| 摘要 |
<p>A pair of coils (1, 2) of elongate transverse cross-section face each other across a coin path, and the changes in shading of the receiver coil (2) by a coin proceeding between the coils (1, 2) is monitored by a track and store unit (6) controlled by software. The emitter coil (1) is subjected periodically to pulses having a 1 MHz frequency component to provide a sharp-edged emitter coil pulse, and the amplitude of the voltage pulse induced in the receiver coil (2) is monitored. The track and store unit (6) is programmed to locate the receiver coil pulse of minimum amplitude produced by maximum shading of the receiver coil, to determine when a coin is positioned symmetrically of the coils for a diameter measurement to be made. In order to discriminate from noise, the storage means (MAXDI) of the track and store software is switched by switch units (20, 21, 22) from storing the most recent maximum value of receiver coil volts (DIAM) to storing the most recent minimum value of receiver coil volts when the receiver coil signal has fallen by a predetermined threshold amount, (set in block 29), and then is switched again (at 18) following a minimum receiver coil signal (at 12) to storing again the most recent maximum value when the receiver coil signal has risen by a further threshold amount (set in block 25).</p> |
