IE38360B1 - Method and apparatus for use in an inductive sensor coin selector - Google Patents

Abstract

1443934 Testing coins MARS Inc 8 Oct 1973 [12 Oct 1972] 47164/72 Heading G4V A method of testing coins comprises subjecting a coin to an alternating magnetic field, producing a first signal indicative of the degree of interaction of the coin with the field, producing a second signal dependent on both the value of the first signal when a coin is in the field and its value when no coin is in the field, and comparing the value of the second signal with that expected for an acceptable coin. This arrangement corrects for changes in the operating parameters and in particular in the preferred structure (Figs. 1 and 2, not shown) where a coin passes between an inductor (20) and a conductive target (40) on opposed walls (32), (34) of a coin passageway and the walls are relatively movable to release jammed coins, for changes in the wall spacing. In the embodiment shown an oscillator 450 is connected to an inductor 420 adjacent the coin passageway and its output is also gated alternately to counters 470, 471 under the control of a flip-flop 461 and timing and reset pulse generator 460. One of the counters 470, 471 therefore stores the value of the oscillator frequency while the other is measuring it. When a coin arrival is detected by detector 455 the timing pulses from the generator 460 to the flip-flop 461 are blocked and one counter therefore stores the last frequency value while the other is connected to the oscillator for the duration of the testing period which comprises a plurality of timed intervals as determined by generator 460. A comparator 473 is connected between counters 470, 471 and controls a flipflop 485 so that when one count exceeds the other further pulses in each testing interval from the oscillator are counted into counter 490 via OR gate 487 and AND gate 489. The highest count received in counter 490 during the testing period is compared with values expected for a genuine coin. In a second embodiment (Fig. 3, not shown) a reference value of the frequency of oscillator (350) is stored in register (370) at predetermined intervals and after other events, e.g. switching on of the power to the circuit. A second register (371) is connected to the oscillator during the testing period and a unit (383) derives the arithmetic difference or another mathematical function of the values in registers (370), (371), the derived value being compared with predetermined limits by comparator 390. Alternatively the amplitude of the oscillator signal may be examined in which case registers (370), (371) may comprise capacitor circuits. [GB1443934A]