Abstract:
The method of the invention uses a spectrophotometric and/or ionisation detection device in which the gas to be analyzed and illuminated by a light source emitting in a range of wavelengths distinct from the one used for spectrophotometry so as to carry out a nephelometric and/or turbidimetric detection. The results of this detection are used to carry out an adjustment of the device for counting the particles and/or for determining the composition of these particles.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention concerns a device for counting and analysing particles or aerosols suspended in air.  
           [0003]    2. Description of the Prior Art  
           [0004]    Advantageously not but exclusively, it combines in a device for analysing a gas composition by means of flame spectrophotometry, for example of the type described in the patent FR No. 98 00761 filed in the name of the Applicant.  
           [0005]    Generally speaking, it is known that flame spectrophotometry is a method consisting of conducting a spectrographic analysis of the radiation produced by the flame of a gas mixture including the elements to be analysed and an oxidant gas, such as hydrogen. This analysis is effected by isolating the characteristic radiations of the sought-after elements and by measuring these radiations by photometric means.  
           [0006]    So as to be able to apply this method to certain elements which do not generate any characteristic light emission, it is necessary to provoke prior to combustion a reaction of these elements with a reactive element so as to obtain a compound producing an identifiable and detectable light emission.  
           [0007]    This prior reaction can be effected out by carrying out a first combustion in the presence of a reactive agent.  
           [0008]    The gas mixture derived from this first combustion is subjected to a second combustion which produces a light emission for which the spectrophotometric analysis is also carried out.  
           [0009]    This spectrophotometric detection can be associated with a detection of ionisation of the flame by means of electrodes placed in the combustion chamber of the burner. These electrodes are connected to an electronic circuit for measuring the conductivity of the zone where combustion occurs.  
           [0010]    This measurement makes it possible to detect the presence of combustible constituents in the sample and in particular organic materials: the combustion of this organic material in fact produces between the measuring electrodes an ionisation current in relation with the organic material concentration.  
           [0011]    The information delivered by the spectrophotometric assembly and detection of ionisation can be sent to a processor programmed so as to interpret this information and deduce from it sought-after element concentrations, whether they be compounds, chemical substances or even biological substances (bacteria).  
           [0012]    In fact, in the case where the gas sample to be analysed contains suspended particles, these particles on burning generate light impulses (flash) of limited period which it is possible to count so as to obtain the number of particles per unit of gas volume to be analysed.  
         OBJECT OF THE INVENTION  
         [0013]    More particularly, the object of the invention is to improve the results of these analyses and countings by extending as much as possible the range of biological substances able to be analysed.  
         SUMMARY OF THE INVENTION  
         [0014]    To this effect, it concerns illuminating the gas current entering the ionisation and/or spectrophotometric detection device with the aid of a light source emitting according to range of wavelengths not used by the spectrophotometric detector and carry out a nephelometric and/or turbidimetric detection of the illuminated gas stream.  
           [0015]    Advantageously, the spectrophotometric detector shall be designed so that the illuminated gas streams flows into the axis of the burner and of the detection optics of the spectrophotometer.  
           [0016]    In this case, the light source shall be centered perpendicular to the flow axis of the gas stream: nephelometric detection could use the optics, even indeed the detector of the device carrying out the spectrophotometric measurements.  
           [0017]    It is clear that by means of these arrangements, the nephelometric and/or turbidimetric detection makes it possible to detect the presence and size of the particles and/or characteristics able to help in identifying them.  
           [0018]    This information is sent to a processor used to carry out adjustments of the spectrophotometer and to process the information detected so as to determine the sought-after element concentrations.  
           [0019]    In the presence of a particle selected according to is size, the processor could carry out the required adjustments so as to obtain a maximum of precision during analysis of the luminous radiation produced during moving of this particle into the flame.  
           [0020]    Of course, this double detection makes it possible to refine the statistical readings and the deductions which are required to identify the particle.  
           [0021]    In particular, this double detection makes it possible to distinguish the humid particles from the dry particles. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    There follows a non-restrictive example of an embodiment of the invention with reference to the accompanying drawings on which:  
         [0023]    The sole FIGURE is a skeleton diagram of an analysis device combining flame ionisation, spectrophotometric and turbidimetric measurements and possibly fluorescence measurements.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    In this example, the analysis device includes a tubular burner  1  including a tubular nozzle  2  connected on one side to an intake pipe  3  for the gas to be analysed, and on the other side and coaxially to this nozzle  2 .  
         [0025]    A first tubular sleeve  4  having a diameter slightly large than that of the nozzle  2  and axially offset with respect to the latter so as to firstly delimit with the nozzle  2  a first annular intake chamber  5  connected to a hydrogen injection circuit  6  originating from a source  7 , and secondly beyond the first nozzle  2  a combustion chamber  8  in which the partial combustion of the gas to be analysed and the hydrogen generates a first flame F 1 : this first tubular sleeve  4  is closed on side on the nozzle  2  and opens on the other side into a second combustion chamber  9 .  
         [0026]    A second tubular sleeve  10  having a diameter larger than that of the first tubular sleeve  4  and delimiting with the latter a second annular intake chamber  11  connected to a circuit  12  for admitting a gas or oxidant gas mixture, such as air; this second sleeve  10  closes on one side on the nozzle  2  and/or on the first sleeve  4  and delimits on the other side beyond the latter the second combustion chamber  9  in which a postcombustion in an oxidant environment of the gases originating from the first combustion chamber  8  and from the intake chamber  11 .  
         [0027]    an annular electrode  14  having an approximately inverted C-shaped section rendered integral via its face of larger diameter  15  with the second sleeve  10  and whose face of smaller diameter  16  having an axial length smaller than that of the face  15  delimits an outlet pipe S of the combustion chamber  9 : beyond the electrode  14  (on the side opposite the sleeve  4 ), the sleeve  11  includes a lateral orifice  17  into which opens is an exhaust pipe fitted with a turbine activated by a motor;  
         [0028]    forcussing optics  19 , such as a lens mounted in the circular opening of a cover closing the sleeve  10  on the side opposite the nozzle  2 , these focussing optics  19  being designed to focus the light radiation emitted in the two combustion chamber  8 ,  9 , in particular the first chamber  8  on the inlet orifice of a spectrophotometric mounting  20 .  
         [0029]    In this example, the tubular sleeve  4  is made of an electrically conductive material and constitutes a second electrode which cooperates with the electrode  14  so as to allow measurement of the conductivity of the zone of the second chamber  9  in which the second flame extends (flame F 2 ).  
         [0030]    These two electrodes are electrically connected to resistor measurement means  21  which include a voltage source  22  mounted in series with a voltmeter  23 , this unit being shunted by a resistor  24 .  
         [0031]    The information delivered by the spectrophotometric mounting  20  and the voltmeter  23  are transmitted to processor/display  25  unit programmed to determine the concentration of elements and or sought-after substances of the gas sample brought be the nozzle  2 .  
         [0032]    As previously mentioned, the external surface of the sleeve  4  could be covered by a coating  26  made of a suitable material for omitting a reactive gas at the temperature to which this sleeve  4  is brought under the effect of the combustion generated in the first combustion chamber  8 . By way of example, this reactive material could consist of indium, the corresponding sought-after elements then being chlorine.  
         [0033]    In this case, burner could include a third tubular coaxial sleeve  30  extending into the intercalated space between the sleeves  4  et  10 . This third sleeve  30  delimits with the sleeve  4  an annular chamber opening into the second combustion chamber  9  and used for admitting into this chamber  9  of hydrogen current derived from the source  7 . To this effect, the annular chamber  31  is connected to the source  7  by means of an intake circuit  32  controlled by a valve  33 .  
         [0034]    The functioning of the previously described burner is as follows:  
         [0035]    Both of the two chambers  8 ,  9  are placed in a partial vacuum by the turbine  18  so as to provoke a sucking up of the gas to be taken from the nozzle  2  through another nozzle provided in the intake circuit  3   
         [0036]    Inside the sleeve  4 , the gas stream (for example air) mixes with the hydrogen current injected by the intake chamber  5  in such a proportion that the combustion produced in the first combustion chamber  8  reduces. The light radiation generated by the flame F 1  present in the first chamber  8  makes it possible to detect by means of the spectrophotometric mounting  20  compounds, such as phosphorous and sulphur, and deduce from these the presence of the sought-after elements.  
         [0037]    The temperature generated by this combustion provokes heating of the sleeve  4  and thus of the coating  26 .  
         [0038]    When its vaporisation temperature is reached or exceeded, this coating  26  emits a reactive vapour which mixes with the hydrogen flow injected by the intake chamber  31  and with the air derived from the intake chamber  11 .  
         [0039]    On leaving these chamber  11  and  31 , the gas mixture reacts (oxidant combustion) with the gas stream resulting from the partial combustion produced in the chamber  8  so as to produce a flame F 2  which emits a light characteristic of a component, such as chlorine, which has reacted with the reactive indium vapour. This light, just like the one produced in the chamber  8 , shall be focussed by the lens  19  at the inlet of the spectrophotometric mounting  20 .  
         [0040]    The information delivered by the mounting  20  and the ammeter  23  (which are representative of conductivity variations of the flame (ionisation) present in the second combustion chamber) are sent to the processor  25  which is programmed so as to interpret this information and deduce from this concentrations of sought-after elements, whether these be compounds, chemical substances or even biological substances (bacteria).  
         [0041]    Of course, in the case where the gas sample to be analysed contains suspended particles (for example bacteria or dust), these particles on burning generate light impulses (flash) of limited period which are possible to count so as to obtain the number of particles per unit of gas volume to be analysed.  
         [0042]    In accordance with the invention, the intake pipe  3  for the gas to be analysed includes a transparent portion  35 , made for example of glass or quartz, and preferably having a square or rectangular section so as to have two parallel plane faces  36 ,  37 .  
         [0043]    The face  36  of this transparent portion is illuminated in normal incidence by a light source  38  centered perpendicular to the path of the stream of the gas to be analysed and thus coaxially to the burner and focussing optics  19 .  
         [0044]    Opposite the source  38  in relation to the transparent portion, an optical sensor  39  is placed and connected to the processor  25 . This optional sensor  39  is used for carrying out a turbidimetric of the gas stream.  
         [0045]    By means of the special characteristics of the burner and due to the fact of its passage into the transparent portion  35 , the gas stream is located in the axis of the focussing optics  19 , the spectrophotometric mounting being used to carry out a nephelometric measurement of this gas stream (detection of the light diffused by the particles present in the illuminated gas stream).  
         [0046]    To this effect, the wavelength of the radiation emitted by the source  38  is selected (here close to the infrared spectrum) so as to avoid disturbing the photometric measurement carried out be the mounting  20 .  
         [0047]    The nephelometric analysis gives an estimate of the light diffused by the particles present in the gas flow. It makes it possible to determine low concentrations of substances by means of measurements of variation of the amount of light.  
         [0048]    The turbidimetric analysis is able to provide a measurement best adapted when the gas to be analysed carries a large number of particles.  
         [0049]    It is clear that the combining of these measurements makes it possible to determine the parameters (size, weight, humidity . . . ) so as to classify the particles, even before analysing them by means of spectrophotometry.  
         [0050]    These two analyses can be possible completed by a fluorescence measurement. In this case, a light source is used functioning in pulsed mode.  
         [0051]    The spectrophotometric mounting associated with the burner could possibly be designed so as to carry out in addition the fluorescence spectroscopic examination of the gas flow upstream of the burner.  
         [0052]    Of course, the microprocessor  25  shall be programmed so as to make use of the results of all these analyses.