loop 3.1. Through manipulation, control device 6 can change the voltage U44 of voltage source 44 and optionally also change the voltage U43 of voltage source 43. Through this manipulation, control device 6 induces different compensator temperatures in two different modes.

[0153] It is possible to change not only the voltage U44 of the power supply 44 but also the resistance of the resistive component R11. It is also possible that only the voltage U44 or only the resistance can be changed.

[0154] According to the design described so far, the gas measuring device 100 can automatically switch from an oxidation measurement mode to a heat conduction measurement mode and then back again, and more specifically, preferably, such a switch is performed based on whether an oxidation criterion is met. Alternatively, the gas measuring device 100 may operate in heat conduction measurement mode without depending on the oxidation criterion. In one design, the gas measuring device 100 includes an actuation element 17, which actuates... Figure 1 and Figure 5 The diagram is schematically shown. The control element 17 can be activated and deactivated, for example, by the user adjusting the control element to on or off. Activating the control element 17 triggers the gas measuring device 100 to switch to a thermal conductivity measurement mode. Preferably, the detector 10 is then additionally deactivated, i.e., no current is supplied to it and thus it is not heated. Deactivating the control element 17 triggers the gas measuring device 100 to switch to an oxidation measurement mode or remain in a thermal conductivity measurement mode depending on whether an oxidation criterion is met.

[0155] List of reference numerals 1. Internal housing, enclosing detector chamber 8 and compensator chamber 5. 2. Fireproof components in the inner casing 1 3.1 The current loop for detector 10 includes voltage source 43 and resistive component R10. 3.2 The current loop for compensator 11 includes voltage source 44 and resistive component R11. 4. Outer housing, surrounding the inner housing 1, components R10, R11, R20, R21, S10, S11, sensors for current intensity and voltage, and voltage sources 42, 43, 44. 5. Expansion chamber, surrounding expansion joint 11, having an opening O2 6. Control equipment to process the measured values ​​from sensors 40, 41, 12.2, and 14. 8. Detector chamber, surrounding detector 10, having an opening O1 9. The signal processing and evaluation unit, which determines the concentration of the target gas, is a component of control device 6 in one design scheme. 10. A detector, including a detector functional component 50 with detector segments 20 and a ceramic sheath 21, and a catalytic coating 23. 11. A compensator, comprising a compensator functional component 51 with compensator segments 38 and a ceramic sheath 21, and a passivation coating 24. 12.1 Voltage sensor, measuring the voltage U10 applied to detector 10, is a total detection parameter sensor in the second design scheme. 12.2 Voltage sensor, which measures the voltage U11 applied to compensator 11, functions as a sensor for detecting parameters of the compensator and is part of the total sensor for detecting parameters in the second design scheme. 13.1 Current intensity sensor, measuring the current intensity I.1 of the current flowing through detector 10. 13.2 Current intensity sensor, measuring the current intensity I.2 flowing through compensator 11. 14. Optional temperature sensor to measure the difference between ambient temperature and a pre-defined reference temperature. 15 Optional oxygen sensor to measure the oxygen content in detector chamber 8. 17. Control element, which allows the user to pre-set the operation in the heat conduction measurement mode. 20. Conductive detector segments, belonging to the functional components of the detector. 50. 21. Ceramic sheath surrounding detector segment 20 and compensator segment 38 22 Mounting Plate 23 The catalytic coating on the ceramic sheath 21 of detector 10 24. Passivation coating on the compensator functional component 51 of the compensator 11 28. A switch that selectively allows or blocks current flow through detector segment 20, the switch determining the mode for operating the gas measuring device 100. 30 conductive printed wires, including detector segments 20 31 Carrier plate for printing conductors 30 33. Wafer substrate for printing wires 30 34 Electrical contact portion for printed conductor 30 35 Protective layer on printed conductor 30 36 Mechanical retainer for detector segment 20 38. Conductive compensator segments, belonging to the functional components of the compensator. 51. 40. Voltage sensor, measuring bridge voltage ΔU_B, functions as the total detection parameter sensor in the first design scheme. 41. Current intensity sensor, used to measure the current intensity I.3 ​​in a Wheatstone bridge. 42. The voltage source of the Wheatstone measuring bridge provides voltage U42. 43. The voltage source of current loop 3.1 provides voltage U43. 44. Voltage source of current loop 3.2, providing voltage U44. 46 Electrical connection portion of printed conductor 30 The functional components of detector 10 include a heated detector segment 20 and a ceramic sheath 21, which are surrounded by a catalytic coating 23. 51 The functional components of the compensator 11, including the heated compensator segment 38 and the ceramic sheath 21, are surrounded by a passivation coating 24. 100 Gas measuring device, including detector 10, compensator 11, temperature sensor 14, control device 6, outer housing 4, inner housing 1, power supply units 42, 43, 44 and fireproof component 2. When the target gas concentration is greater than α* UEG, the gas measuring device 100 outputs a main alarm. When the target gas concentration is greater than α* UEG, the gas measuring device 100 outputs a warning alarm. In space region B, the flammable target gas must be monitored in this space region. Gp, a gas sample from space region B, arrives at compensator chamber 5 and detector chamber 8. I.1 The current intensity flowing through current loop 3.1 and detector segment 20 is measured by current intensity sensor 13.1. I.2 The current intensity flowing through current loop 3.2 and compensator segment 38 is measured by current intensity sensor 13.2. I.3 The current intensity in the Wheatstone measuring bridge is measured by current intensity sensor 41. L10 is a bypass circuit connected in parallel with detector 10, including switch S10 and resistor R10. L11 is a bypass line connected in parallel with compensator 11, including switch S11 and resistor R11. Opening in detector chamber 8 of O1 Opening in O2 compensator chamber 5 O Opening in the outer casing 4 OxM, when operating in oxidation measurement mode, relies on the detection parameters of the target gas concentration. R10 is a resistive component, connected in parallel or series with detector 10, and belongs to the category of resistive component R100. R11 is a resistor component, connected in parallel or series with compensator 11, and belongs to resistor component R110. R20 and R21 are resistors connected in parallel with the series circuit consisting of detector 10 and compensator 11. R100 is a controllable resistive element connected in parallel or series with the detector 10, having a variable resistance value. In one implementation, it includes the resistive element R10 and the switch S10. R110 is a controllable resistive element, connected in parallel or series with the compensator 11, and has a variable resistance value. In one implementation, it includes the resistive element R11 and the switch S11. S10 is a controllable switch connected in parallel with detector 10, and belongs to the resistive component R100. S11 is a controllable switch connected in parallel with compensator 11, and belongs to the resistive component R110. The voltage U10 applied to detector 10 is, in one design, measured by voltage sensor 12.1. The voltage U11 applied across compensator 11 is measured by voltage sensor 12.2 in one design, serving as a probe parameter of the compensator. U110 is the zero value of the compensator voltage U11, used when operating in thermal conduction measurement mode. U11 korr The corrected compensator voltage, equal to U11–U110, functions as a probe parameter of the compensator. The voltage of power supply 42 U42 The voltage of power supply 43 U43 U44 power supply voltage 44 ΔU is the uncorrected voltage difference, equal to U10–U11. ΔU0 is the zero value (zero point) of the voltage difference ΔU, used when operating in oxidation measurement mode. ΔU korr The corrected voltage difference, equal to U10–U11-ΔU0, functions as the total detection parameter. ΔU_B is the bridge voltage of the Wheatstone measuring bridge, measured by voltage sensor 40, and is equal to (U10-U11) / 2. ΔU_B0 is the zero value (zero point) of the bridge voltage ΔU_B, used when operating in oxidation measurement mode. ΔU_B korr The corrected bridge voltage, equal to ΔU_B – ΔU_B0, functions as the total detection parameter. When operating in thermal conduction measurement mode, the detection parameters of WlM;eq depend on the target gas concentration, where the compensator temperature is approximately equal to the detector temperature. When operating in thermal conduction measurement mode, the detection parameters depend on the target gas concentration, wherein, according to the invention, a higher compensator temperature is generated in thermal conduction measurement mode than in oxidation measurement mode.

Claims

1. A gas measuring device (100) for measuring the concentration of a combustible target gas (CH4). The gas measuring device (100) includes - Detector (10) with conductive detector segments (20). - Compensator (11) with conductive compensator segments (38). -Total detection parameters of sensors (40, 12.1, 12.2) and - Compensator detection parameter sensor (12.2). The gas measuring device (100) is configured such that a gas sample (Gp) can flow at least temporarily from the space region (B) to be monitored into the interior of the gas measuring device (100). The gas measuring device (100) can be selectively operated in either an oxidation measurement mode or a heat conduction measurement mode. The gas measuring device (100) is configured to: - At least when operating in oxidation measurement mode, and optionally also when operating in thermal conduction measurement mode, a voltage (U10) is applied to the detector segment (20), causing the detector segment (20) to be heated, and - In both modes, voltage (U11) is applied to the compensator segment (38), causing the compensator segment (38) to be heated. The gas measuring device (100) is configured to: A voltage (U11) is applied to the compensator segment (38) such that the compensator segment (38) is heated more intensely when operating in heat conduction measurement mode than when operating in oxidation measurement mode. The result of heating the detector segment (20) is that - The combustible target gas (CH4) in the gas sample (Gp) is oxidized inside the gas measuring device (100), and - The oxidation increases the temperature of the detector segment (20). The total detection parameter sensors (40, 12.1, 12.2) are configured to measure total detection parameters (ΔU_B, U10, U11), which depend on the temperature of the detector segment (20) and the temperature of the compensator segment (38). The compensator sensing parameter sensor (12.2) is configured to measure the compensator sensing parameter (U11) which depends on the temperature of the compensator segment (38), and The gas measuring device (100) is configured to: - When operating in oxidation measurement mode, based on the measured total detection parameters (ΔU_B, U10, U11) and - When operating in thermal conduction measurement mode, the measured compensator probe parameters (U11) are used. Determine the concentration of the combustible target gas (CH4) in the gas sample (Gp) inside the gas measuring device (100).

2. The gas measuring device (100) according to claim 1. Its features are, The compensator (11) includes a compensator functional component (51) and a passivation coating (24). The compensator functional component (51) includes a conductive compensator segment (38). The passivation coating (24) mentioned above - Surround compensator functional component (51). -The gas sample (Gp) is located inside the gas measuring device (100) and between the compensator functional component (51), and - The gas sample (Gp) is physically and chemically separated from the compensator functional component (51), and The passivation coating (24) is composed of a compound containing iodine in at least 50% by weight, preferably at least 80% by weight, and particularly preferably at least 95% by weight.

3. The gas measuring device (100) according to claim 2. Its features are, The passivation coating (24) is composed of at least 50% by weight, preferably at least 80% by weight, of alkali metal or alkaline earth metal iodides or iodates. The alkali metal or alkaline earth metal of the following compound is preferably potassium, and the passivation coating (24) is composed of at least 50% by weight of the compound, and The compounds are particularly preferred to be potassium iodide (KI) or potassium iodate (KIO3).

4. The gas measuring device (100) according to any one of the preceding claims. Its features are, The gas measuring device (100) is configured to: The voltage (U10) is applied to the detector segment (20) such that the detector segment (20) is heated more intensely when operating in oxidation measurement mode than when operating in thermal conduction measurement mode, and Preferably, when operating in thermal conduction measurement mode, no voltage is applied to the detector segment (20).

5. The gas measuring device (100) according to any one of the preceding claims. Its features are, The gas measuring device (100) includes an electrical bypass line (L11) and a controllable switch (S11) for the bypass line (L11). The bypass line (L11) is arranged in parallel with the compensator (11), and The gas measuring device (100) is configured to operate the switch (S11). The switch (S11) interrupts the bypass line (L11) when operating in the heat conduction measurement mode and releases the bypass line (L11) when operating in the oxidation measurement mode.

6. The gas measuring device (100) according to any one of the preceding claims. Its features are, The gas measuring device (100) is configured such that the intensity (I.1) of the current flowing through the detector segment (20) is at least temporarily different from or can be different from the intensity (I.2) of the current flowing through the compensator segment (38). The gas measuring device (100) is configured to cause the following result: - When operating in oxidation measurement mode, the temperature deviation between the compensator segment (38) and the detector segment (20) is not greater than a pre-defined upper temperature limit, and When operating in thermal conductivity measurement mode, the temperature of the compensator segment (38) is at least as large as a pre-given lower temperature limit, and preferably greater than the temperature of the detector segment (20).

7. The gas measuring device (100) according to any one of the preceding claims. Its features are, The gas measuring device (100) is configured for automatic measurement. - Check whether the pre-defined oxidation criteria are met. If there is sufficient oxygen inside the gas measuring device (100) to oxidize the combustible target gas passing through the detector segment (20), then at least the oxidation criterion is met. - As long as the oxidation criteria are met, remain in the oxidation measurement mode. - If the oxidation criterion is no longer met, switch to the heat conduction measurement mode, and If the oxidation criteria are met again, it is preferable to switch back to the oxidation measurement mode.

8. The gas measuring device (100) according to claim 7. Its features are, The gas measuring device (100) is configured such that If the target gas concentration determined based on the measured total detection parameters (ΔU_B, U10, U11) is lower than a pre-given first upper concentration limit, then at least the oxidation criterion is met.

9. The gas measuring device (100) according to claim 8. Its features are, The gas measuring device (100) is configured such that If the target gas concentration determined by the measured compensator detection parameter (U11) is lower than a pre-given second upper concentration limit, then the oxidation criterion is additionally satisfied at least. The second upper concentration limit is greater than the first upper concentration limit.

10. The gas measuring device (100) according to any one of claims 7 to 9. Its features are, The gas measuring device (100) includes a detector chamber (8) and an oxygen sensor (15). The detector (10) is arranged in the detector chamber (8). The oxygen sensor (15) is configured to measure the oxygen content in a gaseous sample (Gp). Preferably, the gas sample (Gp) is located inside the gas measuring device (100), and The gas measuring device (100) is configured to check whether the pre-given oxidation standard is met based on the measured oxygen content.

11. The gas measuring device (100) according to any one of the preceding claims. Its features are, The gas measuring device (100) includes an operating element (17). The aforementioned manipulation element (17) is capable of being activated and deactivated, and The gas measuring device (100) is configured such that its - As a response to activation of the manipulation element (17), the system switches to and / or remains in the heat conduction measurement mode, and - When the manipulator (17) is deactivated, it can be selectively operated in oxidation measurement mode or thermal conduction measurement mode.

12. An application of a gas measuring device (100) according to any one of the preceding claims for measuring the concentration of hydrogen as a combustible target gas.

13. A gas measurement method for measuring the concentration of a combustible target gas (CH4) using a gas measuring device (100), The gas measuring device (100) includes - Detector (10) with conductive detector segments (20). - Compensator (11) with conductive compensator segments (38). -Total detection parameters of sensors (40, 12.1, 12.2) and - Compensator detection parameter sensor (12.2). The gas measuring device (100) can be selectively operated in either an oxidation measurement mode or a heat conduction measurement mode. The method includes the following steps: - This allows or permits the gas sample (Gp) to flow at least temporarily from the space region (B) to be monitored into the interior of the gas measuring device (100), and - In both modes, voltage (U11) is applied to the compensator segment (38), causing the compensator segment (38) to be heated. The voltage (U11) is applied to the compensator segment (38) such that the compensator segment (38) is heated more intensely when operating in heat conduction measurement mode than when operating in oxidation measurement mode. If the gas measuring device (100) is operated in oxidation measurement mode. The method then includes the following additional steps: - Applying voltage (U10) to the detector segment (20) thereby heating the detector segment (20), Heating the detector segment (20) causes the combustible target gas (CH4) in the gas sample (Gp) to be oxidized inside the gas measuring device (100), and the oxidation increases the temperature of the detector segment (20). - The total detection parameter sensors (40, 12.1, 12.2) measure the total detection parameters (ΔU_B, U10, U11), which depend on the temperature of the detector segment (20) and the temperature of the compensator segment (38), and -Based on the measured total detection parameters (ΔU_B, U10, U11), determine the concentration of the combustible target gas (CH4) in the gas sample (Gp) inside the gas measuring device (100), and If the gas measuring device (100) is operated in heat conduction measurement mode, the method includes the following additional steps: - The compensator sensing parameter sensor (12.2) measures the compensator sensing parameter (U11) which depends on the temperature of the compensator segment (38). -The concentration of the combustible target gas (CH4) in the gas sample (Gp) inside the gas measuring device (100) is determined based on the measured compensator detection parameter (U11), and - Preferably, no voltage is applied to the detector segment (20).

14. The gas measurement method according to claim 13, Its features are, The voltage (U10) is applied to the detector segment (20) such that the detector segment (20) is heated more intensely when operating in oxidation measurement mode than when operating in thermal conduction measurement mode, and Preferably, when operating in thermal conduction measurement mode, no voltage is applied to the detector segment (20).

Images