Patent GB-992811-A (GB)
Title: Classification method and apparatus
IPC: G21C17/06
Filed: 1961-12-29
Abstract: 992, 811. Electric measuring systems: weighing apparatus. NUCLEAR MATERIALS & EQUIPMENT CORPORATION. Dec. 29, 1961 [March 14, 1961], No. 46579/61. Headings G1N and G1W. [Also in Divisions B8 and H3] Apparatus for classifying fuel pellets used in nuclear reactors comprises means for conveying the pellets sequentially along a belt to a measuring station where the length, diameter and weight are measured electrically and compared with values representing standard length, volume and density. If predetermined tolerances are exceeded the pellet is rejected. The sequencing of operations is effected by an electrical program unit. Mechanical construction. Each pellet PE (Fig. 2) is conveyed along a belt 21 between rails 41, which ensure that it is axially aligned, until it displaces a pin 55 operating a switch SW1 (Fig. 4). This causes a plate 62 to push the pellet forward into its gauging position against a wall 107, where its length is measured by a spring-loaded feeler 115 attached to the core of a first differential transformer LVDT1, and its diameter is measured by a vertical spring-loaded feeler 121 (Fig. 11C) attached to the core of a second differential transformer LVDT2. The feelers 115, 121 are retracted by solenoids controlled by the program unit after the gauging has been effected, allowing the pellet to roll into a weighing pan 129 formed at one end of a weighing beam 139, whose other end carries a rigid connection 140 to the core of a differential transformer LVDT5. The beam 139 is torsionally suspended from a bracket 155, and the weight is determined by the current through a balancing coil 175, associated with a permanent magnet 177, to rebalance the beam. The measured characteristics of the pellets are electrically compared with the predetermined standard values, and a flipper 181 ejects the pellet into a guide 187 if satisfactory, or into a guide 189 if rejected, by energization of solenoid SA or SR respectively. Electrical circuitry. (Figs. 11A, 11B, 11C). The length of the pellet PE, as measured by feeler 115, produces an output signal from the secondary winding S1 of differential transformer LVDT1, which is balanced by an equal and opposite signal from secondary winding S3 of transformer LVDT3, any difference being amplified at A1 to energize a motor SM1, which moves the core 301 of transformer LVDT3 to produce rebalance, simultaneously adjusting the slider of potentiometer PL to a potential representing the length of the pellet. The difference between the actual length and the standard length is determined by the unbalance current of a preset bridge BR1, and is indicated on a meter M1. Similarly the diameter as measured by feeler 121 is represented by the slider of potentiometer PD located in a bridge BR3, and the diameter divergence is indicated by meter M2. A further potentiometer PLD is fed with the potential from potentiometer PL and mechanically coupled to potentiometer PD, whereby its output is indicative of the product length x diameter. Another potentiometer PLD2 is fed with the potential from potentiometer PLD and mechanically coupled to potentiometers PD and PLD, whereby its output is indicative of the product length x diameter squared, i.e. volume. The difference between the actual volume and the standard volume is determined by the unbalance current of a bridge incorporating a preset potentiometer P6, and is indicated on a meter M3. The weight of the pellet is measured by the current in coil 175, obtained from transformer LVDT5, to rebalance the beam 139. The transformer is energized with audio frequency A.C. from an oscillator O, and the output from opposing secondary windings S15, S17 when the core 142 is displaced by a pellet is demodulated at DM to energize coil 175. The difference between the actual weight and the standard weight is determined by comparing the output voltage of demodulator DM with that on a preset potentiometer P21, the difference being indicated by a meter M4. The difference between the weight deviation, as measured by a potentiometer P23 in series with P21, and the volume deviation, as measured by potentiometer PLD2, is fed to a meter M5, which thus indicates density variation. The meters M1, M2, M5 have limit contacts, producing energization of selected relay RL11 &c. depending on which measured deviation is excessive, and in which direction, followed by RL7, and reject relay RL8 or accept relay RL9. The apparatus includes indicator lamps G1, G2, G3 which are selectively extinguished when a faulty pellet is measured, and a number of individual counters for accepted and rejected pellets. Specification 992, 812 is referred to.