U.S. patent number 3,746,452 [Application Number 05/889,877] was granted by the patent office on 1973-07-17 for device for determining the transparency of the atmosphere.
Invention is credited to Andre Rene Baude, Jean Schieving, James Remy Albert Teboul.
United States Patent |
3,746,452 |
Teboul , et al. |
July 17, 1973 |
DEVICE FOR DETERMINING THE TRANSPARENCY OF THE ATMOSPHERE
Abstract
Device for determining the transparency of the atmosphere
between two points comprising one light transmitter and one
receiver respectively on the two points, optic fibers connecting
the corresponding transmitters and receivers, means to separate the
data coming through the atmosphere and through the fibers and a
data processing device connected to said means.
Inventors: |
Teboul; James Remy Albert
(Montrouge, Hauts-de-Seine, FR), Baude; Andre Rene
(Arcueil, Val de Marne, FR), Schieving; Jean (Paris,
FR) |
Family
ID: |
27444998 |
Appl.
No.: |
05/889,877 |
Filed: |
September 3, 1969 |
Foreign Application Priority Data
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Sep 5, 1968 [FR] |
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68165207 |
Dec 23, 1968 [FR] |
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68179985 |
Mar 28, 1969 [FR] |
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6909279 |
Sep 27, 1968 [FR] |
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68167867 |
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Current U.S.
Class: |
356/438;
250/227.11; 356/435; 250/565 |
Current CPC
Class: |
G06J
1/00 (20130101); G01J 1/16 (20130101); G01N
21/538 (20130101) |
Current International
Class: |
G01N
21/53 (20060101); G01J 1/10 (20060101); G01J
1/16 (20060101); G01N 21/47 (20060101); G06J
1/00 (20060101); G01n 021/26 () |
Field of
Search: |
;356/36,72,102-104,176-177,201-208,114-117 ;250/218,227 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
weissberger, "Phys. Meth. of Org. Chem.," Interscience Pub.; N.Y.;
1960; pp. 2,125-2,128. .
Ash et al., "Analyt. Chem.," Vol. 43, No. 1, Jan. 1971..
|
Primary Examiner: Wibert; Ronald L.
Assistant Examiner: Evans; F. L.
Claims
We claim:
1. Device for determining the transparency of the atmosphere
between two places fixing a measurement path, comprising
a first light transmitter arranged at one of these two places for
sending a first main light signal to the other place through the
atmosphere of which the transparency is to be determined,
a first light receiver arranged at the said other place for
receiving the first main light signal and producing a first
electrical signal,
a second light transmitter for sending a second main light signal,
different from the first main light signal,
a second light receiver for receiving the second light signal and
producing a second electrical signal,
light conductors isolated from the atmosphere to be studied and
optically connecting :
the first light transmitter and the second light receiver for
sending to the latter a first reference light signal, whereby said
second electrical signal contains a data representative of the
second main light signal and a data representative of the first
reference light signal,
the second light transmitter and the first light receiver for
sending to the latter a second reference light signal, whereby the
first electrical signal contains a data representative of the first
main light signal and a data representative of the second reference
light signal,
a first separating means for differentiating in said second
electrical signal the data representative of the second main light
signal from the data representative of the first reference light
signal,
a second separating means for differentiating in said first
electrical signal the data representative of the first main light
signal from the data representative of the second reference light
signal, and a data processing circuit connected to said first and
second separating means at output thereof, said data processing
circuit comprising :
means for multiplying the data representative of the second main
light signal times the data representative of the first main light
signal whereby is obtained a first product ,
means for multiplying the data representative of the first
reference light signal times the data representative of the second
reference light signal whereby obtaining a second product, and
means for dividing the first product by the second product whereby
obtaining an output signal which is representative of the
transparency of the atmosphere to be determined.
2. Device according to claim 1, comprising :
a first optical system connected to the first light transmitter for
sending the first main light signal to the first light receiver
through the atmosphere to be studied, and
a second optical system connected to the second light transmitter
for sending the second main light signal to the second light
receiver through the atmoshpere to be studied.
3. Device according to claim 1, comprising :
an optical system connected to the first light transmitter for
sending the first main light signal to the first light receiver
through the atmosphere to be studied, and
a light conductor isolated from the atmosphere to be studied and
optically connecting the second light transmitter to the second
light receiver for sending to the latter the second main light
signal.
4. Device according to claim 2, additionally comprising:
a first polarizer screen inserted, at the output of the first light
transmitter, on the path of the first main light signal, and a
first analyzer, screen preceding the first light receiver on the
path of the first main light signal, the polarizing directions of
the said polarizer and analyzer being parallel,
a second polarizer screen inserted, at the output of the second
light transmitter, on the path of the second main light signal, and
a second analyzer screen, preceding the second light receiver on
the path of the second main light signal, the polarizing directions
of the said polarizer and analyzer being parallel but orthogonal to
the polarizing directions of the first polarizer and analyzer
screens.
5. Device according to claim 1 further comprising :
a modulated power generator connected to the first light
transmitter for feeding it at a first frequency and a modulated
power generator connected to the second transmitter for feeding it
at a second frequency, different from the first one,
a filtering circuit tuned to the first frequency and a filtering
circuit tuned to the second frequency both connected to the output
of the second receiver and respectively providing the data
representative of the second main light signal and the data
representative of the first reference light signal,
a filtering circuit tuned to the first frequency and a filtering
circuit tuned to the second frequency both connected to the output
of the first receiver and respectively providing the data
representative of the first main light signal and the data
representative of the second refeence light signal.
6. Device according to claim 1 further comprising an electric power
pulse generator connected to the two light transmitters, this
generator having a period of duration less than the time required
for the light to go from one place to the other and four gate
circuits which are piloted by the pulse generator and connected
:
the first and second ones, to the output of the first light
receiver for producing respectively the data representative of the
first reference light signal and the data representative of the
second main light signal,
the third and fourth ones, to the output of the second light
receiver for producing respectively the data representative of the
first main light signal and the data representative of the second
reference light signal.
7. Device according to claim 1 in which the data processing circuit
comprises :
a first pulse generator,
a first pulse counter,
a first gate circuit inserted between the generator and the
counter,
a first "scale step" numerical-to-analog converter receiving the
data representative of the first reference light signal and
connected to the first counter for producing a "scale step" output
signal increasing of one step when the content of the counter
increases of one unit, every step being proportional to the data
representative of the first reference light signal,
a first comparison circuit receiving the data representative of the
second main light signal and the output signal of the first
converter and connected to the first gate circuit for causing its
locking when the two received signals are equal,
a second pulse generator,
a second pulse counter, having a given capacity,
a second gate circuit inserted between the generator and the
counter, the releasing input of which being connected to the output
of the first gate circuit,
a second "scale step" numerical-to-analog converter receiving the
data representative of the second reference light signal and
associated to the second counter for producing a "scale step"
output signal increasing of one step when the content of the
counter increases of one unit every step being proportional to the
data representative of the second reference light signal,
a second comparison circuit receiving the data representative of
the first main light signal and the output signal of the second
converter and connected to the second gate circuit for causing its
locking when the two received signals are equal,
and a pulse counter connected to the output of the second gate
circuit.
8. Device according to claim 7, in which the frequency of the
second pulse generator is at least M times greater than the
frequency of the first pulse generator.
Description
Numerous devices are known for measuring the dimming or absorption
of light due to the diffusion of water particles contained in the
atmosphere and thus determining the transparency thereof. This
measuring has considerable interest in giving a measure of the
visibility through fog of objects or radiant sources such as ground
lights on airfield runways.
Most of the known devices are based on the measuring of the current
supplied by an electric photosensitive member energized by a
suitable light source through a given path in the atmosphere, to be
studied. The value of this current characterizes, under known and
stable geometric conditions, the fraction of emitted light, or more
generally radiation which reaches the receiver as a function of the
absorption due to diffusion.
The usual parameter employed is the transmissive power of the
atmosphere, which is the percentage of radiation transmitted, the
value 100 percent being attributed to the quantity of radiation
received by the receiver, under the same geometric conditions, when
the atmosphere is perfectly pure.
It will be understood that the measurement can be erroneous if the
radiant source is not of invariable intensity and if the
photosensitive receiver does not have an invariable sensitiveness,
actually the variations in time and variations according to
external phenomena which affect the power radiated by the source,
as well as the sensitiveness of the receiver, cause serious errors
in a device of this kind.
To overcome such drawbacks, it is usual to stabilize the voltage of
the power generator which supplies the radiant source.
Unfortunately, a remedy of this kind is ineffective on the
evolution of the output of the source itself. Also, the stabilizing
of the sensitiveness of the receiver is still more difficult to
obtain.
Most of the known appliances are based upon the principle of
automatic compensation by means of a special optical path provided
with a reference transmission coefficient. It is then necessary
that this reference path be periodically substituted, between the
light source and the photo-sensitive receiver, to the atmospheric
path. Owing to the length of this atmospheric path which is
considered as a sample of the atmosphere and is generally in the
region of 50 meters, this method only applies to an atmospheric
path comprising a return path after reflection on a mirror between
the source and the receiver, then close to each other. This is
disadvantageous, because in the range of transmissive powers of the
atmosphere that the appliance can measure, it divides by two the
length of the atmosphere sample. Moreover, the periodic
substitution of one optical path for another, can only be carried
out conveniently by mechanical means : synchronized shutters,
revolving mirrors, etc.. This type of equipment generally requires
regular maintenance for a permanent service.
The present invention thus has for its object the provision of an
entirely static device, which is not disturbed by variations in the
transmission of the source, as well as in the sensitiveness of the
receivers.
The present device for measuring the transmissive power of the
atmosphere on a given path, is characterized in that it comprises
at each end of said path, an optico-electronic
transmitter-receiver, each transmitter sending light signals to its
associated receiver and towards a distant receiver, means to
separate the signals received by a receiver from its associated
transmitter and distant transmitter, and means to deduce therefrom
a magnitude proportional to the transmittive power by carrying out
the ratio of the products of the values of homologous signals
supplied by each of the receivers.
Moreover, this device also affords the advantage of preserving on
the length of the atmosphere sample, the maximum value permitted by
the equipment. Moreover measurement may be made independent on the
gain variations of electric signal amplifiers, generally associated
with photosensitive receivers used in said optico-electronic
transmitter-receiver.
Lastly, since the invention by calling upon the help of two devices
of identical construction, the case of a defect in any of the
constitutive members of one device, such as : light source,
photosensitive receiver, amplifier, etc . . . , still provides a
measurement which is actually of lesser accuracy but enables the
avoidance of stopping the service while the defect is being
repaired.
Other provisions of the invention enable elimination of the
influence of atmospheric interfering retro-diffusions, either by
using reference paths, or by utilizing polarized light.
The invention will be better understood by referring to the
following description and accompanying drawings, given by way of
non-restrictive example :
In these drawings :
FIG. 1 shows diagrammatically a first embodiment of the
invention.
FIG. 2 shows a transmitter-receiver unit.
FIG. 3 shows, diagrammatically, a variant of embodiment.
FIG. 4 is an explanatory diagram.
FIG. 5 shows diagrammatically a device according to the invention
and comprising reference paths.
FIG. 6 shows diagrammatically a device according to the invention
and, operating in polarized light.
FIG. 7 is a diagram of a processing circuit.
Referring now to FIG. 1, at both ends of an atmospheric path which
has to be studied, there are provided two optico-electronic units
essentially composed of transmitter-receiver members 1a, 5a and 1b,
5b which will be described farther on. The two radiation
transmitters 1a, 1b are respectively fed by power generators 2a, 2b
and are placed behind convergent optics 3a, 3b. Convergent mirrors
4a, 4b each receive a given part of the radiation transmitted by
the source of the opposite unit. These mirrors reflect the
respective radiation on photosensitive receivers 5a, 5b. The
mirrors 4a, 4b and optics 3a, 3b are so oriented so that the optic
axes coincide, which leads to obtaining a maximum connection
between the source 1a and the receiver 5b on the one hand, and the
source 1b and the receiver 5a on the other hand. There are then two
beams of radiation passing through the atmosphere to be studied, a
first beam formed of rays such as 6a and a second beam, directed in
an inverse manner, being formed of rays such as 6b.
Devices 7a, 7b form reference optic paths which are short and
stable, between the source 1a and the receiver 5a and respectively,
between the source 1b and the receiver 5b. Such devices can be made
of combinations of flat mirrors, or more advantageously, as shown
by means of bunches of glass threads called "optic fibres." Thus,
the beam 7a, respectively 7b, send part of the radiations
transmitted by the transmitter 1a, respectively 1b, directly on to
their associated receiver 5a, 5b or by means of a spherical mirror
4a, respectively 4b.
The receivers 5a, 5b are respectively connected to electric signal
amplifier devices 8a, 8b whose outputs are connected to separator
means 9a, 10a and 9b, 10b. Said separator means are described
farther on and have the purpose of distinguishing, among the
signals supplied by each of the two receivers 5a and 5b, those due
to adjacent associated sources (1a for 5a, 1b for 5b) and those due
to distant sources (1a for 5b, 1b for 5a).
At the output of the separator means, there are thus four different
electric signals available on four conductors 11, 12, 13 and
14.
One designates by :
E.sub.1 and E.sub.2 the powers radiated respectively by the sources
1a and 1b.
0.sub.1 and 0.sub.2 the respective transmissions coefficients of
the optics 3a and 3b.
M.sub.1 and M.sub.2 the respective retransmission coefficients of
the mirrors 4a and 4b.
S.sub.1 s.sub.2 the respective sensitiveness of the receivers 5a
and 5b.
R.sub.1 and R.sub.2 the respective transmission coefficients of
theeference devices 7a 7b.
G.sub.1 and G.sub.2 the respective gains of the amplifiers 8a and
8b.
K the transmissive power of the atmosphere for the atmospheric path
under consideration.
A, b, c and D the values of the electric signals on the respective
conductors 11, 12, 13, 14.
It is also assumed that the separator means 9a, 9b, 10a, 10b do not
introduce any appreciable change in the electric signals which are
transmitted. This is rather conveniently the case when electric
filters are used as separator means.
The various signals A, B, C and D have then the following values
:
A = e.sub.1 r.sub.1 s.sub.1 g.sub.1
b = e.sub.2 s.sub.1 o.sub.2 m.sub.1 k g.sub.1
c = e.sub.1 s.sub.2 o.sub.1 m.sub.2 k g.sub.2
d = e.sub.2 r.sub.2 s.sub.2 g.sub.2 (1)
from these signal values, it is possible to extract either by
computation, or by means of an electronic circuit 15, or processing
unit, an electric value independent of the values E.sub.1,E.sub.2,
S.sub.1, S.sub.2, G.sub.1, G.sub.2 and depending only on the
transmissive power of the atmosphere K and constant geometric
characteristics of the device. An embodiment of a processing
circuit which is particularly appropriate is described hereafter
with reference to FIG. 7.
Actually, if one effects the products A .times. D and B .times. C,
and then the quotient B .times. C/A .times. D, one obtains the
following expression :
B .times. C/A .times. D = E.sub.2 S.sub.1 O.sub.2 M.sub.1 K G.sub.1
.times. E.sub.1 S.sub.2 O.sub.1 M.sub.2 K G.sub.2 /E.sub. 1 R.sub.1
S.sub.1 G.sub.1 .times. E.sub.2 R.sub.2 S.sub.2 G.sub.2 (2)
which is simplified down to :
B .times. C/A .times. D = (O.sub.1 O.sub.2 M.sub.1 M.sub.2 /R.sub.
1 R.sub.2) K.sup.2 (3)
if the geometrical characteristics of the installation are
constant, the term placed in front of K.sup.2 in the second member
of the preceding equation is a constant, and we obtain : B .times.
C/A .times. D = (constant) .times. K.sup.2 (4)
one thus provides at the output of the processing circuit 15, an
appliance sensitive to said electric value, for instance, a
numerical counter 16 which thus measures the transmissive power of
the atmosphere.
In a particular embodiments of the invention, each of the two
transmitter-receiver units comprising the optico-electronic means
of FIG. 1, is made, as shown in FIG. 2, of a metal tube 21 which,
at one of its ends, supports a lens 3 of the convergent type and in
the focus of said lens an electro-luminescent diode 1 is mounted.
The other end of the metal tube 21 comprises a filter 22 protecting
the photosensitive receiver 5 against radiations of a wave length
differing from those composing the transmission spectrum of the
electro-luminescent diode 1.
The receiver 5 is a photodiode or 2 phototransistor, fixed on the
axis of the tube so as to be at the converging focus of the
parabolic mirror 4. The feed circuit of the diodes 1 and 5 is shown
diagrammatically at 1' and 5' respectively.
An optic fiber 23 is engaged by its ends in two openings made in
the tube 21, so as to send from the electroluminescent diode 1
towards the phototransistor 5, a slight and constant fraction of
the radiation transmitted.
The mirror 4 and tube 21 unit provided with members 1, 3, 5, 22 and
23, and held by a support 24, is installed in a tubular casing 25
whose length gives protection against direct sun rays as well as
against detrimental weather.
In a particular embodiment of the invention, the electroluminescent
diodes of each of the two optico-electronic units are energized by
generators of electric current with a different modulation
frequency. Each of these generators, designated by 2a, 2b in FIG.
1, is composed of an oscillator connected to an electric amplifier.
The respective frequencies F.sub.1 and F.sub.2 of the two
oscillators being different, this enables very easily to
distinguish, by means of the means 9a, 9b, 10a and 10b of FIG. 1,
which are simple filters respectively tuned on the modulation
frequencies F.sub.1 and F.sub.2, the signals coming either from the
associated electroluminescent diode, or from the distant
electroluminescent diode. These different signals are thus applied
to the processing unit or data processing circuit 15 through wires
11-14, as previously explained.
In another particular embodiment of the invention shown in FIG. 3,
the electroluminescent diodes 1a and 1b are fed by pulse signals.
The duration of the pulses is less than the time taken by light for
passing through the atmospheric path studied. In FIG. 3, where the
same members as those of FIGS. 1 and 2 bear the same reference
numerals, a pulse generator 16 simultaneously feeds electric power
amplifiers 2a and 2b connected to the electroluminescent diodes 1a
and 1b. The pulses E.sub.1, E.sub.2, which are then radiated by the
diodes 1a and 1b, are shown on FIG. 4, lines a and d.
The current pulse E.sub.1 S.sub.1 , delivered by the receiver 5a
under the effect of the radiation from diode 1a, is shown on line
b. It is practically simultaneous with the pulse E.sub.1, line a.
On the contrary, the current pulse delivered by the receiver 5b,
under the influence of the diode 1a, is offset of the time taken by
the light to traverse the atmospheric path as shown at E.sub.1
S.sub.2 , line c.
The lines e and f show that the same takes place with regard to the
pulses transmitted by the electroluminescent diode 1b.
Each of the receivers 5a, 5b thus successively delivers two pulses,
shown by E.sub.1 S.sub.1 (line b) and E.sub.2 S.sub.1 (line f) for
the receiver 5a and by E.sub.2 S.sub.2 (line e) and E.sub.1 S.sub.2
(line c) for the receiver 5b. The separation of these signals is
made by two groups of two electronic switches or gate circuits, for
instance, the circuits AND 19a, 20a, 19b, 20b, which are piloted by
the pulse generator 16 in such a manner that the four signals A, B,
C, D of the group of expressions (1) appear each individually on
the conductors 11, 12, 13, 14 and are applied to the data
processing circuit 15.
Another arrangement, based on the process initially described, has
the object of simplifying said process with a view of obtaining a
signal directly proportional to the transmissive power, while
having still the advantages of being independent of emissivity
variations of the sources as well as sensitivity variations of the
receivers.
The process, according to this arrangement, is modified in that one
of the local transmitters is formed by a reference transmitter
optically coupled with each of the receivers by reference optic
paths.
A device for operating this modified process comprises, at one end
of the measurement path, an optico-electronic transmitter-receiver,
a receiver at the other end, and a reference unit formed by a
reference transmitter optically coupled by reference paths with
each of said receivers, as well as a circuit for carrying out the
ratio of the products of homologous signals from each of these
receivers.
This device affords the advantage of preserving to the measurement
path in the atmosphere, the maximum value provided by the qualities
of the equipment. It is to be noted that the measurement remains
then independent of gain variations of the electric amplifiers
generally associated with the photo-sensitive receivers. Moreover,
the measurements and reference paths can be entirely independent
and isolated, thus avoiding the necessity of eventual protection
against intergering retrodiffusions.
In this device however, it is not possible, in the event of a
defect of a member such as light source, photo-sensitive receiver
or amplifier, to be provided with still a measurement even of less
accuracy, whereas this possibility exists when one uses a
symetrical double channel wherein one of them still supplies a
signal.
Said device is shown in FIG. 5 wherein at one end of the
atmospheric path studied, is shown a transmitter-receiver
essentially composed by a radiation transmitter 31a fed by a power
generator 32a at a given frequency F, and a photo-sensitive
receiver 35a. These various members have been described in
connection with FIG. 1. The transmitter 31a is placed behind a
convergent optic 33a in order to energize, through the measurement
optic path and by means of a convergent mirror the receiver 35b
placed at the other end. The optic 33a and mirror 34b are so
mounted that their optical axes coincide, thus affording a maximum
coupling between the source 31a and the receiver 35b.
A fraction of the radiations transmitted by the source 31a is
directed to the associated receiver 35a by a stable optic path 37a
formed, for instance, by optic fibres and making a constant optic
coupling between the source 31a and the receiver 35a.
A source of reference radiations 37 is fed by a power source 32 at
a given frequency F.sub.2 and simultaneously irradiates
respectively through stable optic paths or reference paths 37 and
37b, the receivers 35a and 35b. The stable optic paths 37a, 37 and
37b can be made in the form of combinations of flat mirrors
connected by enclosures preserved from the atmosphere whose
transmissive power is to be measured, or more advantageously, in
the form of optic fibres as described above.
The electric circuit is made in a similar manner to that shown in
FIG. 1, by means of amplifiers 38a, 38b, and separator means 39a,
40a and 39b, 40b, electric filters for instance, that have the
purpose of distinguishing, among the signals supplied by each of
the receivers 35a and 35b, those due to the source 31a and those
due to the reference source 31.
Thus, four different electric signals A, B, C, D provided at the
output of this circuit unit are present on four conductors 41, 42,
43, 44.
One designates by :
E.sub.1 and E.sub.2 the powers respectively radiated by the source
31a and reference source 31 at respective frequencies F.sub.1 and
F.sub.2 ;
O the transmission coefficient of the optic 33a;
M the retransmission coefficient of the mirror 34b;
S.sub.1 and S.sub.2 the respective sensitivenesses of the receivers
35a and 35b;
R.sub.1 , r.sub.2 and R.sub.3 the respective transmission
coefficients of the reference devices 37a, 37 and 37b;
G.sub.1 and G.sub.2 the respective gains of the amplifiers 38a and
38b;
K the transmissive power of the atmosphere for the atmospheric path
studied;
A, b, c, d the values of the electric signals then respectively
appearing on the conductors 41, 42, 43, 44. One also supposes that
the separator means 39a, 40a, 39b, 40b do not introduce any
appreciable change in the electric signals that they are charged to
transmit, which may be conveniently the case if said means are
frequency filters.
The various signals A, B, C, D have the following expressions :
A = E.sub.1 R.sub.1 S.sub.1 G.sub.1
B = E.sub.2 R.sub.2 S.sub.1 G.sub.1
C = E.sub.1 O M S.sub.2 K G.sub.2
D = E.sub.2 R.sub.3 S.sub.2 G.sub.2 (5)
if, in a particular circuit 45, similar to the data processing
circuit 15, we carry out the ratio of the products B .times. C/A
.times. D, we obtain the following expression :
B .times. C/A .times. D = E.sub.2 R.sub.2 S.sub.1 G.sub.1 .times.
E.sub.1 O M S.sub.2 K G.sub.2 /E.sub.1 R.sub.1 S.sub.1 G.sub.1
.times. E.sub.2 R.sub.3 S.sub.2 G.sub.2 (6)
which may be written : B .times. C/A .times. D = (R.sub.2 O
M/R.sub.1 R.sub.3) K (7)
now, the various factors of the term which precede K are
independent of the transmissive power of the atmosphere, variations
of source characteristics, photosensitive receivers and amplifiers.
If, by construction, the geometrical characteristics of the various
members 33a, 34b, 37a, 37 and 37b are constant, we can put down
:
B .times. C/A .times. D = (constant) .times. K
The circuit 45 thus supplies an information directly proportional
to the transmissive power K, which is measured by any suitable
device, for instance, a counter 46 connected to the output of the
data processing circuit 45.
In a specific form of embodiment, the source 31a, associated with a
lens of photographic converging type 33a, is an electroluminescent
diode placed at the focus of this lens. The receiver 35b is a
photodiode or photo-transistor placed in the focus of the parabolic
or spherical mirror 34b. In the casing containing the source 31a
and lens 33a there is also a photodiode or photo-transistor 35a on
whose input face are applied the ends of two flexible light
conductors, such as optic fibres 37a and 37 which respectively
collect the light from the source 31a and that from the reference
source 31 which is also an electroluminescent diode. On the output
face of the electro-luminescent diode 31 in addition to the light
conductor 37 there is also applied one end of another light
conductor 37b of which the other end is provided to light up the
receiver 35b.
In this specific embodiment, the electroluminescent diodes 31a and
31, are energized by different modulation frequency electric
current generators, as already described with reference to FIG. 1.
It has been shown that by means of simple filters 39a, 40a and 39b,
40b, tuned on one of the two modulation frequencies, it was
possible to separate the respective signals coming from radiations
of the diode 31a, and of the diode 31.
It is quite obvious that the impulsional process described with
reference to FIG. 3 is applicable for distributing and collecting
in time the signals relating to the diodes 31a and 31, which are
similar to the diodes 1a and 1b of said FIG. 3.
The positions of the members 31 and 35a, relatively to the source
31a and to the receiver 35b, as well as the arrangement and length
of the optic fibres which arise out of these relative positions can
be modified without entailing a change in the working of the
device. Preferably, one chooses, for the reference source 31, such
location that the dimming of the light signals in the channels 37
and 37b is substantially the same (R.sub.2 = R.sub.3).
Retrodiffusions interfering with the light on fog particles in
suspension in the atmosphere close to the photosensitive receivers,
introduce an error factor whose eventual disturbing influence is
only partially eliminated in the preceding arrangement on the
reference paths.
A supplementary arrangement enables to cancel, to a large extent,
the disturbing influence of retrodiffusion on the accuracy of the
device of the invention.
According to this arrangement, the light signals transmitted by
each transmitter towards the distant receiver are polarized
according to different respective directions, preferably
orthogonal, and said polarized signals are received by the receiver
through an analyzer whose polarization plane is parallel to the
polarization plane of the light transmitted from the distant
transmitter.
In FIG. 6, which shows some of the members of FIG. 1, each of the
radiation sources 1a, 1b, is provided, on the transmission path
towards the remote receiver 5a, 5b, with a polarizing screen 51a,
51b having the known property of polarizing the light according to
a preferred direction. The direction chosen for the polarizer 51a
is preferably, orthogonal to the direction chosen for the polarizer
51b. This is diagrammatized in the figure by an arrow symbolizing
the polarization plane, said arrow being placed inside a
circle.
Correlatively, each of the photo-sensitive receivers 5a, 5b, is
preceded, on the reception path of the remote transmitter, with a
screen for analyzing the polarized light, said screen having the
known property of dimming the polarized light, except in a
preferred direction. This is also diagrammatized in the figure by
an arrow, symbolizing the polarization plane, said arrow being
placed inside a circle.
The polarizing direction chosen by the analyzer 52a relating to the
receiver 5a is thus parallel to the polarization direction of the
polarizer 51b associated with the transmitter 1b, and hence
orthogonal to the polarization direction of the polarizer 51a
associated with the transmitter 1. In the very same way, the
analyzer 52b associated with the receiver 5b has a polarization
direction parallel to that of the polarizer 51a of the transmitter
1a and orthogonal to that of the polarizer 51b of the transmitter
1b.
The reference optic paths made through the devices 7a, 7b and
intended to provide the automatic compensation of the variations in
the characteristics of the various members are not concerned with
the above polarizers and analyzers, and the transmission on their
path takes place with a non-polarized light.
By referring to the designation previously used and by
incorporating the respective dimmings .gamma.1 and .gamma.2 on the
optic paths 6a and 6b, due to the presence of polarizers and
analyzers, and moreover, by taking into account the interfering
retrodiffusion signals of the light E and F, symbolized in the
figure by the arrows 12 and 14 and provided with a coefficient x
(K) depending on the transparency characteristics of the atmosphere
and also with dimming coefficients .GAMMA.1 and .GAMMA.2 due to the
effect of cossed couples of polarizers and analyzers, 51a, 52a and
51b, 52b, one obtains for the signals A, B, C, D previously
defined, and for E, F, the following values :
A = E.sub.1 R.sub.1 S.sub.1 G.sub.1
B = E.sub.2 S.sub.1 O.sub.2 M.sub.1 K G.sub.1 .gamma..sub.1
C = E.sub.1 S.sub.2 O.sub.1 M.sub.2 K G.sub.2 .gamma..sub.2
D = E.sub.2 R.sub.2 S.sub.2 G.sub.2
E = E.sub.1 .times. (K) .GAMMA..sub.1 S.sub.1 G.sub.1
F = E.sub.2 .times. (K) .GAMMA..sub.2 S.sub.2 G.sub.2 (8)
the modified ratio :
B .times. C/(A + E) .times. (D + F)
has for expression after simplifying :
[O.sub.1 O.sub.2 M.sub.1 M.sub.2 l .gamma..sub.1 .gamma..sub.2
/(R.sub.1 + x (K) .GAMMA..sub.1) (R.sub.2 + x (K) .GAMMA..sub.2)]
K.sup.2 (9)
the geometrical characteristics being supposed to remain constant,
this expression can be put down as follows, after making the
generally accepted approximations on the terms of the denominator
:
(Constant) x (1 - x(K)/R.sub.1 .GAMMA..sub.1) (1 - x(K)/R.sub.2
.GAMMA..sub.2) x K.sup.2 (10)
thus, the error brought by retrodiffusion on the measuring of
K.sup.2, and which is normally figured by the ratios x(K)/R.sub.1
and x(K)/R.sub.2, is multiplied by the dimming coefficients
.GAMMA..sub.1 and .GAMMA..sub.2 introduced by using polarized
light.
The value of the terms R.sub.1 and R.sub.2 which characterize the
conveyance of the light on the reference paths 7a, 7b can be
increased to the point of making negligible the influence of the
variations of x(K). Nevertheless, for avoiding too great an
unbalance between the energies received by the photosensitive
receiver 5a by the path 7a and the path 6b, as well as between the
energies that the receiver 5b receives by the path 7b and the path
6a, it is necessary to substantially have : cl R.sub.1 =O.sub.1
M.sub.1 .gamma..sub.1
R.sub.2 =O.sub.2 M.sub.2 .gamma..sub.2 (11)
these conditions impose an upper limit at R.sub.1 and R.sub.2. It
is then very advantageous to reduce the maximum error by utilizing
the dimmings .GAMMA..sub.1 and .GAMMA..sub.2 which may, for
instance, be of 0.1.
Thus, as it has been explained above, the signals E and F, coming
from the interfering retrodiffusion of the light, respectively
added to the signals A and B coming from the reference path, since
they are of the same modulation frequency (continuous as in FIG. 1
or impulsional as in FIG. 3). This means that the processing of the
signals obtained, according to FIG. 6, is identical to that
obtained according to FIG. 1 or FIG. 3, the signal A of said
figures then being replaced by A + E and the signal D by D + F to
be processed by an electronic circuit analogous to the circuit 15
or 45 of FIGS. 1 and 3.
It should be noticed that without going outside the scope of the
invention, the positions of the electroluminescent diodes and
photo-transistors could be inverted, the colour filters and
photo-transistors then being placed behind the lenses and the
electroluminescent diodes in the focus of the parabolic mirrors.
Likewise, the electroluminescent diodes can be replaced by light or
radiative sources of different types, such as flash lamps, coherent
light transmitters, filament incandescent lamps, fluorescent gas
lamps.
FIG. 7 shows an advantageous embodiment of the processing device
designated by reference number 15 in FIGS. 1 and 3 and by 45 in
FIG. 5. In said FIG. 7, reference letters A, B, C, D designate the
four output magnitudes, under the form of electric voltage, for
instance, whose product of the ratios B/A .times. C/D is to be
made.
The dividend voltage B is applied on the input 69 of a two-input
differential amplifier 61 whose second input is connected by a
connection 70, comprising a resistance 68, to the output of a
numerical-to-analogue converter 66. A gate circuit 62, a flip-flop,
for instance, can be released by a signal applied on the input 72
and re-locked by the output signal of the amplifier 61 applied to
the input 71. The gate circuit 62 is placed between a pulse
generator 63 and a pulse counter 65 of a N capacity, the whole
forming, with the members 61 and 66, an analogue-to-numerical
converter 64. The counter 65 is reset by a signal applied on one of
its connections 73.
The stages of the counter 65 are individually connected to the
numerical-to-analogue converter 66. A network of balanced
resistances 67a-67e is connected to a connection 74 on which is
applied the divider voltage A so that each increase of one unit of
the contents of the counter 65 causes an increase of a constant
value of the output voltage existing on the connection 70. As the
voltage A is applied on the network 67a - 67e, the value of these
steps is proportional to this signal A. Furthermore, the circuit is
dimensioned so that when the counter reaches its full capacity N,
the voltage on 70 is then equal to the voltage A applied on 74. The
whole unit 61 to 74 thus forms a first elementary divider
circuit.
A shunt 75 connected to the output of the circuit 62 transmits the
pulses therefrom on to a second elementary divider circuit 61' to
74' similar to the first elementary divider circuit 61 to 74, on
which are respectively applied through connections 74' and 69', the
dividend voltage C and the divider voltage D of the second C/D term
of the product to be made.
One designates by M the capacity of the counter 65'. The shunt 75
leads, on the one hand, by a connection 72' on the release control
of the gate circuit 62', and on the other hand, by a connection 73'
on the resetting of the counter 65'. The output of the pulses is
collected on a connection 75' and can be connected to a utilization
device, such as a pulse counter 76 analogous to the counters 46 and
16 of the preceding figures.
Working of this device will be now explained. An external signal is
first applied on one hand on the connection 73 to reset the counter
65, and on the other hand on the connection 72 to release the
circuit 62. The counter 65 then being at zero, the output of the
converter 66 is nil.
The pulses from the generator 63 then reach the counter 65 which
begins to totalize them. Correlatively, the output voltage of the
converter 66 increases by one step for each pulse received by the
counter 65, and this output voltage is compared in the amplifier 61
with the input voltage B. When this output voltage reaches the
value of the voltage B, this equality is revealed by the amplifier
61 which supplies, on the connection 71, a signal causing the
locking of the circuit 62 and interrupting the arrival of pulses
from the generator 63 in the counter 65.
If, at this moment, the contents of the counter 65 has reached a
value n and, since the capacity thereof is equal to N, the value N
corresponds to the value A, and one may put down n/B = N/A hence n
= B/A N.
The number n is thus proportional to the quotient B/A.
Each of the pulses n transmitted on the second elementary divider
61'- 74' plays the same part as the external signal applied on the
connections 72 and 73 of the first elementary divider. In this
second divider, the counter 65' receives, for each of the n pulses
arriving on 75, a number m of pulses, so that m = M (C/D).
During the complete working cycle defined by the speed of the
external signals periodically sent on the connections 72 and 73,
the unit supplies on the output 75' a number of pulses :
n .sup.. m = N .sup.. M .sup.. (B/A) .sup.. (C/D)
N and M being the constants, one actually collects a number of
pulses proportional to the product of the two quotients (B/A)
.times. (C/D).
Nevertheless, it should be noted that the choice of frequencies of
the pulse generators 63 , 63' is not totally independent. Actually,
seeing that the time between the pulses of the generator 63 must
eventually contain M pulses from the generator 63', the latter
generator must have a frequency at least M times greater than that
of the generator 63.
It is obvious that one might connect a third elementary divider
circuit in tandem and pilot it by the output pulses appearing on
the connection 75' in like manner to the second divider which is
piloted by the pulses arriving on the connection 75, the generator
frequency of this third divider complying with the condition
previous mentioned, and so on. By thus connecting a number of
elementary dividers on which are respectively applied analogous
signals of dividend and divider of a number corresponding of
quotients, one finally obtains a number of output pulses
proportional to the product of all these quotients.
* * * * *