Arrangement for in situ determination of quantity of turbid matter aerosol and/or dust in fluid which flows through a space

An arrangement for in situ determination of the quantity of turbid matter, aerosol and/or dust in flue gas which flows through a flue by measurement of intensity of light irradiated by means of an optical transmitter in the flue, and dispersed on solid or fluid dispersion particles. The dispersion light is detected by a detector which is arranged outside of the bundle of rays of the transmitter and provided with a wide angle focusing optic. A woodsche horn absorbs the not dispersed part of the bundle of rays of the transmitter. The light source of the transmitter is formed as a xenon spark discharger with intensity maximum in the region of 350-600 nm, the detector signal is evaluated by an evaluating electronic circuit. The arrangement determines extremely low quantities of harmful matter.

BACKGROUND OF THE INVENTION 
The present invention relates to an arrangement for in situ determination 
of the quantity of turbid matter, aerosol and/or dust in a fluid which 
flows through a space, by measurement of light which is scattered on solid 
or fluid particles of turbid matter, aerosols and/or dust of the fluid 
which is located in the space. 
Emission tests are performed in many countries for determining the upper 
limits of harmful matter in exhaust gases. For performing the proper 
determinations and verifying the performance of the determinations, it is 
necessary to have available measuring devices which can measure very small 
quantities of for example dust in an exhaust flue (chimney) with a 
concentration under 100 microgram per cubic meter. 
The known arrangements for conventional measuring processes make 
conclusions from a transmission reduction about the content of harmful 
matter. However, they do not produce useful results with a transmission 
reduction of under 0.1 promill. 
Other processes operate in accordance with the in vitro principle. In 
accordance with this principle a probe is taken from the exhaust flue by a 
suction mechanism and it is supplied for evaluation to a measuring cell. 
In this process inhomogeneties in the stream cannot be taken into 
consideration. 
In accordance with further processes a probe is taken from the measuring 
space and analyzed in a laboratory. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an 
arrangement for in situ determination of the quantity of turbid matter, 
aerosol and/or dust in a fluid which flows through a space, with which 
also a small quantity of harmful matter is determined directly (in situ) 
and exactly in flowing fluid. Thereby a reliable monitoring of the 
quantity of harmful matter is possible over long periods of months. In 
particular, the quantity of turbid matter, aerosol and/or dust of 
particles in submicrometer region for example in flue gases can be 
determined. The quantity in the size order of several 10 microgram per 
cubic meter can be determined also in small spaces with dimensions of the 
cross-section in the region of for example 40 cm. 
In keeping with these objects and with others which will become apparent 
hereinafter, one feature of the present invention resides, briefly stated, 
in an arrangement for in situ determination of the quantity of turbid 
matter, aerosol and/or dust in a fluid which flows through a space by 
measurement of light scattered on solid or fluid particles of turbid 
matter, aerosols and/or dust of a fluid located in a space, wherein the 
arrangement has a light emitting optical transmitter with a light source, 
and a detector with wideangled receiving characteristic arranged so that 
it receives only scattering light scattered on the particles from the 
light emitted by the optical transmitter. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An arrangement shown in FIG. 1 is arranged on a flue (chimney) for 
measuring the quantity of turbid matter, aerosols and/or dust in a flue 
gas which flows through a drafting space 1 of the flue 2. It has an 
optical transmitter 3 with a light source 4 and an optical system 6, a 
photodiode 10 as a detector with a connected wide angle focusing optic 11, 
an optical filter 12 and an evaluating electronic circuit 14, as well as a 
Woodsche horn 20 as an absorber. 
The light source 4 is formed as a xenon spark discharger 4 which radiates 
in a half space and is located in a passage 7 which opens into the flue 
space 1 via an opening in the left flue wall 5. The wall of the passage 7 
is light absorbing. The xenon spark discharger is located in a focus of 
the optical system 6 formed by anastigmats. Two diaphragms 33 and 34 are 
arranged in the passage 7 between the anastigmats 6 and the outlet of the 
passage. The wide angle focusing optic 11 is arranged in an opening of the 
lower flue wall 8. The optical filter 12 and the photodiode 10 located in 
the focus of the optic 11 are arranged after the wide angle focusing optic 
11. The wide focusing optic 11 is an anastigmat or a coma-and opening 
error-free astigmat with an angular field of view of about 40.degree.-80 
.degree.. It can also be formed as a condenser lens. The optical axes of 
the anastigmats 6 and the wide angle optic 11 extend perpendicularly to 
one another. The Woodsche horn 20 extends into the flue space 11 through 
an opening which is provided in a flue wall 41 opposite to the xenon spark 
discharger 4 and which is coaxial with the optical axis of the anastigmats 
6. 
The anastigmats 6 and the wide angle optic or objective 11 are covered from 
the flue space 1 by a respective protective glass 35 and 36. An annular 
nozzle 22 and 23 sits on the protective glasses 35 and 36 coaxially to the 
optical axis of the anastigmats 6 or the wide angle objective 11. The 
diameter of the annular nozzles 22 and 23 is greater than the diameter of 
the opening of the anastigmats 6 or the wide angle objective 11. The 
annular nozzles 22 and 23 are each connected with an air distributor 28 
via a pipe conduit 26 and 27. The air distributor 28 is connected with a 
blower 30 via a fine filter 29 and an air prefilter 32. The air which 
flows from the annular nozzles 22 and 23 radially to the optical axis of 
the anastigmats 6 or wide angle objective 11 prevents depositing of turbid 
matter, aerosol and/or dust on the protective glasses 35 and 36. A further 
pipe conduit 31 leads from the air distributor 28 through the small end of 
the Woodsche horn 20. The Woodsche horn 20 is blown laminarly from its 
small end with cleaned air, so that in its expanded end located in the 
flue space 1 no turbid matter, aerosol and/or dust can penetrate and any 
deposit in the Woodsche horn is prevented. 
The photodiode is connected electrically with the evaluating electronic 
circuit 14 which includes a filter amplifier 15, a gate circuit 16, a 
measuring value preparation 17 and a driver stage 18. The evaluated 
measuring values are supplied via the driver stage 18 and a terminal 28 to 
a peripheral indicating device. 
The xenon spark discharger 4 is supplied from a pulse generator 39 and 
sense polychromatic light pulses with a period of 0.5 to 5 microseconds, 
for example, of 2 microseconds, with a pulse energy of 0.05 to 0.5 J, for 
example 0.1 J in spectral region of 350-600 nm. The sent out light is 
bundled by anastigmats 6 in a parallel or slightly converging bundle of 
rays 9. The bundle of rays 9 is such that after passage through the space 
1 it is completely absorbed by the Woodsche horn 20. 
The inventive arrangement determines the quantity of turbid matter, aerosol 
and/or dust in a flue gas which flows through the drafting space 1 of the 
flue 2 by means of a light scattering measurement. Dielectric and metallic 
dust particles and liquid drops scatter the light sent by the transmitter 
3, and the angle of scattering of the scattered light mainly depends from 
the wave length of the radiated light, the diameter and the dielectric 
constant of the solid or fluid particles. The intensity of the scattering 
light scattered over a predetermined angle depends, with identical 
particles and predetermined light wave lengths, only from the number of 
the particles, or in other words from the quantity of turbid matter, 
aerosol, and/or dust. It has been shown that in flue gases solid and fluid 
particles appear with diameters in sub-micrometer region, which produce an 
especially high scattering light intensity during irradiation with the 
polychromatic light of the xenon spark discharger 4 which emits mainly in 
wavelength region of approximately 350-600 nm. Particles of different 
diameter scatter the light of the xenon spark discharger 4 in the angular 
region detected by the wide angle focusing optic 11. What is important for 
detecting the scattering light of particles of different diameters is, on 
the one hand, the wide angle characteristic of the optic 11 and, on the 
other hand, the spectral band width of polychromatic light sent from the 
spark discharger 4 of approximately 250 nm, with which the angle 
dependency of the scattered light relative to monochromatic light is 
reduced. The number of particles can be determined therefore from the 
intensity of the scattering light detected by the detector 10. With known 
composition of the dispersion particles, the quantity of particles in 
weight per volume can be determined, based on the intensity of the 
detected scattering light. The calibration of the arrangement is performed 
by fluids with known different quantities of particles, and the evaluation 
electronic circuit evaluates the detector signal for each quantity of 
particles. 
The xenon spark discharger 4 has electrodes of a tungsten sintered metal 
with addition of nickel, barium and/or aluminum. For preventing 
evaporation of electrode material from the electrodes which can deposit on 
piston, the xenon spark discharger 4 operates with a fraction of its 
nominal power, for example only approximately 10% of the nominal power. 
The energy per electrical pulse is so small that the electrode material in 
electrical pulse operation remains in the region of elastic deformation 
and thereby does not produce any material losses. The reduction of the 
electrical pulse energy means, however, also a reduction of the emitted 
energy of the light pulse which is compensated by the utilization of the 
anastigmats 6 with high opening ratio. Instead of the anastigmats 6, can 
also be a coma- an opening error-free astigmat can be used. 
Since quantum efficiency of the photodiode 10 is temperature dependent, the 
photodiode 10 is held by a not shown heating device at the highest 
expected ambient temperature of 50.degree. C. Similarly, the whole 
electronic circuit is thermally stabilized by means of the heating 
arrangement to 50.degree. C. 
The Woodsche horn 20 absorb the bundle of rays 9 completely and thereby 
prevents that light from the flue wall 41 be reflected in the detector 10. 
The anastigmat 6 produces scattering light by minimum in homogenities in 
its glass body and on its outer surface. Since the light source 4 with the 
anastigmats 6 in the channel 6 with light absorbing walls is arranged at a 
distance from the space 1, this scattering light is prevented from 
reaching the detector 10. The radial diaphragms 33 and 34 are used for the 
same purpose. 
The optical filter 12 is permeable in the region of 350-500 nm and prevents 
focusing of the falling light (artificial or daylight) which takes place 
in the space 1 from focusing from the wide angle focusing optic 11 onto 
the detector 10. 
The further improvement of the signal-noise ratio is achieved by the 
electrical filter amplifier 15 and the gate circuit 16 which is controlled 
via a trigger conductor 19 from a pulse generator 39 synchronously with 
the sent out light pulses. Thereby the received scattering light is 
evaluated only during the period of each light pulse. 
The light flow process of the light pulses is stable in time and the light 
pulses have a length of 0.5-5 microseconds, for example, 1 microsecond 
with a rise time up to impulse peak of 0.25 microseconds. The time process 
of the scattering pulse corresponds to that of the light pulse sent from 
the xenon spark discharger 4. For allowing a passage of only the 
scattering light pulses, the filter amplifier 15 has a frequency band of 
50-1,000 kHz, which substantially corresponds to the Fourier spectrum of 
the light pulse without direct current portion. 
The measuring value preparation 17 is connected with the output of the gate 
circuit 16 and has a peak value detector which determines the peak values 
of the detector signals, a storage in which respectively a sequence of 
peak values is stored, and an average value generator which calculates the 
average value from the stored peak value sequence and stores the same in 
the storage. The respective average value and in some cases additionally 
the peak value sequence are sent via the driver stage 18 and the terminal 
38 to one or more peripheral not shown recording and/or indicating 
devices. 
For providing especially high sensitivity, it is recommended to use the 
spark discharger of the light source 4 with a xenon filling with a filling 
pressure which is over 1 bar. The electrode material must be extremely 
dust-free. For example, an electrode alloy can be used which is sintered 
together from sintered tungsten and/or nickel. It is thereby achieved that 
the electrodes have a service life of several billions light pulses. 
The evaluating electronic circuit 14 is designed so that a feed current of 
at least 4 mA flows at its output 38. When the feed current exceeds this 
limit, it is connected with a switching defect or a failure of the supply 
voltage and indicated by a not shown alarm generator. 
For operation monitoring, a light dispersion pin 37 is introduced into the 
space 1 so that it extends into the bundle of rays 9. The produced 
additional scattering light results in a noticeable increase of the 
detector signal which is evaluated by the evaluating electronic circuit 14 
and indicates the operational readiness of the arrangement. 
The embodiment of the arrangement shown in FIG. 2 differs from the 
embodiment of FIG. 1 in that instead of the Woodsche horn 20, a laminar 
absorber 40 is arranged at the inner side of the flue wall 41. The outer 
surface of the absorber 40 is protected by clean air which flows from the 
annular nozzle 21 from contamination by turbid matter, aerosol, and/or 
dust. The embodiment of the arrangement shown in FIG. 3 differs from the 
embodiment of FIG. 1 in that, instead of the Woodsche absorber 40, a 
mirror 42, for example, a triple reflector, is arranged opposite to the 
light source 4. It deflects the light beam 9 back to the passage 7. The 
same ray bundle 9 passes therefore twice in the space 1, so that the 
scattering signal is approximately doubled. The mirror 42 is protected 
from contamination by air which flows from an annular nozzle 13, supplied 
to the annular nozzle 13 from a pressure air container 50. The utilization 
of air from the pressure air container 50 is always of advantage when the 
arrangement deals with short measuring time of only several hours and 
network terminals of high power for the blower such as for example in an 
airplane are difficult to install. 
In the embodiment of the arrangement shown in FIG. 4 the spark discharger 4 
irradiates in approximately full spatial angle. A hollow mirror 51 is 
arranged near the spark discharger 4 at its side opposite to the space 1 
and has a focal length which corresponds to that of optical system 6. The 
hollow mirror 51 focuses the light of the spark discharger 4 falling on it 
near its light arc. This doubles the light yield in the bundle of rays 9. 
A further embodiment of the arrangement of FIG. 1 is shown in FIG. 5. It 
provides for a further possibility of operation examination with a light 
conductor 44 which leads from the spark discharger 4 to the detector 10. 
The light conductor 44 has a separation point 46 in which an optic light 
filter 45 is arranged. The filter 45 is composed of several, for example 
three grey stages and a light-impermeable part and for operation 
examination is displaceable by means of an electromechanic displacing 
device 43. In operation the light-impermeable part is located in the 
separation point 46. For operation examination, the filter 45 is displaced 
by means of the displacing device 43 so that light is supplied from the 
spark discharger 4 through the light conductor 44 to the detector 10 and 
is weakened in correspondence with the grey stage. The device is 
operational when the evaluating electronic circuit 14 supplies with the 
selected grey stage a predetermined signal. 
Another embodiment of the arrangement of FIG. 5 is shown in FIG. 6. Here, 
instead of the separated light conductor 44, a light transmitting track 48 
with a deviating mirror 49 is provided. 
Instead of the gas discharge lamp 4 with xenon filling, also other gas 
fillings can be used. Care should be taken only that the light emitted by 
the gas discharge lamp 4 be polychromatic and its average wavelength 
correspond approximately to the diameter of the solid or fluid dispersion 
particles. 
Instead of the photodiode 10, also a high vacuum photocell can be used as a 
detector. 
For flues 2 with great diameters, the provision of openings in the flue 
walls for the transmitter 3, the detector 10 with wide angle focusing 
optic 11 and the absorber 40 can be dispensed with. The above mentioned 
part of the arrangement can be mounted on a frame which is arranged on the 
inner wall of the flue 2 or suspended in the flue 2. 
In a not shown embodiment of the arrangement of FIG. 1 a photodiode 10 can 
be provided with greater aperture angle (angular displacement). Since the 
photodiode 10 has itself wide angle characteristic, the focusing optic 11 
can be dispensed with, while of course the measurement sensitivity of the 
arrangement is reduced. 
The inventive arrangement can be used generally where the measurement of a 
very small quantity of harmful matter must be performed. The fields of 
application include especially flues in the lead, asbestos, or zinc 
industry. Measurements are also possible on airplanes or measurements in 
measuring towers in free atmosphere, in which, for example, the 
concentration of a fume bell contains dust, within approximately 20 km 
visual range, about 20 micrograms per cubic meter. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions differing from the types described above. 
While the invention has been illustrated and described as embodied in an 
arrangement for in situ determination of the quantity of turbid matter, 
aerosol and/or dust in a fluid which flows through a space, it is not 
intended to be limited to the details shown, since various modifications 
and structural changes may be made without departing in any way from the 
spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.