GB1254958A - Checking variations in the diameter of a fibre - Google Patents

Abstract

1,254,958. Monitoring the diameter of fibres. PHILIPS ELECTRONIC AND ASSOCIATED INDUSTRIES Ltd. June 20, 1969 [June 21, 1968], No. 31246/69. Heading G1A. In a method of checking variations in the diameter of a fibre being drawn, the radiation from a source 2 is divided into two parts of which the first part intercepted by the fibre is subsequently incident on a photo-electric cell 4 connected in a circuit whose output is related to the said variations, the second part of the flux from the source bing used to derive a reference signal. As shown, radiation from a tungsten filament lamp 2 is collimated by a lens 3 and split by a halfsilvered mirror 8. The fibre 1 is passed continuously through the first beam part which is focused by an objective lens 5 on to a silicon photo-cell 4. Located in front of the photo-cell are a diaphragm 6 and a diffusing screen 11. A diaphragm 10 ensures that a constant length of the fibre is monitored. The second part of the divided beam is stopped down by an adjustable slit diaphragm 9 and falls on a second silicon photo-cell 7. The difference current i 4 -i 7 from the two photo-cells is fed to a meter M, which records the variations in this difference current. A control arrangement may be provided to stop, or modify the conditions of the fibre drawing operation. In a further embodiment, Fig. 4 (not shown) the second or reference beams, after reflection from the beam-splitter 8, is reflected parallel to the measuring beam by a plane mirror and passes through a reference fibre parallel to the first. This reference beam is focused on to a second photo-cell, and the two photo-cell signals are subtracted as before. In the embodiment shown in Fig. 5, light from a source 2 is focused on to a diaphragm 16 through an opal glass 15 and is then collinated by a lens 17. Two resultant beams are produced by a diaphragm 18 having two adjustable apertures. These beams pass through the transparent tubular fibres 1 and 1a and are focused on to a photo-cell 14. A rotating sectored disc 9 with staggered slots or a polarizing disc associated with two crossed polarizers in each of the beams is utilized so that the two radiation paths are alternately incident on the photo-cell, the AC component of whose output is amplified by an amplifier 12 and rectified by a synchronous detector 13 whose output indicates the variations in diameter of the test fibre. The DC component of the photocell output may be used to regulate the source intensity. In all the above embodiments the fibres may be contained in a liquid whose refractive index is substantially equal to that of the fibres.