Method for testing a gas sensor

Abstract

Method for testing at least one gas sensor (100), wherein the at least one gas sensor (100) for carrying out the method is arranged in an internal volume (1002) in a test chamber (1001), wherein in a first measuring step (10) the gas sensor in the test chamber is exposed to a test gas under first gas conditions including a first pressure of the test gas, wherein in a second measuring step (20) the gas sensor in the test chamber is exposed to a test gas under second gas conditions including a second pressure of the test gas, the second gas conditions being different from the first gas conditions, where the second pressure is different from the first pressure and wherein in an intermediate step (15) between the first measuring step and the second measuring step, the gas sensor is exposed to an intermediate pressure which is different from the first pressure.

Description

Embodiments of the present invention relate to a method for testing a gas sensor.Gas sensors typically include a sensor device in a housing that includes an opening, also referred to as a port, that allows ambient gas to enter the housing and contact the sensor device. Gas sensors according to the prior art usually have large ports in order to provide the possibility of rapid gas exchange. However, it is sometimes necessary to use smaller gas ports, for example, for technical reasons. For example, a small port is required in conjunction with some pick-and-place (pick-and-place) devices. Furthermore, if a filter is needed, a smaller port allows the use of a smaller filter membrane. Consequently, a smaller port may result in lower costs, as some filter material may be very expensive, especially when a filter material that only filters certain gases is necessary. In addition, some small port size may be necessary due to the customer environment. A smaller port may also reduce the risk of particle problems, as particles in the case of a large port may easily enter the sensor and cause malfunctions.However, a small port may result in the disadvantage that the response time of the sensor to gas changes in the ambient atmosphere is increased, since the gas molecules require more time to diffuse through the port. Although the reaction time is not a great problem for many applications because gas rates of change are usually very low, such as in connection with air quality measurements in a room, a small gas port results in long test times when the sensor runs through testing and calibration, which is necessary before the sensor can be sold to a customer. During a usual test procedure, the sensor is exposed to a gas and it is checked whether the sensor responds in the desired manner. Further, calibration coefficients may be calculated based on the test information. In conventional test methods, the sensor to be tested is first exposed to clean air and then to a desired test gas, the air or air / gas mixture being constantly supplied to the test chamber and discharged therefrom. The test gas is contained in pressure bottles and is mixed with air using different flow rates to achieve desired concentrations. If the pressure in the chamber is to remain constant, the total flow under normal conditions must be constant. Gas concentration changes therefore take place due to diffusion in the test chamber. Even when high flow rates are used, gas exchange takes usually several tens of seconds even in an optimized chamber, which is a very long time for high volume production. The gas exchange time may even increase, for example when larger chambers are used with handlers (handlers) and other necessary equipment.The publication EP 1 447 664 A2 describes a method for evaluating the measured values obtained from a gas analysis device for the qualitative and / or quantitative determination of a concentration of at least one gas component by means of at least one gas sensor heated according to a cyclically predefined heating profile. The method creates conductance-time profiles. In this case, the gas concentration is represented for each gas component as a function of the integral of the calibration profile and of the different states of the calibration medium. For each gas component, the conductance change is represented at each measurement point as a function of the integral value and the different states of the calibration medium. To identify the gas component in a sample to be analyzed, the conductance profile is measured and the sample integral value is determined. The data is used to calculate the synthetic sample profile and compare it to the actual sample profile. Hypothesis tests are carried out with the aid of a metric. It is an object to provide a method for testing a gas sensor, in particular a method that avoids or at least reduces some of the above mentioned problems.This object is achieved, among other things, with a method according to independent claim 1. Further embodiments and configurations are subject of the dependent claims.According to at least one embodiment, a method for testing at least one gas sensor comprises the step of exposing the gas sensor to a test gas. Here and in the following, the term "testing" preferably includes steps of fundamentally functionally testing the at least one gas sensor and / or calibrating the at least one gas sensor with respect to at least one test gas species contained in the test gas.Here and below, a gas sensor is a sensor that detects the presence of a gas, i.e. the presence of at least one gas species in a gas atmosphere in contact with the gas sensor. The gas sensor can preferably detect at least one gas species present in a mixture of gases. The gas atmosphere may be or comprise, for example, air, e.g. pure air or normal air, which may be pure or which additionally contains a gas species such as CO, CO 2, ethanol and / or another ambient gas detected by the gas sensor.In operation, the gas sensor supplies an electrical signal, for example an electrical current and / or an electrical voltage and / or an electrical resistance and / or a digital signal and / or a digital word, wherein the electrical signal is a measure of the amount of the at least one detected gas species in the gas atmosphere. By measuring and processing the electrical signal of the gas sensor, preferably when operating under different predetermined gas conditions of the test gas, the testing can be carried out. Consequently, the method may preferably comprise some steps in which the at least one gas sensor is arranged in a test gas having different gas conditions. Here and below, the term "gas conditions" may include one or more characteristics of a gas, which may be selected from, for example, a gas composition, a gas pressure, a gas temperature. More preferably, the change from one gas condition to another gas condition is performed at least partially by means of a pressure change of the test gas, as explained in more detail below.The at least one gas sensor can be or comprise, for example, an electrochemical gas sensor, a pellistor-type gas sensor, a semiconductor gas sensor or a metal oxide semiconductor sensor. These types of gas sensors are well known to those skilled in the art and will therefore not be further explained.According to a further embodiment, the method is carried out in a test chamber. Accordingly, the method may comprise the step of providing a test chamber and arranging the at least one gas sensor in the test chamber. The test chamber preferably has an internal volume in which the at least one gas sensor is arranged and can be provided for the desired test gas conditions. Particularly preferably, a plurality of gas sensors can be arranged in the test chamber, such that the method is carried out simultaneously for the plurality of gas sensors. The method steps and features described above and below apply equally to a method for testing exactly one gas sensor or for testing more than one gas sensor, i.e. a plurality of gas sensors which are arranged at the same time in the test gas atmosphere.According to a further embodiment, the method comprises a first measurement step, wherein in the first measurement step the at least one gas sensor is exposed to a test gas under first gas conditions including a first pressure. Preferably, in the first measurement step, a first electrical signal of the gas sensor is measured. The electrical signal can preferably be a measure of the amount of a gas species which is part of the test gas of the first measurement step and which is detected by the gas sensor. The gas species detected by the gas sensor may be referred to herein and hereinafter as test gas species.According to a further embodiment, the method comprises a second measurement step, wherein the gas sensor is exposed in the second measurement step to a test gas under second gas conditions including a second pressure, wherein the second gas conditions are different from the first gas conditions. Preferably, in the second measurement step, a second electrical signal of the gas sensor is measured, wherein the second electrical signal is preferably a measure of the test gas species in the test gas of the second measurement step.Furthermore, it may be possible for at least one further measurement step to be carried out during which the gas sensor is exposed to a test gas under further gas conditions including a further pressure, wherein the further gas conditions are at least different from the gas conditions of the immediately preceding measurement step. Preferably, in the further measurement step, a further electrical signal of the gas sensor is measured. Furthermore, a plurality of such further measurement steps can be carried out. Although the method is described below mainly with a first and a second measurement step, the description applies correspondingly to a method which has one or more further measurement steps. The measured electrical signals and the information of the associated gas conditions during the first, second and optionally further measurement step can be used for the basic functional testing and in particular for the calibration of the gas sensor.According to a further embodiment, the test chamber has an inlet and an outlet. The inlet is provided and configured for filling the internal volume of the test chamber with a test gas, whereas the outlet is provided and configured for at least partially removing the test gas from the internal volume of the test chamber. The outlet may be connected to a pump or an external volume having a pressure lower than the internal volume. The inlet may be connected to a gas source. When the inlet is closed and the outlet is opened so that the internal volume can be pumped out, a decrease in the pressure in the internal volume can be achieved. The decrease in pressure may result in a vacuum. The term "vacuum" includes gas conditions having a pressure equal to or less than 300 hPa, which may be referred to as a coarse vacuum, equal to or less than 1 hPa, which may be referred to as a fine vacuum, or equal to or less than 10 -3 hPa, which may be referred to as a high vacuum, or even an ultra-high vacuum depending on the pressure. When the inlet is opened and the outlet is closed and the pressure in the internal volume is lower than the pressure of the source gas, gas may be filled into the internal volume. Gas exchange due to pressure differences may be very fast compared to gas changes due to diffusion processes.During the first measurement step and the second measurement step, the inlet and / or the outlet is closed. Preferably, at least the outlet is closed during both the first measurement step and the second measurement step. By closing the outlet or preferably both the inlet and the outlet of the test chamber during the measurement steps, the test gas atmosphere, i.e. the gas conditions of the test gas, can be kept constant in the test chamber. In other words, during each of the measurement steps comprising the first measurement step and the second measurement step, there is preferably no gas flow into, through and out of the test chamber.According to a further embodiment, the second pressure is different from the first pressure. Accordingly, the second pressure is lower than the first pressure or the second pressure is higher than the first pressure. Preferably, the pressure of the test gas is changed upon a change from the first pressure to the second pressure. Particularly preferably, in this case, the test gas is substantially the same in the first and second measurement steps. "Substantially the same" means that the composition of the test gas, i.e. the relative concentration of the one or more gas species of the test gas, is not intentionally changed from the first to the second measurement step and accordingly remains the same. Instead of changing a gas composition of the test gas, only the gas pressure of the test gas may be changed by removing a part of the test gas from the test chamber or increasing the amount of the test gas in the test chamber. Accordingly, the test gas comprises a test gas species having a relative concentration that is substantially the same during the first and second measurement steps.Due to the pressure change of the test gas between the first and second measurement steps, the partial pressure of the test gas species detected by the gas sensor changes. Since a change in partial pressure is equivalent to a change in concentration of the detected test gas species, the gas sensor can respond to the pressure change in a similar manner to the situation when a corresponding change in gas composition is made. If the gas sensor additionally exhibits a pressure dependence, this pressure dependence can be corrected by developing an appropriate model, for example. For example, the first and second measurement steps may be performed a number of times, wherein for each repetition of the first and second measurement steps, the amount of the detected test gas species in the test gas is changed, while each first measurement step is performed at the same first pressure and each second measurement step is performed at the same second pressure.According to a further embodiment, the method comprises an intermediate step between the first measurement step and the second measurement step. During the intermediate step, the gas sensor is subjected to an intermediate pressure that is different from the first pressure. In particular, the intermediate pressure can be as low as possible. Preferably, the gas sensor is subjected to a vacuum during the intermediate step. This can mean that the test gas of the first measurement step is substantially removed from the test chamber during the intermediate step. After the intermediate step, a test gas to be used during the second measurement step is introduced into the test chamber. In this case, it may be possible that the test gas used during the first measurement step and the test gas used during the second measurement step are different. In particular, the concentration of the test gas species detected by the gas sensor is different in the test gases used during the first and second measurement steps. Preferably, the first and second pressures may be the same.Alternatively, the first and second pressures may be different.According to a further embodiment, the different gas conditions in the first and second measurement steps may include different gas temperatures. In other words, alternatively or in addition to the variations of the first and second gas conditions described above, the test gas may have a first temperature during the first measurement step and the test gas may have a second temperature different from the first temperature during the second measurement step. It may be possible that the test gas remains unchanged during the first and second measurement steps, so that the temperature difference causes a pressure difference. Alternatively, the first and second pressures may be the same by adjusting the test gas pressure while the first and second temperatures are different. Furthermore, the first and second measurement steps may differ with respect to other physical stimuli for the gas sensor.According to a further embodiment, the test gas comprises one or more of the following gas compounds: N 2, O 2, CO 2, CO, ethanol, NH 3, N x O x, volatile organic compounds (VOCs). In particular, the test gas can have one or more of the mentioned gas compounds in the first measurement step and in the second measurement step. Furthermore, the test gas may be a mixture with at least two or more of the mentioned gas compounds. For example, the test gas may be or comprise a mixture of N 2, O 2 and at least one of CO 2, CO, ethanol, NH 3, N x O x, VOCs.As described above, the method uses pressure changes to calibrate the at least one gas sensor. In particular, the method comprises pressure changes of the test gas after the first measurement step. While pressure changes occur at sonic speeds that are about 333 m / s, diffusion gas changes commonly used in gas sensor testing methods occur at a typical speed of about 0.1 m / s to 1 m / s. Therefore, changes in the gas conditions between the first and second measurement steps in the method described here take place much more quickly than in conventional test methods. The method described here therefore enables a reduction of the required test time even if the tested gas sensor or the tested gas sensors has / have a small gas port. However, the method described is not limited to certain port sizes and can be performed for gas sensors having any port size.Further features, advantages and embodiments will become apparent from the following description of exemplary embodiments in conjunction with the figures. FIGS. 1 to 3 show schematic representations of gas sensors according to some exemplary embodiments, FIG. 4 shows a schematic illustration of a measuring device according to a further exemplary embodiment, FIG. 5 shows a schematic illustration of method steps of a method for testing a gas sensor according to a further exemplary embodiment, FIG. 6 shows a measurement of a gas sensor, FIG. 7 shows a schematic illustration of a measuring device according to a further exemplary embodiment, and FIG. 8 shows a schematic illustration of method steps of a method for testing a gas sensor according to a further exemplary embodiment.Identical or similar elements and elements having the same function are identified by the same reference numerals in the figures. The figures and the proportions of the elements shown in the figures are not considered to be true to scale. Instead, individual elements, in particular layers, may be shown in exaggerated size for better illustration and / or for better understanding.FIG. 1 shows a gas sensor 100 according to an embodiment. FIGS. 2 and 3 show modifications of the gas sensor 100 according to further exemplary embodiments. The features of the gas sensor 100 as illustrated in FIGS. 1 to 3 and in the following figures are purely exemplary and should not be understood as limiting the method described below.The gas sensor 100 includes a sensor device 101 that is the gas sensitive element of the gas sensor 100 and that may be, for example, an electrochemical gas sensor, a Pellistor-type gas sensor, a semiconductor gas sensor, or a metal oxide semiconductor gas sensor. As indicated in FIG. 1, the sensor device 101 may be a chip or at least one chip-sized device. For example, the sensor device 101 is or comprises a MEMS device (MEMS: microelectromechanical system). Furthermore, the gas sensor 100 may include an electronic device 102 which is or comprises, for example, an ASIC (application-specific integrated circuit). Such a device may control, for example, the function of the sensor device 101 and, accordingly, the gas sensor 100. The electronic device 102 may be mounted together with the sensor device 101 in a common housing 103 or outside the housing 103. Alternatively, it may be possible that the gas sensor 100 does not include an electronic device 102.The housing 103 comprises a carrier 104 comprising the sensor device 101 and the electronic device 102, which may be soldered or glued to the carrier 104 by means of a solder layer or adhesive layer, for example, and electrically contacted via bond wires. Further, the housing 103 includes a cover 105 that covers the sensor device 101 and the electronic device 102. Both the carrier 104 and the cover 105 may comprise a ceramic and / or plastic material. Alternatively, the cover 105 can also comprise or consist of a metal, for example. For the electrical contacting of the components mounted on the carrier 104, the carrier 104 further comprises internal electrical contacts, such as bond pads 106, external electrical contacts, such as solder pads 107, and if necessary internal lines and / or electrical vias. The cover 105 has an opening forming a port 108 through which the surrounding atmosphere can enter the housing 103 so that the gas or one or more gas species of the surrounding atmosphere can be detected by the sensor device 101.As shown in FIG. 1, the port 108 may be located in the upper side of the cover 105 so that the surrounding gas atmosphere may enter the housing 103 from the upper side of the gas sensor 100. Consequently, the gas sensor 100 with the carrier 104 is to be mounted on a support, so that the port 108 is accessible. FIG. 2 shows a further embodiment of a gas sensor 100 with a port 108 in the upper side and a lateral side of the cover 105. FIG. 3 shows a further embodiment of a gas sensor 100 with a port 108 only in the lateral side of the cover 105. In these two embodiments, the gas of the surrounding atmosphere can enter the housing 103 even when the gas sensor 100 is mounted upside down with the cover 105 on a support.FIG. 4 shows a measuring device 1000 configured to carry out a method for testing at least one gas sensor 100. The measuring device 1000 has a test chamber 1001 in which the method is carried out. The test chamber 1001 includes an internal volume 1002 in which the at least one gas sensor 100 is disposed and can be provided for the desired test gas conditions. In the exemplary embodiment shown, a plurality of gas sensors 100 are arranged in the test chamber 1001, so that the method can be carried out for the plurality of gas sensors 100.The test chamber 1001 has an inlet 1003 and an outlet 1004. The inlet 1003 is configured to fill the internal volume 1002 of the test chamber 1001 with a test gas, whereas the outlet 1004 is configured to at least partially remove the test gas from the internal volume 1002 of the test chamber 1001. The gas sensors 100 are arranged in a matrix-like arrangement on a support 1005, which may for example comprise or be a mounting band, and may be contacted by a test device 1006. In order to facilitate contacting by the test device 1006 that needs to access the electrical contacts of the gas sensors 100, the gas sensors 100 are arranged upside down on the support 1005. The gas sensors 100 are formed with a port at least partially on a lateral side of the cover, as explained in connection with FIG. 2, so that the ports of the gas sensors 100 are not blocked by the support 1005. Alternatively, the gas sensors 101 may also be configured as shown in FIG. 3. However, the method may also be performed in conjunction with other gas sensors and other arrangements of gas sensors. The test apparatus 1006 electrically contacts a gas sensor 100 one after another as indicated by the arrows by moving stepwise from the gas sensor 100 to the gas sensor 100, thereby measuring an electric signal of the gas sensors 100 in response to the test gas contained in the test chamber 1001. Alternatively, the measurement device 1000 may include a test device that contacts more than one gas sensor 100 or even all gas sensors 100 at the same time.The inlet 1003 is connected to a gas source 1007, which may comprise one or more pressure cylinders containing gases or gas species. The outlet 1004 may be connected to a pump or an external volume having a lower pressure than the internal volume 1001. In the embodiment shown in FIG. 4, a pressure controller 1008 is connected to the outlet 1004 so that the pressure of the test gas in the internal volume 1002 of the test chamber 1001 can be controlled. When the inlet 1003 is closed and the outlet 1004 is open, a controlled decrease in the pressure in the internal volume 1002 may be achieved via the pressure controller 1008. When the inlet 1003 is opened and the outlet 1004 is closed, gas may be filled into the internal volume 1002.The test gas can preferably comprise one or more of the following gas compounds: N 2, O 2, CO 2, CO, ethanol, NH 3, N x O x, volatile organic compounds (VOCs). For example, the test gas may be or comprise a mixture of N 2, O 2 and at least one of CO 2, CO, ethanol, NH 3, N x O x, VOCs.FIG. 5 shows method steps of a method for testing at least one gas sensor, wherein the method steps are carried out with the measuring device 1000 of the exemplary embodiment shown in FIG. 4.The method has a first measurement step 10. In the first measuring step 10, the at least one gas sensor is exposed to a test gas under first gas conditions including a first pressure. In the first measurement step, a first electrical signal of the at least one gas sensor is measured. As explained in connection with FIG. 4, the test apparatus 1006 is used for measuring the electrical signal of the gas sensor 100 disposed in the test chamber 1001. In particular, in the first measuring step 10, an electrical signal of each gas sensor is measured, wherein the electrical signal depends on the first gas conditions. The electrical signal of each gas sensor is a measure of the amount of a test gas species that is part of the test gas that is present in the internal volume of the test chamber during the first measurement step 10 and that is detected by the respective gas sensor.The method further comprises a second measurement step 20, wherein in the second measurement step the at least one gas sensor, i.e. the plurality of gas sensors in the exemplary embodiment of FIG. 4, is exposed to a test gas under second gas conditions including a second pressure. The second gas conditions are different from the first gas conditions. Similar to the first measurement step 10, in the second measurement step, a second electrical signal is measured by each of the gas sensors, wherein the second electrical signal is preferably a measure of the test gas species in the test gas of the second measurement step 20.During the first measurement step 10 and the second measurement step 20, the inlet and / or the outlet of the test chamber is closed. Preferably, at least the outlet is closed during both the first measurement step 10 and the second measurement step 20. By closing the outlet or preferably both the inlet and the outlet of the test chamber, the test gas atmosphere, i.e. the gas conditions of the test gas, can be kept constant in the test chamber. Consequently, during both the first measurement step 10 and the second measurement step 20, there is no gas flow into, through, and out of the test chamber.The second pressure is different from the first pressure. In particular, in the exemplary embodiment shown, the second pressure is lower than the first pressure. However, it may also be possible for the second pressure to be higher than the first pressure. Particularly preferably, the test gas is substantially the same in the first and second measurement steps 10, 20. Consequently, the first and second gas conditions differ only in gas pressure. Due to the pressure change of the test gas between the first and second measurement steps 10, 20, the partial pressure of the test gas species detected by the gas sensors changes. The partial pressure change is equivalent to a concentration change of the test gas species.For example, if an oxygen sensor, which may be a gas sensor having a sensor device formed by a metal oxide gas sensor, is to be tested and, in particular, calibrated, the test chamber may be filled with clean air at a pressure of 1000 hPa as the test gas for the first measurement step 10. The partial pressure of oxygen is about 200 hPa. The gas sensor can therefore be tested at a concentration of (200 / 1000)*(1 / 22.4) mol / l=4.48 mol / l. For the second measuring step 20, the pressure in the test chamber is reduced to 500 hPa, for example, which results in an oxygen concentration of 2.24 mol / l. The gas sensor can then also be tested at this concentration and subsequently calibrated. Due to the fact that gas changes in a gas maintained at the same pressure are purely diffusion-induced and occur at a rate of about 0.1 m / s to 1 m / s, whereas changes in pressure occur at a speed of sound, i.e. at a rate of about 333 m / s, the method described herein is much faster than conventional gas sensor calibration methods. If the gas sensor additionally has a pressure dependence, this pressure dependence can be corrected by developing an appropriate model, for example.FIG. 6 shows an exemplary measurement with a gas sensor in a measuring device as explained above. The top measurement shows as sensor reading, i.e. as the electrical signal of the gas sensor, the electrical resistance RS of the gas sensor in response to pressure changes of the pressure P (bottom measurement) and the temperature T measured with respect to a heater resistance RH (middle measurement) in a test chamber, while a sequence of first and second measurement steps is performed during a time T. As can be readily seen, the pressure changes of about 200 hPa cause significant changes in sensor readings of about 3.8 kΩ. Although the temperature change in the test chamber causes a shift of the sensor reading at a time T = 810 s, the sensor reading difference between the first and second measurement steps may remain the same.FIG. 7 shows a measuring device 1000 configured to carry out a method for testing at least one gas sensor 100, according to a further exemplary embodiment, the method being shown in FIG. 8. The method, which is a modification of the method shown in FIG. 5, comprises an intermediate step 15 between the first and second measurement steps 10, 20. Preferably, the gas sensors 100 are exposed to a vacuum during the intermediate step 15. Consequently, the test gas contained in the test chamber during the first measuring step 10 is substantially removed from the test chamber 1001 in the intermediate step 15. For this purpose, the measuring device 1000 comprises a vacuum generating device 1009, for example a pump or a large vacuum reservoir, which is connected to the outlet 1004.After the intermediate step 15, a test gas, which is then used during the second measuring step 20, is introduced into the test chamber 1001 via the inlet 1003. In particular, the test gas used during the first measurement step 10 and the test gas used during the second measurement step 20 are different. For example, the test gas used during the first measurement step 10 is clean air and the test gas used during the second measurement step 20 is clean air mixed with a test gas species, which may be, for example, CO, CO 2, ethanol, and / or other ambient gases. Generally, the concentration of the test gas species detected by the gas sensor is different in the test gases used during the first and second measurement steps 10, 20. Preferably, the first and second pressures may be the same. Alternatively, the first and second pressures may be different. Since the gas sensor is exposed to vacuum during intermediate step 15, the exchange of test gases is much faster than in a process in which changes in the concentration of the test gas species occur only by diffusion.In the above-explained methods, repetition of the first and second measurement can be performed as also mentioned in connection with FIG. 6. Additionally or alternatively, one or more further measurement steps can be carried out, wherein in each of the further measurement steps the gas sensor(s) is(are) exposed to a test gas under further gas conditions including a further pressure, wherein the further gas conditions are at least different from the gas conditions of the immediately preceding measurement step.Alternatively or in addition to the features described in connection with the figures, the exemplary embodiments shown in the figures can have further features which are described in the general part of the description. In addition, features and exemplary embodiments of the figures can be combined with one another even if such a combination is not explicitly described.The invention is not limited by the description based on the exemplary embodiments. Instead, the invention includes any new feature and also any combination of features, which in particular comprises any combination of features in the claims, even if this feature or this combination itself is not explicitly stated in the claims or embodiments.List of reference characters10 Measurement step 15 Intermediate step 20 Measurement step 100 Gas sensor 101 Sensor device 102 Electronic device 103 Housing 104 Carrier 105 Cover 106 Bond pad 107 Solder pad 108 Port 1000 Measurement device 1001 Test chamber 1002 Internal volume 1003 Inlet 1004 Outlet 1005 Support 1006 Test device 1007 Gas source 1008 Pressure controller 1009 Vacuum generating element

Claims

Method for testing at least one gas sensor (100), wherein the at least one gas sensor (100) is arranged for carrying out the method in an internal volume (1002) in a test chamber (1001), wherein in a first measurement step (10) the gas sensor in the test chamber is exposed to a test gas under first gas conditions including a first pressure of the test gas, wherein in a second measurement step (20) the gas sensor in the test chamber is exposed to a test gas under second gas conditions including a second pressure of the test gas, wherein the second gas conditions are different from the first gas conditions, wherein the second pressure is different from the first pressure and wherein in an intermediate step (15) between the first measurement step and the second measurement step the gas sensor is exposed to an intermediate pressure which is different from the first pressure.The method of claim 1, wherein the second pressure is lower than the first pressure.The method of claim 1, wherein the second pressure is higher than the first pressure.The method according to any of the preceding claims, wherein between the first and second measurement steps, the pressure of the test gas is changed for changing from the first pressure to the second pressure.The method according to any of the preceding claims, wherein the test gas is substantially the same during the first and second measurement steps.The method of the preceding claim, wherein the test gas comprises a test gas species having a relative concentration that is substantially the same during the first and second measurement steps.The method according to any one of claims 1 to 4, wherein during the intermediate step, the test gas of the first measurement step is removed from the test chamber.Method according to the preceding claim, wherein the gas sensor is subjected to a vacuum during the intermediate step.The method of claim 7 or 8, wherein the test gas is different during the first and second measurement steps.The method according to any of the preceding claims, wherein the method is performed in a test chamber having an inlet (1003) and an outlet (1004), wherein during the first measurement step and the second measurement step at least the outlet is closed.The method of any preceding claim, wherein a plurality of gas sensors are disposed in the test chamber such that the method is performed simultaneously for the plurality of gas sensors.The method of any preceding claim, wherein the test gas comprises a mixture of N 2, O 2 and at least one of CO 2, CO, ethanol, NH 3, N x O x, volatile organic compounds.

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