Double optical probe device for the determination of the refractive index of a liquid reduced to a predetermined reference temperature

• US 4,427,293 A
• Filed: 09/17/1981
• Issued: 01/24/1984
• Est. Priority Date: 09/18/1980
• Status: Expired due to Term

• Current Assignee: Stanley Electric Company Limited
• Original Assignee: Battelle Memorial Institute
• Inventors: Harmer, Alan L.
• Primary Examiner(s): ROSENBERGER, RICHARD A
• Application Number:
  US06/303,083
• Time in Patent Office: 859 Days
• Field of Search: 356/128, 356/133, 356/135, 356/136, 356/137, 250/227
• US Class Current: 356/133
• CPC Class Codes: G01N 21/431 Dip refractometers, e.g. using optical fibres

Abstract

The device comprises two optical probes (51 and 52) consisting of a light conducting body which are designed to be immersed in the liquid by an intermediate section (53, 54) of the body, two light sources (60, 70) illuminating an extremity respectively of one (58) and of the other (68) body of the probes, two photoelectric transducers (61 and 72) located at the other extremity respectively of the first (58) and of the second (68) body of the probes, a member (73) which divides the signals originating from these transistors and a member (74) for the display of the resulting signal originating from that divider member.

Claims

1. A double optical probe device for the determination of the refractive index of a liquid reduced to a predetermined reference temperature, said device being adapted to give rise to an error which is more positive than the negative error inherent to a single optical probe device, characterized by the fact that said device comprises:

a first and second optical probe each consisting of a light conducting body comprising an inlet section and an outlet section connected to each other by an intermediate section, at least said intermediate section of each of said probes being designed to be immersed in said liquid, and this intermediate section being, furthermore, adapted to convey light between said inlet section and said outlet section by giving rise to a quantity of light emerging from said outlet section of each of said probes which varies linearly as a function of the refractive index of said liquid,

at least one source of light associated with said inlet section of said first and second probes, for the injection of a quantity of predetermined light into each of these inlet sections,

and means associated with said outlet section of said first and second probes, for the elaboration of a resulting signal corresponding to the difference in the quantities of light respectively emerging from said outlet sections, said intermediate sections of said first and second probes being, in addition, chosen, on the one hand, as regards their geometric arrangement, so as to have respective sensitivities "m₁ " and "m₂ " relative to the variations in the refractive index of the liquid which are such that "m₁ " is greater than "m₂ " and, on the other hand, as regards the constituent material thereof, so as to have apparent respective sensitivities "q₁ " and "q₂ " relative to the variations in temperature of this liquid which are such that "q₁ " is lower than "q₂ ", so that said resulting signal elaborated at the outlet of said probes constitutes a signal which is representative of said refractive index of the liquid reduced to said reference temperature, the refractive index thus determined being, furthermore, tainted, for temperatures that are different from this reference temperature, with an error which is more positive than that which would result from the use of a single probe.

2. A device according to claim 1 characterized in that each of said intermediate sections consists of a prism comprising at least two reflecting surfaces, provided so as to successively reflect at least a part of the light originating from said inlet section up to said outlet section of each of said bodies.

3. A device according to claim 1, designed to provide a substantially perfect temperature compensation, characterized in that the geometric arrangement as well as the constituent material of each of said intermediate sections of said probes are chosen so as to have, respectively, respective effective sensitivities "m₁ " and "m₂ " relative to the variations in the refractive index of the liquid, as well as respective apparent sensitivities "q₁ " and "q₂ " relative to the variations in temperature of that liquid, which substantially obey the relation:

m₁ q₁ =m₂ q₂.

4. A double optical probe device for the determination of the refractive index of a liquid reduced to a predetermined reference temperature, said device being adapted to give rise to an error which is more positive than the negative error inherent to a single optical probe device, characterized in that said device comprises:

a first and second optical probe each consisting of a light conducting body comprising an inlet section and an outlet section connected to each other by an intermediate section, at least said intermediate section of each of said probes being designed to be immersed in said liquid, and this intermediate section being, furthermore, adapted to convey light between said inlet section and said outlet section by giving rise to a quantity of light emerging from said outlet section of each of said probes which varies exponentially as a function of the refractive index of said liquid,

at least one light source associated with said inlet section of said first and second probes, for the injection of a predetermined quantity of light into each of these inlet sections,

and means associated with said outlet section of said first and second probes, for the elaboration of a resulting signal corresponding to the quotient of light quantities respectively emerging from said outlet sections, said intermediate sections of said first and second probes being, in addition, chosen, on the one hand, as regards their geometric arrangement, so as to have respective exponentiality coefficients "k₁ " and "k₂ " relative to the variations of the refractive index of the liquid such that "k₁ " is higher than "k₂ ", and, on the other hand, as regards the constituent material thereof, so as to have apparent respective sensitivities "q₁ " and "q₂ ", relative to the variations in temperature of this liquid such that "q₁ " is lower than "q₂ ", so that said resulting signal elaborated at the outlet of said probes constitutes a signal which is representative of said refractive index of the liquid reduced to said reference temperature, the refractive index thus determined being, furthermore, tainted, for temperatures differing from this reference temperature, with an error which is more positive than that which would result from the use of a single probe.

5. A device according to claim 4, characterized in that each of said intermediate sections consists of a curved longilinear section the curvature of which is sufficiently pronounced to give rise to a non negligible passage of light in the liquid through refraction, said inlet and outlet sections to which is connected each of the intermediate sections being longlinear as well.

6. A device according to claim 4 designed to provide a substantially perfect temperature compensation, characterized in that the geometric arrangement as well as the constituent material of said curved intermediate sections are chosen so as to have, respectively, respective exponentiality coefficients "k₁ " and "k₂ " relative to the variations in the refractive index of the liquid, as well as respective apparent sensitivities "q₁ " and "q₂ " relative to variations in temperature of this liquid, which substantially obey the relation:

k₁ q₁ =k₃ q₂.