US 4,225,245 AGranted

Apparatus for measuring the optical transmissive power of the atmosphere

AssigneeSociete Nationale d'Etude et de Construction de Moteurs d'Aviation "S.N.E.C.M.A."

InventorsMichel Roiret, Aime Salles, Michel Dupitier

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Abstract

An apparatus for measuring the optical transmissive power of the atmosphere, having particular application to measuring visibility at airports, in which luminous flux from a source passes to a remote first detector through the atmosphere, and flux from the source also passes to a second detector through a fibre optic arrangement. The output of the second detector is compared with a reference signal and the difference signal from the comparator is fed to a variable gain amplifier which controls the light source to remove errors in the output of the first detector which would otherwise occur by virtue of aging of the detectors and/or by virtue of changes in the luminosity of the source. Also described is an arrangement for compensating for accumulation of dirt on the detectors and/or the luminous flux source without cleaning off the dirt.

Claims7

Dependent claims

An apparatus for measuring optical transmissive power of the atmosphere comprising:

(a) an electrically driven source for producing luminous flux;
(b) a current supply device arranged to supply an electric current to drive said source,
(c) a receiver station remote from said source and including first and second detectors for producing electrical signals indicative of luminous flux incident thereon from said source, said detectors having substantially the same operating characteristics, said first detector being arranged to receive luminous flux from said source through the atmosphere;
(d) a fibre optic light guide arranged to supply light directly from said source to said second detector;
(e) means for establishing a substantially constant reference signal;
(f) a comparator for comparing the signal produced by said second detector with the said reference signal, the comparator being arranged to produce an output signal in accordance with said comparison;
and
(g) means for varying the electric current supplied by said current supply device in accordance with said output signal and in such a manner as to cancel the difference between electrical signals produced by said second detector and said reference signal.

5 more elements

Dependencies are inferred from the claim text.