Patent Application
20240418664
This application claims the benefit of priority under 35 U.S.C. § 119 of German Application 10 2023 115 582.2, filed Jun. 15, 2023, the entire contents of which are incorporated herein by reference.
The invention relates to a gas detection device and a gas detection process which are configured to detect the presence of at least one combustible target gas in a gas sample and/or to determine the concentration of the target gas in the gas sample.
Gas detection devices comprising a detector and a compensator have become known. The detector and the compensator are heated by applying an electrical voltage to each. The heated detector oxidizes combustible target gas. A detection variable that correlates with the target gas concentration is measured. The heated compensator is able to oxidize combustible target gas to a lesser extent than the detector or even not at all. Because ideally the detector and the compensator react in the same way to ambient conditions, the compensator makes it possible to compensate for the influence of ambient conditions on the detection variable. Such a device is also known as a heat tone sensor. In order to oxidize sufficient target gas even at lower temperatures, the detector often includes catalytic material. Such a device is therefore also referred to as a catalytic sensor.
It is an object of the invention to provide a gas detection device and a gas detection process which, with the same energy consumption, achieve a higher reliability and/or, with the same reliability, a lower energy consumption than known gas detection devices and gas detection processes each having a detector and a compensator.
The problem is solved by a gas detection device with features according to the invention and by a gas detection process with features according to the invention. Advantageous embodiments of the gas detection device according to the invention are, where appropriate, also advantageous embodiments of the gas detection process according to the invention and vice versa.
The gas detection device according to the invention is capable of determining the presence of at least one combustible target gas in a gas sample. Alternatively or additionally, the gas detection device is capable of determining the concentration of the target gas or at least one target gas in the gas sample. Optionally, the gas detection device is able to determine the summed concentrations of multiple target gases in the gas sample. The gas detection process according to the invention is carried out using a gas detection device according to the invention.
The gas detection device according to the invention comprises a detection arrangement. The detection arrangement includes at least three detection units. The term “detection unit” may denote a detector or a compensator. At least two different detection units of the detection arrangement are detectors. At least one further detection unit is a compensator. Therefore, the detection arrangement provides at least two different detector-compensator pairs. Each detector-compensator pair comprises exactly one detector and exactly one compensator and is sometimes abbreviated as a “pair”.
According to the invention, the number of detectors is greater than the number of compensators. At least one compensator therefore belongs to at least two different detector-compensator pairs. It is even possible for a compensator to belong to at least three different detector-compensator pairs.
The gas detection device according to the invention is capable of switching on each pair, i.e. energizing the pair, and switching off the pair again, independently of any other pair. According to the invention, at most one detector-compensator pair is switched on at any time during an operation. The or every other detector-compensator pair is switched off. It is possible that in an idle state of the gas detection device each pair is switched off. It is also possible that a first pair is switched on in a first period, then no pair is switched on in an intermediate period, and then a second pair is switched on, wherein the second pair is different from the first pair or is the same pair as the first pair.
If a pair is switched on, an electrical voltage is permanently or at least temporarily present at the detector. In addition, an electrical voltage is applied to the compensator permanently or at least intermittently. The term “intermittent” refers in particular to the embodiment in which the electrical voltage is applied in pulsed form, which saves electrical energy compared to an embodiment in which the voltage is applied continuously. The pulse frequency, the pulse duration, and/or the duty cycle of the pulsed voltage applied to a detector may correspond to or differ from the pulse frequency, the pulse duration and/or the duty cycle of the voltage applied to a compensator.
Preferably, a pair is switched on by applying an electrical voltage to both the detector and the compensator, i.e. energizing the pair. The two electrical voltages can have the same value or two different values. The electrical voltage that is permanently or temporarily applied to a detection unit of a switched-on pair causes the detection unit to heat up.
A detection unit comprises a heating segment. If voltage is applied to the detection unit, electric current flows, and this heating segment is heated. A detector differs from a compensator as follows: Heating the detector causes oxidation of the target gas—of course only if there is an oxidizable target gas with a sufficiently high concentration in the vicinity of the detector. Oxidation releases heat energy and the detector is heated further. Heating the compensator, on the other hand, causes less oxidation than heating a detector. In one embodiment, heating the compensator causes no oxidation of the target gas at all.
Each detector unit and therefore each detector-compensator pair has a detection variable. This detection variable correlates with the thermal energy released by the detector oxidizing combustible target gas and therefore with the target gas concentration. In one embodiment, the detection variable of a pair depends on the respective electrical resistance or other electrical variable of the two detection units. As is known, the electrical resistance of an electrically conductive component depends in many cases on the temperature of the component. The respective temperature itself or the supplied electrical power, which is required to heat the heating segments, can also be a detection variable. As a rule, all detector-compensator pairs have the same detection variable, although the values of this detection variable differ or at least may vary for different pairs. If a detection unit of a pair oxidizes target gas, the detection unit heats up further and as a result the value of the detection variable of the pair changes. An example: As is well known, the electrical resistance of an electrically conductive component increases with the temperature of the component. Another example: Because heat energy is released when combustible target gas is oxidized, the greater the target gas concentration before oxidation, the less electrical power is required to bring a detector to a certain temperature.
The detection variable of a detector-compensator pair is influenced by the respective temperature of the two detection units. Oxidizing the target gas releases heat energy. The released heat energy and therefore the detection variable correlating with the released heat energy are an indicator of the target gas concentration.
The gas detection device according to the invention further comprises a measuring unit. This measuring unit is able to measure for each switched-on detector-compensator pair which value the detection variable currently assumes for this pair. For example, the measuring unit measures the respective voltage at the detector and the compensator or at a bridge voltage of a Wheatstone measuring bridge. Preferably, the measuring unit generates a respective time course of the detection variable for each pair.
The gas detection device according to the invention further comprises a signal-processing evaluation unit which receives a signal from the measuring unit and automatically evaluates (processes) the signal. For each pair that is switched on, the evaluation unit therefore receives at least one measured value that the detection variable assumes for the pair, for example the value that the detector of the pair assumes, as well as a measured value that the detection variable assumes for the compensator of the pair, or the value that an optional bridge circuit of the pair assumes. Using the or at least one value for the pair, e.g. the two values for the detector and for the compensator, the evaluation unit decides whether or not target gas with a concentration above a given lower concentration threshold is present and/or derives an estimated value (an indicator value) for the target gas concentration.
If, for example, an indicator of electrical resistance is measured as a detection variable, in many cases the greater the electrical resistance of the detector is, the greater is the estimated value for the target gas concentration, and sometimes the smaller the electrical resistance of the compensator is, the greater is the estimated value. In particular, the greater the difference between the two electrical resistances is, the greater is the estimated value.
As already mentioned, each detector-compensator pair can be switched on and off again independently of any other detector-compensator pair. When the pair is switched on, an electrical voltage is applied to both the detector and the compensator of the pair, preferably pulsed. When the pair is switched off, no electrical voltage is present, neither at the detector nor at the compensator, not even pulsed.
The gas detection device can perform the following steps for each pair:
The feature according to the invention that at most one pair is switched on saves electrical energy compared to an embodiment in which at least sometimes two pairs are switched on simultaneously.
Ambient (environmental) conditions also generally influence the temperature of the switched-on detector, in particular the temperature, humidity and air pressure in the environment. Ideally, these ambient conditions have the same effect on the detector as on the compensator. Thanks to the compensator, the influence of the ambient conditions can be compensated to a certain extent by the configuration and/or by calculation using the value that the detection variable assumes for the compensator or for the pair.
Substances, especially siloxanes and H2S, can be deposited on the surface of a detector. The detector is “poisoned”. As a result, the detector is less able to oxidize combustible target gas, and with the same target gas concentration, the detector releases less and less thermal energy with increasing poisoning, in extreme cases no thermal energy is released at all. Because at least two detectors are present according to the invention, the service life (life time) of the gas detection device can be extended compared to an embodiment with only one detector.
It is possible, but not necessary thanks to the invention, to position a filter between the detection arrangement and a spatial area to be monitored, whereby this filter reduces the inflow of harmful gases. Such a filter often reduces the usefulness (possible uses) of a gas detection device because the filter can reduce or even prevent the inflow of some target gases and the gas detection device is therefore unable to detect these target gases. In addition, a filter can become clogged and allow a gas sample to pass through more slowly or not at all.
As a rule, the compensator or each compensator is less strongly poisoned than each detector. The main reason is that the compensator oxidizes target gas than the detector to a smaller extent and is therefore less strongly poisoned by deposits. In particular for this reason, the feature according to the invention is advantageous that the same compensator of the gas detection device is a component of at least two different pairs. The gas detection device according to the invention requires fewer detection units and often also less electrical energy than a gas detection device comprising multiple detectors and as many compensators as detectors.
In some cases, target gas with a sufficiently high concentration can still be detected even if each detector is heavily poisoned. In one embodiment, the value that the detection variable assumes for the compensator is measured. Many target gases have a greater thermal conductivity than air, so that the compensator is cooled by a target gas, which changes the detection variable of the compensator and thus the or a detection variable of the pair, even if the detector is completely poisoned. However, the influence of the reduced thermal conductivity is much smaller than the influence of the released thermal energy on the detector due to the oxidation of target gas.
According to the invention, there are more detectors than compensators. This feature has the following advantages in particular:
Embodiments of the inventions define various options for the order in which and the frequency with which pairs are switched on and off.
In one embodiment, the detector-compensator pairs are switched on and off during a period of use in such a way that, measured over the entire period of use, all pairs are switched on for the same length of time and switched off for the same length of time. In another embodiment, a first detector-compensator pair is switched on for a longer time period than a second detector-compensator pair. In a further embodiment or modification, the first pair is switched on N1 times and the second pair N2 times during the period of use. N1 and N2 are two numbers, N2 is at least 1, preferably at least 2, and N1 is greater than N2. Preferably, the same amount of time elapses between the time at which a pair is switched on and the time at which this pair is switched off again. The pair is therefore always switched on for the same activation period. However, different activation periods are also possible for one pair or for two different pairs.
In one embodiment, the gas detection device performs at least once during the period of use a sequence comprising the following steps: First, the first detector-compensator-pair is switched on N times and switched off again, while the second detector-compensator-pair remains switched off throughout. Then the second pair is switched on once and switched off again. Here, N is a number greater than 1, which means that the first pair is generally subjected to more stress (strain) than the second pair.
In many cases, these configurations result in the detector of the second pair being poisoned more slowly than the detector of the first pair. If the detector of the first pair is so heavily poisoned that it no longer oxidizes sufficiently reliably, in many cases a target gas can still be detected with the second pair. As already explained, the same compensator can belong to both the first pair and the second pair.
Multiple embodiments have been described above in which the first pair is switched on for longer than the second pair. The first pair is therefore also more heavily stressed than the second pair, and at least its detector is in many cases more heavily poisoned than the detector of the second pair. Preferably, the two pairs provide respective a target gas concentration value (an estimate or indicator of the target gas concentration). Generally, a target gas concentration does not change significantly between an activation period of the first pair and the subsequent activation period of the second pair.
In one embodiment, the evaluation unit is able to compare these estimations of the target gas concentration provided by the two pairs with each other. If these two concentration value estimations differ from each other by more than one threshold, this is an indication that one pair is defective. In response, the evaluation unit-optionally after a check-triggers one of the following two steps:
This configuration allows the gas detection device to automatically check itself with a relatively high degree of reliability. If the two target gas concentration estimates of the two pairs differ by more than the threshold, this is an indication that a detector is relatively heavily poisoned. In many cases, a plausibility check can automatically determine whether the deviation between the two estimated values is caused by poisoning of a detector or by another fault, e.g. an interrupted electrical contact. Because the detector of the first pair is switched on longer than the detector of the second pair according to the embodiment, the detector of the first pair is usually the poisoned detector and not the detector of the second pair. Any other error can of course affect the first pair or the second pair.
In one embodiment, at least one pair has a detection variable that is influenced by both the temperature of the detector and the temperature of the compensator. This embodiment applies if a bridge circuit is used, e.g. In another embodiment, at least one pair has two different detection variables, namely a detection variable of the detector and a detection variable of the compensator. These two detection variables can vary independently of each other over time. The measuring unit is capable of measuring both detection variables.
In one embodiment, when a pair is switched on, an electrical voltage, preferably a pulsed electrical voltage, is applied continuously to both the detector and the compensator. In a different embodiment, when a pair is switched on, an electrical voltage is only temporarily present at the detector and an electrical voltage is only temporarily present at the compensator. If an electrical voltage is present at the detector, the detection variable of the detector is measured. If an electrical voltage is applied to the compensator, the detection variable of the compensator is measured. The two measured values of the two detection variables are then compared with each other in order to decide on the presence of a target gas and/or to determine the target gas concentration. In some cases, this embodiment places less strain on the detector and/or saves electrical energy compared to an embodiment in which an electrical voltage is at least temporarily applied simultaneously to both the detector and the compensator.
In a further embodiment of this configuration, at one time point an electrical voltage is only present at one of the two detection units, i.e. either at the detector or at the compensator, but not at both detection units, even when the pair is switched on. The electrical voltage can also be pulsed in this configuration. This configuration saves electrical energy.
According to the invention, one pair is switched on during an activation period, and the or each other pair is switched off during this activation period. In one implementation of the embodiment just described, an electrical voltage is applied to the compensator for a shorter time during this activation period than to the detector. It is particularly preferable that the measuring unit measures the detection variable for the compensator only once during the activation period, but measures the detection variable for the detector at least two times. This implementation saves even more electrical energy and takes into account the fact that the compensator is essentially influenced by ambient conditions and these ambient conditions generally change only slowly, whereas a target gas concentration and thus the detection variable of the detector can change more quickly.
Preferably, the detection arrangement extends in a plane. According to this preferred embodiment, the maximum dimension of the detection arrangement perpendicular to this plane is at most 20% of the maximum extension in the plane. Particularly preferably, the vertical dimension is at most 10%, especially at most 5%. For example, a circuit board extends in this plane, and the detection units are arranged on and/or in this circuit board. In a viewing direction perpendicular to the plane, the detection units are arranged without overlapping, preferably in at least one row, optionally in a rectangle with at least two rows. Preferably the or every compensator is arranged between two respective detectors. In one embodiment the detection units are arranged in a rectangle with K lines and L columns wherein K>=3 and L>=3 is valid and wherein the or every compensator is arranged in the interior of this rectangle. It is also possible that the detection units are distributed over at least two circuit boards. The two boards can extend in the same plane or in two different planes, whereby the two different planes are preferably parallel to each other. Preferably, a gas sample flows around the two boards.
Such a flat configuration reduces the thermal mass of the detectors and compensators compared to e.g. spherical components (pellistors). As a result, the detection units reach a respective desired operating temperature more quickly. This in turn makes it possible to switch on the pairs for shorter time periods, for example with shorter pulses and/or longer intervals between the individual pulses and/or smaller duty cycles. This in turn reduces the consumption of electrical energy, which is particularly desirable for a device with its own power supply. Alternatively, a higher sampling rate can be achieved with the same energy consumption. In addition, this configuration often saves installation (construction) space and/or weight.
In many cases, the flat configuration just described in conjunction with a pulsed voltage with shorter pulses causes a detector to have a longer service life because it is less poisoned compared to a configuration in which an electrical voltage is permanently applied to the switched-on detector or the pulses must be longer in order to sufficiently heat a spherical component, for example. The detection arrangement is also often easier to produce than a detection arrangement with spherical detection units, for example. This applies in particular to highly automated production.
In one embodiment, all detection units are arranged in the same plane. Because the detection units are arranged in this plane without overlapping, a gas sample that is to be analyzed for the target gas or a target gas reaches all detection units relatively quickly. If two detection units were to overlap, in many cases more time would elapse before the target gas reached all detection units. As a result, the detection arrangement would require more time to provide a reliable measurement result. In addition, in some cases the flow of gas to the detection units would be more difficult, which can lead to incorrect measurement results.
According to the invention, the detection arrangement comprises two detector-compensator pairs. In a preferred embodiment, the detection arrangement additionally comprises a third detector-compensator pair, which also comprises exactly one detector and exactly one compensator. In total, the detection arrangement according to this embodiment comprises at least three detectors and at least one compensator.
The first detector-compensator pair provides a first target gas concentration estimate. The second pair provides a second target gas concentration estimate. The evaluation unit is able to compare these two estimated values with each other. The third pair preferably remains switched off if these two estimated values do not differ from each other by more than a predetermined threshold. How large this threshold is can depend on the time that elapses between the state in which the first pair is switched on and the second pair is switched off, and the state in which the second pair is switched on and the first pair is switched off. If the two estimated values differ by more than this threshold, the gas detection device causes the third pair to be switched on.
The third pair is therefore in reserve and is not switched on and therefore not used as long as the two estimated values of the first pair and the second pair do not differ from each other by more than the threshold. The third pair is therefore not poisoned for this period during which the third pair is not switched on. If the difference is below the threshold, both the first pair and the second pair are intact. The third pair is not poisoned as long as it remains switched off. If the two estimated values differ by more than the threshold, this is an indication that the more heavily loaded detector of the first and/or second pair is heavily poisoned. In this situation, the third pair is used at least temporarily. In many cases, the measured value of the detection variable of the third pair can be used to decide whether the detection variable value of the first pair or the detection variable value of the second pair is correct and therefore the pair that provides a presumably incorrect detection variable value must be switched off and/or checked. For example, the first pair and/or the second pair can be checked or even readjusted/calibrated.
Each detector of these at least three pairs has an effective surface. This effective surface comes into contact with a gas sample. The detector is capable of oxidizing a target gas in this gas sample by means of the effective surface—of course only if the gas sample comprises at least one oxidizable target gas. Preferably, the detector of the third pair has a larger effective surface area than the detector of the first pair and larger than the detector of the second pair. In many cases, the detector of the third pair is therefore able to provide a measured value with a particularly high reliability.
In one embodiment, a respective zero value is specified for each detector-compensator pair. The zero value is set or determined in a previous calibration, for example. The detection variable of the pair assumes this zero value if no target gas is present in the vicinity of the pair. In many cases, the detection variable of a pair does not assume the value zero even if there is no target gas in the vicinity. In other words, the zero value is usually not equal to zero. A common reason is the following: The zero values of the detector and the compensator of a pair differ from each other, especially due to configuration and/or manufacturing differences. Thanks to the zero value, it is not necessary to bring these differences to zero in advance.
A detector-compensator pair that is switched on provides a measured value for the detection variable. The evaluation unit preferably uses the difference between the measured value and the specified, e.g. stored, zero value of this pair as the detection variable value. The evaluation unit determines the presence of the target gas and/or measures the target gas concentration depending on this difference. In one embodiment, the evaluation unit is able to calculate the difference between the value that the detection variable currently assumes and the zero value of the detection variable for each detection unit. This means that there are two differences for each pair that is switched on. It is also possible to specify a zero value for a bridge circuit.
This configuration with the zero values eliminates the need to implement and manufacture the detection units with the same configuration in such a way that the detection variable assumes the same value for each detection unit in the absence of target gas and under the same ambient conditions. Instead, the zero values compensate to a certain extent for configuration-related differences.
In one embodiment, the gas detection device comprises a housing (enclosure, case) which accommodates at least the detection arrangement and the measuring unit, optionally an own power supply unit. The evaluation unit can also be located inside this housing. It is also possible for the evaluation unit to be spatially remote from the housing and connected to the measuring unit via a data link, in particular via a data link by radio waves or by cable. This configuration eliminates the need to arrange the evaluation unit inside the housing. It is possible for the same evaluation unit to be connected to different gas detection devices.
In one embodiment, the gas detection device comprises its own power supply unit. In another embodiment, the gas detection device can be connected to a stationary power supply network.
In one embodiment, the gas detection device comprises an output unit that outputs a measurement result in at least one form that can be perceived by a human being, in particular visually, acoustically and/or haptically (by vibrations). In another embodiment, the gas detection device comprises a communication unit that is capable of transmitting a message with a measurement result to a spatially remote receiver. These two embodiments can be combined with each other.
The invention is described below with embodiment examples. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.
In the drawings:
Referring to the drawings, the gas detection device according to the invention is used to detect at least one combustible gas and/or to determine the concentration of the combustible gas. This combustible gas is hereinafter referred to as the “target gas”. In one embodiment, if multiple target gases are present, the sum of the target gas concentrations is determined.
In one application, the gas detection device is used to monitor a spatial area and to detect at least one combustible target gas and/or to determine the target gas concentration or to ensure that no combustible target gas above a detection threshold is present. The spatial area is, for example, a refinery or other production plant, the interior of a building, a mine, the interior of a vehicle or the interior of an aircraft. The combustible gas is, for example, methane (CH4).
In another application, the gas detection device is used to test a subject for a substance that can be detected in exhaled air, in particular alcohol. As is known, the air exhaled by a subject contains breath alcohol, provided that the subject has consumed alcohol and that this alcohol has not yet been completely broken down in the subject's body. In this case, alcohol is still present in the subject's blood and/or lungs and mouth. In this application, the subject injects (expels) a breath sample into a mouthpiece of the gas detection device. At least part of the delivered breath sample reaches the inside of the gas detection device. In this application, gaseous breath alcohol is the combustible target gas.
In one embodiment, the gas detection device is a portable device that a person can hold in one hand or attach to his/her clothing or protective equipment. For example, a user carries such a gas detection device with him/her while he/she are in an area where at least one flammable target gas may be present. Or the gas detection device is held in front of a subject's mouth so that the subject injects a breath sample.
Preferably, in the first application, and optionally also in the second application, the gas detection device generates an alarm in at least one form that a person can perceive when a target gas concentration occurs above a predetermined threshold. The alarm is emitted visually, acoustically and/or haptically (by vibrations), for example. In these applications, the gas detection device comprises its own power supply unit.
In the embodiment shown in
The gas detection device 100 comprises a detector 10.p and a compensator 11.p. In the following, the generic term “detection unit” is used for both a detector and a compensator. The component of the gas detection device 100 that comprises the detector or each detector as well as the compensator or each compensator and the electrical contacts is referred to as the “detection arrangement” DA. Preferably, the detection arrangement DA is located entirely inside the inner housing 1.
The detector 10.p comprises an electrically conductive component with a heating segment 20 and with two electrical contacts 36, the two electrical contacts 36 being mounted on a plate 22. In the implementation shown, the heating segment 20 has the form of a spiral wire and is preferably made of a material which ideally does not react chemically with a target gas to be detected, i.e. is inert. A ceramic coating 21 surrounds the heating segment 20 and has in the shown implementation the shape of a solid sphere. A catalytic coating, indicated by circles 23, is applied to the outer surface of the ceramic coating 21. The catalytic material used is, for example, platinum or palladium or another suitable metal or alloy. Preferably, the ceramic coating 21 is porous so that the gas sample can also reach the inside of the ceramic coating 21.
When an electrical voltage is applied to the electrical contacts 36, a current flows through the heating segment 20 and the heating segment 20 heats up. The heated heating segment 20 oxidizes a combustible target gas inside the inner housing 1, in interaction with the catalytic material 23 in the ceramic coating 21. As an example, it is indicated that methane is converted into carbon dioxide and water during oxidation, i.e. that the chemical reaction
CH4+2O2→2H2O+CO2
takes place. Heat energy is released during this chemical reaction. This released heat energy further heats the temperature of the heating segment 20. The temperature of the heating segment 20 is therefore an indicator of the concentration of target gas inside the housing 1.
An indicator of the temperature of the heating segment 20 is measured. In one embodiment, the electrical resistance of the heating segment 20 is measured. As is known, the electrical resistance of many electrically conductive materials changes with temperature. As a rule, the greater the temperature, the greater the electrical resistance.
However, the temperature of the heating segment 20 is not only influenced by the target gas concentration, but also by ambient conditions, in particular by the ambient temperature and/or by the temperature of the gas sample inside the inner housing 1. For this reason, the compensator 11.p is also arranged inside the housing 1. The compensator 11.p also comprises a heating segment and a ceramic coating, but in the embodiment example no catalytic coating and in another possible embodiment a lower catalytic coating. Therefore, the compensator 11.p is not able to oxidize any combustible target gas or at least do so more slowly and/or to a less extent. The ambient conditions, on the other hand, ideally have the same effect on the compensator 11.p as on the detector 10.p. Therefore, the compensator 11.p makes it possible to mathematically compensate for the influence of ambient conditions on the detector 10.p to a certain extent.
In the embodiment shown in
Note: The term “electrical resistance” refers to both a component and an electrical property of a component.
In the embodiment shown in
Ideally, the bridge voltage ΔU is zero if there is no flammable target gas inside the housing 1. However, due to design-related differences in particular, the bridge voltage ΔU is usually not equal to zero, even if there is no combustible target gas. Therefore, a so-called zero point ΔU,0 is determined in advance, preferably empirically. The zero point ΔU,0 is the bridge voltage ΔU in the absence of combustible target gas.
A measured detection variable correlates with the concentration of combustible target gas. A signal-processing evaluation unit not shown in
In one form of implementation, the current I3 is kept constant by closed-loop control. The voltage ΔU then correlates with the electrical resistance and therefore with the temperature change caused by the target gas oxidation. The difference ΔU-ΔU,0 acts as the detection variable.
The detector 10.m and the compensator 11.m each comprise the following components:
The protective layer 35 covers at least the conductor track 30, preferably the entire carrier plate 31, and prevents the conductor track 30 from coming into direct contact with a gas sample. In one embodiment, the protective layer 35 is made of silicon nitride. In the detector 10.m, catalytically active material is applied to the protective layer 35, at least in an area 24 above the heating segment 32.
The compensator 11.m comprises the same components as the detector 10.m. Preferably, the compensator 11.m differs from the detector 10.m in that the protective layer 35 of the compensator 11.m has less or even no catalytic material embedded in it, so that the catalyst 11.m is not able to oxidize any combustible target gas or is able to do so to a lesser extent than the detector 10.m.
The conductor track 30 can be made of the same electrically conductive material as the component 20 of the detector 10.p of
The carrier plate 31 preferably has a thickness of less than 10 μm, particularly preferably less than 2 μm, in particular a thickness of at most 1 μm, and is preferably made of a material which contains silicon, for example a glass-like material. In the embodiment example, the carrier plate 31 is attached to the wafer substrate 33 by means of four webs. During manufacture, a gripper of a manipulator is able to grip and mount the compensator 11.1 on the wafer substrate 33.
The electrically conductive conductor track 30 is applied to a surface of the carrier plate 31 and preferably embedded in the surface of the carrier plate 31. Preferably, the conductor track 30 has a maximum thickness, i.e. a maximum dimension perpendicular to the plane of the carrier plate 31, of no more than 1 μm, particularly preferably of no more than 0.5 μm. The carrier plate 31 thermally and preferably also electrically decouples the conductor track 30 from the environment. The carrier plate 31 is in contact with the surrounding air on at least one side, which ensures good thermal insulation of the conductor track 30. The carrier plate 31 can contain recesses 15.1, . . . . The recesses 15.1, . . . can lead to a strip-shaped carrier plate 31. The carrier plate 31 can also be formed over the entire surface.
In one embodiment, the wafer substrate 33 is less than 1 mm thick, particularly preferably less than 0.4 mm thick, and has a maximum diameter of multiple millimeters. The carrier plate 31 is applied to the wafer substrate 33, for example by chemical vapor deposition or by evaporation deposition. Preferably, a recess is made in the area of the wafer substrate 33 that 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 produced, for example, by etching the recess into the material.
The electrical connection 46 connects the heating segment 32 to the electrical contact points 34 on the carrier plate 31. The protective layer 35 electrically insulates the conductive track 30 and thus the heating segment 32 from the environment and reduces the risk of damage. In particular, the protective layer 35 prevents the conductor track 30 from coming into contact with a gas from the environment, in particular with a gas that is potentially damaging to the conductor track 30, for example hydrogen.
The gas detection device 100 of
The configuration shown in
The spatial area B to be monitored and arrows illustrating how a gas sample flows from area B through the opening Ö into the interior of the housing 1 are also indicated. The flame arrester 2 is not shown.
The voltage sensor 40.10 measures the electrical voltage U10 applied to the detector 10.p, while the voltage sensor 40.11 measures the voltage U11 applied to the compensator 11.m. In contrast to the configuration shown in
Preferably, the two currents I10 and I11 are kept constant by means of closed-loop control. The temperature of the heating segment 20 of the detector 10.p correlates with the electrical resistance, and at constant current I10 the electrical resistance correlates with the voltage U10. Accordingly, the temperature and the electrical resistance of the heating segment 32 of the compensator 11.m correlate with the voltage U11. Preferably, two zero values for the voltages are determined in advance, namely a zero value U10.0 for the voltage U10 at the detector 10.p and a zero value U11.0 for the voltage U11 at the compensator 11.m in the absence of combustible target gas. Preferably, the difference (U10-U10,0)-(U11-U11,0) is used as the detection variable.
In order to save electrical energy, the control unit 6 in the embodiment example causes a pulsed voltage to be applied to the detector 10.p and the compensator 11.m instead of a continuous electrical voltage. The control unit 6 controls the two switches 7.10 and 7.11 with the aim of pulsing the electrical voltage U10 and U11 applied to the detector 10.p and the compensator 11.m respectively. Preferably, the pulse rate and/or the pulse duration of the electrical voltage U10 applied to the detector 10.p can be set and changed independently of the pulse rate and the pulse duration of the electrical voltage U11 applied to the compensator 11.m.
Seen in the viewing direction of
Of course, a different number of rows and/or columns of a board with detector units as well as a different number of detector units per row and/or per column is also possible. The compensator 11 is preferably, but not necessarily, arranged in the center. The gas detection device 100 can also comprise multiple such boards with detector units, whereby these boards are preferably arranged parallel to each other and a gas sample can reach each board.
It is possible that all nine detector units 10.1, . . . , 10.8, 11 have the same effective surface, whereby the effective surface comes into contact with a gas sample that is arranged inside the housing 1. In the example shown, however, eight detector units 10.1, . . . , 10.7, 11 each have the same effective surface area. The detector 10.8 has a larger effective surface area, preferably an effective surface area at least half as large, particularly preferably an effective surface area twice as large, as the detectors 10.1 to 10.7 and twice as large as the compensator 11.
In the implementation shown, eight detector-compensator pairs P.1, . . . , P.8 are implemented on the carrier plate 31, the detector-compensator pair P.x comprising the detector 10.x (x=1, . . . , 8) and the compensator 11. The single compensator 11 thus belongs to each of the eight detector-compensator pairs P.1, . . . , P.8. In general, a gas detection device 100 according to the invention comprises m detectors and n compensators, where m>n>=1, and m>1. Preferably, m>=2*n, particularly preferably m>=5*n. With m detectors and n compensators, a total of up to m*n pairs are formed, each with one detector and one compensator. One advantage of the preferred embodiment of having more detectors than compensators is the following: Deposits often form on the heated surface of a detector. The detector becomes poisoned in the course of use. As a rule, significantly fewer deposits form on the heated surface of the compensator. If there are more detectors than compensators, in many cases the gas detection device can be operated for longer, even if individual detectors have failed.
The control unit 9, which is shown schematically in
According to the invention, the gas detection device 100 is operated in such a way that, during an operation, exactly one pair P.x is switched on most of the time and the other pairs are switched off. “Most of the time” means that between the activation period of one pair P.x and a subsequent activation period of another pair P.y, an intermediate period elapses in which all pairs are switched off, the intermediate period preferably being shorter than the or each activation period. During a rest period (idle period), all pairs are generally switched off. The switched-on pair P.x supplies a value for the detection variable, for example a value for the bridge voltage (using a Wheatstone bridge configuration) or a value for the detector voltage and a value for the compensator voltage (embodiment according to
When a detector-compensator pair P.x is switched on, an electrical voltage is applied to both the detector 10.x and the compensator 11. In a first implementation, the electrical voltage is applied continuously to both the detector 10.x and the compensator 11 during the period in which the pair P.x is switched on, preferably in pulsed form.
In a preferred implementation, during the period in which the pair P.x is switched on, the electrical voltage is only present continuously at the detector 10.x, preferably pulsed, while an electrical voltage is only present intermittently (temporarily) at the compensator 11. The preferred implementation can be implemented using the circuit in
As already explained, poisoning pollutants are often deposited on a heated detector 10 during use. These deposits can limit or even completely prevent the ability of the detector 10 to oxidize combustible target gas. The detector 10 then becomes increasingly poisoned. A detector-compensator pair P.x with a poisoned detector 10.x is often no longer able to reliably detect a combustible target gas. In the following, embodiments are described as to how the gas detection device 100 according to the invention is able to automatically detect poisoning of a detector 10. Preferably, a detector-compensator pair P.x with a detector 10.x is no longer switched on if a significant poisoning of the detector 10.x has been automatically detected. Because multiple detector-compensator pairs P.x are present according to the invention, the gas detection device 100 can nevertheless continue to be used. The invention thus extends the service life of the gas detection device 100.
In a preferred embodiment, one detector is held in reserve. In the embodiment example shown in
It is possible that at least one detector-compensator pair P.1, . . . , P.8 is poisoned, in particular because contaminants have deposited on the heated surface of the detector 10.1, . . . , 10.8, or due to other ageing. In this case, the pair with this detector is unable to detect the target gas, and the measured values of this pair result in a value for the target gas concentration that is too low. As a rule, however, the measured values of a poisoned or otherwise aged pair do not lead to a value for the target gas concentration that is significantly too high.
The gas detection device 100 of the embodiment example detects a suspected poisoning preferably as follows, namely during operation or in a special check phase: The control unit 9 switches the pairs P.x on and off again one after the other. Each pair P.x provides a respective value for the detection variable. The evaluation unit 6 derives for each pair P.x that is switched on a value (estimated value or indicator) con.x for the current target gas configuration. For this purpose, the evaluation unit 6 applies a predefined functional relationship to the measured value of the detection variable. The evaluation unit 6 thus provides a time sequence con.x (1), con.x (2), . . . of estimated values for the current target gas concentration. Each value con.x (1), con.x (2), . . . refers to a respective sampling time t (1), t (2), . . . with t (1)<t (2)< . . . and x=1, . . . . Each pair P.x provides at least one value con.x (i) for the current target gas concentration.
The evaluation unit 6 checks whether the target gas concentration rises or falls sharply between two successive sampling times t (1), t (2), . . . . The first alternative is described first, i.e. the detection of a strong increase.
For the following description, con.a (j) denotes a value for the target gas concentration which was derived on the basis of at least one detection parameter value of the pair P.a (a=1, . . . , 7) and relates to the sampling time t (j) (j=1, 2, . . . ). With con.b (j) a value of the pair P.b (b=1, . . . , 7) is designated, with con.8 (j) a value of the pair P.8. As already mentioned and shown in
The evaluation unit 6 checks whether a difference con.b (i)-con.a (i−1) of the target gas concentration values at the two successive sampling times t (i−1) and t (i) is greater than a predetermined absolute or relative threshold, wherein the two values con.a (i−1) and con.b (i) were determined on the basis of measurements of two different pairs P.a and P.b and wherein this threshold may depend on the distance (time gap) between t (i−1) and t (i). The pair P.a provides the value con.a (i−1), the pair P.b provides the value con.b (i).
A measured strong increase in the target gas concentration between the two sampling times t (i−1) and t (i) can have the following reasons:
These two situations are now automatically distinguished from each other. To check the gas detection device 100, the control unit 9 switches on the pair P.8.
The evaluation unit 6 derives a value con.8 (i+1) for the target gas concentration from measured values of the pair P.8. The value con.8 (i+1) refers to a subsequent sampling time t (i+1) and is considered correct. The evaluation unit 6 compares this value con.8 (i+1) with the two values con.a (i−1) and con.b (i). Depending on the result of the evaluation unit 6, the control unit 9 triggers the following steps:
However, if the pair P.a delivers a small value con.a (i+2), the control unit switches the pair P.8 on again. This provides a value con.8 (i+3) for a sampling time t (t+3). If the pair P.8 delivers a large value con.8 (i+3) again, the value con.a (i+2) is incorrect and the pair P.a is defective and is no longer used.
If, on the other hand, the pair P.8 also delivers a small value con.8 (i+3), the target gas concentration has fallen sharply again after the sampling time t (i+2). One possible reason for this is that the gas detection device 100 has been moved from an area with a high target gas concentration to an area with a low target gas concentration or without target gas. The pair P.a will then also continue to be used.
The second alternative is now described, i.e. the detection of a strong drop (decrease). To be more precise: The value con.b (i) for the sampling time t (i) is significantly lower than the value con.a (i−1) for the sampling time t (i−1). The evaluation unit 6 has derived the value con.b (i) on the basis of measured values of the pair P.b, and the value con.a (i−1) on the basis of measured values of the pair P.a.
Again, a value con.8 (i+1) is used for checking, which refers to the sampling time t (i+1).
First of all, the situation is described in which the value con.8 (i+1), which is considered to be correct, is approximately as large as or even larger than the larger value con.a (t−1). In this case, the control unit 9 switches the pair P.b on again. The measured value when switching on again leads to a value con.b (i+2), which refers to the sampling time t (i+2).
If the value con.b (i+2) for the sampling time t (i+2) is approximately as large as the value con.8 (i+1), which is regarded as correct, the pair P.b is regarded as intact and continues to be used. This situation is illustrated in
If, on the other hand, the value con.b (i+2) for the sampling time t (i+2) is also significantly lower, for example about the same as the value con.b (i) for the sampling time t (i), the pair P.8 is preferably switched on again. This provides a value con.8 (i+3) for a sampling time t+3. If this value con.8 (i+3) is again large, the pair P.b is defective and is no longer used. This situation is shown in
As already explained, pair P.8 is only switched on for checking purposes (verification) in the embodiment example. In one embodiment, all other pairs P.1, . . . , P.7 are switched on the same number of times and for the same length of time, for example in turn.
In another embodiment, the procedure is as follows:
Initially, only pair P.1 is used, whereby pair P.1 is switched on and off again N times, N>=2. The other pairs P.2, . . . , P.8 remain switched off. Pair P.2 is then switched on once and switched off again. The last two measurements con.1 (i−1) and con.2 (i) are compared with each other, for example as described above with reference to
If the check shows that both pairs P.1 and P.2 are still intact, the sequence just described is repeated, i.e. first the pair P.1 is switched on and off again N times and then pair P.2 is switched (on and off) once. The other pairs remain switched off. Pair P.1 is therefore loaded N times more than pair P.2.
Because the pair P.1 is loaded N times more, the pair P.1 is usually poisoned more quickly than the other pairs P.2 to P.8. If it is detected that the pair P.1 is poisoned, it is not used any further. The sequence just described is now carried out with pairs P.2 and P.3. First, a sequence is carried out in which pair P.2 is switched on and off N times and then pair P.3 is switched (on and off) once. The last two values for the target gas concentration are compared with each other again. The pair P.2 acts as the pair P.a, the pair P.3 acts as the pair P.b.
This procedure is carried out until the pairs P.1 to P.6 are poisoned so that self-control is no longer possible. It is also possible to switch on one pair N times and the other pair M times, whereby N>M>1 applies. The above applies accordingly.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2023 115 582.2 | Jun 2023 | DE | national |
