Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Chemical analysis
Reexamination Certificate
2000-10-24
2003-10-21
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Chemical analysis
C702S022000, C702S023000, C702S025000, C702S030000
Reexamination Certificate
active
06636811
ABSTRACT:
The Invention relates to a method for determining gasous compounds, wherein a sample gas stream is lead to a sensory array with several gas sensors (
2
), wherein the electrical output signals of the individual gas sensors (
2
) are captured by the evaluation computer.
Such methods and apparatuses are employed for the identification of gas mixtures, in particular in the food processing industry.
By now it has become of large importance to investigate and monitor, for example, food products with respect to quality or the environment with respect to a loading of the environment. For this purpose gas mixture samples are taken from the products with desired quality features and characteristic images are generated with the aid of suitable sensors. These images are stored and serve as comparison patterns for all successive investigations.
Such methods are known for a longer time. Apparatuses and arrangements operating according to this method have been employed more heavily in recent times as ‘electronic nose’. These apparatuses comprise a unit for taking gas samples with a pump and a gas flow sensor, a sensor array with several, for example, 10 different gas sensors, and an evaluation computer. For example, semiconductor gas sensors are unspecific sensors such that in the presence of gas mixtures all sensors react, however, each sensor delivers a different signal. All these different signals result in an overall picture diagram. The shape of this image characterizes the gas mixture and forms the basis as a pattern for the further investigations. It is also known to employ a spectrometer instead of a sensor array with several gas sensors, for example, an ion mobility spectrometer or an optical spectro-scope or a combination of the recited apparatuses.
However, it has been shown that such method is unsuitable for such gas mixtures, where in addition to the compounds of interest there are present also other compounds in much larger concentrations. These are in general easily volatile compounds such as for example ethanol in alcoholic beverages. Because of the high concentration of the ethanol the sensors react mainly relative to the ethanol and not to aroma materials and the sensors thereby falsify the measurement results. A further disadvantage of this method comprises that many gas sensors do not generate linear concentration characterizing curves with the same materials and different concentrations. This leads to different patterns and thus to an increased expenditure for rerecognition of a gas mixture. It is also disadvantageous that the sensors change in the course of time and that for this reason, the patterns have to the renewed again and again.
There exists therefore the purpose to develop a method and an apparatus of the recited kind, which linearizes the characterizing curves of the individual sensors.
A further object comprises to create the possibility to further free, as required, the gas samples in addition from easily volatile gas components.
This object is accomplished the method for determining gaseous compounds, wherein a sample gas stream is thinned with a stream of air prior to the feeding into the sensor array and wherein thereby the concentration of the sample gas stream is kept constant to a predetermined value. The electrical output signal gas sensor array are captured by the evaluation computer and converted into a characterizing diagram, are stored and are compared with the diagrams of other gas mixtures. The apparatus for determining of gaseous compound, comprising also a transfer and control unit (
16
) for the controlled transport of a sample gas stream through the sensor array (
1
), a switchable three way valve (
6
) is disposed in a feed line (
3
) with an inlet port (
4
). The switchable three way valve (
6
) is in connection with a selective collection unit (
7
) and wherein a sideline (
12
) with a thinning unit (
13
) joins between the three-way valve (
6
) and the sensor array (
1
).
The recited disadvantages of the state-of-the-art are eliminated with the present invention. Thus, gaseous compounds can now be recognized with high precision and independent of their concentration. This improves the quality of the comparison measurements substantially. The gas sensors are thereby treated with care such that they are loaded only with a concentration degree far below the saturation limit.
The method is also advantageous with respect to that also gaseous compounds with non-selectionable components can be subjected to such a comparative investigation by a preceding treatment of the gas sample stream in a selective collection unit. This extends the field of application substantially for the method.
The apparatus according to the present invention is constructed based on the switchable three way valve of the apparatus dispsoed in the feed line to the sensor array such that the sample gas stream can be lead as desired over the selective collection unit or passed by the selective collection unit. This selective collection unit is equipped in a special way with a reversible feed transport pump, wherein the reversible feed transport pump fills the selective collection unit by its suction power and empties then again the selective collection unit based on its pressure power. This simplifies the device-technical construction of the apparatus.
It is also advantageous to employ generally known absorbents for the enrichment of the selectionable gas components.
The invention is to be illustrated in more detail by way of a schematic illustration.
The device for the performing of the method for determining the gaseous component comprises mainly a sensor array
1
with for example ten gas sensors
2
formed as semiconductor gas sensors. This sensor array
1
comprises on the one hand a feed line
3
with an inlet port
4
and on the other hand a discharge port
5
. A switchable three way valve
6
is disposed in the feed line
3
, and a selective collection unit
7
is connected to the switchable three way valve
6
. This collection unit
7
comprises a special adsorbent
8
and a heater
9
as well as a separate feed transport pump
10
with the a flow sensor
11
for the feed transport pump
10
. A sideline
12
connects to the feed line
3
between the three way valve
6
and the sensor array
1
, wherein a thinning unit
13
is disposed in the sideline
12
. This thinning unit
13
is also furnished with a feed transport pump
14
and a flow sensor
15
for the feed transport pump
14
as well as with an air filter not illustrated. A transport and control unit
16
is disposed in the region of the discharge port
5
of the sensor array
1
, wherein the transport and control unit
16
again comprises a feed transport pump
17
and a flow sensor
18
for the feed transport pump
17
. An electric conduit branches off from the sensor array
1
and leads to an evaluation computer
20
, wherein the evaluation computer
20
is furnished with contact to all flow sensors
11
,
15
and
18
through connection lines not illustrated.
A sample is taken off a gas mixture for determining the gas mixture, wherein the feed transport pump
17
of the transport and control unit
16
sucks in a predetermined flow of the gas mixture through the inlet port
4
and transports the predetermined flow of the gas mixture through the sensor array
1
. At the same time the feed transport pump
14
of the thinning unit
13
feeds a predetermined flow of filtered fresh air to the sample gas stream in the feed line
3
. The mixing ratio of the sample gas stream and of the air stream is selected such that the work point of the gas sensor
2
is fixed in the lower region of its nonlinear concentration curve. The most sensitive or the quickest gas sensor reacts thereby preferably always at a certain work point such that always the same images of different measurements of a same sample gas stream result independently of the concentration of the gas mixture. As required and in the following, the concentration of the gas mixture can be calculated through the mixing ratio displayed at the evaluation co
Dohren Stefan
Hunte Torsten
Matz Gerhard
Munchmeyer Wolf
Walte Andreas
Hoff Marc S.
Kasper Horst
Suarez Felix
WMA Airsense Analysentechnik GmbH
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