Abstract:
A measuring technique and method are provided to simultaneously determine the molecular density of several molecular species and the temperature within a closed process room in a melting or combustion process. In such processes in the industry, e.g. in metallurgic process industry, it is important to determine the temperature and the contents within the gas or flame without physically connect to or disturb the process. This has shown to raise large problems especially at high temperatures. The radio signal over a frequency band is measured on the outside of the process room through a window in the mantel covering as a function of frequency and registered on a computer as a radio spectrum. The system is calibrated by using a known signal transmitted through the process room. The spectral lines are identified by their frequency from a database. The temperature is determined from several lines of the same molecular specie and the molecular densities are determined from the intensities of the lines. The method is suitable to determine vibrational and rotational excitation of molecular species in the radio wavelength range of 30μm to 500 m. The densities of molecular species and the temperature can be imaged in three dimensions inside the process room or exhaust channel if interferometers are used for simultaneous two dimensional imaging from several azimuth directions.

Description:
This is a divisional, of U.S. Ser. No. 08/510,444, filed on Aug. 2, 1995, now, U.S. Pat. No. 5,829,877, which claims continuation-in-part status from International Appln. No. PCT/SE94/00100, filed Feb. 3, 1994 and which claims priority from Swedish Patent Appln. No. 9300347-3, filed Feb. 3, 1993. 
     International Application No. PCT/SE94/00100 was pending as of the filing date of the present U.S. application and the U.S. was an elected state in the International Application No. PCT/SE94/00100. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a method for measuring temperature, molecular densities and molecullar coniposition or any combination thereof, in gases and/or flames in melting and/or combustion processes. 
     BACKGROUND OF THE INVENTION 
     Conventional gas analysis methods using IR-paramagnetic and mass spectrometer technology need a physical contact with the gas to be analysed. This means that the gas has to be cooled before entering the analyzer which may affect the results of the measurements. Another disadvantage with conventional gas analyzers is that they can not simultaneously measure the temperature of the gas and analyze the gas. 
     It is known that the attenuation of a continuum radio signal can be used to recover the amount of black smoke in exhaust fumes, JP 60-64234. This patent method does not determine any molecular content, nor does it determine any temperature. 
     It is also known that the changes in the refractive index of flying ash can be used to determine the carbon content therein, WO 90/03568. This patent method does not distinguish between molecular species and does not measure any spectral lines or determine molecular densities, configuration, or temperature. 
     It is also known that attenuation and reflection in the exhaust fumes from a reaction engine can be used to determine changes in the exhaust fume composition, WO 90/03568. This method does not determine any molecular species or temperature. 
     It is also known that the existence of a specific molecular specie can be decided if the molecular gas is first mixed with a drive gas and then injected into a cavity chamber, patent U.S. Pat. No. 5,124,653. The cavity is then adjusted to the wavelength of the molecular transition and the molecular gas is excited by injecting a radio signal. The radio transmitter is then turned off and the molecule will emit at its specific frequency if it is present. This method measures a single molecular line at the time and can only detect the molecular species for which it is specifically adjusted. This method does not measure the temperature or the molecular density within the process since the molecular gas has to be taken out of the process-room to the special cavity and the gas is also contaminated with a drive gas. 
     None of the above patents discloses, discusses, or makes possible the simultaneous determination of a multiple of molecular lines and species or can determine molecular densities and temperature in a working melting process or combustion process without any interaction with the gas flow. 
     Changes in the pattern of electromagnetic wave fronts represent the most sensitive probes in physics. Electromagnetic waves may penetrate media of varying physical properties, clanging its amplitude and phase in a way which is specific to the content of the media. Thus molecular gas will emit or absorb electromagnetic radiation mainly depending on its density, the physical temperature, or the radiation field in the area where the gas resides. Continuum radiation will also be affected when penetrating a media in the sense that the amplitude will be attenuated and the propagation velocity will change, resulting in a sudden change of phase in the interface area. The radioband is of particular interest in that here waves can penetrate deeper into dusty areas and also detect and measure complicated molecules by their rotational transitions. 
     OBJECT OF THE INVENTION 
     It is an object of the invention to provide an accurate and reliable method to analyze a gas and to determine the temperature of a gas directly in an industrial process without physical contact with the gas that is being analyzed and without disturbing the gas and the process. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described more closely with reference to the drawings. 
     FIG. 1 shows an experimental set up. 
     FIG. 2 shows schematically a more sophisticated apparatus. 
     FIG. 3 is a top view of the apparatus in FIG. 2. 
     FIG. 4 is a representation of a spectrum observed in the radio band of 20-40 GHz in a chimney. 
     FIG. 5 illustrates the determination of gaseous components from the radio band spectrum. 
     FIG. 6 is a flow diagram illustrating the sequence of steps performed by a computer program &#34;MOLTOM5&#34; set forth hereinbelow. 
     FIG. 7 shows schematically an exhaust channel. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Each molecular species has its own fingerprint in the form of a spectrum of lines, in the radio domain mainly determined by the quantified transitions between vibrational- and/or rotational states. Molecular lines in the atmosphere are very much broadened due to the relatively high pressure. The most significant exception is if the molecular flow is highly directive, e.g. if we are looking through the flow at an angle perpendicular to that of the flow. In that case the pressure broadening will be much less and molecular lines can be well separated. This exception is the case for the gas flow in chimneys or through the gas flow from any burning process if viewed across the flow. 
     The invention can be best described with an experimental set-up shown in FIG. 1. Here a chimney (11) is made out of ceramic material, chrome-magnesite and charmotte, and covered with steel. The chimney has an opening (12) for an oil burner. The steel cover has two opposite windows (13), with intact ceramic material. Outside the windows (13) and in line with the windows are two parabolic antennas (14,15). One or the parabola is connected to a transmitter (16) and the other parabola (15) is connected to a receiver (17). The transmitter consists of a signal generator which is stepped in frequency over a wide frequency band. The received signal is compared with the transmitted signal in a cross-correlator (18) connected to a computer (19). 
     The received signal consists of a number of spectral lines emitted from the gas inside the chimney overlaid on the background transmitted signal. The transmitted signal is used to calibrate the frequency response of the system and the attenuation through the chimney walls by looking at the received signal between the molecular lines. This baseline will then be subtracted from the received signal and the intensities of the molecular spectral lines can be determined as calibrated inside the chimney. 
     The system is further calibrated by measuring the signal transmitted through the chimney as a function or frequency when the chimney is empty. 
     The registered spectrum is stored in a computer. A database is searched for known lines which coincide in frequency with maxima within the observed spectrum. Thereafter a Gaussian model fit is made to the line in order to determine the amplitude, frequency, anti line width, A line is considered to be detected if the amplitude of the Gaussian fitted line is more than three times the calculated noise level. The measured amplitudes are then calibrated to an absolute temperature scale. 
     If a number of lines from the same molecular specie can be detected, then the relative population of the various energy levels may be determined. This relation is mainly determined by the physical temperature of the gas and the density of the molecular specie as: N u  /g u  =N rot  /Q(T rot ) e -Eu/T  rot where N u  is the number of molecules in the upper energy level of the transition), g u  is the statistical weight of the transition, E u  is the energy of the upper energy level in Kelvin, Q is the rotational constant. T rot  is physical temperature, in the case of burning processes where the excitation is dominated by collisions due to the high temperature, and N rot  is the column density of the molecules of this particular specie. N u  /g u  is directly proportional to the intensity integrated over the spectral line and can therefore be measured. If a number of spectral lines from a molecule arc available, then both the density (if the path length is known) and the physical temperature (if the molecule is predominantly collision excited) can be determined simultaneously. If lines from other molecules are also present, then also the densities of these molecules may be measured from the intensity of a single molecular line. 
     The radio antenna can also consist of an interferometer where the elements are radio horn antennas mounted in plane (31,32) and with properly adjusted delay lines as shown in FIG. 2. Then the two dimensional distribution of molecular densities and temperature can be reconstructed by transforming from the aperture (u,v) plane to the image plane. 
     If then the system consists of interferometer (32) which are looking into the process room (35) or exhaust channel (100) from different angles as is shown in FIG. 3, then the densities and the temperature may also be recovered in three dimensions by a Radon transform, similar to what is used in computer tomography. Such a system can recover the temperature distribution in three dimensions within a hot gas (or a flame). It can also, which will be more important, simultaneously recover the three dimensional density distribution of each detectable molecular specie. These measurements are also performed without any physical probe since the radio signal may, as indeed was the case in our pilot experiment, that will be described penetrate through the ceramic wall of the chimney. 
     In the apparatus shown in FIG. 2, an experiment was carried out. An oxy/oil burner was installed and was burning in a steady state. 
     FIG. 4 shows the spectrum observed in the radioband 20-40 GHz through the flow in the chimney. Most of these lines come from SO 2 , some others from NH 3  and other molecules. It is therefore clearly possible to detect molecules within the radioband in gas flows on earth. As a consequence it is then also possible to make images of such a flow. FIG. 5 shows the identifications of some of the lines from one observation. Using SO 2  as a tracer it was possible to determine the temperature as well as the density of SO 2  as function of time. 
     An actual working example of the invention has been carried out, wherein, referring to FIG. 1, the following components were employed: 
     
         ______________________________________12  opening for oil-burner13  window through steel cover                Chrome-magnesite and Chamotte14  transmitting antenna                1.2 m diameter offset parabola                from Parabolic AB    rectangular feed horn                Quasar Technology for 26-40                Ghz band    converter waveguide to                Quasar Technology for 26-30    coaxial cable    GHz band15  receiving antenna                1.2 m diameter offset parabola                from Parabolic AB    rectangular feed horn                Quasar Technology for 26-40                Ghz band    converter waveguide to                Quasar Technology for 26-30    coaxial cable    Ghz band16  signal generator Wiltron System Signal Source                type 360SS6917  receiver         Wiltron Active Device Test Set                type 3621A18  data acquisition Wiltron Vector Network                Analyser type 360B19  data storage     PC computer with GPIB                Interface______________________________________ 
    
     Addresses for these companies are as follows: 
     Quasar Microwave Technology Ltd 
     Battle Road, Heathfield, Newton Abbot Devon TQ12 6XU 
     United Kingdom 
     Wiltron Company 
     490 Jarvis Drive 
     Morgan Hill, Calif. 95037-2809 
     USA 
     Parabolic AB 
     Box 10257 
     S-434 23 Kungsbacka 
     SWEDEN 
     As for the inter-unit connections, the radio frequency output of the transmitter 16 is connected to a power divider type Wiltron K24OC with a steel semirigid coaxial cable of 30 cm in length. The two output signals from the power divider are connected to the transmitting antenna 14 and the receiver 17 with steel coaxial cables. The other radio frequency port of the receiver 17 is connected to the receiving antenna 15. The data acquisition system 18 is connected to the transmitter 16 and the receiver 17 via GPIB bus cables. The computer 19 is also connected using a GPIB interface. 
     The data acquisition unit 18, i.e., the Vector Network Analyser, was set to step in 501 frequency steps between 30 and 40 Ghz and the division of the amplitudes of the received signal and the reference signal from the transmitter were stored for each frequency channel. A total integration time of 10 secs. was used for each frequency spectrum. 
     The data was stored on computer discs and each spectrum was then analyzed off line with a special computer program. A theoretical description of the analysis of molecular densities and temperatures can be found in &#34;Microwave Spectroscopy&#34;: C. H. Townes and A. L. Schawlow, Dover Publications Inc. New York, ISBN 0-486-61798-X, which publication is hereby expressly incorporated by reference herein. 
     The computer program used is referred to internally as &#34;MOLTOM5&#34; and is illustrated in the form of a flow diagram shown in FIG. 6. 
     The actual computer program &#34;MOLTOM5&#34; is set forth immediately below. &#34;MOLTOM5&#34; and another computer program referred to internally as &#34;SLAGG&#34; make subroutine calls to four commercially available software packages. [The computer program &#34;SLAGG&#34; is more particularly utilized in conjunction with the invention disclosed in published International Application No. PCT/SE94/00099 (which corresponds to Swedish Patent Application No. 9300348-1).] These four commercially available software packages are: 
     PGPLOT from Dr. Tim Pearson, California Institute of Technology, Pasadena, Calif.; 
     LMSTR1 and GETERR from the Astronomical Image Processing System (AIPS) of National Radio Astronomy Observatory (NRAO), Socorro, New Mexico; and 
     SVDFIT from Numerical Recipes, Press, Flannery, Teukolsky and Vetterling, Cambridge University Press, isbn 0 521 30811 9. 
     Each of the four commercial software packages referred to immediately above is hereby expressly incorporated by reference herein. 
     The &#34;MOLTOM5&#34; computer program used in the above-described working example is as follows: 
     
         __________________________________________________________________________  INTEGER IS,PGBEGIN  integer*2 status, dummy  character*15 frame1, frame2, frame3  character*128 record  character*80 title  character*16 mol  REAL*4 FR1(512), AMP1(512), PH1(512)  REAL*4 FR2(512), AMP2(512), PH2(512)  REAL*4 FR3(512), AMP3(512), PH3(512)  REAL*4 FR4(1024), AMP4(1024), x1(2), y1(2)  REAL*4 xmin, xmax, ymin, ymax, fleal, flmag, *   tpl, x, ampsum, xnv(2), xv(2), xnvl(2), xnvh(2)  integer gfunc, lpvl(12)  external glunc  REAL*4 xb(2), yb(2)  real*8 data(1024), xtr(1024), enorm, dpar  real*8 palms(12), ljac(12, 12), work(2148), *    lvec(2048), tol, sparms(12), tnormREAL *4 X01(500), Y01(500)INTEGER NP01c***********************************************************************integer      pd, CDAT, DMAX, NWMAXc    parameter    (CDAT=2048, DMAX=21, NWMAX=10)c    real u(CDAT+1, DMAX+1), V(DMAX+1, DMAX+1), w(DMAX+1)REAL SIGM(500)real     A01(DMAX)REAL   A(DMAX), B(DMAX)clogical  accept, skipc  common/gdata/data, xfrC  data clight/299792.0e0/---------------------------------------------------------------CC  ler=pgbegin(0, `/MSOFT`, 1, 1)  open(unit=22, file=`lbb\moltom, lit`)  open(unit=18, file=`lbb\moltom7.prm`)  open(unit=23, file=`lbb\moltom.tlm`)C   write(6,*)`Input file name:`900 read(18, `(A)`, END=999) fname tIF(Iname1(1:4).sq.`slop`) goto 999C   write(6,*) `Input ref. file name:`OPEN(UNIT=17, FILE=Iname1)100 lead(17,2000) recordIf(record(1:9).ne.`FREQUENCY`) goto 100c  write(6, `(A)`) record(1:30)tpl=2.0*3.1415265350d0xmin=999999999.99xmin=-xminymin=xminymax=-yminIN=01  read(17,2000, end=10, err=1) record  record(42:43)=` `2000    formal(A)Ind=Index(record, `m`)If(Ind.gt.0) record(ind:ind)=` `read(record, 1000, err=1, end=1) lS, X, Y, Z1000    FORMAT(13,3F15.0)If(is.it.1) goto 1IN=IN+1FR1(IN)=XAMP1(IN)=Y*10.0e0PH1(IN)=Z*lpl/360.0e0c   write(6,*) ln, ls, x, y, zIf(1S.eq.501) goto 10GOTO 1 10 CONTINUEclose(unit=17)do l=1.501If(xmin.gt.fr1)(i)) xmln=fr1(1)If(xmax.lt,fr1(1)) xmax=fr1(1)If(ymin.gt.amp1(1)) ymin=amp1(1)If(ymax.lt.amp1(1)) ymax=amp1(i)enddoif(xmin.lt.29.99) goto 900ymin=0.0ymax=120.0c   xmin=30.0c   xmax=40.0c   write(6,*) xmin, xmax, ymin, ymaxc   call pgsls(1)c   CALL PGSLW(5)call pgscl(1)CALL PGENV(XMIN, XMAX, YMIN, YMAX, 0, 0)call pgsci(3)CALL PGLINE(501, FR1, AMP1)open(unit-21, file=`lbb\moltom.dat`)write(22, `(A)`) fname1(1:16)il0=04  read(21, `(110.3), A, 2110.3)`, end=40) xx, mol, eu, sui  If(xx.it.1.0) goto 40  x1(1)=xx  x1(2)=xx  do 1=1.501df=abs(lri(i)-xx)If(df.it.0.02) then1x-1endifenddoyynax=ampi(ix)ii=1x-2jjx=1xdo jx=1, 3ii=11+1If(abs(amp1(ii)).gl.abs(yynax)) thenyynax=amp1(ii)jjx=iiendifenddoc   write(6,*) ix, jjx, yynax, amp1(ix), amp1(jjx)ix=jjxxstr=fr1(1x-2)xstp=fr1(1x+2)parms(1)=amp1(1x)C   If(dabs(parms(1)).it.0.02) goto 4C   xsgn=1.0C   If(parms(1).it.0.0) thenC     xsgn=-1.0C     parms(1)=-parms(1)C   endifparms(2)=fr1(1x)parms(3)=0.020jj=0do 1=1.501If(Ir1(1).ge.xstr.and.fr1(1).le.xstp) thenjj=jj+1data(jj)=amp1(1)If(yynax.gl.0.0.and.amp1(1).it.0.0) then   data(jj)=0.0d0else if(yynax.it.0.0.and.amp1(1).gt.0.0) then   data(jj)=0.0d0endifC       If(xsgn.it.0.0) thenC         data(jj)=-data(jj)C       endifxfr(jj)=fr1(1)endifenddoC   write(6,*) If.parms(1), parms(2), parms(3)do jjk=1,3lol=1.0d-5call lmstr1(gfunc, jj, 3, parms, fvec, fjac, 12, tol, info,         lpvt, work, 2108)enddoinpnts=jjfnorm=enorm(inpnts, ivec)call getorr(1, lpvt, ijac, eparms, 3, jj, 12, lnorm, work, lol)C   eparms(2)=eparms(2)*3.0d0C   eparms(3)=eparms(3)*3.0d0dpar=parms(1)/eparms(1)C   parms(1)=xsgn*parms(1)dfr=xx.parms(2)dfr=abs(dir)if(dpar.ge.3.0d0.and.dir.it.0.2) thenc   if(dpar.ge.3.0d0.and.dir.it.0.02) thenIf(eu.gt.0.0) then   xeu=eu*1.440e0c         dp=1.0e0   dp=2.0e0*parms(3)*1.06/parms(2)*clight*1.67c         dp=dp*dp   xnu=log(parms(1)*dp/parms(2)/sul/1.634/1.634)c         xnu=log(parms(1)/parms(2)/sul)   110=110+1   x01(110)-xeu   y01(110)=xnu   slgm(110)= *            (log((parms(1)+eparms(1))*dp/ *                parms(2)/sul/1.634/1.634)- *            log((parms(1)-eparms(1))*dp/ *                parms(2)/sul/1.634/1.634))/4.0e0elsexeu=0.0e0xnu=0.0e0endifwrite(22,3331) mol(1:8), xx, yynax, parms(1), eparms(1), parms(2), *              eparms(2), parms(3), eparms(3), xnu, xeux1(1)=parms(2)x1(2)=parms(2)y1(1)=yminy1(2)=0.80*ymaxif(eu.gt.0.0) thenc     call pgsls(2)c     CALL PGSLW(1)call pgscf(2)call pgline(2, x1, y1)endifx1(1)=xxx1(2)=xxy1(1)=0.80*ymaxy1(2)=0.03*ymaxc     call pgsls(1)c     CALL PGSLW(3)call pgscl(6)call pgline(2, x1, y1)y1(1)=0.84*ymaxcall pgsci(2)call pgptext(x1(1), yl(1), 90.0, 0.0, mol)endif3331  formal(A, 2x, F12.5, 18.2, 18.2, `+/-`, 17.2, 115.5, `+/-`, 110.5,       4112.5)Cgoto 4 40 CLOSE(UNIT=21)np01=110a01(1)=0.0a01(2)=0.5pd=2mp=cdat+1np=dmax+1CALL SVDFIT(X01, Y01, SIGM, NP01, A01, PD, U, V, W, MP, NP, CHISQ)trol=-1.0e0/a01(2)xlol=exp(a01(1))*6916.978*((trol/300.0e0)**1.50e0)*1.0e+14xlol2=a01(1)write(22,*)`next`, trol, xlol, xlol2write(23,*) fname1(1:16), trol, xlolwrite(title,2222) fname1(1:15), trot, xlol2222  format(A,`Trol=`, 18.0, `Kelvin`,`N(SO\d2\u)=`, e12.4, *      *cm\U-2\d`)call pgscl(1)CALL PGLABEL(`frequency (GHz)`, `amplitude`, title)GOTO 900 999    CALL PGENDwrite(22,*) `slop`close(unit=22)close(unit=23)C  STOP  END  SUBROUTINE GFUNC (M, N, parms, FVEC, fjrow, IFLAG)C                 Variables used as adjustableC                 array dimension specifiersC                 should be declared simply asC                 INTEGERINTEGER M, N, LDFJAC, lflagREAL*8 parms(N), FVEC(M), fjrow(N), xreal*8 data(1024), amp, pos, sig, xfr(1024), res2, tslg2, elactcommon/gdata/data, xlrCC     If IFLAG = 1 calculate the functions at X andC     return this vector in FVEC. Do not alter FJAC.(If(lflag.gf.f) goto 100do ldata=1, mamp=parms(1)pos=parms(2)slg=parms(3)c       slg=0.0250res2=2.772d0*(xlt(ldata)-pos)**2tslg2=sig**2fvec(idata)=data(ldata)-amp*dexp(-1.d0*res2/tslg2)enddogoto 999C     If IFLAG = 2 calculate the Jacobian at X andC     return this matrix in FJAC. Do not alter FVEC. 100   continue  x=xfr(iflag-1) amp=parms(1) pos=parms(2) slg=parms(3)c       slg=0.0250res2=2.772d0*(x-pos)**2tslg2=slg**2elact=dexp(-1.d0*res2/tslg2)fjrow(1)=efactfjrow(2)=-5.544d0*amp`efact*(x-pos)/(slg*slg)fjrow(3)=-2.d0*amp*efact*res2/(slg**3) 999  continueCRETURNEND__________________________________________________________________________ 
    
     FIG. 6 illustrates in the form of a flow diagram the sequence of steps carried out by the above computer program &#34;MOLTOM5&#34;. 
     FIG. 7 shows an exhaust channel 100, in which exhaust channel 100, the temperature of at least one of gases and flames can be measured by an arrangement similar to the arrangement for measuring temperature illustrated in FIG. 1. 
     The published PCT application to which the present U.S. application corresponds, namely PCT/SE94/00100, the published Swedish application from which it claims priority SE 9300347-3, as well as all documents cited in the International Search Report issued thereon, including U.S. Pat. No. 5,124,653 issued to Andresen et al. on Jun. 23, 1992, U.S. Pat. No. 4,693,614 issued to Hatono et al. on Sep. 15, 1987, U.S. Pat. No. 4,438,069 issued to Peterman et al. on Mar. 20, 1984 and Great Britain Patent 2030414 (and its U.S. counterpart, U.S. Pat. No. 4,275,787, issued on Jun. 30, 1981), are hereby expressly incorporated by reference as if set forth in their entirety herein. Additionally, published PCT application PCT/SE94/00100 is directed to similar subject matter disclosed in published PCT application PCT/SE94/00099, which PCT application, the published Swedish application from which it claims Priority, SE 9300348-1, together with all documents cited in the International Search Report issued thereon, namely U.S. Pat. No. 4,737,791 issued to Jean et al., U.S. Pat. No. 5,115,242 issued to Nagamune et al., German Auslegeschrift 28 12 871 (and its U.S. counterpart, U.S. Pat. No. 4,210,023, issued on Jul. 1, 1980) and European Patent No. 0060597 (and its U.S. counterpart, U.S. Pat. No. 4,458,530, issued on Jul. 10, 1984), are also hereby expressly incorporated by reference into the present application. 
     One feature of the invention resides broadly in a method for measuring temperature, molecular composition or molecular densities or any combination thereof in gases and/or flames in melting and/or combustion processes, characterized in that it comprises measuring electromagnetic radiation in the radio range defined as wavelengths between 500 m and 30 μm with a radio antenna positioned outside a process room and/or exhaust channel, performing the measurements during a continuous melting and/or combustion process, and measuring spectral lines emitted by the high temperature collision excited molecules, and absorbed from a background signal when the population of energy levels for the collision excited molecule permits this. 
     Another feature of the invention resides broadly in a method characterized in that molecular species are identified from the measured spectrum by comparing the detected spectral lines with molecular lines from an identification data base. 
     Yet another feature of the invention resides broadly in a method characterized in that the temperature is measured inside the process room and/or exhaust channel by measuring the relative intensities of several lines from the same molecular specie and comparing with a theoretical relation calculated for the expected population of energy levels as a function of temperature. 
     Still another feature of the invention resides broadly in a method characterized in that the density of the molecular species are determined by measuring the absolute intensity of a spectral line from that specie and compare with the theoretically expected intensity for the already determined temperature. 
     Another feature of the invention resides broadly in a method characterized in that the electromagnetic radiation is measured in narrow frequency channels resulting in a frequency spectrum which is compared with a known reference signal and is calibrated against the back of the process room and/or exhaust channel transmitted copy of the reference signal. 
     Yet another feature of the invention resides broadly in a method characterized in that the reference and background signal is created in steps of narrow frequency channels by stepping a signal generator in frequency. 
     Still another feature of the invention resides broadly in a method characterized in that the receiving antenna is an interferometer and that the two dimensional distribution of densities and temperature are reconstructed from the cross correlation of the signal of the individual interferometer elements. 
     Another feature of the invention resides broadly in a method characterized in that the signal is received simultuaneously by interferometers placed at several azimuth angles around the processroom and/or exhaust channel and the three dimensional distribution of densities and temperature are reconstructed by projections. 
     The components disclosed in the various publications, disclosed or incorporated by reference herein, may be used in the embodiments of the present invention, as well as, equivalents thereof. 
     The appended drawings in their entirety, including all dimensions, proportions and/or shapes in at least one embodiment of the invention, are accurate and to scale and are hereby included by reference into this specification. 
     All, or substantially all, of the components and methods of the various embodiments may be used with at least one embodiment or all of the embodiments, if more than one embodiment is described herein. 
     All of the patents, patent applications and publications recited herein are hereby incorporated by reference as if set forth in their entirety herein. 
     The corresponding foreign and international patent publication applications, namely, Swedish Patent Application No. 9300347-3, filed on Feb. 3, 1993, and PCT/SE94/00100, filed on Feb. 3, 1994, having inventor Lars Baath, and SE-OS 9300347-3 and SE-PS 9300347-3 and International Application No. PCT/SE94/00100, and International Publication No. WO94/18550, are hereby incorporated by reference as if set forth in their entirety herein. 
     The invention as described hereinabove in the context of the preferred embodiments is not to be taken as limited to all of the provided details thereof, since modifications and variations thereof may be made without departing from the spirit and scope of the invention.