Patent GB-623178-A (GB)
Title: Apparatus for gauging and measurement
IPC: G01R1/30
Filed: 1945-07-25
Abstract: 623,178. Linear dimension gauges. FOOTE, PIERSON & CO., Inc. July 25, 1945, No. 19012. Convention date, June 20, 1944. [Class 106 (ii)] [Also in Groups XXXVIII and XL (c)] Gauging-apparatus comprises a fixed coil system for producing two overlapping opposed alternating electromagnetic fields, a non-magnetic device which is adjustably positioned to enable the two fields to be balanced so as to produce a linear fieldstrength/displacement relationship along a rectilinear path, a coil or coil system movable along said path in accordance with the displacement to be measured and means for measuring the voltage induced in the movable coil or coil system. Within a casing 57, Fig. 11, which is adjustably supported on a rack 52 above an anvil 55 formed on a base, are two coils 62, 63 wound upon an insulating former carried by a non- magnetic support 59. Disposed within the coils is a spindle 64 having a non-magnetic sleeve 65 which carries an insulating former on which is wound a coil 67. The leads of this coil are attached to resilient connectors 75, 76, having terminals to which a cable may be secured. The spindle 64 is urged downwardly by a spring 82, the pressure of which may be adjusted by means of a plate 83 and a screw 84. The upper end of the spindle 64 passes through a bearing in the casing 57 and is protected by a dust cap while the lower end passes through a bushing 89 in a support 87 and carries a hardened end 92. Rotation of the spindle 64 is prevented by a collar 93 having a vertical slot which is engaged by a guide screw. Alternating voltages are applied in antiphase to the fixed coils 62, 63 so that the voltage induced in the moving coil varies linearly with its position over a large range and changes in phase at the central position. Eddy currents induced in a non-magnetic metallic plate 101 and in the support 59 affect the phases of the voltages in the fixed coils and by adjusting the plate 101 by means of a screw 104, an exact antiphase relationship between these voltages may be obtained. Within the effective magnetic field of the fixed coils, the spindle 64 is of uniform diameter and surrounded by the non-magnetic coil former so that spindle movement may have negligible effect on the phase balance. An alternating voltage is supplied to the fixed coils 62, 63, Fig. 14, from a conventional valve oscillator 159 supplied from a power pack 153, and the measuring voltage induced in the moving coil 67 is applied across an attenuator 168 which may be set to provide different sensitivities. The measuring voltage is then applied to an amplifier 170, the output of which is rectified by a triode valve 173, to the grid of which an alternating voltage is supplied from the oscillator 59 so that the valve will conduct when the measuring voltage is of one phase, but not when it is of opposite phase. The triode 173 will thus only conduct if the coil 67 moves, say, upwardly from its zero position. The rectified voltage is then applied to a meter 175 which may be calibrated in terms of spindle movement and have several scales to correspond to different settings of the attenuator 168. In order to facilitate accurate adjustment of the gauge, the measuring voltage induced in the moving coil 67 is combined with a balancing voltage supplied by means of a variable coupling 106 from the same source as the fixed coils 62, 63. Adjustment of the coupling 106, which varies the resultant measuring voltage, is thus equivalent to a linear movement of the gauging feeler and the coupling may be calibrated in terms of linear movement. When used as a comparator, the gauge is set by inserting a standard gauge block and adjusting the coupling 106 until the meter 175 reads zero or any other desired value. The apparatus may be used to provide indications or to operate auxiliary equipment when the dimension measured is within certain limits. For this purpose, two or more triode valves 179, 180, Fig. 14, have their grids biassed by means of adjustable potentiometers 183, 184, respectively. The rectified measuring voltage is also applied to the grids so that, if this voltage exceeds a value dependent on the grid bias of the triode 179, the latter will conduct and operate a relay 188, thus switching off a lamp 192 and illuminating a lamp 193. When the measuring voltage exceeds a value dependent on the grid bias of the second triode 180, both valves will conduct and a second relay 189 will operate to extinguish the lamp 193 and illuminate a lamp 194. Solenoids, motors or the like may be operated in place of the lamps to control sorting equipment or other machinery and, if the gauging is to take place at a high speed, a circuit for prolonging the indicating or like impulse may be employed (see Group XL (c)]. Each limit may be set by adjusting the coupling 106 from the balancing position by the desired amount as shown by its scale and then adjusting the corresponding potentiometer, until the associated lamp is just illuminated.