Patent GB-285005-A (GB)
Title: Improvements in means for measuring characteristics of material
IPC: G01N27/22
Filed: 1927-12-12
Abstract: 285,005. Atlantic Precision Co., (Assignees of Allen, A.). Feb. 8, 1927, [Convention date]. Thickness of paper. gauging. - A characteristic of a material is determined without segregation from the mass by causing changes in such characteristic to effect corresponding changes in the capacity of a condenser in an oscillatory circuit. Apparatus is shown for measuring the running weight of non- conducting sheet material 24, variations in which cause corresponding variations in the capacity of a condenser formed by a lower fixed plate 21, Fig. 2, and an upper plate 29, which may be raised by a hand-lever 38 and allowed to return to its normal position as determined by the engagement of stop pins on guide posts 28 with adjusting screws 31. A dash-pot 39 may be provided. Fig. 4 shows the circuit connections, in which the condenser C formed by the plates 21, 29 and the material 24 to be tested is connected in parallel with adjustable condensers 45, 46 in a closed oscillatory circuit R containing a secondary coil 42 and a thermoammeter 44, which may have a suppressed zero. Coupled to the circuit R by means of a primary coil 43 is a high-frequency oscillatory exciting circuit which, in the example shown, comprises a 7-5 watt three-electrode valve 77 with a constant or variable grid leak 78 and fed from a 110 volt. 60 cycle, singlephase circuit 79 connected to the primary winding 80 of a transformer having a secondary winding 81 applying 550 volts to the anode, and a secondary winding 82 supplying a suitable voltage for the filament, as measured by a voltmeter 84 A reaction coil 85 is variably coupled with an inductance coil 85<1> in series with an adjustable condenser 86, an ammeter 87, and the primary coil 43. The condensers 45, 46 are adjusted so that, with material 24 of the required running weight, the circuit R operates at a sensitive point of the resonance curve, ond variation in the running weight causes a deflection of the thermoammeter 44 from ts normal reading. In order to check the reading of the instrument when no material 24 is between the plates 21, 29 a variable condenser 47, previously adjusted but normally disconnected, is arranged to be substituted for the condenser 45, either manually or automatically, when there is no solid dielectric passing between the plates of the condenser C. The substitution may be effected by a switch 53 operated by a cam on the shaft of the condenser 45 when this is turned to its zero position. The indicating arm of the condenser 45 may be provided at its end with a sharp point which may be pressed into the soft metal of the dial to enable a definite setting to be recorded. The substitution of the checking condenser 47 may be effected automatically by means of a rider 61, Fig. 7, resting on the sheet material and closing the circuit of a relay 74 when no sheet material is present The relay 74, on operation, may close a switch inserting the condenser 47, at the same time disconnecting the condenser 45, or, as shown, it may close a switch 75 which inserts the condenser 47 in parallel with a condenser 76, the condenser 45 being left in circuit. The condensers 45, 76 are mounted on the same shaft and arranged to vary oppositely, so that the combined capacity of the condensers 45, 76, 47 is constant for all positions of the condenser 45. For calibration purposes, standard samples of material are employed or samples of material having more permanent properties are made to have the same capacities as such standard samples, for example a hard rubber sheet. slightly too thick, may have material drilled out near the centre to correct the value of its capacity. In order to increase, the range of the instrument when required to measure characteristics that may vary widely for example the weights of different grades of writing paper, the coupling between the generating and receiving circuits S, R, Fig. 4, may be varied. This may be effected simultaneously with a change in the capacity of the condenser 45, as shown in Fig. 15. Separate stator plates are connected to contacts 91, 92. 93 over which moves a switch arm 95 operating the coupling-coil 43 through worm gearing 96, 97. The change in capacity may be continuous as shown in Fig. 16, in which the rotor of the condenser 45 is operated by a knob 105 through gearing 103, 102 such that a number of revolutions of the knob 105 are required to produce one revolution of the rotor, these revolutions being indicated by a counter 106. The shaft of the coupling-coil 43 is geared to the shaft 101 of the condenser 45 through bevel gears 111. Fig. 17 shows a modification in which the coupling between the exciting and receiving circuits is through condensers 114, 115, the latter of which is varied simultaneously with the adjustment of the condenser 45. As shown in Fig. 18 the shaft 116 of the condenser 45 is in two parts copled by an insulating sleeve 117. The condenser 115 comprises a fixed plate 120 and a plate 123 rotatable with the shaft 116. The plate 123 Is carried by a screwed sleeve on a screwed portion of the shaft 116, so as to be adjustable axially and angularly with regard to the plate 120. The screwed sleeve is split and tapered and clamped in adjusted positions by a nut. The invention is applicable for testing the composition of rubber compounds containing different proportions, of rubber, sulphur, and filler, or for testing fabrics coated or impregnated with other materials. Characteristics of materials, such as moisture content, may be caused to change capacity or inductance by mechanical means. Specifications 276,468, 276,469 and 281,693 are referred to.