GB1312784A - Scientific instruments - Google Patents

Abstract

1312784 Measuring angles; measuring refractive index electrically BELLINGHAM & STANLEY Ltd 15 Dec 1970 [19 Dec 1969] 62018/69 Headings G1J G1N and G1X [Also in Divisions G2 and G4] A refractometer includes an arrangement for producing an output proportional to the refractive index. In one form Fig. 4 a prism 6 is illuminated at grazing incidence and a telescope mounted on pivoted link 11 aligned at the critical angle, the length of a telescopic link 17, 18 then being directly proportional to the sine of the critical angle and therefore to the refractive index in a modification Fig.6, the telescope is stationary and the prism rotated, the length of telescopic link 29, 30 being proportional to the refractive index. The length of the telescopic link may be read by a pointer and scale Figs. 4, 6, a linear potentiometric transducer Fig. 11 (not shown), in association with a recorder or a digital voltmeter, an optical grating the lines of which are counted photo-electrically, or by an optical grating cooperating with a matching segment to produce a fringe pattern counted photo-electrically Fig.8. The critical angle may be detected by means of a cross wire or a photo-electric device and a servocontrolled drive may be produced for automatically aligning the telescope to the critical angle. In the automatic refractometer of Fig. 8, a motor 47 drives a pin 48 engaging slot 49 in link 42 and oscillates the prism through an angular range. As the critical angle is passed through, this is detected by photo-cell 63 which prevents further counting of the fringes produced by grating 52 so that the reading representing the refractive index is maintained in the counter. A second scale may be provided to indicate a function of the refractive index such as sugar concentration. Alternative by the output of a potentiometric transducer representing the refractive index may be processed electronically to produce a signal representing the sugar concentration Fig. 11 (not shown). The arrangement of links may be modified so that the devices of figs. 4 and 6 produce an output proportional to the cosine in addition to or instead of that proportional to the sine.