Patent GB-831957-A (GB)
Title: Photoelectric measuring means
IPC: G01D5/34
Filed: 1956-03-26
Abstract: 831,957. Electronic counting apparatus. TRIGGS, W. W. (National Research Corporation). March 26, 1956, No. 9357/56. Class 106 (1). [Also in Group XL (b)] Apparatus for determining the average diameter and the diameter distribution of a sample of fibres includes means for scanning across the sample fibres, which are arranged parallel to each other, and by a photo-electric device obtaining electrical signals representing the diameters of each of the fibres. In preparing the sample short lengths of the fibres may be rubbed on a grooved surface which will retain a single fibre in each groove. The fibres are then lifted off the groove surface, as, for example, by the use of transparent adhesive tape, and mounted on a transparent support. This support 6 is arranged in an optical system including a light source 2, lens 4, lens 8, slit 9 and photoelectric device 12. The width of the slit is made considerably smaller than the projected diameter of one of the fibres. Constant velocity movement of the support 6 in a direction perpendicular to the fibre lengths causes the images of the fibres to move across the photo-cell 12 and produce pulses width-modulated in accordance with the diameter of the fibres. The pulses are amplified and applied to a counter circuit 16 which counts the number of pulses and thus the number of fibres. If the average is to be taken of, say, 1000 fibres, circuit 16 will close gate 18 when this number has been reached. The amplified pulses which are passed by gate 18 are fed to an integrator averaging device 20 which may be calibrated to give a direct reading of average width having regard to the setting of counter 16. They are also fed to an arrangement indicating the diameter distribution in the sample. As shown, this arrangement only indicates the number of fibres in two groups of diameters but the number of subdivisions may be increased as required. Pulses are fed, for this purpose, to the grids of normally conductive valves T 1  and T 2  fed from a stabilized voltage source. The pulses serve to cut off the valves for their duration and cause the charging of capacitors C 1  and C 2  respectively. When C 1  is sufficiently charged valve D 1  conducts and registers a " count " at counter 26. The time constant of the circuit including C 2  may be made such that C 2  is only charged to a level at which D 2  conducts after a longer pulse so that counter 30 counts only the number of fibres in a larger diameter group. For longer pulses both counters are operated and a subtraction device 29 may be used to obtain a count for the group of fibres producing pulses rendering D 1  conductive but not D 2 . Various optical arrangements may be used to cause the fibres (or photographs or the like thereof) to produce light pulses or dark pulses in the illumination on the photo-cell. In one arrangement linear polarizing filters 5 and 7 having their planes of polarization at 90 degrees to each other are included in the optical system and have these planes at about 45 degrees to the direction of fibre alignment. As many textile fibres are anisotropic the system will pass light only when a fibre is positioned in the effective light path. Counter arrangements. A suitable decade counter circuit for use at 26 or 30 comprises an " add " input feeding through monostable multivibrator 51 and a " subtract " input fed through similar multivibrator 53. The output of the two units 51 and 53 are fed to the two control electrodes G 1  and G 2  of a first glow decade counter 50. They energize these electrodes in the opposite order to each other, thus providing an " add " count or a " subtract " count respectively. The cathodes K9 and K10 of this tube control a further glow decade counter 52 through a circuit capable of passing either " add " or " subtract " impulses. Still further decade counters may be added if required coupled by similar circuits. The coupling circuit is arranged so that a glow on cathode 9 produces a voltage across R11 fed to the grid of amplifier 54 to partially overcome the bias voltage generated across R15. When the glow shifts to cathode 10 the voltage generated across R12 causes current to flow in valve 54 and an " add " pulse to be applied to multivibrator 57. If counter 50 is subtracting the current in R12 first partially overcomes the bias on amplifier 56 and a move to cathode 9 causes a pulse which renders this amplifier conductive to provide a " subtract " pulse input to multivibrator 59. Multivibrators 57 and 59 control counter 52 in the same way that units 51 and 53 control counter 50.