FI96903B - Method for determining the content of foreign matter in gas and apparatus therefor - Google Patents

Description

96903

METHOD OF DETERMINING THE CONTENT OF CONTAMINANTS IN GAS AND EQUIPMENT FOR THEM

The present invention relates to a method and an apparatus for determining the contaminant content of a gas.

Contaminants are examined and their concentration is determined to monitor air respiration. When certain already very small amounts of toxic substances are determined from a gas, other components can interfere with detection.

Concentrations of various components, such as carbon dioxide, may vary in air. There are often problems with detecting various molecules or groups of molecules from gas or vaporization of vaporized solids or liquids. In particular, the rapid and reliable detection of toxic substances in the air, nerve gases released into the air at low concentrations, has been problematic. Observations should be available in a few seconds. The most effective 20 nerve gases should be detected already at a concentration of 1/100 ppm.

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The most sensitive analysis devices are based on ionizing air, eg with alpha or beta radiation, and measuring ions under different conditions. In one way, the ions 25 thus formed are made to migrate through a certain kind of labyrinth, and the remaining ions are measured on the basis of the current they cause. In another way, the mobility of the ions formed through the different gratings is studied and finally the ion current is measured. These two methods usually detect very heavy molecules in the air, like most combat gases. In one method, the ionized molecules are passed through chambers with different electric fields, after which a current is detected from the measuring electrodes, on the basis of which the quality and quantity of the foreign matter molecules can be identified.

Such a fast and reliable method is disclosed in FI-96903 2 patent 75055. In a method for determining the contaminant content of a gas, the gas and the substances contained therein are ionized in an ionization state. We are led to a narrow analyzer channel where they are exposed to capillary action in the center of the 5-channel channel. From there, they are further deflected by electric fields caused by different voltages to an electrode at the edge of the channel, where they cause an ionic current. The current spectrum based on ion currents identifies different substances and determines the pi-10 concentrations of ions in the gas by comparing them with the corresponding spectra obtained from standard samples of different substances. A solution has also been proposed in which the ions contained in the gas are separated in the separator section before the measurement into positive and negative ions, from which the second-character ions are analyzed.

DE-A-2028805 discloses a method for detecting small amounts of vapors that undergo ionic molecular reactions and for separating, concentrating and measuring the small amounts of molecules in gas samples. In an electric field substantially parallel to the gas flow between the two electrodes arranged in the detector chamber, detection and measurement are accomplished by utilizing the difference in the velocity and travel time of ions of different masses in the electric field produced in the gas flow. The electric field causes the primary ions to travel from the rectangular and parallel to the gas flow towards the plurality of ion ports placed between the electrodes, during which the primary ions react with the detectable gas molecules, converting the molecules to secondary or product ions, thus measuring and classifying the ions.

EP-A-21 518 discloses a method for detecting the amounts of chemical substances determined in a gas mixture, similar to the previous one 35, by ionizing some of the molecules and passing these gas molecules through an electric field,

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96903 3 arranged as above in the detector chamber.

CH publication 550 399 describes an air pollution measuring apparatus comprising first and second air condensers 5, each of a suitable length, through which ionized contaminated air flows laminarly at a constant speed. Capacitors may have planar or cylindrical electrodes and may have two or more electrodes. In order to provide different electric fields 10 for generating the first and second variable measurement signals in the air stream generated by the suction fan as a function of low and high positive ion concentration, the electrodes of the capacitors are provided with different voltages. The output signals measured through the electrodes of the capacitors affect the inputs of the distribution and sum circuit means, the output providing a final output signal which is the basis for the measurement of air pollution.

The method and apparatus according to the invention provide a decisive improvement over the above methods. To achieve this, the method and apparatus according to the invention are mainly characterized by what is set forth in the characterizing parts of claims 1 and 5.

The main advantage of the invention is that the inaccuracy of the analysis due to the humidity of the air or gas can be eliminated. The reliability of the analysis is improved. Sensitivity is high and response time low. Other organic substances or solvents or tobacco smoke do not interfere with the contaminant analysis.

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In the following, the invention will be explained with reference to the accompanying drawings, in which figures

Figure 1 shows a schematic diagram of a measuring-35 apparatus according to the invention.

Figure 2 shows a schematic diagram of another embodiment of the hardware.

96903 4

Figure 1 shows an apparatus according to the invention. The gas to be analyzed is sucked into the tube 1, filtered by a heated filter 2 and passed to an ionization cell 3, which may be several in parallel or in succession, and which may be e.g. F1 patent 75055 or any other gas ionization gas analyzer, and then the gas is passed a semiconductor cell, which may be several in parallel or in series.

An alternative solution is to place the ionization cells and semiconductor cells from the parallel gas flow, as shown in Figure 2, so that the gas is distributed to both cells / cells for analysis.

In the solution, the semiconductor cell can be any gas sensor based on the reaction between the surface of the semiconductor and the gas, which is in itself based on the prior art. In the apparatus according to the invention, the signals given by all measuring cells 20 are used simultaneously to perform gas analysis, performing calculations and other conclusions from them in order to better separate the gases from each other under different conditions.

The gas is charged, for example, by radiation emitted from an alpha or beta radiation source 4 25. The gas is led to the measuring pipe 5. In the collection field, the field electrodes have voltages Vlf V2, ... Vn. The backplane voltage is VT. In the collection field, the charged light ions of the gas are collected off at the field electrodes Vn. The remaining heavy ions 30 that have reached further in the measuring chamber cause an ionic current In at the electrodes at the edge of the chamber, which is registered. For each value In, where n is an integer, e.g. 1-6, a diagram is formed, the shape of which describes the analyte.

Further, the gas is passed to a semiconductor cell 6 formed of, for example, a tin dioxide (SnO 2) crystal. By changing the mixture, it is made sensitive to various substances, e.g. mustard gas

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96903 5 analyzer. The signals obtained by the above-mentioned method and the semiconductor cell are collected and analyzed together, e.g. in a data processing device 7. The gas to be analyzed together by the semiconductor cell is preferably a gas which, when wet, does not give a signal by the above ionization method but only by semiconductor measurement. An example of such a gas is mustard gas.

10 Tests on gas containing dangerous substances have been carried out at different moisture contents with the ionizer cell and the semiconductor cell installed in series or side by side. The relative humidities were 10, 50 and 90%. The gas flow was directed through the duct by a pump. In Table A, it corresponds to the ionization cell 15 and B to the semiconductor cell.

The following table shows the results of the experiments:

Apparatus, Concentration Moisture Response time 20 which gave a response in mg / m3% s B 0.2 90 1 B 0.2 10 9 B 6 90 12 25 A 6 10 28 B 10 50 9 A 10 10 9

The results show that the presence of mustard gas can be most effectively detected by using a combination of an ionization cell and a semiconductor cell at low concentrations and at all relative humidity concentrations, and especially at moderate and higher humidity concentrations.

We have explained the invention with reference to only one preferred embodiment thereof. The solutions presented above and in the drawings are examples by which it is not intended to limit the invention in any way, but all modifications within the scope of the inventive idea 40 defined by the claims are of course possible.

Claims (5)

96903 A method for detecting the contaminant content of a gas, which method enters the gas into a flow channel (1), where the gas is filtered and heated, after which the gas is directed to measuring cells (3, 6), characterized in that the gas to be analyzed is passed in parallel or in series to at least one ionization and to at least one semiconductor cell (3, 6). 10 Method according to Claim 1, characterized in that the signals from the ionization cells (3) and the semiconductor cells (6) arranged in parallel or in series are used simultaneously to analyze the gas for analyzing the gas under different conditions. A method according to claim 1, characterized in that the gas is charged and led to the flow channel, the light ions of the gas are collected in the collection field, the field currents caused by the heavy ions of the gas are registered. A method according to claim 1, characterized in that the same gas is further directed to the semiconductor cell (6) to determine the presence of a certain substance. Apparatus for detecting the foreign matter content of a gas, the apparatus comprising a flow channel (1, 5) for introducing gas therein, gas filtration and heating devices (2) and measuring cells (3, 6), characterized in that the measuring cells (3) used for analyzing the gas 6) consist of at least one ionization cell and at least one semiconductor cell (3, 6) arranged in parallel or in series. 35 I! 96903