Title of Invention

"A REFRACTOMETER SENSOR"

Abstract

This invention relates to a refractometer sensor characterised in that a source of light to provide a divergent beam of light in the form of a cone, a prism (P) having a first face (F1) to receive said cone of light, a part of the rays of said cone of light having an angle  greater than the critical angle, a base of said prism interfaced with the ambient (u9-ug) that the light beam at said interface is partially transmitted and partially reflected, the reflected light passing through a second face (F2) of said prism carrying with it the information about the refractive index ua of the ambient.

Full Text

FIELD OF INVENTI ON The present invention relates to a refractometer sensor. By way of example,. and without. implying any limitation thereto, the sensor may advantageously be employed in the determination of ariu.1 terete on in petrol. Primarily the sensor of the present. invention may be employed for the measurement of the refractive index of a mtediutn or object. Abbe and Pulfrich type re-fractometers Advanced practical phye-ics for students,. B.L. Worsnop and H.T. Flint, Asia Pubiishing House , N.V., 9th ed. , Reprinted 1971) have long been in use for determining the refractive index (e.i.) of liquids. Operation of these opto mechanical devices be dependent on the observance of total .internal reflect a on froof the surface of liquid under investigation. The measurement of critical angles on a pre-cal ibratied scale carried out by optical components with the heip of mechanical drivers gives the value of the refractive index. In some of the- automatic versions of these refractometers available in the market the mechanical drivers, have been replaced by opto-electronic scanners. The continuous monitoring of the refractive index of a liquid in an assembly line is same times required to be carried out. am! therefore there is a need for the development of an opto-electr oni c ref ractometer device capable of measuring refractive indices on line, The commercial type of automatic refrectometers make use of an opto-electronic scanner to detect the position of the bright draft border line similar to those achieved by mechanical drivers in case of the conventional refractometers resulting in a complex design and a very large size for the instrument. Designs available for fibre optical sensors ( K, Spenner, H.D.Singh, H.SchuIte and H. I.Roehnel , SPIE MS108, 424-426) use uncladed glass fibre as sensing probe,. Consequently, these devices are very fragile necessitating very careful handling. Also, the process for cleaning the sensor probe after each use is very cumbersome as it involves cleaning of the fibre with acid as well as in an ultrasonic bath containing alcohol. OBJECTS OF THE INVENTION The main object of the present invention is to propose a refractometer sensor which is not only highly sensitive but is also sturdy, cost effective and user friendly. Another object of the present invention is to propose a refractometer sensor which is opto-electronic in nature. Yet another object is to propose a refractometer sensor which can measure refractive index of the ambient on-line, continuously. Still another object of the present invention is to propose a refractometer sensor which has no moving parts. A further object is to propose a refractometer index which can be determine proportional composition of liquids in a mixture. A still further object is to propose a refractometer sensor which can determine adulteration in petrol. STATEMENT OF INVENTION According to this invention there is provided a refractometer sensor characterised in that a source of light to provide a divergent beam of light in the form of a cone, a prism (P) having a first face (F1) to receive said cone of light, a part of the rays of said cone of light having an angle i greater than the critical angle, the apex angle of the input light beam cone may be such that the minimum angle of incidence of the rays constituting the input beam cone at the prism base-ambient µg-µa interface is equal to or smaller than the critical angle at this interface for the lowest value of refractive index µa of the ambient under investigation, a base of said prism interfaced with the ambient (µa-µg) that the light beam at said interface is partially transmitted and partially reflected, the reflected light passing through a second face (F2) of said prism carrying with it the information about the refractive index µa of the ambient. DESCRPITION OF INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS: Fig. 1 shows the refractometer sensor of the present invention. The refractometer design shown in fig. 1 consists of preferably an isoscelese prism P of glass with base angles 6i and refractive index µg. The base of the prism has an attached temperature controlled steel bath to fill the ambient (of refractive index µa) thus forming a glass-ambient, µg-µa, interface. A small temperature controlled air blower is positioned at a constant height just above this steel bath, particularly in the application for determining adulteration in petrol. Light from light source (not shown) such as a laser or a LED of intensity, Ii is guided by an optical fibre OF1 upto a point P from where it is allowed to fall on one of the isoscelese faces F1 of prism P. The half of the beam divergence 2a of the light coming out of the fibre is equal to its numerical aperture. The reflected light rays of intensity Ir emerging out of the other isoscelese face F2 of prism P are focussed by a converging lens CL on an optical fibre OF2 through which they are fed into an optical power meter (not shown) for measurement. The prism for this configuration is fabricated in such a way that the central ray of the beam cone with its apex at P* is incident at right angle (or an angle close to it) on isoscelese face F1 of prism P, and also that the minimum angle of incidence of the rays constituting the input beam cone at the ug - ua interface is equal to or smaller than the critical angle at this interface for the lowest value of refractive index of the ambient under investigation. The sensitivity of the refractometer refers to the ratio of change in Ir/Ii to the change in µa for a given µg. In another embodiment of the invention the reflected light rays of intensity Ir emerging out of isoscelese face F2 of prism P may be allowed to fall on a photosensitive film for measuring Ir ,Ii and therefore Ir/Ii. In another embodiment of the invention the input cone of divergent light may be allowed to fall on the isoscelese face Fl of prism P directly from its source without being guided by the optical fibre. In yet another embodiment of the invention a part of the input beam of light may be used as reference beam of light to facilitate measurement of Ir/Ii. In yet another embodiment of the invention microprocessors may be used to read and analyse Ir/li Determination of adultration in petrol: At present petrol pump stations in the country are required to keep standard temperature versus density calibration tables for the petrol. Each filling of petrol these stations receive through the tankers is marked with its density and the temperature at which it is measured. Deviation from the density as given in the calibration table found in any sample of petrol by the consumer indicates that it is aduitrated. Above mentioned calibration data is however insufficient to either identify the adultrant or to find its concentration in the sample. The present invention removes these drawbacks. The steps given below identify the adultrant as well as determine the proportion in which it is present. Use of the Refractometer in the determination of adulteration in Petrol. Step-1: Put the sample of petrol in the steel bath maintained at a constant temperature. Step-2: Switch on the air-blower to effect evaporation at the same temperature as in step-1. Step—3s Measure Ir /Ii at regular intervals for few minutes at the seme temperature as in step-1 Step- 4s Comparison of measurements made in step-3 with the reference value for µa and the calibration charts or graphs for various possible adulterants completely identifies the adulterant. and determines it's perceritage concentration in the sample of petrol under investigation. Step-5: .If the retractometer sensor is microprocessor based, Step-3 may be accomplished with its heip. Step 6: Steps i to 5 may be repeated at one more temperature to check and confirm the results. WE CLAIM: 1. A refractometer sensor characterised in that a source of light to provide a divergent beam of light in the form of a cone, a prism (P) having a first face (F1z) to receive said cone of light, a part of the rays of said cone of light having an angle  greater than the critical angle,the apex angle of the input light beam cone may be such that the minimum angle of incidence of the rays constituting the input beam cone at the prism base-ambient µg-µa interface is equal to or smaller than the critical angle at this interface for the lowest value of refractive index µa of the ambient under investigation, a base of said prism interfaced with the ambient (µa-µg) that the light beam at said interface is partially transmitted and partially reflected, the reflected light passing through a second face (F2) of said prism carrying with it the information about the refractive index µa of the ambient. 2. A refractometer sensor as claimed in claim 1 wherein said prism is an isoscelese prism. 3. A refractometer sensor as claimed in claims 1 and 2 wherein the light reflected from the prism-ambient interface and emerging out of the other isoscelese face of the prism is focussed by a converging lens on an optical fibre through which it is fed into a measuring means as herein described. 4. A refractometer sensor as claimed in claims 1 to 3 wherein the input light beam falls on the isoscelese face of the prism directly from its source without being guided by the optical fibre. 5. A refractometer sensor substantially as herein described and illustrated with the help of accompanying drawings.

Documents:

968-del-1999-abstract.pdf

968-del-1999-claims.pdf

968-del-1999-correspondence-other.pdf

968-del-1999-correspondence-po.pdf

968-del-1999-description (complete).pdf

968-del-1999-drawings.pdf

968-del-1999-form-1.pdf

968-del-1999-form-19.pdf

968-del-1999-form-3.pdf

968-del-1999-gpa.pdf