Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/0004—Gaseous mixtures, e.g. polluted air
  • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
  • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
  • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/0004—Gaseous mixtures, e.g. polluted air
  • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
  • G01N33/0011—Sample conditioning
  • G01N33/0016—Sample conditioning by regulating a physical variable, e.g. pressure or temperature

Definitions

• the invention relates to a method for gas detection with a gas-selective membrane, the permeability of which for a specific gas is temperature-dependent.
• a detector which can be a gas measuring device, such as a mass spectrometer, or a pressure measuring device that measures the total pressure of the gas.
• a total pressure measurement of the gas is advantageous if the membrane is highly selective for a certain gas type.
• the measurement signal of the gas is overlaid by an offset signal that depends, for example, on the temperature or the age of the gas sensor.
• the gas upstream of the sensor can be removed by evacuation with the aid of pumps in order to measure the offset signal in a vacuum without gas.
• the invention is based on the object of creating a method for gas detection with a gas-selective membrane in which the influence of the offset signal on the measurement signal is reduced.
• the gas detection according to the invention takes place with the aid of a gas-selective membrane with temperature-dependent permeability for the gas to be detected.
• a temperature device is designed to change the temperature of the membrane.
• the temperature device is preferably a heater.
• a cooling device is also conceivable if the permeability of the membrane at a temperature which is lower than that Ambient temperature of the membrane, is maximum.
• a detector is provided and designed to detect a measurement signal as a function of the amount of gas passing through the membrane.
• the detector can be a gas measuring device, such as a mass spectrometer, or a pressure measuring device, such as a total pressure measuring device.
• the temperature of the membrane is changed with the temperature device in order to set the membrane temperature one after the other in chronological order to at least two different values which are not equal to zero.
• At least one first measured value is recorded from the measurement signal of the detector at a first point in time at which the membrane temperature assumes a first temperature value.
• at least one second measured value of the measurement signal is recorded, the membrane temperature at the second point in time assuming a second temperature value different from the first temperature value.
• the difference is formed from the two recorded measured values.
• the assessment of whether a gas to be detected is present and has been measured is based on the difference signal formed.
• the permeability of the gas-selective membrane for the gas to be detected should be greater at one of the two membrane temperatures than at the other membrane temperature.
• the permeability at the first temperature value of the membrane temperature can be greater than at the second temperature value.
• the permeability is preferably maximum at the first temperature value.
• the proportion of the offset in the second measured value is lower than in the first measured value.
• that portion of the measurement signal is greater that is due to the increased permeability is generated by the gas to be detected.
• the offset component is reduced due to the formation of the difference.
• the membrane temperature is preferably changed periodically in such a way that the membrane temperature takes the two temperature values alternately one after the other at periodically recurring intervals, the measured values for the respective temperatures being recorded in at least two different intervals.
• the first measured value is recorded in subsequent intervals when the membrane temperature assumes the first temperature value.
• the second measured value is recorded at successive intervals in each case when the membrane temperature assumes the second temperature value.
• the membrane temperature can be changed in the form of a regulation between two temperature values not equal to zero.
• the temperature can be regulated by measuring the membrane temperature using a temperature measuring device and heating the membrane using a heating device in order to regulate the temperature of the membrane from a lower temperature value to a higher temperature value.
• mean values of the measured values over the following intervals can be formed and used.
• the difference can be formed from the mean value of the first measured values of at least two different intervals and the second measured value lying between these two first measured values.
• the difference can also be formed from the mean value of the second measured values at least two different intervals and the first measured value lying between the two second measured values.
• a parameter influencing the membrane temperature can be set and changed on the temperature device. Between changing this parameter and the resulting change in the membrane temperature from one temperature value to the next temperature value should only take place after a period of at least 2 seconds and preferably after a period in the range between approx. 5 and 15 seconds.
• the difference between the various temperature values of the membrane temperature, which are set and changed with the aid of the temperature device, should be between approx. 2 K and 10 K and preferably between approx. 3 K and 6 K. This applies in particular to the difference between the first temperature value and the second temperature value.
• the temperature device is preferably designed as a heater, at least the first temperature value of the membrane temperature being greater than the temperature of the surroundings of the membrane. Before a subsequent, new temperature value of the membrane temperature is set, the heating can be switched off for a few seconds, the set first temperature value and the set second temperature value of the membrane temperature each being above the ambient temperature of the membrane.
• the measured values of the measurement signal are advantageously recorded in each relevant interval only after a few seconds, preferably after about 2 to 5 seconds, after a new temperature value has been set on the temperature device or the parameter influencing the membrane temperature has been changed.
• no pump is used in order to generate a pressure difference between the pressure of the gas upstream of the membrane and the pressure of the gas downstream of the membrane.
• the method according to the invention can in particular be used for the detection of a gas in a room of a building.
• Figure 1 is a schematic representation of the gas detector
• Figure 2 shows a schematic representation of the measurement signal
• FIG. 3 shows a schematic representation of the temperature and control devices according to FIG. 1.
• the gas detection device 10 is shown schematically with a gas-selective membrane 12 with temperature-dependent permeability.
• the membrane 12 is heated by a temperature device 14 in the form of a heater with heating elements arranged on the membrane 12.
• the heating is controlled via a control device 16.
• the control device 16 is part of the temperature device 14.
• the control device 16 is used to input parameters that affect the heating power and thus the heating effect
• Affect membrane 12 As a result, a control device 16 can be used
• Parameters are changed, which influences the heater 14 and changes the temperature of the membrane 12.
• the heater 14 is attached to the membrane 12 in such a way that gas can pass through the heater 14 and through the membrane 12 from the direction of the arrow 18 in FIG. 1.
• a detector 20 in the form of a pressure measuring device is arranged downstream, i.e. behind the membrane 12. Gas permeating through the membrane 12 reaches the detector and increases the measured pressure there.
• the detector 20 can also be a gas detector, for example in the form of a
• Temperature sensor 14a for measuring the membrane temperature and a Membrane heater 14b for heating the membrane 12 and that the control device 16 has a temperature specification device 16a for inputting the membrane temperature to be set via the membrane heater 14b and a control logic 16b, which is dependent on the membrane temperature measured with the temperature sensor 14a and the temperature specification Device 16a predetermined membrane temperature regulates the heating power of the membrane heater 14b.
• the detector 20 is connected to an evaluation unit 22, which receives and evaluates the measurement signal from the detector 20. With the aid of the evaluation device 22, the measured values of the measurement signal generated by the detector 20 are recorded and the difference formation according to the invention of measured values is carried out.
• the measurement signal S of the detector 20 is plotted over the time t in seconds.
• the heater 14 is activated via the control device 16 and a first parameter Pi is specified, which causes the heater 14 to heat the membrane 12 to a first membrane temperature Ti that is greater than the room temperature in the vicinity of the gas detection device 10.
• the temperature Ti can be 80 ° C.
• the temperature Ti is the temperature at which the membrane 12 has a comparatively high permeability for the gas to be detected, in the present exemplary embodiment helium.
• the measurement signal S rises, for example in the form of an electrical measurement current, as shown in FIG. 2, to a maximum value which is measured as the first measurement value H n at a point in time t of approximately 10 seconds.
• the parameter of the heating device 14 is changed from Pi to P2, with the result that the membrane temperature drops from the value Ti to the value T2.
• the second membrane temperature T2 is lower than the first membrane temperature Ti and is nevertheless above the room temperature in the vicinity of the Gas detection device 10.
• the second membrane temperature T2 is a temperature at which the permeability of the membrane 12 for the gas to be detected is lower than for Ti.
• the measurement signal S therefore falls from its local maximum due to the temperature Ti to a local minimum due to the temperature T2 and is measured as the second measured value Ln at a point in time t of approximately 20 seconds.
• the parameter is then changed again from P2 to Pi via the control device 16 and a further cycle of the periodic repetition of the temperature change is thus started.
• the resulting first interval is designated as n in FIG. 2 and extends from 0 to a point in time t of 20 seconds.
• the following interval n + 1 of the periodic repetition of the temperature switch then begins at time t of 20 seconds. Changing the parameter of the control device 16 from P2 to Pi results in an increase in the membrane temperature towards the first membrane temperature Ti.
• the first measured value of the second interval n + 1 is then measured as H n + i before the parameter is changed back to P2 and as a result the membrane temperature is lowered to T2.
• the resulting measurement signal is measured as the second measurement value L n + i of the second interval n + 1.
• the second interval then ends at 40 seconds and the third interval n + 2 begins.
• a linear drift of the offset of the measurement signal can be eliminated as follows:
• the first measured values H n , Hn + i, Hn + 2 etc. and the second measured values Ln, L n + i etc. of the respective intervals n, n + 1, n + 2 etc. are recorded by the evaluation device 22.
• the evaluation device 22 forms a difference from the first measured value and the second measured value, with the mean value as (H n + H n + i ) from the first measured values H n , H n + i of the following intervals n, n + 1 in the present exemplary embodiment. / 2 is formed and from this mean value the second recorded between the two first measured values Hn, H n + i Measured value L n is subtracted.
• the mean values of both the first and the second measured value can be formed, with the mean values also being able to be formed over two or more intervals.
• the second measured value Ln, L n + i is recorded in each interval at a point in time at which the membrane temperature was set to the second temperature T2 and, as a result, the permeability of the membrane 12 is minimal.
• the second measured value L n , L n + i thus corresponds approximately to the offset signal which does not result from a gas that has passed through the membrane 12.
• the evaluation unit 22 makes an assessment of whether the measurement signal S results from a gas to be detected and the amount of this gas present on the basis of the difference signal D Sn, because the influence of the offset signal on the difference signal is reduced.
• the membrane temperature is regulated via the control device 16 and the heater 14 by first measuring the membrane temperature with the aid of a measuring device not shown in the figures. In dependence of Based on the temperature measurement result, the control device 16 causes the membrane 12 to be heated with the aid of the heater 14 until the higher, desired temperature value is reached.
• the invention is thus based on the principle of a periodic change in the membrane temperature in order to distinguish the offset signal from a useful signal resulting from a detected gas.
• the amount of gas which passes through the membrane in front of and behind the membrane for a given partial pressure difference in the gas pressures is periodically changed.
• the signal difference in the measurement signal between two temperature levels Ti, T2 is proportional to the partial pressure difference and independent of the sensor offset. If the signal difference is measured and the system is then calibrated, the wanted signal is obtained regardless of the interfering offset signal from the sensor.
• the difference between the two temperature levels Ti, T2 is in the present embodiment only 5 K.
• the signal swing DS between the two temperature levels may be composed of the averaging of two adjacent signals of high temperature, H n + H n + i, and the intermediate signal of the lower temperature levels Ln can be obtained. In principle, it is also possible to obtain the signal from averaging two low levels and the intermediate high level. In this way, a linear drift of the underground is also compensated. The drift can be seen in FIG. 2 as a negative slope of the dashed lines of the signal amplitudes falling from left to right.
• the method according to the invention is preferably used for monitoring room air.
• the sensor does not necessarily have to react quickly. Active pumping of air is also not absolutely necessary.
• the membrane temperature Ti, T2 is varied in order to change the permeability of the membrane 12 and thus the sensor sensitivity of the gas detection device 10. This change in sensitivity is accompanied by a change in the measurement signal S, in the present case a change in current, which is proportional to the partial pressure of the gas to be detected (helium).
• the membrane temperature is varied by changing the parameters Pi, P2.
• the parameters are set to the lowest possible values in order to generate the smallest possible permanent sensor current (measurement signal S) at atmospheric pressure in order not to unnecessarily reduce the service life of the sensor.
• measurement signal S the smallest possible permanent sensor current

Landscapes

• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Health & Medical Sciences (AREA)
• Analytical Chemistry (AREA)
• Food Science & Technology (AREA)
• Medicinal Chemistry (AREA)
• Physics & Mathematics (AREA)
• Combustion & Propulsion (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Examining Or Testing Airtightness (AREA)
• Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

Family

ID=76250314

Family Applications (1)

Country Status (7)

Families Citing this family (2)

Citations (5)

Family Cites Families (18)

• 2020
  • 2020-06-24 DE DE102020116660.5A patent/DE102020116660A1/de active Pending
• 2021
  • 2021-05-25 US US18/009,584 patent/US20230204552A1/en active Pending
  • 2021-05-25 EP EP21729459.4A patent/EP4172618B1/de active Active
  • 2021-05-25 CN CN202180044106.XA patent/CN115769072B/zh active Active
  • 2021-05-25 JP JP2022580240A patent/JP7642685B2/ja active Active
  • 2021-05-25 WO PCT/EP2021/063924 patent/WO2021259581A1/de not_active Ceased
  • 2021-05-25 KR KR1020227044834A patent/KR20230027064A/ko active Pending

Patent Citations (5)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events