Gas measuring device and gas measuring method for measuring high-concentration target gases.

Abstract

The present invention provides a gas measuring device and a gas measuring method capable of measuring the concentration of a target flammable gas. [Solution] When operating in oxidation measurement mode, the detector and compensator are heated. The heated detector oxidizes the flammable target gas, and this oxidation further heats the detector. The heated compensator compensates for the effects of ambient conditions on the detector. The total detected amount, which depends on the detector temperature and compensator temperature, is measured, and the target gas concentration is determined depending on the measured total detected amount. When operating in thermal conduction measurement mode, the compensator is heated, and the flammable target gas cools the compensator more strongly than the ambient air. The compensator detected amount, which depends on the compensator temperature, is measured, and the target gas concentration is determined depending on the measured compensator detected amount. When operating in thermal conduction measurement mode, the compensator is heated more strongly than when operating in oxidation measurement mode.

Description

[Technical Field]

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

[0002] Gas measuring devices including a detector and a compensator are well known. The conductive segment of the detector is heated to oxidize the flammable target gas in the gas sample. Of course, this is only possible if the gas sample contains a sufficient amount of the flammable target gas. The oxidation of the target gas releases thermal energy, which further heats the detector segment. Therefore, the temperature of the detector segment correlates with the concentration of the target gas to be measured. A measure of the temperature of the detector segment is taken.

[0003] This compensator can at least partially compensate for the effects of ambient conditions on the detector, particularly the effects of ambient temperature, ambient pressure, and ambient humidity. Measuring at least one, or even all, relevant ambient conditions is unnecessary, but is possible thanks to the compensator. Ideally, the compensator does not oxidize the target gas, but reacts to ambient conditions in the same way as the detector. This type of gas measuring device is sometimes referred to as a "thermally controlled sensor" or "catalytic sensor." This invention also utilizes this principle. In many cases, both the detector and the compensator are configured as so-called peristaltic sensors.

[0004] The inventors internally recognized the following problem: the temperature of the detector segment is reliably correlated with the target gas concentration being sought only as long as the detector segment is still able to oxidize the flammable target gas. In the case of high concentrations of target gas (hereinafter also referred to as high-concentration target gas), a situation may arise where the flammable target gas is present inside the gas measuring device, but there is not enough oxygen to oxidize this flammable target gas. In such a situation, if the determination of the target gas concentration is supported by the total amount detected by the detector segment, and therefore by the temperature, the gas measuring device may produce erroneous results. In particular, there is a risk that high concentrations of flammable target gas will not be detected.

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

[0006] This problem is solved by a gas measuring device having the features of claim 1 and a gas measuring method having the features of claim 13. Advantageous configurations are shown in the dependent claims. As long as the advantageous configuration of the gas measuring device according to the present invention is significant, the advantageous configuration of the gas measuring method according to the present invention will also be significant, and vice versa.

[0007] The gas measuring device and gas measuring method according to the present invention can measure the concentration of a flammable target gas, in which case the target gas is present or may be present in the spatial area to be monitored. The target gas is, for example, methane (CH4) or hydrogen (H2). Typically, the gas measuring device and gas measuring method according to the present invention provide an estimate of the actual target gas concentration, in which case this estimate may deviate from the actual value.

[0008] In a spatial domain, multiple flammable target gases may be generated simultaneously. In this case, it is advantageous to measure the sum of the concentrations of these flammable target gases. In the following, even when multiple flammable target gases are present and the sum of their concentrations is measured, the term "target gas concentration" will be used as an abbreviation.

[0009] The gas measuring device can operate in oxidation measurement mode and, in addition, in thermal conduction measurement mode. These two modes are described in more detail below. Optionally, the gas measuring device can also operate in a dormant 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. Voltage is applied to the compensator in two modes, and voltage is applied to the detector at least when operating in oxidation measurement mode, and optionally, though not always necessary, also when operating in thermal conduction measurement mode. The voltage applied to the compensator may always be the same as the voltage applied to the detector. Alternatively, the two applied voltages may differ from each other, at least temporarily and / or when operating in thermal conduction measurement mode. The voltage applied to the detector and / or the voltage applied to the compensator may be constant over time or can vary over time. Preferably, the voltage is applied in pulse control to conserve electrical energy. Preferably, in an optionally idle state, no voltage is applied to either the detector or the compensator.

[0011] At least temporarily, the gas sample flows from the area to be monitored into the gas measuring device, for example, because the gas measuring device draws in the gas sample and / or diffuses the gas sample inside. 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 a voltage is applied to the detector, a current flows through the detector segment. Thereby, the detector segment is heated. The heating of the detector segment causes oxidation of the combustible target gas inside the gas measuring device. This oxidation releases thermal energy. This thermal energy increases the temperature of the detector segment through which the current flows. This effect occurs when the gas sample contains a sufficient amount of combustible target gas and there is sufficient oxygen for the oxidation. Otherwise, there may be a situation where the combustible target gas is present, but the detector does not oxidize this combustible target gas due to oxygen deficiency, and thus no thermal energy is released.

[0013] As long as a voltage is applied to the compensator, a current flows through the compensator segment. Thereby, the compensator segment is heated. The gas measuring device is configured such that, ideally, even when the compensator segment is heated, the compensator does not oxidize any combustible target gas inside the gas measuring device. This goal can only be approximately achieved for many combustible target gases, especially hydrogen.

[0014] The gas measuring device includes a total detection amount sensor. This total detection amount sensor can measure the total detection amount. This total detection amount depends on both the temperature of the detector segment and the temperature of the compensator segment. In a first alternative configuration, the higher the temperature of the detector segment, the greater the total detection amount, and the higher the temperature of the compensator segment, the smaller the total detection amount. In a second alternative configuration, conversely, the higher the temperature of the detector segment, the smaller the total detection amount, and the higher the temperature of the compensator segment, the greater the total detection amount. In one configuration, the total detection amount sensor can measure a detector detection amount that depends on the temperature of the detector segment and a compensator detection amount that depends on the temperature of the compensator segment, and derive the total detection amount therefrom, for example, as a difference.

[0015] Note: In the following, when it comes to the topic that a sensor is capable of measuring a physical quantity, this means the following. That is, the sensor directly measures this physical quantity or correlates with the physical quantity to be measured and thus measures another quantity that serves as a scale of the physical quantity to be measured.

[0016] Ambient conditions, particularly ambient temperature, ambient humidity, and ambient pressure, affect both the detector and the compensator. The ideal state where the compensator reacts to ambient conditions in exactly the same way as the detector can usually only be achieved approximately. Therefore, the total detected amount is usually affected not only by the target gas concentration but also by ambient conditions. Nevertheless, when sufficient oxygen is present, usually the total detected amount is a good scale for the target gas concentration being searched for.

[0017] As long as there is still a sufficient amount of oxygen available for the oxidation of the combustible target gas within the gas measuring device in the detector segment, the total detected amount correlates with the target gas concentration being searched for. In the oxidation measurement mode, the gas measuring device can determine the target gas concentration depending on the measured total detected amount. For example, in the oxidation measurement mode, the gas measuring device applies a preset proportionality factor or other preset functional dependencies to at least one measured value of the total detected amount. Optionally, the gas measuring device additionally uses the measured ambient conditions, particularly the ambient temperature.

[0018] The gas measuring device includes a compensator detected amount sensor. This compensator detected amount sensor can measure the compensator detected amount. The compensator detected amount depends on the temperature of the compensator segment and usually depends only to a relatively small extent on ambient conditions, but depends even less on the temperature of the detector segment and ideally not at all. Preferably, the temperature of the detector segment affects the compensator detected amount with a strength at most half, particularly preferably at most one quarter, and especially at most one tenth of the influence that the temperature of the compensator segment has on the compensator detected amount. The compensator detected amount increases in one configuration and decreases in another configuration as the temperature of the compensator segment increases.

[0019] In thermal conduction measurement mode, the gas measuring device determines the target gas concentration based on the measured compensator detection amount, preferably without using the total detection amount. The gas measuring device applies a preset functional relationship to the compensator detection amount. Frequently, the measured target gas concentration is higher as the compensator detection amount decreases. The measured compensator detection amount can additionally be used to derive the total detection amount in oxidation measurement mode and / or to inspect the detector.

[0020] When operating in thermal conductivity measurement mode, the fact that many flammable target gases, particularly methane and hydrogen, have higher thermal conductivity than ambient air is utilized. Thermal conductivity, also called the thermal conductivity or thermal conductivity coefficient of a medium, represents the transfer of heat without the transfer of active materials and has units of measurement, for example, [W / m·K]. Typically, the respective thermal conductivity for each target gas observed is known. Due to the higher thermal conductivity, the heated compensator segment is cooled by the gas sample containing the flammable target gas compared to the state without the flammable target gas. Therefore, for many target gases, the temperature of the compensator segment decreases as the concentration of the target gas in the gas sample increases, provided that the applied voltage remains constant and other ambient conditions remain constant. Thus, the temperature of the compensator segment, and consequently the compensator detection amount, correlates with the concentration of the target gas being sought.

[0021] As already explained, the gas measuring device can apply a voltage to the compensator segment in two modes. The gas measuring device can apply the voltage as follows: When operating in thermal conduction measurement mode, the compensator segment is heated more strongly 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%, when operating in thermal conduction measurement mode than when operating in oxidation measurement mode. This is true for the same target gas concentration and the same ambient conditions. In one configuration, the temperature of the compensator segment is at least 50°C, particularly preferably at least 100°C, and especially at least 200°C, when operating in thermal conduction measurement mode than when operating in oxidation measurement mode, for example, by a temperature between 180°C and 220°C. This stronger heating is preferably caused by the compensator segment accepting more power. This is because, for example, in the heat conduction measurement mode, the applied voltage and / or current intensity is greater than in the oxidation measurement mode, or, if the voltage is applied in pulsed mode, the pulse width is longer and / or the pause time between two pulse widths is shorter. When the voltage is applied in pulsed mode, power consumption should preferably be understood as the power consumption averaged over time.

[0022] As already explained, when operating in thermal conduction measurement mode, the fact that many flammable target gases cool the heated compensator segment more strongly than air is utilized. This cooling effect correlates with the concentration of the target gas being sought. In internal tests, the inventors confirmed that the stronger the compensator segment is heated, the greater the cooling effect, and consequently this correlation, generally becomes. On the other hand, stronger heating consumes more electrical energy. Therefore, the compensator segment is heated more strongly when operating in thermal conduction measurement mode than when operating in oxidation measurement mode.

[0023] In contrast, in oxidation measurement mode, the compensator should react to ambient conditions in much the same way as the detector. Ideally, the compensator segment should not oxidize the flammable target gas. Typically, both the detector and compensator segments often oxidize more of the flammable target gas the more they are heated. When operating in oxidation measurement mode, the temperature of the compensator segment should not deviate too much from the temperature of the detector segment, thereby allowing the compensator to react to ambient conditions in much the same way as the detector. For these reasons, it is significant that the compensator segment is not heated as strongly in oxidation measurement mode as it is in thermal conductivity measurement mode. This often results in the following: In oxidation measurement mode, ambient conditions are compensated relatively well. In thermal conductivity measurement mode, the cooling induced is relatively strongly dependent on the target gas concentration and the temperature of the compensator segment. In addition, electrical energy is saved compared to configurations in which the compensator segment is heated strongly in both modes. Saving electrical energy is particularly important when the gas measuring device is not connected to or cannot be connected to a stationary voltage grid during use.

[0024] While oxygen is indeed present inside the gas measuring device, it may be present in such small quantities that it can only oxidize a relatively small portion of the flammable target gas. In this situation, especially when operating in thermal conductivity measurement mode, two opposing effects can act on the temperature of the compensator segment. In this case, the two effects depend on the target gas concentration, as follows:

[0025] - The flammable target gas cools the heated compensator segment more strongly than ambient air or another gas mixture that does not contain the flammable target gas.

[0026] - Typically, oxidation of the flammable target gas by the heated compensator segment cannot be completely avoided. Oxidation releases thermal energy that further heats the compensator segment.

[0027] Ideally, the heated compensator segment should not oxidize the flammable target gas at all, preferably not in two modes. Below, we describe how this goal can be achieved, at least approximately, using one configuration in combination with other configurations, which can be optionally combined. In other words, the configurations described below increase the reliability that the temperature of the compensator segment depends significantly more on the cooling effect of the flammable target gas than on the heating effect due to oxidation.

[0028] In this configuration, the passivation coating is applied to the compensator functional component of the compensator. The compensator functional component includes a conductive compensator segment that is heated by the current flowing through it, and preferably an electrical insulating portion around the compensator segment. The compensator functional component may have, for example, a spherical, elliptical, or plate-like form and house the conductive compensator segment inside.

[0029] The passivation coating surrounds the compensator functional component, forming its outer surface, and therefore comes into contact with the gas sample inside the gas measuring device. Ideally, the passivation coating covers the entire compensator functional component, meaning no voids are created within the passivation coating. The passivation coating separates the gas sample from the compensator functional component, and ideally completely. This prevents the passivation coating from reaching physical and chemical contact between the compensator functional component and the gas sample, and ideally completely prevents the heated compensator segment from oxidizing the flammable target gas. However, thermal contact occurs between the gas sample and the compensator functional component, and consequently between the gas sample and the heated compensator segment, thereby causing the modified thermal conductivity of the gas sample to act on the compensator segment in a measurable manner, allowing the compensator detection sensor to measure the modified thermal conductivity.

[0030] The passivation coating contains a compound, which preferably contains iodine (Iod,I), particularly iodide or iodate. The passivation coating may additionally contain further components, especially based on impurities that are usually not completely avoidable. The proportion of the iodine-containing compound in the passivation coating, measured in weight percent (W%), is at least 50%, preferably at least 80%, and particularly preferably at least 95%.

[0031] In internal testing, the inventors discovered that a passivation coating with this compound and its weight percentage particularly effectively prevents the undesirable phenomenon of a heated compensator segment oxidizing a significant amount of the flammable target gas. This desired blocking effect persists even during long-term use of the gas measuring device, even if the use lasts for several days, weeks, or months. In contrast, other compounds that can be used for the passivation coating do not achieve this desired blocking effect so steadily over long periods. This desired effect also occurs when hydrogen (H2) is the flammable target gas.

[0032] Particularly preferably, the compound constituting at least 50% by weight, and especially at least 80% by weight, of the passivation coating consists of an alkali metal or alkaline earth metal iodide or iodate. The alkali metal or alkaline earth metal is preferably potassium. Particularly preferably, the compound is potassium iodide (KI) or potassium iodate (KIO3). These two compounds have been proven in internal tests to be particularly suitable for inhibiting the relevant oxidation of flammable target gases over long periods of use. Internal tests have also found that this desired effect can be obtained with hydrogen as the flammable target gas. The compound can also be a mixture of potassium iodide (KI) and potassium iodate (KIO3).

[0033] The following describes preferred configurations of the present invention. These preferred configurations of the present invention can be realized in relation to the passivation coating described herein, or in relation to compensators of other configurations.

[0034] According to the present invention, both the detector segment and the compensator segment are heated when current flows through these two segments. Preferably, the detector segment is heated to a high temperature. This temperature is preferably between 450°C and 550°C in order to steadily oxidize all possible flammable target gases. If only hydrogen (H2) is likely to be the flammable target gas to be detected and it is to be steadily oxidized, it is often sufficient to heat the detector segment to a temperature between 150°C and 250°C. Preferably, when operating in oxidation measurement mode, the temperature of the heated compensator segment is such that it is a deviation of up to 150°C, preferably up to 100°C, from the temperature of the detector segment, and in one embodiment, it is heated to a temperature lower than that of the detector segment.

[0035] The gas measuring device applies voltage to both the detector segment and the compensator segment. According to the present invention, the gas measuring device applies voltage to the compensator segment such that the compensator segment is heated more strongly when operating in thermal conduction measurement mode than when operating in oxidation measurement mode. In one configuration, the gas measuring device applies voltage to the detector segment such that the detector segment is heated identically in both modes.

[0036] In contrast, in a preferred configuration, the gas measuring device applies a voltage to the detector segment such that the following occurs: the detector segment is heated more strongly, preferably at least twice as strongly, when operating in oxidation measurement mode than when operating in thermal conduction measurement mode. Particularly preferred is that no voltage is applied to the detector segment when operating in thermal conduction measurement mode, and therefore, the detector segment is ideally not heated at all. A configuration in which the detector segment is heated less strongly or not heated at all when operating in thermal conduction measurement mode has the following advantages, particularly with respect to oxidation measurement mode: heating reduces the risk of material depositing on the detector surface, thereby preventing the detector from reliably oxidizing the flammable target gas when operating in oxidation measurement mode (the detector becoming "poisoned" or "carbonized"). In addition, less heating consumes less electrical energy.

[0037] According to the present invention, the gas measuring device applies a voltage to the compensator, causing the following: the compensator segment is heated more strongly when operating in thermal conduction measurement mode than when operating in oxidation measurement mode. The following describes how this is achieved in various configurations. Many of these configurations can be combined with each other.

[0038] In one configuration, an electrical bypass line is arranged in parallel with the compensator. A driveable switch can selectively open or close (interrupt) the bypass line. When the switch opens the bypass line, a parallel circuit is formed. Only a portion of the current flows through the compensator, heating the compensator segment. The remaining portion of the current flows through the parallel bypass line and does not contribute to heating the compensator segment. As is known, the current intensity of the current flowing through the compensator segment and the current intensity of the current flowing through the bypass line depends on the electrical resistance of the compensator segment and the electrical resistance of the bypass line. When the switch closes the bypass line, the bypass line theoretically has infinite electrical resistance, and the total current flows through the compensator, heating the compensator segment. The gas measuring device can drive-control the switch as follows: when operating in heat conduction measurement mode, the drive-controlled switch closes the bypass line, and when operating in oxidation measurement mode, the drive-controlled switch opens the bypass line. As a result, the compensator segment is heated more strongly in the thermal conduction measurement mode than in the oxidation measurement mode.

[0039] In one variation or generalization of this configuration, a driveable electrical resistance component is placed within the bypass line. By controlling the drive of this component, the signal processing control equipment of the gas measuring device can change the electrical resistance of the resistance component. The higher the electrical resistance of the component, the more intensely the compensator segment is heated. The resistance component is driven and controlled as follows: when operating in thermal conduction measurement mode, its electrical resistance is greater than when operating in oxidation measurement mode. The configuration described here using a switch can be called a special case of variable electrical resistance.

[0040] In one variant of this configuration, there is a bypass line in parallel with the compensator, or alternatively, an additional bypass line is arranged in parallel with the detector. An additional driveable switch can selectively open or close (interrupt) the additional bypass line. The gas measuring device can be driven to control the switch so that the additional bypass line is opened when operating in thermal conduction measurement mode and closed when operating in oxidation measurement mode. This causes the detector segment to be heated with less intensity when operating in thermal conduction measurement mode than when operating in oxidation measurement mode. Instead of the additional switch, an additional driveable electrical resistance component with variable electrical resistance may be arranged in the additional bypass line.

[0041] In one configuration, the gas measuring device is configured as follows: 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 circuits. In the case of pulse-controlled voltage, current intensity refers to the average current intensity.

[0042] In this configuration, in one implementation, the compensator segment is heated more strongly when operating in thermal conduction measurement mode than when operating in oxidation measurement mode, as follows:

[0043] -When operating in oxidation measurement mode, the voltage is applied to the compensator segment continuously or in pulse control as follows: That is, at least when no flammable target gas is present inside the gas measuring device, the temperature of the compensator segment deviates from the temperature of the detector segment by up to a predetermined upper temperature limit. This upper limit is preferably 150°C, and particularly preferably 100°C.

[0044] -When operating in thermal conduction measurement mode, the voltage is applied to the compensator segment and / or pulse-controlled as follows: That is, at least when no flammable target gas is present inside the gas measuring device, the temperature of the compensator segment is at least the same as a preset lower temperature limit, and is independent of the temperature of the detector segment and also independent of the cooling effect of the flammable target gas. Preferably, the temperature of the compensator segment in thermal conduction measurement mode is higher than the temperature of the detector segment.

[0045] The gas measuring device achieves this effect, preferably by setting the voltage applied to each gas measuring device or by appropriately setting the electrical resistance components through appropriate drive control.

[0046] According to the present invention, the gas measuring device can selectively operate in oxidation measurement mode or thermal conduction measurement mode. Preferably, the gas measuring device is configured for the following operation: that is, the gas measuring device is configured to measure the target gas concentration in oxidation measurement mode as long as sufficient oxygen is present so that the heated detector segment can oxidize the flammable target gas in the gas sample, i.e., all flammable target gases. Only if this prerequisite is not met with sufficient safety, the gas measuring device automatically switches to thermal conduction measurement mode. One reason for this is that, normally, the concentration measurements achieved when the gas measuring device is operating in oxidation measurement mode are more reliable and / or accurate than the measurements in thermal conduction measurement mode, provided that 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 as much as possible, and only operates in thermal conduction measurement mode when oxidation measurement mode no longer yields sufficiently reliable measurements. This configuration often leads to the steady detection of target gases, particularly those with relatively low target gas concentrations, compared to other possible procedures for determining the operating mode of the gas measuring device.

[0047] In this preferred configuration, the oxidation criterion is preset in a computer-evaluable form. This oxidation criterion is preset to be satisfied as long as there is still enough oxygen inside the gas measuring device so that the heated detector segment can oxidize the flammable target gas internally, and therefore the total detected amount is sufficient to reliably determine the target gas concentration.

[0048] In a preferred embodiment, the oxidation criterion is met if at least the following condition is satisfied: namely, the target gas concentration determined when the gas measuring device is operating in oxidation measurement mode is lower than a preset first upper concentration limit. This first upper concentration limit is preset such that at least sufficient oxygen is always present when the target gas concentration is lower than this upper concentration limit. In this preferred embodiment, preferably, the interior of the gas measuring device is in continuous fluid communication with the space region to be monitored, thereby allowing continuous oxygen flow through the interior.

[0049] In other words, with this configuration, the gas measuring device automatically switches to thermal conduction measurement mode when the target gas concentration, which is determined based on the total detected amount, exceeds a first upper concentration limit.

[0050] After being switched on, the gas measuring device preferably operates first in oxidation measurement mode. However, it is also possible for the gas measuring device to initially operate in thermal conductivity measurement mode. The gas measuring device preferably remains in oxidation measurement mode and determines the target gas concentration depending on the total detected amount, as long as sufficient oxygen is still present. Typically, the gas measuring device can reliably detect flammable target gases, even those with relatively low target gas concentrations, in this case. As soon as the gas measuring device automatically detects that the oxidation criterion is no longer met, the gas measuring device automatically switches to thermal conductivity measurement mode and measures the target gas concentration depending on the compensator detected amount. Preferably, as soon as the gas measuring device detects that the oxidation criterion is again met, it automatically switches back to oxidation measurement mode.

[0051] Preferably, the first upper concentration limit of the oxidation criterion is determined empirically in advance, and more preferably, according to the following pre-settings: As long as the target gas concentration has not yet reached or exceeded the first upper concentration limit, the detector segment can safely oxidize all further target gases as long as a sufficient amount of oxygen is available. As soon as the target gas concentration reaches or exceeds the first upper concentration limit, an undesirable situation may arise where sufficient oxygen is no longer available. In this situation, the total detected amount is no longer a steady measure of the target gas concentration. Preferably, when the target gas concentration determined using the compensator detected amount falls again below this first upper concentration limit or below a further upper concentration limit, the gas measuring device switches back to oxidation measurement mode.

[0052] In one configuration, when the gas measuring device operates in oxidation measurement mode, the target gas concentration can be determined not only by the total detected amount but also additionally by the compensator detected amount. For example, the higher thermal conductivity of the target gas can be utilized. Typically, the two estimates obtained in these different ways will differ from each other for the actual target gas concentration.

[0053] Comparing these two estimates often allows us to check whether the detector is still functioning adequately, or whether it is still functioning but not severely poisoned. Detector "poisoning" should be understood as the process where hazardous substances accumulate on the heated surface of the detector segment, resulting in the detector segment no longer being in a state sufficient to oxidize the flammable target gas, even if sufficient oxygen is present. Typically, the detector segment is heated more strongly than the compensator segment, so the detector becomes poisoned faster than the compensator. In one configuration, the gas analyzer itself can automatically check for poisoning. Often, comparing these two estimates also allows the gas analyzer to automatically check whether sufficient oxygen is still present.

[0054] Furthermore, the above describes a configuration in which the gas measuring device automatically switches from oxidation measurement mode to heat conduction measurement mode when a predetermined oxidation criterion is no longer met. In one implementation, the oxidation criterion is not met if at least the following conditions occur: namely, the target gas concentration determined based on the total detected amount exceeds a preset first concentration limit, and moreover, for at least one measurement value, preferably all measurement values, exceeds the preset first concentration limit within a duration of at least the same length as the preset minimum duration. Preferably, the minimum duration is preset so that at least the minimum duration elapses, even when the flammable target gas is at a high concentration, until all of the flammable target gas is oxidized inside the gas measuring device, even if oxygen does not flow through afterward.

[0055] In an advanced version of this implementation, a second upper concentration limit is set in advance. This second upper concentration limit is higher than the first upper concentration limit. This advanced version of the implementation utilizes the configuration described here, in which the gas measuring device additionally determines the target gas concentration based on the compensator detection amount when operating in oxidation measurement mode. If the following condition is met, i.e., if the target gas concentration determined based on the compensator detection amount exceeds the preset second upper concentration limit, the oxidation criterion is no longer met, and the gas measuring device automatically switches to thermal conduction measurement mode in this case as well.

[0056] Preferably, the gas measuring device switches to the heat conduction measurement mode whenever the conditions dependent on the compensator detection amount are met, and it does not depend on which target gas concentration the gas measuring device determined based on the total detection amount.

[0057] This configuration provides possible support in particular in the following situations: for example, the target gas concentration in the area to be monitored may fluctuate significantly, or at least significantly, because the user has brought the gas measuring device into an area loaded with various amounts of the target gas, or because a flammable target gas suddenly leaks or is likely to leak (strong rise), or because a leak point from which the flammable target gas leaks is blocked (strong drop). The target gas concentration may also rise significantly when many flammable target gases are present inside a sealed container but not outside the container, and the probe of the gas measuring device is inserted into the container from the outside. The step in which the gas measuring device measures the target gas concentration based on the total detected amount inevitably requires a certain processing time. Therefore, in some situations, the gas measuring device, when operating in oxidation measurement mode, may not be able to detect suddenly occurring high concentrations of target gas quickly enough. The second implementation with an upper concentration limit described here reduces the risk that a dangerous event may not be detected in such cases, and therefore no subsequent alarm will be issued. Normally, the cooling effect of many flammable target gases can be confirmed quickly.

[0058] Preferably, the gas measuring device includes a detector chamber. The detector is located within the detector chamber. The detector chamber is located inside the gas measuring device. At least a portion of the gas sample from the spatial region to be monitored reaches into the detector chamber and, consequently, the area around the detector. Preferably, the compensator is located outside the detector chamber and / or is thermally separated from the detector by another or additional means.

[0059] In one configuration, the gas measuring device includes an oxygen sensor. This oxygen sensor can measure the oxygen content in a gas sample present inside the gas measuring device. The oxygen sensor may be positioned to measure the oxygen content of the gas sample in the detector chamber. The oxygen sensor can often additionally measure the oxygen content of another gas sample that originates from a similar spatial region to be monitored and has similarly reached the inside of the gas measuring device, in which case this other gas sample has not yet reached the detector chamber, and therefore oxygen has not yet been used for oxidation in this other gas sample. Frequently, such oxygen sensors are already available as components of the gas measuring device.

[0060] The gas measuring device can use at least one measurement from an oxygen sensor, preferably the measured time course of oxygen content, to check whether an oxidation criterion is met. Preferably, the oxidation criterion is met if the oxygen content in the detector chamber remains above a preset lower oxygen limit for a sufficiently long period of time, and not met otherwise. In one embodiment, the lower limit for oxygen content is between 10% and 15% by volume, particularly preferably 12% by volume of oxygen. This lower oxygen limit applies at least when the oxygen sensor measures the oxygen content in another gas sample outside the detector chamber.

[0061] According to the present invention, the gas measuring device can operate in thermal conduction measurement mode. In thermal conduction measurement mode, the gas measuring device determines the target gas concentration depending on the measured compensator detection amount. In one configuration, when the gas measuring device operates in thermal conduction measurement mode, no voltage is continuously or at least temporarily applied to the detector segment. This configuration has the following advantages, in particular, compared to a configuration in which voltage is applied to the detector segment even in thermal conduction measurement mode.

[0062] - Typically, the gas sample present inside the gas measuring device and surrounding the detector contains a high concentration of flammable target gas when the gas measuring device is operating in thermal conductivity measurement mode. If the detector segment oxidizes the flammable target gas even in this situation, oxidation releases a particularly large amount of thermal energy, and the detector segment could become very hot. This could lead to unwanted deposition ("carbonization," "poisoning") on the detector segment, potentially causing the detector to malfunction.

[0063] - A strongly heated detector segment may also heat the compensator segment, which reduces the desired cooling effect on the flammable target gas to be detected.

[0064] Furthermore, during normal operation in thermal conductivity measurement mode, there is not enough oxygen inside the gas measuring device to oxidize all of the flammable target gas. Therefore, strong heating can lead to the detector chemically reacting with the target gas, which is heated undesirably and only partially oxidized. For example, the target gas may be able to extract oxygen from the ceramic coating of the detector. This chemical reaction could damage the detector.

[0065] - The process by which the voltage applied to the detector segment heats it inevitably consumes electrical energy. Typically, gas measuring devices include their own voltage supply unit rather than being connected to a stationary voltage supply network or at least not continuously connected. In particular, in such cases, it is important that they consume relatively little electrical energy.

[0066] In one configuration, the gas measuring device includes an operating element that can be operated by the user. This operating element can be activated or deactivated. When the operating element is activated, the gas measuring device switches to and remains in the heat conduction measurement mode, independently of whether the oxidation criterion is met, and independently of the measured target gas concentration and oxygen concentration. When the operating element is deactivated, the gas measuring device switches to the oxidation measurement mode or remains in the heat conduction measurement mode, as described above, and preferably depends on whether the oxidation criterion is met. Preferably, activation of the operating element additionally results in no voltage being applied to the detector segment, i.e., no heating.

[0067] In particular, under the following circumstances, it may be advantageous to cause the gas measuring device to operate in thermal conduction measurement mode through the settings.

[0068] - Within the area to be monitored, there is a gas that eliminates oxygen, such as an inert gas, particularly nitrogen. This situation may be intentionally induced to prevent fire or other oxidation in the area. In this situation, there is often insufficient oxygen, and occasionally the gas measuring device may not be able to detect this situation or may not be able to detect it quickly. This situation may also occur unexpectedly.

[0069] - Within the spatial area to be monitored, there may be or may be at least one flammable target gas at a high concentration. In this case, the detector may be subjected to a heavy load when operating in oxidation measurement mode. High-concentration target gases are usually identified relatively reliably even when operating in thermal conduction measurement mode.

[0070] In one application of the present invention, the gas measuring device is used to determine the concentration of hydrogen as a flammable target gas. Hydrogen is expected to become increasingly important, particularly as a low-emission energy carrier for drive systems, for generating electrical energy, or as a starting material in the chemical industry. In one embodiment, the gas measuring device can be configured to identify whether hydrogen or other flammable target gases should be detected. As already described above, for the detection of hydrogen, it is sufficient to heat the detector segment to a temperature below 200°C, while for the detection of other flammable target gases, significantly higher temperatures are usually required.

[0071] In one configuration, the gas measuring device according to the present invention has an output unit. The gas measuring device causes the output unit to output a warning in at least one human-perceptible form as soon as it determines a target gas concentration outside a preset range, particularly exceeding a preset limit. Alternatively or additionally, the gas measuring device causes the determined target gas concentration itself to output. In particular, the output unit can output the warning visually, audibly, and / or tactilely (by vibration). Optionally, the gas measuring device additionally causes the output unit to output in which mode the gas measuring device is currently operating. Typically, the gas measuring device includes a proprietary voltage supply unit, and in one configuration, the output unit additionally outputs the current charge status of the voltage supply unit.

[0072] Such a gas measuring device can be guided by a person, while the person remains in an area where a flammable target gas may be present. The gas measuring device may be located in this area, with at least one person performing the work there, and it may be fixed, for example, to a wall or ceiling, or installed on the floor.

[0073] In one alternative configuration, the gas measuring device according to the present invention has a communication unit, but does not necessarily need to have a dedicated output unit that outputs the measured target gas concentration. Using this communication unit, the gas measuring device can transmit a message at least once, preferably repeatedly, to a spatially separated receiver, in which case the message includes information about the desired target gas concentration. This receiver is located, for example, in an operation center that remotely monitors a spatial area where a flammable target gas may be generated. Optionally, the message includes information about the mode in which the gas measuring device is currently operating. The receiver's display unit can output the received message in at least one human-perceptible format. Such a gas measuring device can be installed in a stationary (fixed position) manner within or in the spatial area to be monitored. Preferably, multiple such gas measuring devices are installed within or in this area.

[0074] Possible applications of this alternative configuration are as follows: The gas measuring device, or at least one of the measuring device's detectors, is located within a fully enclosed space or at least a sufficiently enclosed space, for example, inside a can, or in piping, or in a container, or in a room with combustion equipment, or in a storage space belonging to a building or vehicle. Initially, the enclosed space is closed off. The receiver's display unit is located outside this enclosed space and outputs the determined value for the target gas concentration visually and / or audibly. If the determined target gas concentration is lower than a preset concentration limit and therefore not dangerous to humans, the user or control equipment also releases access to the enclosed space. This enclosed space is then "freely measured". For example, work that could lead to sparks is permitted to be performed within the enclosed space only when the target gas concentration is sufficiently low.

[0075] In one implementation, the gas measuring device is located completely outside the enclosed space. A hose or other fluid guide unit connects the gas measuring device to the enclosed space. The pump or other fluid discharge unit of the gas measuring device draws the gas sample from the enclosed space through the fluid guide unit. Alternatively, the gas sample diffuses through the fluid guide unit to the gas measuring device.

[0076] In one configuration, a gas measuring device can control a spatially separated warning unit. As soon as the measured target gas concentration is outside the acceptable range, the gas measuring device causes the warning unit to output a warning in at least one form perceptible to humans, particularly audibly.

[0077] The present invention will be described below based on examples. [Brief explanation of the drawing]

[0078] [Figure 1] This is a schematic diagram showing a first configuration of a gas measuring device, in which the detector and compensator are located within a Wheatstone measuring bridge. [Figure 2] Figure 1 shows the two switches of the gas measuring device. [Figure 3] This diagram illustrates a detector configured as a peristaltic detector. [Figure 4] This diagram illustrates a detector configured as a flat component. [Figure 5] This is a schematic diagram showing the second configuration of the gas measuring device. [Figure 6] This figure exemplifies the detection quantity used as a function of the target gas concentration.

[0079] The gas measuring device and gas measuring method according to the present invention can monitor a spatial region for the presence of at least one flammable target gas and / or measure at least approximately the concentration of the flammable target gas in this region. The gas measuring device utilizes principles known from the prior art to examine a gas sample from the spatial region for the presence and / or concentration of the flammable target gas.

[0080] The detector is located inside the housing of the gas measuring device. Through one opening in the housing, the gas mixture diffuses from the area to be monitored into the interior of the housing or is drawn in and discharged into the interior, for example by a pump. In this embodiment, the interior of the housing is in continuous fluid communication with the area to be monitored throughout the period of use, thereby allowing a continuous flow of the gas sample into the interior of the housing. Typically, this gas sample contains the target gas to be detected or each of the target gases to be detected, along with oxygen, assuming that the target gas is present in the spatial area. It is also possible that the interior of the gas measuring device is in fluid communication with the spatial area only during the process of discharging the gas sample into the interior.

[0081] The detector includes a conductive wire having a heating segment, in this case referred to hereafter as the detector segment. The detector segment is, for example, a coil forming one segment of the wire. The conductive material is, for example, platinum, rhodium, tungsten, or an alloy using at least one of these metals. A voltage U is applied to the wire at least temporarily, thereby causing a current I to flow through the wire. The flowing current heats the detector segment, and the heated detector segment releases thermal energy. The released thermal energy oxidizes at least one flammable target gas inside the housing, usually each flammable target gas. Of course, this only occurs if the area, and by extension the interior, contains at least one flammable target gas and there is sufficient oxygen for oxidation.

[0082] In one application, methane (CH4) is one or more of the flammable target gases to be detected. With the supply of thermal energy, methane reacts with oxygen to produce water and carbon dioxide. That is, CH4 and 2O2 produce 2H2O and CO2. In another application, the target gas is hydrogen (H2). As is known, hydrogen reacts with oxygen to form water (H2O).

[0083] During the oxidation of the target gas, thermal energy is released within the housing. This thermal energy acts on the detector, increasing the temperature of the detector segment through which the current flows. This temperature increase correlates with the released thermal energy and, consequently, with the concentration of the target gas within the housing. Gas measuring devices with such detectors are sometimes referred to as "thermal-controlled sensors."

[0084] A rise in temperature alters the measurable properties of the detector, in this case, the measurable properties correlate with the temperature of the detector segment. For example, a rise in temperature alters the electrical resistance R of the detector segment through which current flows. It is known that for many conductive materials, the electrical resistance R increases with increasing temperature. A gas measuring device measures at least one measurable quantity, hereafter referred to as the "detector detection quantity," which is affected by the properties of the detector segment and, consequently, by temperature. The detector detection quantity is, for example, a quantity directly correlated with temperature or the electrical resistance R of the detector segment, such as the voltage U or current intensity I applied to the detector, or the power P consumed by the detector segment.

[0085] Figures 1 and 2 illustrate a first configuration of the gas measuring device 100 according to the present invention. The same reference numerals have the same meaning.

[0086] In this embodiment, the detector 10 is located in the detector chamber 8, and the compensator 11 is located in the compensator chamber 5 (see Figure 1). The detector chamber 8 containing the detector 10 and the compensator chamber 5 containing the compensator 11 are housed within a robust housing 1. Thanks to the opening O, the robust housing 1 is in fluid communication with the area to be monitored, thereby allowing the gas sample to reach the interior of the housing 1 from the area to be monitored, and further from there to the interior of the detector chamber 8. A flame guard 2, such as a metal grid within the opening O, reduces the risk of flame leakage from the interior to the exterior of the robust housing 1. The robust housing 1 is preferably surrounded by a schematicly shown outer housing 4 that allows for good gripping and holding.

[0087] The voltage U10 applied to the detector 10 causes a current I to flow. The flowing current I heats the detector segment 20 of the detector 10 to its operating temperature. This temperature is often between 450°C and 550°C, provided that the heated detector segment 20 is in a state where it can oxidize all flammable target gases to be considered. When hydrogen is used as the flammable target gas, an operating temperature between 150°C and 250°C is often sufficient. However, this operating temperature alone is usually insufficient to oxidize the flammable target gas in the inner housing 1. Higher operating temperatures are often undesirable because they can lead to combustion or explosion of the flammable target gas, which is often undesirable and also consumes a lot of electrical energy.

[0088] In order to oxidize a flammable target gas even at operating temperatures below 550°C, or below 250°C in the case of hydrogen, the detector 10 includes a catalytic material that works in conjunction with a heated detector segment 20 to oxidize the target gas. Therefore, a gas measuring device having such a detector 10 is sometimes referred to as a "catalytic sensor" or "sensor with catalytic activity."

[0089] In a frequently used implementation, the detector segment 20 is surrounded by an electrical insulator, such as a ceramic sheath. This electrical insulator electrically isolates the detector segment 20, particularly preventing unwanted short circuits. Because the electrical insulator is thermally conductive, the detector segment 20 can dissipate thermal energy into the surroundings of the detector 10, and conversely, thermal energy from the surroundings can further heat the detector segment 20. This electrical insulator is covered with a coating made of a catalytic material, or the catalytic material is embedded in the electrical insulator. This catalytic coating comes into contact with the gas mixture in the inner housing 1, and consequently with the flammable target gas. A detector 10 configured in this way is often referred to as a "peristor."

[0090] Figure 3 illustrates a detector 10 configured as a peristaltic and schematically shows the conversion of methane (CH4) to CO2 and H2O. The detector 10 consists of the following components: - A helically wound conductive wire 20, made from, for example, platinum or tungsten, which functions as a detector segment, -A ceramic casing 21 surrounds the detector segment 20 and, in the illustrated example, has a spherical shape. -The catalyst coating on the outer surface of the ceramic outer covering 21, shown as circle 23 in Figure 3, - Mounting plate 22, -Includes an electrical connection part and a mechanical holding part 36 for the wire 20.

[0091] The detector segment 20, ceramic casing 21, mounting plate 22, connection part, and retaining part 36 belong to the functional components 50 of the detector 10. The catalyst coating 23 surrounds the detector functional components 50 or is located inside the detector functional components 50.

[0092] For example, platinum or palladium can be used as the catalyst material. Alternatively or additionally to the catalyst coating 23, the catalyst material 23 may be embedded within the ceramic outer covering 21.

[0093] In one preferred configuration, the entire sphere of the detector 10 has a porous surface with a catalyst coating 23. In one configuration, this porous surface is manufactured as follows: a detector functional component 50, i.e., a detector 10 having a porous surface but no catalyst coating, is prepared. The catalyst coating 23 is applied to the porous surface, for example, in an immersion bath, and a portion of the catalyst material penetrates into the interior of the detector 10. It is also possible to mix a ceramic material and a catalytic substance together and apply them together to the detector segment 20, for example, in an immersion bath.

[0094] Thanks to this porous surface, the detector 10 has a larger surface area compared to a smooth surface. This larger surface area allows the detector segment 20 to oxidize the flammable target gas more effectively, because, in particular, a larger amount of the target gas comes into contact with the catalyst material. The gas can also reach lower layers of the detector 10 thanks to this porous surface.

[0095] Figure 4 shows different configurations in which the detector 10 is configured as a flat component. The detector segment 20 is a component of a conductive conductor path 30, which additionally has electrical connections 46 and electrical contact points 34. The conductor path 30 is deposited on a support plate 31. A wafer substrate 33 supports the support plate 31. A protective layer 35 is deposited on the conductor path 30 having the detector segment 20. In one embodiment, this protective layer 35 is catalytic. In another embodiment, a catalytic layer is deposited on this protective layer 35, and is deposited at least in the region of the detector segment 20. In a third possible embodiment, the protective layer 35 is permeable to gas and covers the catalytic layer on the detector segment 20.

[0096] In one configuration, the manufacturing of the detector 10 includes the following steps: - A step of preparing wire for the detector segment 20 of the detector 10, - The step of applying a liquid (coating suspension) to the wire in order to adhere a ceramic coating, - The step of applying a heating current to the detector segment 20, thereby drying and evaporating the liquid.

[0097] The liquid contains the following three components: - Materials that are catalytically activated after drying, such as palladium nitrate [Pd(NO3)2] or hexachloroplatinic acid (H2PtCl6), -For example, a carrier material containing oxides of the elements aluminum, silicon, cerium and / or zirconium, -Includes a solvent, such as water.

[0098] The following description relates to the two realization forms of the detector 10 described earlier. However, the temperature of the detector 10, and consequently the detector's detection amount, is affected not only by the emitted thermal energy, but also by the ambient conditions within 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 noble gases. These ambient conditions can also change the conditions inside the inner housing 1. In detail, these ambient conditions can similarly affect the detector temperature, and consequently the detector's detection amount, because, for example, the thermal conductivity around the detector 10 changes. It is desirable that the gas measuring device 100, despite changing ambient conditions, be able to reliably detect the flammable target gas on the one hand, and generate relatively few false alarms on the other hand, that is, it is relatively rare for it to determine that the target gas is present even though there is actually no generation of target gas exceeding the detection limit, and that this leads to erroneous results.

[0099] In this embodiment, the gas measuring device 100 includes an optional temperature sensor 14, which measures the ambient temperature around the gas measuring device 100 (see Figure 1). Preferably, the temperature sensor 14 measures the difference between the ambient temperature and a preset reference temperature.

[0100] In contrast, the gas measuring device 100 of this embodiment does not include either an ambient pressure sensor or an ambient humidity sensor. The gas measuring device of this embodiment does not necessarily need to be able to process signals from either an ambient pressure sensor or an ambient humidity sensor. Rather, this gas measuring device 100 structurally and / or computationally compensates to a certain extent for the influence of ambient conditions that are not directly measured on the temperature-dependent detection amount of the detector segment 20.

[0101] For this purpose, the gas measuring device 100 has a compensator 11 in addition to the detector 10 (see Figure 1). This compensator 11 also includes a wire having compensator segments. A voltage U11 is also applied to the compensator 11, causing a current to flow and similarly heating the segments of the compensator 11. This compensator 11 is also similarly exposed to variable ambient conditions.

[0102] In a preferred embodiment, the compensator 11 also includes a helically wound conductive wire, which functions as a compensator segment and is indicated by reference numeral 38. The compensator 11 also includes a ceramic sheath, a mounting plate, electrical connections, and a mechanical retaining part. However, in contrast to the detector 10, the ceramic sheath of the compensator 11 does not have a catalytic coating. The compensator segment 38, ceramic coating, mounting plate, connections, and retaining part all belong to a compensator functional component 51, which can take the form of a spherical or plate in particular, i.e., the shape of the detector 10 in Figure 3 or the shape of the detector 10 in Figure 4.

[0103] Figures 1, 2, and 5 show the compensator 11 within the compensator chamber 5. In Figure 1, it can be seen that the detector 10 includes a detector segment 20, and the compensator 11 includes a compensator segment 38. In the examples of Figures 1, 2, and 5, the compensator 11 is similarly configured as a spherical or ellipsoidal peristaltic, but unlike the detector 10 in Figure 3, it does not include a catalytic active coating 23. The compensator 11 may also be configured as a flat component, i.e., as the detector 10 shown in Figure 4.

[0104] Figures 1 and 2 show the following further components of the gas measuring device 100. That is, - A specific voltage source 42, for example, a set of rechargeable batteries, - An electrical line 3 connecting the voltage source 42 to the detector 10 and the compensator 11, - Voltage sensor 40 (Figure 1 only), - Voltage sensor 12.2 (Figure 1 only), -Current strength sensor 41 (Figure 1 only), -Two electrical resistance components R100 and R110 having variable resistance, - With two electrical resistance components R10 and R11 (Figure 2 only), -Two electrical resistance components R20 and R21, -Operation element 17 and (Figure 1 only), -A signal processing and control device (control unit) 6 (Figure 1 only) can be seen.

[0105] Optionally, a thermal barrier (not shown) inside the gas measuring device 100 thermally separates the detector 10 from the compensator 11. The present invention can also be realized without such a thermal barrier.

[0106] The gas measuring device 100 shown in Figures 1 and 2 is configured as a Wheatstone measuring bridge. The voltage sensor 40 measures the bridge voltage ΔU_B in the Wheatstone measuring bridge. In the configuration shown in Figures 1 and 2, this bridge voltage ΔU_B functions as the total detected amount. In the first configuration shown in Figures 1 and 2, this total detected amount depends on the voltage U10 applied to the detector 10 and the voltage U11 applied to the compensator 11, as follows: That is, the total detected amount increases as the detector voltage U10 increases, and decreases as the detector voltage U11 increases. The voltage sensor 12.2 measures the voltage U11 applied to the compensator 11. The current intensity sensor 41 measures the intensity I.3 ​​of the current flowing through the line 3.

[0107] The compensator 10 and the detector 11 are connected in series in Figures 1 and 2. The electrical resistance component R100 is connected in parallel to the detector 10, and the electrical resistance component R110 is connected in parallel to the compensator 11. The electrical resistance components R20 and R21 are connected in parallel to the series circuit having the detector 10 and the compensator 11.

[0108] Figures 1 and 2 show, -The voltage U42 of the voltage source 42, -The voltage U10 applied to the detector 10, -The voltage U11 applied to the compensator 11, This is shown.

[0109] The measured values ​​from sensors 40, 41, 12.2, and 14 are transmitted to the control device 6 and processed by the control device 6. The signal-processed evaluation unit 9 derives an estimated value for the target gas concentration in the gas sample, in this case, the concentration of methane or hydrogen. In this embodiment, the evaluation unit 9 is a component of the control device 6.

[0110] In the examples shown in Figures 1 and 2, these components form a Wheatstone measuring bridge. Detector 10 and compensator 11 are connected in series. The electrical resistance of voltage sensor 40 is higher compared to the electrical resistances of components 10, 11, R10, R11, R20, and R21. In one configuration, voltage sensor 40 directly measures the so-called bridge voltage ΔU_B = (U10 - U11) / 2. Closed-loop control keeps the current intensity I.3 ​​constant, thereby making the voltage U, particularly the bridge voltage ΔU_B, proportional to the electrical resistance R and thus correlated with the temperature of detector segment 20 and the target gas concentration. For this closed-loop control, the actual current intensity I.3 ​​measured by current intensity sensor 41 is used.

[0111] In one implementation, a pulse-controlled voltage is applied to conserve electrical energy. The control objective of keeping the current intensity I.3 ​​constant is related to the current intensity in the electrical pulse. In another implementation, a voltage is continuously applied to the detector 10 and the compensator 11.

[0112] Modified bridge voltage ΔU_B korr =ΔU_B-ΔU_B0 correlates with the target gas concentration being searched for. Here, ΔU_B0 is the bridge voltage ΔU_B that occurs when the flammable target gas is not present in the zero point, i.e., within the area to be monitored, and consequently inside the gas measuring device 100. This zero point ΔU_B0 is preferably determined empirically in advance. The correction using the zero point ΔU_B0 compensates for potential differences between the detector 10 and the compensator 11 due to the structural configuration. During the service life of the gas measuring device 100, it is possible to determine the zero point ΔU_B0 at least once through at least one second adjustment.

[0113] In the configurations shown in Figures 1 and 2, the modified bridge voltage ΔU_B korr =ΔU_B-ΔU_B0 functions as the total detected quantity.

[0114] Figure 5 shows a second configuration of the gas measuring device 100. Matching reference numerals have the same meaning as in Figures 1 and 2. The detector chamber 8 is in fluid communication with the region B to be monitored through opening O1, and the compensator chamber 5 is in fluid communication with the region B to be monitored through opening O2. The distance between the catalytic coating 23 and the remainder of the detector 10, and the distance between the further passivation coating 24 described below and the remainder of the compensator 11, are shown in exaggeration.

[0115] According to the second configuration, the detector 10 and the compensator 11 are supplied with electrical energy independently of each other. The first current circuit I.1 connects the detector 10 to the first voltage source 43, and the second current circuit 3.2 connects the compensator 11 to the second voltage source 44. A selectively driveable switch 28, depending on its position, either opens or interrupts the current circuit 3.1 between the detector 10 and the voltage source 43. The current circuit 3.2 is preferably not interrupted.

[0116] Voltage sensor 12.1 measures the voltage U10 applied to detector 10. Current intensity sensor 13.1 measures the current intensity I.1 flowing through the current circuit 3.1 for detector 10. Voltage sensor 12.2 measures the voltage U11 applied to compensator 11. Current intensity sensor 13.2 measures the current intensity I.2 flowing through the current circuit 3.2 for compensator 11. Each of the current intensities I.1 and I.2 are kept constant by a single closed-loop control.

[0117] In the implementation of the second configuration, the total detected amount is derived depending on the voltage difference ΔU = U10 - U11. This voltage difference ΔU = U10 - U11 is ideally zero when there is no flammable target gas, but in reality, it is not zero even when there is no flammable target gas. Therefore, the modified voltage difference ΔU korr =U10-U11-ΔU0 is calculated and used as the total detected amount. This total detected amount ΔU korrThis correlates with the target gas concentration. A zero value ΔU0 occurs when no flammable target gas is present, and here again compensates for the difference caused by the structural configuration between the detector 10 and the compensator 11. Here again, the zero value ΔU0 can be reset by at least one new adjustment during the service life.

[0118] The procedure for measuring the target gas concentration described here assumes the following: sufficient oxygen is required in the detector chamber 8, so that the detector 10 can oxidize all flammable target gases. Only in this case can the thermal energy released during oxidation be reliably used as a measure of the target gas concentration. In the case of high-concentration target gases, this prerequisite does not need to be met. In particular, it is possible that a flammable target gas is indeed present in the detector chamber 8, but oxygen for oxidation is not present. Oxygen may also be absent if another gas, which does not necessarily have to be the target gas, eliminates oxygen. This other gas is inert gas, in particular, which should prevent unwanted oxidation in the spatial domain. Nevertheless, in cases where the target gas concentration would be measured using only the thermal energy released during oxidation, there is a risk of measuring an excessively low target gas concentration, i.e., failing to detect dangerous high-concentration target gases. This could endanger the user and is therefore undesirable.

[0119] Therefore, if the target gas concentration, measured based on the released thermal energy, reaches a predetermined upper concentration limit, a different procedure is preferably applied. This upper concentration limit is selected such that if it is reached or exceeds, there is a possibility that almost all of the flammable target gas in the detector chamber 8 has been oxidized. In other words, as long as the upper concentration limit has not yet been reached, there is certainly still enough oxygen in the detector chamber 8 for oxidation.

[0120] In an alternative procedure, that is, when the target gas concentration reaches the upper concentration limit, the detection quantity correlated with the temperature of the detector segment 20 is not used to determine the target gas concentration. In other words, in this embodiment, in an alternative procedure, the voltage U10 applied to the detector 10 is not used. This alternative procedure takes advantage of the fact that hydrogen and many other flammable target gases to be detected have a higher thermal conductivity than air. Therefore, this flammable target gas cools the heated compensator segment 38 of the compensator 11 more strongly than the ambient air.

[0121] In another procedure, the temperature of the compensator segment 38 is measured, or more precisely, a measure of temperature is measured. The temperature of the compensator segment 38 correlates with the concentration of the target gas being sought. More precisely, compared to the absence of the flammable target gas, if all other conditions remain the same, the higher the concentration of the target gas being sought, the lower the temperature. In this embodiment, the current intensity I.3 ​​(Figures 1 and 2) or I.2 (Figure 5) of the current flowing through the compensator 11 is also kept constant by the corresponding control. The voltage U11 applied to the compensator 11 correlates with the temperature of the compensator segment 38. Here again, the zero point is determined empirically, and more specifically, the voltage U110 applied to the compensator 11 when the flammable target gas is absent is determined. In this embodiment, the modified compensator voltage U11 korr U11-U110 are used as compensator detection quantities.

[0122] The gas measuring device 100 can be optionally and additionally operated in a dormant state in at least two different modes. The control device 6 causes the following: that is, the gas measuring device 100 in this embodiment automatically switches from one mode to the other, and the switching depends on a preset oxidation criterion. In this embodiment, the gas measuring device 100 can operate in the following modes: that is - The gas measuring device 100 measures the corrected bridge voltage ΔU_B korr (Depending on the configuration shown in Figures 1 and 2) or the modified voltage difference ΔU korrDepending on the configuration according to FIG. 5, that is, depending on the total detection amount, in the oxidation measurement mode for obtaining the target gas concentration, or - The gas measurement device 100 can operate in the thermal conductivity measurement mode that obtains the target gas concentration depending on the corrected compensator voltage U11 korr = U11 - U110, that is, depending on the compensator detection amount.

[0123] That is, in this embodiment, as the total detection amount, the corrected bridge voltage ΔU_B korr (configuration according to FIGS. 1 and 2) or the corrected voltage difference ΔU korr (configuration according to FIG. 5) functions, and as the compensator detection amount, the corrected compensator voltage U11 korr functions.

[0124] As described here, the gas measurement device 100 can operate in two different modes. Preferably, different zero values are used in these two modes. The zero value ΔU_B0 of the bridge voltage ΔU_B or the zero value ΔU of the voltage difference ΔU = U10 - U11 is used during operation in the oxidation measurement mode to calculate the total detection amount. The zero value U110 of the compensator voltage U11 is used during operation in the thermal conductivity measurement mode to calculate the compensator detection amount U11 korr . Note: The compensator 11 can have a different zero value U110 from that during operation in the thermal conductivity measurement mode, especially due to the different temperatures of the compensator segment 38, during operation in the oxidation measurement mode.

[0125] The evaluation unit 9 applies a first evaluation rule preset in a computer - evaluable form to the measured total detection amount ΔU_B korr or ΔU korr during operation in the oxidation measurement mode. This first evaluation rule is for the total detection amount ΔU_B korr or ΔU korrThe measurement depends optionally on the measured ambient temperature and optionally on further measured ambient conditions. As described above, the optional temperature sensor 14 can measure the ambient temperature, preferably as a difference from a preset reference temperature. When operating in heat conduction measurement mode, the evaluation unit 9 uses the measured compensator detection amount U11 korr The second evaluation rule is applied to the compensator detection amount U11. korr And, optionally, it depends on the measured ambient temperature and / or further measured ambient conditions.

[0126] In this embodiment, the two evaluation rules are determined by a learning method using pre-randomized sampling tests. For example, the two evaluation rules are pre-defined and each includes at least one model parameter. Preferably, the model parameter is the reciprocal of an empirically determined proportionality coefficient, in which case this proportionality coefficient describes the effect of the target gas concentration on the amount of detection used. Optionally, a further model parameter is the reciprocal of another empirically determined proportionality coefficient, in which case this further proportionality coefficient describes the effect of the measured ambient temperature on the amount of detection used.

[0127] The oxidation criterion is preset to be satisfied when there is at least enough oxygen in the detector chamber 8 to oxidize all the target flammable gases. Preferably, the oxidation criterion depends on the measured target gas concentration. Different realizations of the oxidation criterion are possible.

[0128] Preferably, the gas measuring device 100 initially operates in oxidation measurement mode. The control device 6 repeatedly checks whether the oxidation criterion is still met, preferably using a fixed sampling rate. For example, the evaluation unit 9 compares the target gas concentration obtained in oxidation measurement mode with a preset first upper concentration limit. Alternatively, the evaluation unit 9 checks how long the obtained target gas concentration exceeds a preset lower concentration limit.

[0129] As soon as the control device 6 detects that the oxidation criteria are no longer met with sufficient safety, the control device 6 causes the gas measuring device 100 to automatically switch to thermal conduction measurement mode. In one implementation, the control device 6 drives switch S10 in Figure 2 or switch 28 in Figure 5, causing no voltage to be applied to the detector segment 20 anymore.

[0130] Preferably, the evaluation unit 9 continuously monitors the compensator detected amount U11 during use, even when the gas measuring device 100 is operating in oxidation measurement mode. korr An estimated value for the target gas concentration is obtained based on this. In one implementation, a second upper concentration limit higher than the first upper concentration limit is set in advance. The control device 6 causes the gas measuring device 100 to switch to heat conduction measurement mode when the evaluation unit 9 detects the following event: namely, the compensator detection amount U11 korr This is an event in which the target gas concentration determined by the method exceeds the second upper concentration limit. Preferably, the control device 6 triggers this switching regardless of which target gas concentration was measured based on the total detected amount.

[0131] As already explained, the oxidation criterion is met if there is sufficient oxygen in the detector chamber 8, thereby allowing the detector 10 to oxidize all the flammable target gas present therein. Furthermore, the above describes a configuration in which the control device 6 determines whether the oxidation criterion is met depending on the measured target gas concentration. It is also possible for an optional oxygen sensor 15 to measure the oxygen content in the gas sample present in the detector chamber 8, and for the control device 6 to check whether the oxidation criterion is met depending on the measurement value of the oxygen sensor 15.

[0132] Preferably, the control device 6 causes the gas measuring device 100 to switch back to oxidation measurement mode when a preset feedback switching criterion is met.

[0133] In a preferred implementation, the feedback switching criterion is met when the evaluation unit 9 detects the following event: namely, in the heat conduction measurement mode, i.e., the compensator detected amount U11 korr This refers to an event in which the target gas concentration, measured using a specific method, is lower than a predetermined upper concentration limit. This upper concentration limit is preferably lower than the first upper concentration limit described above.

[0134] Up to this point, a configuration has been described in which the gas measuring device 100 automatically switches from one mode to the other. The gas measuring device 100 may also include a selection switch, in which case the user can operate this selection switch. By operating the selection switch accordingly, the user determines how the gas measuring device 100 should operate as follows.

[0135] - The gas measuring device 100 operates selectively in either oxidation measurement mode or thermal conductivity measurement mode, depending on the oxidation criterion.

[0136] - The gas measuring device 100 operates in thermal conductivity measurement mode, independent of the oxidation standard.

[0137] For illustrative purposes, Figures 1 and 5 show a selection switch in the form of the operating element 17.

[0138] It is also possible that the control device 6 detected the following event based on, for example, captured user input: namely, that the detector chamber 8 was cleaned with a gas sample containing sufficient oxygen. For example, the user brought the gas measuring device 100 into an area containing sufficient oxygen and free of the flammable target gas. As a result, for example, the user operated the operating element 17, thereby enabling the oxidation measurement mode again.

[0139] The following configuration is also possible: a configuration in which an arbitrarily selected oxygen sensor 15 measures a sufficiently high oxygen concentration within the detector chamber 8.

[0140] Figure 6 schematically shows how the detection doses used depend on the target gas concentration. The results of internal tests are shown. The x-axis plots the concentration of the flammable target gas, methane (CH4), in [volume %], and the y-axis plots the resulting values ​​for the detection doses used in [mV]. Curve OxM shows how the target gas concentration depends on the total detection dose, i.e., the modified bridge voltage ΔU_B. korr =ΔU_B - ΔU_B0 (configured according to Figures 1 and 2) or the modified voltage difference ΔU korr This relates to the oxidation measurement mode, which is determined by =U10-U11-ΔU0 (configuration shown in Figure 5). Curves WIM,eq and WIM,high show that the target gas concentration depends on the compensator detection amount, i.e., here, the modified compensator voltage U11 korr This relates to the heat conduction measurement mode determined by U11-U110.

[0141] In the example in Figure 6, methane is the target flammable gas. The lower explosive limit (UEG, LEL) in this example is 4.4% by volume. The gas measuring device 100 is α * If a target gas concentration higher than UEG is measured, the gas measuring device 100 will output an alarm or cause a spatially remote receiver to output a warning. This applies regardless of the mode in which the target gas concentration was measured. The coefficient α is between 0 and 0.6, preferably less than 0.5. In one implementation, the gas measuring device 100 will output an alarm if the target gas concentration is α1 * If the UEG exceeds the limit, a pre-warning is issued, and the target gas concentration is α * A major alarm is triggered if the UEG exceeds the limit. Here, the condition 0 < α1 < α ≤ 0.6 applies. For example, α1 = 0.2 and α = 0.4.

[0142] As already explained, in this embodiment, during the period of use of the gas measuring device 100, the detection chamber 8 maintains continuous fluid communication with the spatial region B to be monitored, and the gas sample continuously flows into the detector chamber 8. Total detected amount ΔU_B korrOr ΔU korr The maximum value is reached at a target gas concentration of 9.6 volume percent methane in the air, which is the so-called stoichiometric concentration at which all oxygen in the detector chamber 8 is consumed. At higher target gas concentrations, the following two effects occur.

[0143] - Because there is not enough oxygen in the detector chamber 8, the heated detector segment 20 oxidizes only a small amount of the flammable target gas, and the temperature of the detector segment 20 drops again.

[0144] Furthermore, the gas samples in the detector chamber 8 and the compensator chamber 5 each have higher thermal conductivity because methane has a higher thermal conductivity than air.

[0145] For these two reasons, the total detected amount (corrected bridge voltage ΔU_B korr See Figures 1 and 2, or the modified voltage difference ΔU korr (See Figure 5) becomes smaller again.

[0146] Furthermore, as already mentioned above, in a preferred configuration, the control device 6 causes the gas measuring device 100 to automatically switch to the heat conduction measurement mode when the target gas concentration determined in oxidation measurement mode reaches or exceeds a preset first upper concentration limit. This first upper concentration limit is smaller than the stoichiometric concentration and is 6 volume percent in the illustrated example.

[0147] In addition, the above describes an embodiment in which the control unit 6 causes the gas measuring device 100, which is operating in heat conduction measurement mode, to switch back to oxidation measurement mode when a preset feedback criterion is met. This feedback criterion is met when the target gas concentration determined in heat conduction measurement mode is lower than a preset feedback limit. In the illustrated example, this feedback limit is 3.8 volume%.

[0148] When the target gas concentration changes rapidly, the 6 vol% limit described here may be insufficient in some cases when operating in oxidation measurement mode. For safety, a second upper concentration limit, for example 11 vol%, i.e., preferably above the stoichiometric concentration, is pre-set. The control device 6 causes the gas measuring device 100 to switch from oxidation measurement mode to thermal conduction measurement mode when the following event is detected: that is, the evaluation unit 9 detects the compensator detection amount U11 korr This is an event in which the target gas concentration that exceeds the second upper concentration limit is determined depending on the total detected amount ΔU_B. The control device 6 does not depend on the target gas concentration determined in the oxidation measurement mode, that is, the total detected amount ΔU_B korr Or ΔU korr This triggers a switch to the heat conduction measurement mode.

[0149] When operating in oxidation measurement mode, the compensator segment 38 must be heated to approximately the same temperature as the detector segment 20, so that the detector 10 and compensator 11 react to ambient conditions in sufficiently similar terms, and the total detected amount ΔU_B korr Or ΔU korr To at least approximately compensate for the influence of the ambient conditions on the gas, the device also responds to ambient conditions that are not directly measured. These ambient conditions include, in particular, ambient pressure, ambient humidity, and the chemical composition of the ambient air. If the gas measuring device 100 does not have a temperature sensor 14, ambient temperature also belongs to the category of ambient conditions that are not measured.

[0150] Nevertheless, in this embodiment, the compensator 11 should not oxidize the flammable target gas, and should not oxidize the flammable target gas even when the measured value for the target gas concentration is derived depending on the detector voltage U10 and the compensator voltage U11, or even when this measured value is derived depending solely on the compensator voltage U11. In particular, the compensator 11 should not oxidize the flammable target gas within the relevant range when the target gas concentration is calculated depending on the amplified thermal conductivity and, consequently, on the compensator voltage U11. Even if the compensator 11 oxidizes only a relatively small amount of flammable target gas, this effect masks the effect of the amplified thermal conductivity, i.e., the cooling effect, thus increasing the risk of supplying an incorrect measurement. Moreover, the following undesirable effect may occur: namely, the oxidation of the target gas by the compensator 11 cancels out the amplified thermal conductivity, thereby causing the gas measuring device 100 to supply an incorrect result that the target gas is not present.

[0151] In this embodiment, during the manufacture of the compensator 11, the wire for the compensator segment 38 of the compensator 11 is prepared. This wire is coated with a ceramic that does not contain catalytic materials. In one embodiment, aluminum oxide is used for this purpose.

[0152] As already explained, the wire of the compensator segment 38 is coated with ceramic. Subsequently, the ceramic is coated with a passivation coating 24. This passivation coating 24 is applied as follows: the wire having the ceramic coating is immersed in an immersion bath having a chemical composition and a solvent, such as water. Subsequently, the coated wire is removed from the immersion bath and then dried. This causes the solvent to evaporate. When the gas measuring device 100 is in use, 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 wire of the compensator 11 from the gas sample.

[0153] In this embodiment, the passivation coating 24 consists of at least 50% by weight, preferably at least 80% by weight, and particularly preferably at least 95% by weight of an iodine-containing compound. Preferably, the passivation coating 24 consists of at least 50% by weight, preferably at least 80% by weight, of an alkali metal or alkaline earth metal iodide or iodate. This alkali metal or alkaline earth metal is preferably potassium. Particularly preferably, the compound is potassium iodide (KI) or potassium iodate (KIO3).

[0154] As already explained, the gas measuring device 100 can selectively operate in oxidation measurement mode or thermal conductivity measurement mode. In oxidation measurement mode, the gas measuring device 100 determines the target gas concentration as the total detected amount ΔU_B korr Alternatively, it is determined by ΔUkorr, and in the heat conduction measurement mode, the compensator detected amount U11 korr This is determined by the compensator 11. In oxidation measurement mode, the compensator 11 compensates for the effects of ambient conditions. Therefore, in oxidation measurement mode, the compensator temperature does not deviate too much from the detector temperature, and more specifically, the deviation is preferably limited to a maximum of 150°C, and particularly preferably to a maximum of 100°C. This limit does not exist in thermal conduction measurement mode because the compensator detected amount U11 korr This is because it depends solely on the compensator temperature.

[0155] The inventors have found that in internal testing, in the heat conduction measurement mode, the higher the compensator temperature, the greater the compensator detection amount U11 korr However, it was confirmed that this serves as a good indicator of the target gas concentration being searched for. The background to this is that, as is known, most target gases to be detected have a higher thermal conductivity than air, and therefore, the compensator 11 is cooled more strongly as the target gas concentration increases. The inventors confirmed that, internally, the higher the compensator temperature, the greater the cooling effect. Compensator temperature refers to the temperature obtained when a voltage is applied to the compensator 11 and current flows through the wire 38.

[0156] Exemplary, Figure 6 shows which effect has two different temperatures in compensator segment 38. Curve WlM;eq is the compensator detected, here U11 korr The dependency is shown in the following possible realizations. That is, in both the oxidation measurement mode and the heat conduction measurement mode, the compensator temperature deviates only slightly from the detector temperature as described above and is generated to be the same in both modes. In contrast, curve WIM;high represents the compensator detection amount U11 when the present invention causes a higher compensator temperature in the heat conduction measurement mode than in the oxidation measurement mode. korr This shows the dependency. Please understand that the curve shown in Figure 6 is only a rough representation.

[0157] From the principles described herein, the following technical teachings according to the present invention are derived. Specifically, in the heat conduction measurement mode, the compensator temperature is caused to be higher than in the oxidation measurement mode. In other words, when switching to the heat conduction measurement mode, the control device 6 causes an increase in 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 causes a decrease in the current intensities I.2 and I.3 again.

[0158] There are various ways in which this can be brought about.

[0159] Figure 2 shows a possible implementation that can be applied to the Wheatstone measuring bridge according to Figure 1. A bypass line L11 having an electrical resistance component R11 and a switch S11 is arranged in parallel with the compensator 11. The resistance component R11 and the switch S11 together form one implementation of the resistance component R110 in Figure 1. When the switch S11 is closed, only a portion of the current I.3 flows through the compensator 11 and heats the compensator segment 38. A further portion of the current I.3 flows through the bypass line L11 in parallel with the compensator 11 by the closed switch S11. When the switch S11 is open, the total current I.3 flows through the compensator 11. As a result, i.e., when the switch S11 is open, the compensator segment 38 is heated more strongly than when the switch S11 is closed. The switch S11 is drive-controllable. The control device 6 drives the switch S11 as follows: In other words, the switch S11 is controlled to open when operating in heat conduction measurement mode and to close when operating in oxidation measurement mode.

[0160] One further result is that when switch S11 is closed, the electrical resistance of the circuit with compensator 11 and resistor R11 is smaller than when switch S11 is open. In one configuration, the voltage U11 applied to compensator 11 is closed-loop controlled so that the current strength I.3 is kept constant regardless of the position of switch S11. This is, of course, after the transient response time.

[0161] In an alternative configuration, the compensator voltage U11 is kept constant by closed-loop control.

[0162] Optionally, a bypass line L10 having an electrical resistance component R10 and a switch S10 is connected in parallel to the detector 10. The resistance component R10 and the switch S10 together form an implementation of the resistance component R100 in Figure 1. When the switch S10 is closed, only a portion of the current I.3 flows through the detector 10, and the other portion of the current I.3 flows through the bypass line L10. When the switch S10 is open, the total current I.3 flows through the detector 10. The control device 6 drives the switch S10 so that the following occurs: namely, the switch S10 is opened in oxidation measurement mode and closed when operating in heat conduction measurement mode. This configuration reduces the risk of damage to the detector 10, in particular when a high concentration of target gas is generated in the detector chamber 8 and therefore the gas measuring device 100 is operating in heat conduction measurement mode.

[0163] Figure 5 shows an applicable implementation when the detector 10 and compensator 11 are supplied with electrical energy independently of each other, as shown in Figure 5, and therefore the current I.1 flowing through the detector 10 can deviate from the current I.2 flowing through the compensator 11. The control device 6 can drive and control the voltage source 43, and preferably additionally, the voltage source 44 can also be driven and controlled independently of the voltage source 43. This drive control results in the following: the voltage U11 applied to the compensator 11 is higher when operating in the heat conduction measurement mode than when operating in the oxidation measurement mode. Preferably, conversely, the voltage U10 applied to the detector 10 is higher when operating in the oxidation measurement mode than when operating in the heat conduction measurement mode. The electrical resistance in current circuit 3.1 and the electrical resistance in current circuit 3.2 are the same in both modes in one configuration.

[0164] According to the configuration in Figure 5, an additional electrical resistance component R110 with a variable resistance value is placed within the circuit 3.2 for the compensator 11. The control device 6 can drive and control the resistance component R110. This drive and control results in the following: when operating in oxidation measurement mode, the electrical resistance of the resistance component R110 is greater than when operating in heat conduction measurement mode, preferably at least twice as great.

[0165] In an advanced version of this configuration, an electrical resistance component R100 with a variable resistance value is placed within the circuit 3.1 for the detector 10. The control device 6 can drive and control the resistance component R100. This drive and control results in the following: when operating in oxidation measurement mode, the electrical resistance of the resistance component R100 is smaller than when operating in thermal conduction measurement mode, preferably up to half the value.

[0166] In an alternative configuration, the control device 6 can drive and control the voltage source 44 in the current circuit 3.2, and optionally additionally drive and control the voltage source 43 in the current circuit 3.1. This drive control allows the control device 6 to change the voltage U44 of the voltage source 44, and optionally also change the voltage U43 of the voltage source 43. This drive control allows the control device 6 to produce different compensator temperatures in two different modes.

[0167] It is possible to change both the voltage U44 of the voltage source 44 and the electrical resistance of the resistor component R11. It is also possible to change only the voltage U44 or only the electrical resistance.

[0168] According to the configuration described above, the gas measuring device 100 can automatically switch from oxidation measurement mode to thermal conduction measurement mode and back, and preferably, it can switch automatically depending on whether the oxidation criteria are met. The gas measuring device 100 can also be operated in thermal conduction measurement mode independently of the oxidation criteria. In one configuration, the gas measuring device 100 includes an operating element 17 schematically shown in Figures 1 and 5. This operating element 17 can be activated and deactivated, for example, by the user setting it on or off. The step of activating the operating element 17 triggers the step of switching the gas measuring device 100 to thermal conduction measurement mode. Preferably, the detector 10 is then deactivated, i.e., no current is supplied and therefore it is not heated. The step of deactivating the operating element 17 triggers the step of switching the gas measuring device 100 to oxidation measurement mode or maintaining thermal conduction measurement mode, depending on whether the oxidation criteria are met. [Explanation of symbols]

[0169] 1. Inner housing surrounding the detector chamber 8 and compensator chamber 5 2. Flame guard inside inner housing 1 3.1 Current circuit for detector 10, including voltage source 43 and resistor R10 3.2 Current circuit for compensator 11, including voltage source 44 and resistor component R11 4. Outer housing surrounding the inner housing 1, components R10, R11, R20, R21, S10, S11, current intensity and voltage sensors, and voltage sources 42, 43, 44. 5 Compensator chamber having an opening O2 and surrounding the compensator 11 6. Control equipment for processing measurement values ​​from sensors 40, 41, 12.2, and 14. 8 Detector chamber having an opening O1 and surrounding the detector 10 9. A signal processing and evaluation unit for determining the target gas concentration; in one configuration, it is a component of control device 6. 10 A detector including a detector functional component 50 having a detector segment 20 and a ceramic outer covering 21, and a catalyst coating 23. 11 Compensator including compensator functional component 51 having compensator segment 38 and ceramic coated portion 21, and passivation coating 24 12.1 The voltage U10 applied to the detector 10 is measured, and in the second configuration, the voltage sensor belongs to the total detection amount sensor. 12.2 A voltage sensor that measures the voltage U11 applied to the compensator 11, functions as a compensator detection amount sensor, and in the second configuration belongs to the total detection amount sensor. 13.1 Current intensity sensor for measuring the current intensity I.1 of the current flowing through detector 10 13.2 Current intensity sensor for measuring the current intensity I.2 of the current flowing through the compensator 11 14. An optional temperature sensor that measures the difference between ambient temperature and a preset reference temperature. 15. Optional oxygen sensor for measuring the oxygen content in detector chamber 8. 17 User-preconfigurable operating elements for thermal conduction measurement mode 20 Conductive detector segment belonging to detector functional component 50 21 Ceramic casing surrounding detector segment 20 and compensator segment 38 22 Mounting plate 23 Catalytic coating on the ceramic outer covering 21 of the detector 10 24 Passivation coating on compensator functional component 51 of compensator 11 28 A switch that selectively allows or blocks current from flowing through the detector segment 20, and determines the mode in which the gas measuring device 100 operates. 30 Conductive conductor path including detector segment 20 31 Support plate for conductor track 30 33 Wafer substrate for conductor path 30 34 Electrical contact points for the conductor circuit 30 35 Protective layer on the conductor path 30 36 Mechanical holding section for detector segment 20 38 Conductive compensator segment belonging to compensator functional component 51 40 In the first configuration, it functions as a total detection amount sensor and is a voltage sensor that measures the bridge voltage ΔU_B. 41. Current intensity sensor for measuring current intensity I.3 ​​in a Wheatstone measuring bridge. 42 Voltage source for the Wheatstone measuring bridge supplying voltage U42 43 Voltage source of current circuit 3.1 that supplies voltage U43 44 Voltage source of current circuit 3.2 that supplies voltage U44 46 Electrical connection part of the conductor path 30 50 Functional components of the detector 10, including a heated detector segment 20 and a ceramic casing 21, surrounded by a catalytic coating 23. 51 Functional components of the compensator 11, including heated compensator segments 38 and ceramic casing 21, surrounded by a passivation coating 24. 100 Gas measuring device including detector 10, compensator 11, temperature sensor 14, control equipment 6, outer housing 4, inner housing 1, voltage supply units 42, 43, 44, and flame guard 2 α Target gas concentration is α * The main warning output by the gas measuring device 100 when the level is higher than the UEG. The target gas concentration of α1 * A pre-warning is issued by the gas measuring device 100 when the level is higher than the UEG. B. Spatial area where flammable target gases are monitored. Gas sample that reached compensator chamber 5 and detector chamber 8 from Gp spatial region B I.1 Current intensity of the current flowing through the current circuit 3.1 and detector segment 20, as measured by the current intensity sensor 13.1 I.2 Current intensity of the current flowing through the current circuit 3.2 and compensator segment 38, as measured by the current intensity sensor 13.2 I.3 Current intensity in the Wheatstone measuring bridge as measured by the current intensity sensor 41 L10 includes switch S10 and resistor R10, and is a bypass line in parallel with detector 10. L11 includes switch S11 and resistor R11, and is a bypass line in parallel with compensator 11. O1 detector chamber 8 opening Opening of O2 compensator chamber 5 O Opening of outer housing 4 Detection amount dependent on target gas concentration when operating in OxM oxidation measurement mode. R10 is an electrical resistance component connected in parallel or in series to the detector 10 and belongs to the resistor component R100. R11 is an electrical resistance component connected in parallel or in series to compensator 11 and belongs to the resistor component R110. R20, R21 are electrical resistance components in parallel with the series circuit consisting of detector 10 and compensator 11. R100 is a driveable electrical resistance component connected in parallel or in series to the detector 10, having a variable electrical resistance value, and in one implementation, including the resistance component R10 and the switch S10. R110 is a driveable electrical resistance component connected in parallel or in series to the compensator 11, having a variable electrical resistance value, and in one implementation, including the resistance component R11 and the switch S11. S10 A driveable switch connected in parallel to detector 10 and belonging to resistor component R100. S11 is a driveable switch connected in parallel to compensator 11 and belonging to resistor component R110. U10 is the voltage applied to the detector 10 and, in one configuration, is measured by the voltage sensor 12.1. U11 is applied to the compensator 11 and, in one configuration, is measured by the voltage sensor 12.2, and functions as a compensator detection quantity. Zero value of the compensator voltage U11 used when operating in U110 thermal conduction measurement mode. U11 korr Modified compensator voltage, equal to U11-U110, which functions as a compensator detection quantity. Voltage of voltage source 42 U42 Voltage of voltage source 43 (U43) U44 Voltage of voltage source 44 ΔU is equal to U10-U11, and is the uncorrected voltage difference. The zero value (zero point) of the voltage difference ΔU used when operating in ΔU0 oxidation measurement mode. ΔU korr The corrected voltage difference, equal to U10 - U11 - ΔU0, serves as the total detected amount. The bridge voltage of the Wheatstone measuring bridge, measured by the voltage sensor 40, is equal to ΔU_B (U10-U11) / 2. The zero value (zero point) of the bridge voltage ΔU_B used when operating in oxidation measurement mode. ΔU_B korr The modified bridge voltage, equal to ΔU_B - ΔU_B0, which functions as the total detected amount. WIM;eq A detection amount dependent on the target gas concentration when operating in thermal conduction measurement mode, in which case the compensator temperature is approximately equal to the detector temperature. WlM;high is a detection amount dependent on the target gas concentration when operating in thermal conduction measurement mode, in which case, according to the present invention, a higher compensator temperature is caused in thermal conduction measurement mode than in oxidation measurement mode.

Claims

1. Flammable target gas (CH ４ A gas measuring device (100) for measuring the concentration of ), The aforementioned gas measuring device (100) - A detector (10) having a conductive detector segment (20), - A compensator (11) having a conductive compensator segment (38), - Total detection amount sensors (40, 12.1, 12.2), - Compensator detection amount sensor (12.2) and, The gas measuring device (100) is configured such that, at least temporarily, the gas sample (Gp) can flow from the spatial region (B) to be monitored into the gas measuring device (100). The gas measuring device (100) can be selectively operated in oxidation measurement mode or thermal conductivity measurement mode. The aforementioned gas measuring device (100) - At least when operating in oxidation measurement mode, and optionally when operating in heat conduction measurement mode, a voltage (U10) is applied to the detector segment (20), thereby heating the detector segment (20), and - In the two modes described above, a voltage (U11) is applied to the compensator segment (38), thereby heating the compensator segment (38). The aforementioned gas measuring device (100) The compensator segment (38) is configured to be heated more strongly when operating in the heat conduction measurement mode than when operating in the oxidation measurement mode by applying the voltage (U11) to the compensator segment (38). The heating of the detector segment (20) is performed as follows: - The combustible target gas (CH) in the gas sample (Gp) inside the gas measuring device (100) ４ Oxidize ) - The oxidation causes the temperature of the detector segment (20) to rise, The total detection amount sensors (40, 12.1, 12.2) are configured to measure total detection amounts (ΔU_B, U10, U11) that depend on the temperature of the detector segment (20) and the temperature of the compensator segment (38). The compensator detection amount sensor (12.2) is configured to measure a compensator detection amount (U11) that depends on the temperature of the compensator segment (38). The gas measuring device (100) measures the combustible target gas (CH) in the gas sample (Gp) inside the gas measuring device (100). ４ The concentration of ) - When operating in oxidation measurement mode, it is determined depending on the total amount detected (ΔU_B, U10, U11), - A gas measuring device (100) is configured to determine the value depending on the measured compensator detection amount (U11) when operating in heat conduction measurement mode.

2. The compensator (11) includes a compensator functional component (51) and a passivation coating (24), The compensator functional component (51) includes the conductive compensator segment (38), The passivation coating (24) is - Surrounding the compensator functional component (51), - Present between the gas sample (Gp) inside the gas measuring device (100) and the compensator functional component (51), and - The gas sample (Gp) is physically and chemically separated from the compensator functional component (51). The gas measuring device (100) according to claim 1, wherein the passivation coating (24) consists of at least 50% by weight, preferably at least 80% by weight, and particularly preferably at least 95% by weight of an iodine-containing compound.

3. The passivation coating (24) consists of at least 50% by weight, preferably at least 80% by weight, of alkali metal or alkaline earth metal iodides or iodates. Preferably, the alkali metal or alkaline earth metal of the compound that constitutes at least 50% by weight of the passivation coating (24) is potassium. Particularly preferred is the compound being potassium iodide (KI) or potassium iodate (KIO ３ The gas measuring device (100) according to claim 2.

4. The aforementioned gas measuring device (100) When the detector segment (20) is operating in oxidation measurement mode, a voltage (U10) is applied to the detector segment (20) such that it is heated more strongly than when it is operating in heat conduction measurement mode. Preferably, the gas measuring device (100) according to any one of claims 1 to 3 is configured such that no voltage is applied to the detector segment (20) when operating in heat conduction measurement mode.

5. The gas measuring device (100) includes an electrical bypass line (L11) and a driveable switch (S11) for the bypass line (L11), The bypass line (L11) is arranged in parallel with the compensator (11), The gas measuring device (100) is configured to drive and control the switch (S11), thereby The gas measuring device (100) according to any one of claims 1 to 4, wherein the switch (S11) interrupts the bypass line (L11) when operating in heat conduction measurement mode, and opens the bypass line (L11) when operating in oxidation measurement mode.

6. The gas measuring device (100) is configured such that the intensity (I.1) of the current flowing through the detector segment (20) deviates, or may deviate, at least temporarily, from the intensity (I.2) of the current flowing through the compensator segment (38). The aforementioned gas measuring device (100) - When operating in oxidation measurement mode, the temperature of the compensator segment (38) does not deviate from the temperature of the detector segment (20) by more than a preset upper temperature limit. - The gas measuring device (100) according to any one of claims 1 to 5, wherein when operating in thermal conduction measurement mode, the temperature of the compensator segment (38) is configured to be at least as high as a preset lower temperature limit, and preferably higher than the temperature of the detector segment (20).

7. The gas measuring device (100) automatically - Check whether a preset oxidation criterion is met, and the oxidation criterion is met if, at a minimum, there is still sufficient oxygen inside the gas measuring device (100) for the oxidation of the flammable target gas by the detector segment (20). - As long as the oxidation criteria are met, the system remains in oxidation measurement mode. - If the oxidation criteria are no longer met, the system switches to thermal conduction measurement mode. - Preferably, the gas measuring device (100) according to any one of claims 1 to 6 is configured to switch back to oxidation measurement mode when the oxidation criterion is met again.

8. The gas measuring device (100) according to claim 7, wherein the gas measuring device (100) is configured such that the oxidation criterion is at least satisfied when the target gas concentration, which is determined depending on the total amount detected (ΔU_B, U10, U11) measured, falls below a predetermined first upper concentration limit.

9. The gas measuring device (100) is configured such that the oxidation criterion is additionally satisfied when the target gas concentration, determined based on the measured compensator detection amount (U11), falls below a preset second upper concentration limit. The gas measuring device (100) according to claim 8, wherein the second upper concentration limit is higher than the first upper concentration limit.

10. The gas measuring device (100) includes a detector chamber (8) and an oxygen sensor (15). The detector (10) is located inside the detector chamber (8), The oxygen sensor (15) is configured to measure the oxygen content in the gas sample (Gp), Preferably, the gas sample (Gp) is located inside the gas measuring device (100). The gas measuring device (100) according to any one of claims 7 to 9, wherein the gas measuring device (100) is configured to check whether a preset oxidation standard is met depending on the measured oxygen content.

11. The gas measuring device (100) includes an operating element (17), The aforementioned operating element (17) is activatable and deactivatable. The gas measuring device (100) is configured as follows, namely, - In response to the activation of the operating element (17), the system switches to the heat conduction measurement mode and / or remains in the heat conduction measurement mode. - The gas measuring device (100) according to any one of claims 1 to 10, wherein when the operating element (17) is deactivated, it can be selectively operated in oxidation measurement mode or heat conduction measurement mode.

12. Use of the gas measuring device (100) according to any one of claims 1 to 11 for measuring the concentration of hydrogen as a flammable target gas.

13. Using the gas measuring device (100), the combustible target gas (CH) ４ A gas measurement method for measuring the concentration of ) The aforementioned gas measuring device (100) - A detector (10) having a conductive detector segment (20), - A compensator (11) having a conductive compensator segment (38), - Total detection amount sensors (40, 12.1, 12.2), - Compensator detection amount sensor (12.2) and, The gas measuring device (100) can be selectively operated in oxidation measurement mode or thermal conductivity measurement mode. The above method involves the following steps: - A step of causing or enabling, at least temporarily, that the gas sample (Gp) flows from the spatial region (B) to be monitored into the gas measuring device (100), - In the two modes described above, a voltage (U11) is applied to the compensator segment (38), thereby heating the compensator segment (38), The voltage (U11) includes the step of applying the compensator segment (38) such that the compensator segment (38) is heated more strongly when operating in the heat conduction measurement mode than when operating in the oxidation measurement mode, When the gas measuring device (100) is operating in oxidation measurement mode, The above method involves the following further steps: - A step of applying voltage (U10) to the detector segment (20) and thereby heating the detector segment (20), - Heating of the detector segment (20) causes the flammable target gas (CH) in the gas sample (Gp) inside the gas measuring device (100) to be affected. ４ The steps include: oxidizing the detector segment (20), and the oxidation causing the temperature of the detector segment (20) to rise; - The total detection amount sensor (40, 12.1, 12.2) measures a total detection amount (ΔU_B, U10, U11) that depends on the temperature of the detector segment (20) and the temperature of the compensator segment (38), - The combustible target gas (CH) in the gas sample (Gp) inside the gas measuring device (100) ４ The step includes determining the concentration of ) depending on the measured total detected amount (ΔU_B, U10, U11), When the gas measuring device (100) is operating in heat conduction measurement mode, The above method involves the following further steps: - The compensator detection amount sensor (12.2) measures a compensator detection amount (U11) that depends on the temperature of the compensator segment (38), - The combustible target gas (CH) in the gas sample (Gp) inside the gas measuring device (100) ４ The steps include determining the concentration of ) depending on the measured compensator detection amount (U11), - Preferably, a gas measurement method comprising the step of not applying voltage to the detector segment (20).

14. The voltage (U10) is applied to the detector segment (20) such that when the detector segment (20) is operating in oxidation measurement mode, it is heated more strongly than when it is operating in heat conduction measurement mode. Preferably, the gas measurement method according to claim 13, wherein no voltage is applied to the detector segment (20) when operating in heat conduction measurement mode.

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