GAS DETECTION DEVICE WITH A DETECTOR AND WITH A COMPENSATOR AND GAS DETECTION PROCESS WITH SUCH A GAS DETECTION DEVICE

Abstract

A gas detection device and a gas detection process monitor an area for a combustible target gas. A detector (10), a compensator (11.1), a sensor array (40, 41) and an analysis unit (9) are arranged in a gas detection device housing. The detector includes an electrically conductive wire with a heating segment (20), electrical insulation around the wire and a catalytic material in the electrical insulation. The compensator extends in a plane and includes an electrical strip conductor (32) with a heating segment and a carrier plate for the strip conductor. The gas detection device applies an electrical voltage to the detector and to the compensator. The detector oxidizes the target gas with the heating segment. The sensor array measures detection variables (U10, U11) for the detector and the compensator. The analysis unit compares the two detection variables to determine if a combustible target gas is present.

Claims

1. A gas detection device for monitoring an area for a combustible target gas to be detected, the gas detection device comprising: a housing with an interior and an opening, the opening configured to establish a fluid connection between an interior of the housing and the area; a detector arranged in the housing, the detector comprising: an electrically conductive wire with a helical heating segment; electrical insulation around the heating segment; and a catalytic material provided at least one of in and on the electrical insulation, wherein the detector is configured to oxidize a combustible target gas located in the interior of the housing by heating the heating segment; a compensator arranged in the housing, the compensator extending in a plane and comprising: an electrical strip conductor with a heating segment and a carrier plate, in which plate the strip conductor is embedded or onto which the strip conductor is applied; a sensor array, wherein the gas detection device is configured to apply an electrical voltage to the detector such that an electric current flows through the wire of the detector and heats the heating segment of the wire; and to apply an electrical voltage to the compensator such that an electric current flows through the strip conductor of the compensator and heats the heating segment of the strip conductor and wherein the sensor array is configured to measure a detection variable, which depends on a temperature of the detector, and a detection variable, which depends on a temperature of the compensator or to measure a detection variable, which depends both on the temperature of the detector and on the temperature of the compensator; and a signal-processing analysis unit connected to the sensor array and configured to at least one of: determine whether the target gas is present in the area to be monitored or not as a function of the measured detection variable or of each measured detection variable; and determine a concentration of the target gas in the area to be monitored as a function of the measured detection variable or of each measured detection variable.

2. A gas detection device in accordance with claim 1, wherein the gas detection device is configured: such that the helical heating segment of the detector wire is heated to at least 300° C.; and such that the heating segment of the strip conductor is heated to a maximum temperature which deviates from the maximum temperature of the heating segment of the detector wire by at most 200° C.

3. A gas detection device in accordance with claim 1, wherein the heating segment of the strip conductor is heated to a maximum temperature which is above the ambient temperature by at least 100°.

4. A gas detection device in accordance with claim 1, wherein: the gas detection device is configured to apply the electrical voltage to the compensator as electrical pulses; the electrical pulses applied to the compensator having a first pulse duration.

5. A gas detection device in accordance with claim 4, wherein: the gas detection device is configured to apply the electrical voltage to the detector as electrical pulses with a second pulse duration; the electrical pulses have a second pulse duration; and the second pulse duration is preferably longer than the first pulse duration.

6. A gas detection device in accordance with claim 1, wherein: the gas detection device is configured to be selectively operated in a monitoring mode or operated in a measuring mode; the gas detection device is configured to apply the electrical voltage to the detector such that the energy consumption of the detector is higher during the operation of the gas detection device in the measuring mode than during the operation in the monitoring mode; the analysis unit is configured to determine, in the monitoring mode, whether an indicator of the presence of a target gas is present or not; and the gas detection device is configured to switch over from the monitoring mode into the measuring mode when the analysis unit has detected the indicator.

7. A gas detection device in accordance with claim 6, wherein: the sensor array is configured to measure a detection variable, which depends on the temperature of the compensator; in the monitoring mode, the analysis unit is configured to determine whether an indicator of the presence of the target gas is present or not as a function of the detection variable, which depends on the compensator temperature.

8. A gas detection device in accordance with claim 6, wherein the gas detection device is configured: to apply the electrical voltage to the detector in the monitoring mode as electrical pulses with a first pulse rate; to apply the electrical voltage to the detector in the measuring mode as electrical pulses with a second pulse rate or to apply the electrical voltage to the detector in the measuring mode continuously; and the second pulse rate is greater than the first pulse rate.

9. A gas detection device in accordance with claim 1, wherein: the detector has a controllable electrical variable, which correlates with the temperature of the detector when an electrical voltage is applied thereto; the compensator has a controllable electrical variable, which correlates with the temperature of the compensator when an electrical voltage is applied thereto; the gas detection device is configured to carry out a control with a control gain that the controllable electrical variable for the detector follows a predefined time course and the controllable electrical variable for the compensator follows a predefined time course.

10. A gas detection device in accordance with claim 9, wherein: both the controllable electrical variable of the detector and the controllable electrical variable of the compensator comprise a current intensity of electrical current, which flows through the detector and through the compensator, respectively; the detector and the compensator are electrically connected in series; and a control gain during the control is that the controllable electrical variable for the detector and the controllable electrical variable for the compensator takes a same predefined target value.

11. A gas detection device in accordance with claim 9, wherein: the gas detection device is configured to specify a value of the controllable electrical variable for the detector and a value of the controllable electrical variable for the compensator, which respective value is used for the control gain during the control; the gas detection device is configured to carry out the specification of the target value as a function of a respective value, at which respective value the controllable variable has been set in a situation in which no target gas has been detected and to use the respective value used in this situation as a predefined target value for the control gain.

12. A process for the monitoring of an area for a combustible target gas to be detected, the process comprising the steps of: providing a gas detection device comprising: a housing with an opening configured to establish a fluid connection between an interior of the housing and the area; a detector arranged in the housing, the detector comprising: an electrically conductive wire with a helical heating segment; electrical insulation around the heating segment; and a catalytic material provided at least one of in and on the electrical insulation; a compensator arranged in the housing, the compensator extending in a plane and comprising: an electrical strip conductor with a heating segment and a carrier plate, in which the strip conductor is embedded or onto which the strip conductor is applied; a sensor array; and an analysis unit at least temporarily being in data connection with the sensor array; applying an electrical voltage to the detector such that an electric current flows through the wire of the detector and heats the heating segment of the wire; applying an electrical voltage to the compensator such that an electric current flows through the strip conductor of the compensator and heats the heating segment of the strip conductor; with the detector oxidizing a target gas located in the interior of the housing by heating the heating segment; with the sensor array measuring a detection variable which depends on the temperature of the detector, measuring a detection variable which depends on the temperature of the compensator or measuring a detection variable which depends both on the temperature of the detector and on the temperature of the compensator; and one of: determining whether a target gas is present in the area to be monitored as a function of the measured detection variable or each measured detection variable; determining a concentration of a target gas in the area as a function of the measured detection variable or each measured detection variable; and determining whether a target gas is present in the area and determining a concentration of the target gas in the area as a function of the measured detection variable or each measured detection variable.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0112] In the drawings:

[0113] FIG. 1 is a schematic view showing a gas detection device according to the state of the art, in which both the detector and the compensator are configured as pellistors;

[0114] FIG. 2 is a perspective schematic view showing the compensator of the gas detection device according to the present invention;

[0115] FIG. 3 is a top view showing the compensator from FIG. 2;

[0116] FIG. 4 is a schematic view showing an embodiment of the gas detection device according to the present invention, in which the current intensity from the detector and from the compensator can be changed independently of each other;

[0117] FIG. 5 is a schematic view showing a configuration of the gas detection device according to the present invention as a Wheatstone measuring bridge;

[0118] FIG. 6a is a graph showing how the compensator is pulse operated in the monitoring mode;

[0119] FIG. 6b is a graph showing how the detector is pulse operated in the monitoring mode;

[0120] FIG. 6c is a graph showing how the compensator is pulse operated in the measuring mode;

[0121] FIG. 6d is a graph showing how the detector is pulse operated in the measuring mode;

[0122] FIG. 7a is a schematic view showing a detector control; and

[0123] FIG. 7b is a schematic view showing a compensator control.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0124] Referring to the drawings, the gas detection device according to the exemplary embodiment monitors a spatial area for at least one predefined combustible target gas and uses a principle known from the state of the art to detect the target gas. The gas detection device comprises a detector and a compensator, which are both arranged in the interior of a housing of the gas detection device. A gas mixture from an area to be monitored, which may contain the target gas, flows into the interior of the housing and reaches both the detector and the compensator. The gas detection device may be provided with a pump that suctions in the gas mixture. The gas detection device may be configured such that the gas mixture by itself diffuses into the interior of the housing.

[0125] The detector is capable of oxidizing a combustible target gas. During the oxidation, the target gas reacts chemically with oxygen under the effect of the detector, and water and carbon dioxide are formed. During this chemical reaction, heat energy is released, which heats the detector and as a result increases the temperature of the detector. This changes an electrical property of the detector. For example, the heating is such as to bring about an increase of the electrical resistance of the detector because of the heat energy released. If no combustible target gas is present and hence also no target gas is oxidized, the temperature and the electrical resistance do not increase. This electrical resistance, which is variable over time, can be measured by the voltage and current intensity being measured.

[0126] Note: The term “electrical resistance” designates below, depending on context, on the one hand, an electrical property of a component of the gas detection device 100 and a component, which acts as electrical resistance, on the other hand.

[0127] The temperature of the detector is, however, influenced not only by the oxidation of a target gas to be detected, but also by the temperature and other ambient conditions in the area to be monitored. In order to detect and to compensate by calculation the influence of the ambient conditions, the detector and the compensator are exposed at the same time to the same gas or gas mixture from the area to be monitored. As a result, the ambient conditions act both on the temperature of the detector and on the temperature of the compensator. By contrast, the compensator does not have the ability to oxidize the target gas. In case of the presence of target gas, therefore, only the detector is heated to a significant extent due to the oxidation of the target gas, but not the compensator. Thanks to the compensator, it is in many cases not necessary to measure the ambient temperature.

[0128] In a preferred embodiment, the detection variable or each detection variable is an electrical variable, which correlates with the electrical resistance and therefore with the temperature of the detector and with the temperature of the compensator. In many possible embodiments of the detector and of the compensator, the higher the temperature is, the higher is the electrical resistance. The relationship between the temperature and the electrical resistance can be determined beforehand. In many cases it can be assumed to be linear. The detection variable, which depends on the temperature, is preferably the electrical voltage that is applied to the detector and to the compensator. If the current intensity of the current flowing through the detector and through the compensator is known, the electrical resistance can be calculated from the measured electrical voltage. If the current intensity is held constant, then the electrical voltage being applied is an indicator of the electrical resistance and thus an indicator of the temperature of the detector and of the compensator. If the current intensity is constant and the relationship between the temperature and the electrical resistance is linear, then the electrical voltage depends linearly on the temperature.

[0129] Since only the detector oxidizes a combustible target gas to a significant extent and therefore since only the detector, but not the compensator is heated significantly in the presence of the target gas, the concentration of the target gas influences only the detection variable for the detector to a significant extent. By contrast, ambient conditions, especially the ambient temperature, act both on the detection variable for the detector and on the detection variable for the compensator. Therefore, the detection variable for the compensator is used to compensate by calculation the influence of ambient conditions on the detection variable for the detector. Both many gas detection devices known from the state of the art and the gas detection device according to the present invention use this principle to detect a target gas and/or to determine the concentration of a target gas. In the exemplary embodiment, the electrical voltage is used as a detection variable.

[0130] FIG. 1 schematically shows a gas detection device 101 according to the state of the art which uses the just described principle with a detector and with a compensator. The following components are shown: [0131] a detector 10, [0132] a compensator 11.2, [0133] an outer housing 4, [0134] a sufficiently stable inner housing 1, which preferably consists of a metal, wherein the housing 1 accommodates the detector 10 and the compensator 11.2 and is able to withstand an explosion of target gas in the interior of the housing 1, [0135] a separate voltage source 42, so that the gas detection device 101 can be operated independently of a stationary voltage supply network, [0136] an electrical line 3, which electrically connects the detector 10 and the compensator 11.2 to the voltage source 42, [0137] two electrical resistors R20 and R21, [0138] a current intensity sensor 41 and [0139] a voltage sensor 40.

[0140] In addition, the gas detection device 101 comprises a signal-processing analysis unit which analyzes measured values from the sensors 40, 41 and which is not shown in FIG. 1.

[0141] The outer housing 4 accommodates the inner housing 1 together with the detector 10 and with the compensator 11.2 as well as the electrical line 3, the electrical resistors R20 and R21, the sensors 40 and 41 as well as the voltage source 42.

[0142] In the example shown, the detector 10 and the compensator 11.2 are connected in series. The two electrical resistors R20 and R21 are likewise connected in series. The component, which consists of the detector 10 and the compensator 11.2, is connected parallel to the component, which consists of the two resistors R20 and R21. In addition, the electrical resistance R10 of the detector 10 as well as the electrical resistance R11 of the compensator are suggested. An electrical voltage U10 is applied to the detector 10, an electrical voltage U11 is applied to the compensator 11.2.

[0143] Both the detector 10 and the compensator 11.2 are configured as pellistors in the embodiment being shown. In FIG. 1 at the bottom, the detector 10 is shown schematically in an enlarged view. A helically wound and electrically conductive wire 20 is thinner than 50 preferably not thicker than 25 μm and acts as a heating segment in one embodiment. The heating segment 20 is connected to the voltage source 42 via the line 3 and via two electrical connections 36. Electrical current flows through the line 3 and heats the heating segment 20 to an operating temperature, which may be between 400° C. and 500° C., during the operation. The operating temperature is preferably between 400° C. and 450° C. At an operating temperature above 400° C., the detector 10 is capable of oxidizing methane and other hydrocarbons to be detected in a sufficient quantity, so that a sufficient quantity of heat energy is released. In case of a heating to a temperature below 550° C., the detector 10 ages more slowly than a more intensely heated detector.

[0144] A ceramic jacketing 21 in the form of a solid sphere, which is shown schematically, insulates the wire 20 electrically and especially prevents a short circuit. It is also possible that the ceramic jacketing 21 forms a coil around the wire 20. A mounting plate 22 holds the wire 20 and the ceramic jacketing 21. The electrical connections 36 are led through the mounting plate 22.

[0145] The ceramic jacketing 21 establishes a thermal contact between the heating segment 20 and the environment. On the one hand, the heating segment 20, through which current flows and which is heated, brings about that a target gas is oxidized thanks to the thermal contact. On the other hand, the heat energy, which is released during the oxidation, acts, thanks to the thermal contact, on the heating segment 20 and heats same further. In one embodiment, the ceramic jacketing 21 has the shape of a sphere or of an ellipsoid. The ceramic jacketing 21 preferably fully encloses the heating segment 20.

[0146] The operating temperature, which the wire 20, through which current flows, of the detector 10, is capable of generating is not solely sufficient, as a rule, to oxidize a relevant quantity of a combustible target gas. Therefore, a coating consisting of a catalyst is applied to the outer surface of the ceramic jacketing 21, wherein this coating brings about an oxidation of the target gas. This catalytic coating is suggested by dots 23. For example, platinum or palladium or a different metal is used as catalytic material. As an alternative or in addition, catalytic material 23 may also be present in the ceramic jacketing 21 and may especially be embedded in the ceramic jacketing 21.

[0147] The coating 23 on the ceramic jacketing 21 is preferably porous, as a result of which the detector 10 has a larger thermally active surface than when the ceramic jacketing 21 has a smooth surface. This larger surface improves the oxidation operation. Gas can penetrate into the interior of the ceramic jacketing 21.

[0148] A gas mixture from the area to be monitored diffuses through the opening Ö in the housing 1 into the interior of the housing 1 and reaches the detector 10 and the compensator 11.2. When this gas mixture contains a combustible target gas, then the heated detector 10 oxidizes this target gas. As is schematically shown in FIG. 1 at the bottom, the detector 10 oxidizes a combustible target gas, here methane (CH.sub.4). The detector 10 in this example thus converts CH.sub.4 and O.sub.2 into CO.sub.2 and H.sub.2O.

[0149] The compensator 11.2 in the embodiment according to FIG. 1 also has an electrically conductive wire 20, a ceramic jacketing 21 and a mounting plate 22, but no coating that is made of a catalytic material. Therefore, the compensator 11.2 is not capable of oxidizing a combustible target gas, even if it is heated intensely similar to the detector 10.

[0150] The electrical resistance R10 of the detector 10 and the electrical resistance R11 of the compensator 11.2 depend on the temperature of the wire 20. The higher this temperature is, the higher is also the electrical resistance R10 or R11. These electrical resistances R10 and R11 are shown schematically in FIG. 1. The voltage U42 that the voltage source 42 generates is divided—except for negligibly small voltage losses—into an electrical voltage U10 applied to the detector 10 and an electrical voltage U11 applied to the compensator 11.2. Thus, U42=U10+U11 approximately.

[0151] In the example being shown, the detector 10 and the compensator 11.2 are connected in series. The detector 10, the compensator 11.2, the two resistors R20 and R21 as well as the voltage source 42 form a Wheatstone measuring bridge. The voltage sensor 40 measures half the voltage difference ΔU=U10−U11, namely the so-called bridge voltage ΔU/2. The current intensity I is ideally identical in the entire current circuit of FIG. 1 because of the series connection. In practice, the current intensity I is different at different measuring points, namely especially because of the only finite electrical resistance of the voltage sensor 40. The current intensity sensor 41 measures this current intensity I. According to Ohm's law, ΔR=(U10−U11)/I thus holds true for the difference ΔR between the two electrical resistances R10 and R11. The current intensity I is measured and is hence known. The measured voltage difference ΔU is thus an indicator of the resistance difference ΔR. As was just explained, the resistance difference ΔR correlates with the difference between the temperatures of the detector 10 and of the compensator 11.2. The relationship between the temperature and the electrical resistance and thus the relationship between the temperature difference and the resistance difference can in many cases be assumed to be linear. Therefore, the voltage difference ΔU correlates with the temperature difference.

[0152] A zero voltage ΔU0, i.e., the voltage difference ΔU=U10−U11 in a situation, in which no target gas is present, is predefined. The subtraction of the zero voltage compensates by calculation the fact that different electrical properties of the detector 10 and of the compensator 12, as a rule, lead to the voltage difference ΔU being unequal to zero. The compensated voltage difference ΔU−ΔU0 correlates with the concentration of a target gas to be detected in the area B to be monitored and thus in the interior of the housing 1. The analysis unit calculates the compensated voltage difference ΔU−ΔU0 and checks whether or not this difference is the zero point within a predefined tolerance range. If the compensated voltage difference ΔU−ΔU0 is outside of the tolerance range, then the event is detected that a target gas with a concentration above a detection limit is present in the area B. Optionally, the analysis unit applies a functional relationship F to this difference in order to determine the target gas concentration Con, namely according to the calculation rule Con=F(ΔU−ΔU0). This functional relationship is preferably established beforehand and is especially preferably determined empirically by a plurality of measurements at known concentrations of the target gas. In a simple embodiment, Con=β*(ΔU−ΔU0) with a predefined and, for example, empirically determined factor β.

[0153] The housing 1 is stable enough to not break into pieces even if a combustible target gas ignites or even explodes in the interior of the housing 1. The housing 1 is preferably made of metal. It shall, of course, be avoided that flames from the interior of the housing 1 reach the environment and can ignite combustible target gas there. Therefore, a flame arrester 2, for example, a metallic grid or a sintered layer, is inserted into the opening Ö. The metallic grid cools off flames, which reach the metallic grid. In the exemplary embodiment, the housing 1 comprises no filter, which can prevent a target gas from reaching the interior of the housing 1.

[0154] The gas detection device 100 according to the present invention likewise comprises a detector 10 and a compensator. The detector 10 is configured in the exemplary embodiment precisely like the detector 10 of the gas detection device 101, which was described with reference to FIG. 1.

[0155] By contrast, the compensator is not configured as a pellistor, which is why the reference number 11.1 is used for the compensator of the gas detection device 100 according to the present invention. Except for the compensator 11.1, the gas detection device 100 according to the present invention can be configured mechanically as the gas detection device 101 from FIG. 1. In one embodiment, the gas detection device 100 determines, as just described, the compensated voltage difference ΔU−ΔU0 and uses this difference to make a determination (decide) about the presence and/or the concentration of a combustible target gas.

[0156] FIG. 2 schematically shows in a perspective view an exemplary embodiment of the compensator 11.1 according to the present invention. FIG. 3 schematically shows the compensator 11.1 from FIG. 2 in a top view. FIG. 2 and FIG. 3 are not necessarily true-to-scale views.

[0157] The compensator 11.1 of the exemplary embodiment comprises the following components: [0158] an electrically conductive strip conductor 30 comprising a heating segment 32 and an electrical connection 46, [0159] a protective layer 35 over the strip conductor 30 with the heating segment 32, [0160] a carrier plate 31, which extends in a plane, which is at right angles to the drawing plane from FIG. 2 and lies in the drawing plane of FIG. 3, [0161] a wafer substrate 33, which the carrier plate 31 carries, and [0162] electrical contact points 34 for the electrical strip conductor 30.

[0163] The electrical strip conductor 30 can be manufactured from the same material as the wire 20 of the detector 10. The heating segment 32 is embodied by the strip conductor 30 being bent or wavy in a zigzag-shaped manner or in another manner and/or has a cross section varying over the length, so that when current flows through the strip conductor 30, a sufficiently high operating temperature is obtained. The maximum dimension of the strip conductor 30 and thus of the heating segment 32 in the plane of the carrier plate 31 is preferably less than 1 mm, especially preferably less than 0.5 mm, especially preferably between 0.1 μm and 0.9 μm.

[0164] The carrier plate 31 preferably has a thickness of less than 10 μm, especially preferably less than 2 μm, especially a thickness of 1 μm, and is preferably manufactured from a material, which contains silicon, for example, from a glass-like material. In the exemplary embodiment, the carrier plate 31 is fastened to the wafer substrate 33 by means of four webs. A gripper is capable of gripping and mounting the compensator 11.1 on the wafer substrate 33.

[0165] The electrically conductive strip conductor 30 is applied onto a surface of the carrier plate 31 and is preferably embedded in same. The carrier plate 31 uncouples the strip conductor 30 thermally and preferably also electrically from the environment. The carrier plate 31 is, on at least one side, in contact with the surrounding air, which brings about a good thermal insulation. The carrier plate 31 may contain recesses. The recesses may lead to a strip-shaped carrier plate. The carrier plate 31 may also have a full-surface configuration.

[0166] In one embodiment, the wafer substrate 33 is less than 1 mm thick, especially preferably less than 0.4 mm thick, and has a maximum diameter of several mm. The carrier plate 31 is applied to the wafer substrate 33, for example, by means of chemical vapor deposition or by vaporizing. A recess is formed in the area of the wafer substrate 33, which is located below the heating segment 32, so that the heating segment 32 is surrounded by air on two sides. This improves the thermal insulation. The recess is manufactured, for example, by being etched into the material.

[0167] The electrical connection 46 connects the heating segment 32 to the electrical contact points 34 on the carrier plate 31. The protective layer 35 insulates the strip conductor 30 and thus the heating segment 32 electrically from the environment and reduces the risk of damage. In particular, the protective layer 35 prevents the strip conductor 30 from coming into contact with a gas from the environment, and especially with a gas that is potentially harmful for the strip conductor 30, for example, hydrogen. Precisely like the compensator 11.2 from FIG. 1, the compensator 11.1 from FIG. 2 and FIG. 3 also comprises no catalytic material.

[0168] The compensator 11.1 is not capable of oxidizing a burning target gas. However, many target gases have at least one physical property, which deviates in a measurable manner from the corresponding physical property of the air. Many target gases, especially the target gas methane, has the following property: A sufficiently high concentration of the target gas brings about that the compensator 11.1, through which electric current flows, is cooled off—in comparison to a lower concentration of the target gas or in a situation entirely without target gas. One reason for the brought-about cooling off is that the target gas has a higher heat conductivity and/or a higher heat capacity than the ambient air, as a result of which the target gas derives more heat energy than the ambient air without the target gas. This cooling off changes an electrical property of the compensator 11.1, for example, this cooling off reduces the electrical resistance. Since the detection variable of the compensator 11.1 is measured and measured values are analyzed, the event that a combustible target gas (more precisely: a target gas that has a higher heat conductivity or different heat capacity or another deviating physical property than the ambient air) with sufficiently high concentration is present in the area B to be monitored can in many cases be detected.

[0169] Compared with a compensator 11.2, which is configured as a pellistor as shown in FIG. 1, the compensator 11.1 configured according to the present invention consumes less electrical energy. During continuous operation, the detector 10 and the compensator 11.2, which are both configured as pellistors, consume each, for example, about 100 mW of electrical power. The compensator 11.1 only consumes 60 mW, by contrast. Another advantage is that the compensator 11.1 according to the present invention, after the application of an electrical voltage, reaches a stable thermal state more rapidly than the compensator 11.2, namely in less than 0.5 sec, often in 0.2 sec or less, compared with 2 sec of the compensator 11.2. This advantage is the result of the fact that the compensator 11.1 has a thermal mass, which is less than one-fourth of the thermal mass of the detector 10 and less than one-fourth, and preferably less than one-tenth, of the thermal mass of the compensator 11.2. How this advantage can be utilized is described farther below.

[0170] FIG. 4 schematically shows the gas detection device 100 according to one embodiment of the exemplary embodiment. Identical reference numbers have the same meaning as in FIG. 1. The gas detection device 100 comprises [0171] a detector 10, which is configured as a pellistor as shown in FIG. 1, [0172] a compensator 11.1, which is configured as described with reference to FIG. 2 and FIG. 3, [0173] a voltage source 42, which is configured in this case as a set of rechargeable batteries and has the electrical voltage U42, [0174] an arrangement with electrical lines 3, which connect the detector 10 and the compensator 11.1 to the voltage source 42 such that the current intensity of the current flowing through the detector 10 and the current intensity of the current flowing through the compensator can be changed independently of one another, [0175] a switch 7.10, which selectively bridges or interrupts the electrical line 3 via the detector 10 and as a result brings about that the detector 10 is supplied in a pulsed manner with current from the voltage source 42, [0176] a switch 7.11, which selectively bridges or interrupts the electrical line 3 via the compensator 11.1 and as a result brings about that the compensator 11.1 is supplied in a pulsed manner with current from the voltage source 42, [0177] an actuatable voltage actuator 8.10, which is capable of changing the electrical voltage U10 that is applied to the detector 10, [0178] an actuatable voltage actuator 8.11, which is capable of changing the electrical voltage U11 that is applied to the compensator 11.1, [0179] a voltage sensor 40.10, which is capable of measuring the electrical voltage U10 that is applied to the detector 10, [0180] a voltage sensor 40.11, which is capable of measuring the electrical voltage U11 that is applied to the compensator 11.1, [0181] a current intensity sensor 41.10, which is capable of measuring the intensity I10 of the electric current, which flows through the detector 10, [0182] a current intensity sensor 41.11, which is capable of measuring the intensity I11 of the electric current, which flows through the compensator 11.1, [0183] a signal-processing control device 6, which receives signals from the sensors 40.10, 40.11 as well as 41.10, 41.11 and is capable of actuating the switches 7.10, 7.11 and the voltage actuators 8.10, 8.11 as a function of sensor signals, as well as [0184] a signal-processing analysis unit 9, which in the exemplary embodiment is a component of the control device 6 (comprising one or more processors and a memory) and will be described below.

[0185] In addition, the electrical resistance R10 of the detector 10, the electrical resistance R11 of the compensator 11.1, the electrical voltage U10 being applied to the detector 10 and the electrical voltage U11 being applied to the compensator 11.1 are indicated in FIG. 4. Furthermore, FIG. 4 indicates how a gas mixture flows from the area B to be monitored through the opening Ö into the interior of the housing 1. This gas mixture may contain a target gas to be detected.

[0186] FIG. 5 shows an alternative embodiment, in which the detector, the compensator 11.1, two electrical resistors R20, R21 and the voltage source 42 together form a Wheatstone measuring bridge. Just as in FIG. 1, the component, which consists of the detector 10 and the compensator 11.1, is connected parallel to the component, which consists of the two electrical resistors R20 and R21. The control device 6 and the voltage actuators 8.10 and 8.11 are not shown in FIG. 5. The voltage sensor 40 measures an indicator of the voltage difference ΔU=U10−U11. The electrical resistance of the voltage sensor 40 is high, compared with the electrical resistances of the components 10, 11.1, R20 and R21. Ideally, the intensity I3 of the current, which flows through the detector 10, is identical to the intensity I3 of the current, which flows through the compensator 11.1. The current intensity sensor 41 measures this current intensity I3.

[0187] In the exemplary embodiment, an electrical voltage is continuously applied neither to the detector 10 nor to the compensator 11.1. Rather, a pulsed electrical voltage is applied in the current circuits, which FIG. 4 and FIG. 5 show, by means of the switches 7.10 and 7.11 and as a result a pulsed electrical current is generated, as a result of which—compared to a continuous operation—electrical energy is saved. The pulse rates (pulse frequencies) and pulse durations for the detector 10 and for the compensator 11.1 differ from one another and can be changed independently of one another. This is especially achieved by the two switches, namely switch 7.10 for the detector 10 and switch 7.11 for the compensator 11.1.

[0188] The gas detection device 100 according to the exemplary embodiment can be selectively operated in a monitoring mode or in a measuring mode. In the monitoring mode, the gas detection device 100 is capable of detecting an indicator of the presence of at least one combustible target gas. In the measuring mode, the gas detection device 100 is capable of determining the concentration of this target gas approximately. The number of false alarms is, as a rule, lower in the measuring mode than in the monitoring mode.

[0189] In the monitoring mode, the gas detection device 100 consumes less electrical energy than in the measuring mode. Therefore, the gas detection device 100 is preferably operated in the monitoring mode as long as possible. As soon as the gas detection device 100 operated in the monitoring mode has detected an indicator of the presence of a target gas, the gas detection device 100 is switched over into the measuring mode. As soon as the gas detection device 100 operated in the measuring mode no longer detects any target gas, the gas detection device 100 is switched over again into the monitoring mode. This switching over is preferably carried out automatically but may also be triggered by a user of the gas detection device 100.

[0190] FIGS. 6a-6d schematically illustrate the electrical pulses, with which an electrical voltage is applied to the detector 10 and to the compensator 11.1 each. The time is plotted on the x-axis, and the respective applied electrical voltage U10 or U11 is plotted on the y-axis. The designation n on the x-axis denotes the time n*Δt. The value 1 of the y-axis denotes the maximum value for the voltage U10 which is applied to the detector 10, or for the voltage U11 which is applied to the compensator 11.1. FIG. 6a and FIG. 6b show the pulses in the monitoring mode, FIG. 6c and FIG. 6d show the pulses in the measuring mode. In the example shown, no electrical voltage is applied outside of a pulse. It is also possible that a lower volume is applied outside of a pulse than during a pulse.

[0191] FIG. 6a and FIG. 6c show the electrical pulses, with which an electrical voltage is applied to the compensator 11.1. The pulse rate and the pulse duration for the compensator 11.1 preferably are identical to one another in both modes. FIG. 6b and FIG. 6d show the electrical pulses for the detector 10. The pulse durations of the pulses are identical, while the pulse rate is greater in the measuring mode than in the monitoring mode. A respective thermally stable state is reached at the end of each pulse, and the compensator 11.1 and the detection 10 yield a respective measured value.

[0192] In the time period from 0*Δt to 40*Δt, which is shown as an example, the compensator 11.1 yields 20 measured values. In the monitoring mode, the detector 10 yields two measured values in this time period. The two times t1 and t2, at which the detector 10 yields a respective measured value, are shown in FIG. 6b. The analysis unit 9 sends, for the two times t1 and t2, a respective signal that contains information about the concentration of the target gas in the area B to be monitored.

[0193] Both in the monitoring mode and in the measuring mode, the compensator 11.1 is supplied with current only over half the time, namely in every other interval of the length Δt. Therefore, the compensator 11.1 also consumes only half of the electrical energy—compared with a continuous operation.

[0194] In the monitoring mode, which is shown in FIG. 6a and FIG. 6b, the detector 10 is supplied with current in an interval of the length 6*Δt and then is not supplied with current in an interval of the length 18*Δt, so that it only consumes 6/(6+18)=¼ of the electrical energy—compared with a continuous operation. Of course, it is possible to increase the duration between two consecutive pulses and to maintain the duration of an electrical pulse, which saves electrical energy. However, a measured value is then yielded more rarely.

[0195] The control device 6 actuates the switches 7.10 and 7.11 of the arrangement shown in FIG. 4 and as a result brings about the pulses. The analysis unit 9 receives signals from the voltage sensors 40.10 and 40.11 and from the current intensity sensors 41.10 and 41.11 and determines whether a target gas is present or not. Or else, the analysis unit 9 determines a target gas concentration.

[0196] In the monitoring mode the detection variable U11 for the compensator 11.1 is measured such that there is a time interval of 2*Δt between two consecutive measured values. This time interval can be selected to be so rapid that the gas detection device 100 can sufficiently rapidly detect an indicator of this target gas after the release of a target gas. As already explained, many target gases bring about that the compensator 11.1 is cooled off and as a result its electrical resistance decreases. This decrease of the temperature leads to a decrease of the electrical voltage, which the analysis unit 9 detects. Changed ambient conditions may, of course, also lead to a decrease of the compensator temperature.

[0197] Also in the monitoring mode the analysis unit 9 in one embodiment determines the difference ΔU=U10−U11 between the voltages U10 of the detector 10 and U11 of the compensator 11.1, optionally corrected by a correction factor α according to the calculation rule ΔU=U10−α*U11. If the compensated voltage difference ΔU−ΔU0 is outside of the predefined interval, then a combustible target gas is detected. The compensated voltage difference ΔU−ΔU0 is, in addition, an indicator of the concentration of this target gas. A large compensated voltage difference ΔU−ΔU0 is a more reliable indicator of a target gas than a decrease of the temperature and thus of the voltage U11 of the compensator 11.1. However, the detection variable U10 for the detector 10 in the monitoring mode is measured such that there is a time interval of 24*Δt between two consecutive measured values. In the monitoring mode, the sampling frequency for the voltage difference ΔU is thus 1/24*Δt.

[0198] FIG. 6c and FIG. 6d illustrate the switching over into the measuring mode. In the example shown, the analysis unit 9 has detected in the monitoring mode at the time tx that the temperature of the compensator 11.1 has decreased, which is an indicator of a target gas and which is shown by an ! in FIG. 6c. As a response to this detection, the control device 6 switches the gas detection device 100 over into the measuring mode. In the measuring mode, the detector 10 is supplied with electrical energy more frequently than in the monitoring mode. FIG. 6d shows as an example that in the measuring mode the detector 10 is supplied with current in an interval of the length 6*Δt, then is not supplied with current in an interval of the length 6*Δt, etc. In addition, the times t1, t2, t3, at which the detector 10 yields a respective measured value, are shown in FIG. 6d. In the measuring mode, the pulsed detector 10 thus consumes only half the energy—compared with a continuous operation—while it consumes even only one-fourth of the energy in the monitoring mode. In the measuring mode, the sampling frequency for the voltage difference ΔU is thus 1/12*Δt, is accordingly twice as high as in the monitoring mode. The detector 10 then also consumes twice as much electrical energy.

[0199] It is also possible to operate the gas detection device 100 without the two switches 7.10 and 7.11 and to supply the detector 10 and the compensator 11.1 continuously with current. In this case, the energy consumption is higher. Because the switches 7.10 and 7.11 are, however, not absolutely necessary, it is also possible to convert an available gas detection device with a detector and with a compensator such that the present invention is embodied by means of this gas detection device. For example, a gas detection device 100 according to FIG. 5 can be produced from the gas detection device 101 from FIG. 1. In many cases, it is sufficient to replace the available compensator 11.2 with a compensator 11.1 according to the present invention.

[0200] Also in case of the gas detection device 100 according to the present invention, the compensator 11.1 has the task of sending a signal, with which the analysis unit 9 can compensate by calculation environmental effects on the temperature of the detector 10. If no target gas is present in the area B to be monitored and the gas mixture, which flows into the housing 1, therefore does not contain any combustible target gas, a detection variable for the detector 10 and for the compensator 11.1 shall have the same value. This detection variable correlates with the temperature of the detector 10 and of the compensator 11.1. In the exemplary embodiment shown, the electrical voltage U10 or U11 being applied and corrected (compensated) by a zero value is this detection variable.

[0201] The present invention does not necessarily require that the detector 10 and the compensator 11.1 have the same electrical resistance R10 and R11 when no target gas is present, and therefore, the detection variable for the detector 10 and for the compensator 11.1 has the same value. This facilities the manufacture of the two components 10 and 11.1. An initial calibration is preferably carried out before the first use of the gas detection device 100. A re-calibration is carried out as needed.

[0202] During such an initial calibration the following steps are carried out for the gas detection device 100 from FIG. 4: [0203] At least one situation is established, in which no combustible target gas is located in the interior of the housing 1 and the ambient conditions correspond to typical ambient conditions during a use. [0204] An electrical voltage U10 is applied to the detector 10, an electrical voltage U11 is applied to the compensator 11.1. For example, these voltages U10, U11 are applied continuously or as in the measuring mode, which was described with reference to FIG. 6c and FIG. 6d. [0205] The voltage sensors 40.10, 40.11 measure the respective electrical voltage U10 or U11 actually being applied. The current intensity sensors 41.10, 41.11 measure the respective current intensities I10, I11 of the electric current, which flows through the detector 10 and through the compensator 11.1. [0206] The control device 6 carries out a control. The control gain during this closed-loop control is that the voltage difference ΔU=U10−U11 becomes zero. The controlled variable is the actual voltage difference. The two voltages U10 and U11, which can be changed by the two actuators (final control elements) 8.10 and 8.11, are manipulated variables. The control device 6 actuates these two actuators 8.10, 8.11. [0207] During this control, in addition, predefined boundary conditions are complied with, especially the condition that the temperature of the detector 10 is so high that the detector 10 is capable of oxidizing a target gas, if a target gas were present in the housing 11, which is not the case during the initial calibration. On the other hand, the temperature and thus the current intensity I10 of the detector 10 shall not be higher than necessary, so that energy is saved and an as long as possible service life is achieved. [0208] As soon as the control gain has been achieved with sufficient accuracy and thus a stable state is reached, the two current intensities I10_ref of the current flowing through the detector 10 and I11_ref of the current flowing through the compensator 11.1 are measured at least once. These two current intensities I10_ref and I11_ref are reference values for the subsequent use of the gas detection device 100. These two reference values lead ideally to the voltage difference ΔU=U10−U11 becoming zero. [0209] It is possible to establish situations with different ambient conditions, wherein no target gas is present each time. Each ambient condition leads to two respective reference current intensities I10_ref and I11_ref. An average is formed between these values in a suitable manner. [0210] If the electrical resistances of the detector 10 and of the compensator 11.1 differ greatly, then the following specification can also be used as a control gain: ΔU=U10−a*U11 becomes zero, wherein a is a predefined correction factor, which approximately compensates the different electrical resistances and/or other differing electrical properties of the detector 10 and of the compensator 11.1. In this embodiment as well, the electrical resistances R10 and R11 do not need to be known precisely.

[0211] During an initial calibration for the gas detection device 100 from FIG. 5, the current intensity I3 is preferably used as a controlled variable. The control gain during this control is, in turn, that the voltage difference ΔU=U10−U11 becomes zero. The variable voltage U42 of the voltage source 42 is used, for example, as a manipulated variable. It is also possible that the resistance values of the two electrical resistors R20 and R21 can be changed and the control device 6 actuates these resistors. The two resistance values are then the two manipulated variables of the control.

[0212] The control device 6 also carries out a control during use of the gas detection device 100. For the gas detection device 100 from FIG. 4, this control is described below with reference to FIG. 7.

[0213] FIGS. 7a and 7b schematically show two control circuits, namely a detector control circuit, which FIG. 7a shows, and a compensator control circuit, which FIG. 7b shows.

[0214] The detector control circuit comprises [0215] a detector control system, [0216] the voltage actuator 8.10 as a final control element for the manipulated variable U10, and [0217] the current intensity sensor 41.10 as a sensor for the controlled variable I10.

[0218] The detector control system comprises [0219] the detector 10, [0220] the electrical line 3, and [0221] the voltage sensor 40.10, which measures the electrical voltage U10 being applied to the detector 10.

[0222] The compensator control circuit comprises [0223] a compensator control system, [0224] the voltage actuator 8.11 as a final control element for the manipulated variable U11, and [0225] the current intensity sensor 41.11 as a sensor for the controlled variable I11.

[0226] The compensator control system comprises [0227] the compensator 11.1, [0228] the electrical line 3, and [0229] the voltage sensor 40.11, which measures the electrical voltage U11 being applied to the compensator 11.1.

[0230] The detector control circuit is controlled with the target that the actual current intensity I10 of the current flowing through the detector 10 is equal to the reference current intensity I10_ref, which was specified in the just described initial calibration and is preferably updated at least once in a subsequent calibration, which will be described farther below. The control device 6 actuates the voltage actuator 8.10, and the actuated voltage actuator 8.10 sets the voltage U10, which is applied to the detector 10, and thus the current intensity I10 of the current flowing through the detector 10 at a respective value.

[0231] The compensator control circuit is controlled with the target that the actual current intensity I11 of the current flowing through the compensator 11.1 is equal to the reference current intensity I11_ref, which was specified in the just described initial calibration and is preferably updated at least once. The control device 6 actuates the voltage actuator 8.11, and the actuated voltage actuator 8.11 sets the electrical voltage U11, which is applied to the compensator 11.1, and thus the current intensity I11 of the current flowing through the compensator 11.1 at a respective value.

[0232] As just described, the analysis unit 9 determines the voltage difference ΔU=U10−U11 or more generally the voltage difference ΔU=U10−αU11 with the predefined correction factor α. The control with the two control circuits, which was described with reference to FIGS. 7a and 7b, ensures that the compensated voltage difference ΔU−ΔU0 is equal to zero when no target gas is present—more generally: is about zero in a predefined tolerance range.

[0233] In the control which was described with reference to FIGS. 7a and 7b, the current intensities I10 and I11 are the two controlled variables in the two control circuits shown. It is also possible to use a different controlled variable in at least one control circuit, which controlled variable correlates with the concentration of the oxidized target gas, for example, the electrical resistance, the temperature, the respective consumed electrical power or even the electrical voltage being applied.

[0234] In the just described control, it is the control gain to keep the respective current intensity I10 and I11 at a constant reference current intensity I10_ref and I11_ref. It is also possible that a time course of the current intensity I10 or I11 is predefined, for example, a sinusoidal or rectangular or zigzag-shaped time course around the reference current intensity I10_ref and I11_ref. In some applications, this embodiment improves the reliability, with which the gas detection device 100 measures the concentration of the target gas.

[0235] As already described, FIG. 5 shows an alternative embodiment, in which the detector 10 and the compensator 11.1 belong to a Wheatstone measuring bridge. In this case as well, a control is preferably carried out, wherein a required value I3_ref or a required time course for the common current intensity I3 at the detector 10 and at the compensator 11.1 is used as a reference variable. The current intensity sensor 41 measures the actual current intensity I3. The control device changes, for example, the voltage U42 of the voltage source 42 as a manipulated variable.

[0236] The two just described controls require that a respective value I3_ref, I10_ref, I11_ref be predefined as a reference variable for the current intensity I3, I10, I11. This value is determined by means of the initial calibration described above in one embodiment. The gas detection device 100 is itself preferably calibrated automatically during the use and automatically updates the values I3_ref, I10_ref, I11_ref, especially preferably always when the gas detection device 100 is operated in the measuring mode and thereby has detected no target gas. The gas detection device 100 determines the respective actual value for the current intensity I3, I10, I11 that has been set during a state free from target gas, and uses this actual value as a new reference value I3_ref, I10_ref, I11_ref, i.e., as a new target value of the reference variable during the respective control. Thanks to this automatic calibration during the use, the gas detection device 100 is automatically adapted to varying ambient conditions. This embodiment further increases the reliability of the gas detection device 100 in detecting an actually present target gas and in avoiding false alarms as much as possible.

[0237] In addition to this automatic calibration, a manual calibration is preferably routinely carried out, as it is known from the state of the art.

[0238] At least one respective change limit is preferably predefined for each reference value I3_ref, I10_ref, I11_ref, which can be changed during the automatic calibration. This limit specifies by what amount or what percentage this reference value I3_ref, I10_ref, I11_ref may be maximally changed since the last manual calibration. The limit may also specify a maximal reliable absolute or relative change per time unit, for example, per month. This embodiment makes possible that the gas detection device 100 is adapted to gradual changes of the detector 10, of the compensator 11.1 or is adapted to gradually changed ambient conditions, but is not adapted to a target gas appearing suddenly, as a rule, such that the gas detection device 100 is not capable of detecting this target gas.

[0239] A bracket is preferably attached to the gas detection device 100 according to the present invention as well, so that a user may carry the gas detection device 100 on his clothing. The gas detection device 100 preferably comprises, furthermore, an alarm unit, not shown, which is capable of outputting an alarm in a form perceptible by a person, for example, optically/visually, acoustically or by touch, i.e., a vibration motor of the gas detection device 100 generates vibrations, which a user of the gas detection device 100 can perceive. Optionally, the gas detection device 100 comprises a transmitting unit, which is capable of transmitting a message to a receiver located at a distance in space. This message may comprise information about the presence or the absence of a combustible target gas and/or information about the measured concentration of the target gas.

[0240] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

LIST OF REFERENCE CHARACTERS

[0241] 1 Stable inner housing of the gas detection device 100; it accommodates the detector 10 and the compensator 11.1, 11.2 [0242] 2 Flame arrester in the opening Ö; it is configured as a metallic grid and/or as a sintered plate [0243] 3 Electrical line or line arrangement that connects the detector 10 and the compensator 11.1, 11.2 to the voltage source 42 and as a result supplies same with electric energy [0244] 4 Outer housing of the gas detection device 100; it accommodates the inner housing 1 as well as the optional electrical resistors R20 and R21 and the sensors 40 and 41; it has the opening Ö [0245] 6 Signal-processing control device; it receives signals from the sensors 40, 40.10, 40.11 as well as 41, 41.10, 41.11; the signal-processing control device controls the switches 7.10, 7.11 and the voltage actuators 8.10, 8.11 as a function of the sensor signals; the signal-processing control device comprises the analysis unit 9 [0246] 7.10 Switch, which pulses the current I10 in the electrical line 3 for the detector 10 [0247] 7.11 Switch, which pulses the current I11 in the electrical line 3 for the compensator 11.1 [0248] 8.10 Voltage actuator; it is actuated by the control device 6; it changes the electrical voltage U10 that is applied to the detector 10 [0249] 8.11 Voltage actuator; it is actuated by the control device 6; it changes the electrical voltage U11 that is applied to the compensator 11.1 [0250] 9 Signal-processing analysis unit; it receives measured values from the sensors 40, 40.10 and 40.11; it determines the voltage difference ΔU; it detects a combustible target gas or determines that no combustible target gas is present; it is a component of the control device 6 [0251] 10 Detector; it comprises the wire 20, the ceramic jacketing 21, a coating 23 made of a catalytic material and the mounting plate 22, which is preferably configured as a pellistor [0252] 11.1 Compensator according to the present invention; it comprises the strip conductor 30 with the heating segment 32 and with the connection 46, the carrier plate 31, the wafer substrate 33, the contact points 34 and the protective layer 35, it extends in a plane [0253] 11.2 Compensator according to the state of the art; it is configured as a pellistor [0254] 20 Helical electrically conductive wire; it functions as the heating segment of the detector 10 [0255] 22 Mounting plate of the detector 10, which holds the wire 20 and the ceramic jacketing 21 [0256] 23 Coating of the ceramic jacketing 21 made of a catalytic material; it preferably leads to a porous surface of the detector 10 [0257] 30 Electrical strip conductor of the compensator 11; it comprises the heating segment 32 and the electrical connection 46 [0258] 31 Carrier plate on the wafer substrate 33; it carries the strip conductor 30 [0259] 32 Heating segment of the strip conductor 30 [0260] 33 Wafer substrate, which carriers the carrier plate 31; it comprises a recess under the heating segment 32 [0261] 34 Electrical contact points for the strip conductor 30; they are connected to the electrical connections 46 [0262] 35 Protective layer over the heating segment 32 [0263] 36 Electrical connection between the heating segment 20 and the electrical line 3 [0264] 40 Voltage sensor; it measures the bridge voltage, namely half of the voltage difference ΔU=U10−U11 [0265] 40.10 Voltage sensor; it measures the electrical voltage U10 that is applied to the detector 10 [0266] 40.11 Voltage sensor; it measures the electrical voltage U11 that is applied to the compensator 11.1 [0267] 41 Current intensity sensor; it measures the current intensity I in the line 3 [0268] 41.10 Current intensity sensor; it measures the current intensity I10 in the section of the line 3, which supplies the detector 10 with electric current [0269] 41.11 Current intensity sensor; it measures the current intensity I11 in the section of the line 3, which supplies the compensator 11.1 with electric current [0270] 42 Voltage source; it comprises a set of rechargeable batteries; it supplies the detector 10 and the compensator 11.1, 11.2 with electric current via the electrical line 3 [0271] 46 Electrical connection between the heating segment 32 and the contact points 34; it belongs to the strip conductor 30 [0272] 100 Gas detection device according to the present invention; it comprises the housing 1, the detector 10, the compensator 11.1, the electrical line arrangement 3, the sensors 40, 40.10, 40.11, 41, 41.10, 41.11, the switches 7.10, 7.11, the actuators 8.10, 8.11, the control device 6 with the analysis unit 9, the voltage source 42 and optionally a mechanical bracket; it is in a fluid connection with the area B [0273] 101 Gas detection device according to the state of the art; it comprises the housing 1, the detector 10, the compensator 11.2, the electrical line 3 and the voltage sensor 40 [0274] B Area, which shall be monitored for the appearance of a combustible target gas [0275] F Functional relationship between the target gas concentration and the compensated voltage difference [0276] I3 Consistent intensity of the current which flows through the detector 10 and through the compensator 11.1 [0277] I3_ref Reference value for the intensity I3 of the current flowing through the detector 10 and through the compensator 11.1; it is determined during the calibration; it is a reference variable in the control in the Wheatstone measuring bridge [0278] I10 Intensity of the current, which flows through the detector 10 [0279] I10_ref Reference value for the intensity of the current flowing through the compensator 11.1; it is determined during the calibration; it is a reference variable in the control in the compensator control circuit [0280] Ö Opening in the housing 1, through which a gas mixture can flow from the area B into the interior of the housing 1 and in which the flame arrester 2 is inserted [0281] R10 Electrical resistance of the detector 10; it correlates with the temperature of the detector 10 [0282] R11 Electrical resistance of the compensator 11.1, 11.2; it correlates with the temperature of the compensator 11.1, 11.2 [0283] R20 Component configured as an electrical resistor; it is part of the Wheatstone measuring bridge [0284] R21 Component configured as an electrical resistor; it is part of the Wheatstone measuring bridge [0285] t1, t2, . . . Times, at which the detector 10 yields a respective measured value [0286] U42 Electrical voltage of the voltage source 42 [0287] U10 Electrical voltage that is applied to the detector 10 [0288] U11 Electrical voltage that is applied to the compensator 11.1, 11.2 [0289] ΔU Difference between the voltage U10 being applied to the detector 10 and the voltage U11 being applied to the compensator 11 or the bridge voltage (U10−U11)/2 [0290] ΔU0 Voltage difference ΔU in a situation, in which no combustible target gas is present; it is used as a zero value