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
• • 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
  • G01N33/0022—General constructional details of gas analysers, e.g. portable test equipment using a number of analysing channels
  • G01N33/0024—General constructional details of gas analysers, e.g. portable test equipment using a number of analysing channels a chemical reaction taking place or a gas being eliminated in one or more channels

Definitions

• the invention relates to an apparatus for detecting the loading of a carrier gas with small concentrations of trace gases, in particular the loading of air with war gases.
• the invention for this purpose uses an apparatus where a gas mixture containing said trace gases flows through a labyrinth cell comprising a radiation source for ionizing the gas molecules, a recombination zone consisting of baffles or similar devices for labyrinth-like increasing the length of the flow path, and a collector electrode at the outlet of said recombination zone.
• An apparatus of this type is known from U.S. patent 38 35 328. Further improvements of this ionization detector are described in U.S. patents 40 57 550, 42 38 6 ⁇ 8 and 43 62 941.
• baffle cells an airstream is generated through the cell by means of a ventilator or a pump.
• an ionization means such as a radiation source is provided and the gas stream flows through a flow path, the length of which is increased in the form of a labyrinth.
• Vithin this labyrinth path most of the ionized carrier gas molecules recombine, whereat the trace gases together with ions of the carrier gas form molecule packets or clusters which do not recombine within said labyrinth. These clusters rather move to the collector electrode and there generate a corresponding electrical current.
• a trace gas detector in particular a LOST detector whose accuracy and reliability is not impaired by internal interference such as non-recombined carrier gas ions or a remainder of water vapor, nor is impaired by external interferences such as temperature changes, changes of the supply voltages or by external electromagnetic radiation.
• the output signals of the first labyrinth cell through which the gas mixture flows and the output signals of the second labyrinth cell through which the filtered gas stream flows are electrically compared by a differential cir ⁇ uit, and where at the output of said differential circuit a signal is available corresponding to the concentration of the trace gas to be detected.
• the labyrinth or baffle cell located in the closed gas loop in front of the filter and/or in front of the drying means delivers an output current which depends on the trace gas to be detected as well as on eventual internal interference influences.
• the baffle cell detector behind the filter and/or the drying means responds only to those interference influences. Forming the difference of the two output signals removes the influence of those internal and external interferences so that the differential output signal depends only on the concentration of the trace gas.
• This problem can be solved in that according to a further improvement of the invention the gas mixture is fed to the closed gas loop via a water vapor barrier such as a silicon diaphragm.
• This closed gas loop then only contains a very small remainder of water vapor which in addition by means of a dryer can be stabilized to a dew point smaller than 30 ⁇ C.
• Such dryer simultaneously works as a filter or can be combined with an active charcoal filter.
• the invention discloses a compact trace gas detector which doesn't need high voltage but can be operated from low voltage batteries. Said detector in view of its small power consumption and small dimensions can be combined with another detector responsive to other war gases, such as nerve agents, into a compact universal detector.
• a suitable nerve agent detector comprising a so-called dynamic grid cell is described in U.S. patent 47 75 795.
• Fig. 1 shows an example for a blister agent detector comprising a closed gas loop in accordance with the invention
• Fig. 2 shows the combination of such detector with two further detectors into a single compact universal war gas detector unit, whereat a second detector comprises a dynamic grid cell for nerve agent detection and the third detector is an electrochemical cell for the detection of shocking agents.
• FIG. 1 shows a closed loop gas channel 1 in which a first baffle cell 2, a pump 3, a filter 4 and a second baffle cell 5 are positioned one behind the other.
• the gas which, has, to be investigated is supplied into this gas channel 1 via a water vapor barrier formed by a diaphragm 6.
• the two baffle cells 2 and 5 may have the structure as known from U.S. patent 38 35 328. Each of them comprises a source electrode 21 and 51, respectively, and a collector electrode 22 and 52, respectively.
• each of the two baffle cells 2 and 5 comprises a radioactive radiation source, e.g.
• junction 9 is connected to the input of preaiu.pl;ifier 7.
• a switch 8 periodically interrupts the differential current and during the current pauses the differential amplifier works with open or grounded input and therewith by means of a control circuit can be automatically adjusted and balanced. All noise or interference caused by temperature changes of the gas or of the measuring apparatus or caused by changes of the supply voltage at the two baffle cells or by changes of the speed of the pump will effect the output signals of both baffle cells in the same sense and amount and therefore are compensated by the difference-forming circuit.
• Both baffle cells 2 and 5 are chosen such that their characteristic values correspond to each other.
• the measuring apparatus may be balanced or adjusted by first feeding the apparatus with a carrier gas which does not comprise any trace gases, and at the output 10 of the amplifier 7 the subsequent measuring circuit is balanced such that it in this case shows a zero output signal (no trace gases).
• the source electrode 21 of the first baffle cell 2 and the collector electrode 52 of the second baffle cell 5 are connected to voltages (-20V and +20V, respectively) of identical amplitude but opposite polarity.
• the combined war gas detector shown in Figure 2 includes in its lower portion the blister agent detector as described above with reference to Figure 1.
• This is a module of the entire detecting apparatus and is coupled to the flow path 40 of a further detector via diaphragm 6.
• This diaphragm 6 is provided between a membrane holder 61 of the blister agent detector and a membrane holder 62 of the second flow path 40.
• the second detector comprises between its gas inlet 41 and the aforementioned membrane holder 62 a second detector module comprising a particle filter 42, a dynamic grid cell 43 and a temperature sensor 44.
• An example of such a second detector responsive to shocking agents is known from U.S. patent 47 75 795.
• the gas flow through the dynamic grid cell 43 is accomplished by a ventilator or a pump 45.
• An electrochemical cell 47 is provided between said pump and the gas outlet 46.
• This electrochemical cell 47 may be used for the detection of shocking agents.
• the structure of this electrochemical cell 47 is not part of this invention.
• the block diagram according to Figure 2 further shows that here three filter modules are combined to a compact war gas detector with these three modules responding to all presently known war gases. None of the ionizing cells 43, 2 and 5 requires a high voltage supply and for detecting the various war gases no chemicals must be supplied, monitored and disposed.
• the principle of the present invention namely using two measuring cells connected via a filter into a closed gas loop and forming the difference of the output signals, cannot only be used for detecting mustard gas or other war agents, but may also be used for detecting other trace gases.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Pathology (AREA)
• Food Science & Technology (AREA)
• Medicinal Chemistry (AREA)
• Immunology (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Combustion & Propulsion (AREA)
• Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
• Glass Compositions (AREA)
• Measurement Of Radiation (AREA)
• Sampling And Sample Adjustment (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

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Citations (5)

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• 1989
  • 1989-02-11 DE DE3904168A patent/DE3904168A1/de active Granted
• 1990
  • 1990-01-10 IL IL93021A patent/IL93021A/xx not_active IP Right Cessation
  • 1990-02-07 US US07/730,957 patent/US5223712A/en not_active Expired - Fee Related
  • 1990-02-07 ES ES199090902220T patent/ES2038514T3/es not_active Expired - Lifetime
  • 1990-02-07 JP JP2502602A patent/JPH03505256A/ja active Pending
  • 1990-02-07 KR KR1019900702236A patent/KR910700455A/ko not_active Ceased
  • 1990-02-07 DK DK90902220.4T patent/DK0457776T3/da active
  • 1990-02-07 AT AT90902220T patent/ATE85125T1/de not_active IP Right Cessation
  • 1990-02-07 DE DE9090902220T patent/DE69000832T2/de not_active Expired - Fee Related
  • 1990-02-07 CA CA002046329A patent/CA2046329A1/en not_active Abandoned
  • 1990-02-07 EP EP90902220A patent/EP0457776B1/en not_active Expired - Lifetime
  • 1990-02-07 WO PCT/EP1990/000195 patent/WO1990009586A1/en not_active Ceased
• 1991
  • 1991-08-08 FI FI913762A patent/FI94466C/fi not_active IP Right Cessation

Patent Citations (5)

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