| 摘要 |
<p>A coin selector of the kind comprising three frequency-deviation sensors (A,B,C) sensitive to the geometric parameters of the coins (M) being tested and to their material, circuit means (20) for logic processing the data detected by the sensors and voltage/frequency converter means (15) interposed between the material sensor and the logic processing means. In order to eliminate the influence of temperature on selectivity, the selector comprises, associated with the input of the voltage/frequency converter (15), a temperature-stabilized reference voltage source (17), and a switch (16) controlled by the logic processing circuit means to selectively connect the input of the converter (15) to the output of the voltage source (17) or the output of the material sensor (B). When each coin passes, the switch (16) is activated to detect an operating frequency (f min t) corresponding to the voltage of the source (17). Such operating frequency, by comparison with a stored reference frequency (f min r) produced by the converter at the voltage fed by the source at a preset temperature, provides a differential datum which depends on the effect of the temperature itself; the detected differential datum being used by the logic processing means (20) to determine in each instance corresponding correct minimum and maximum acceptance thresholds for the signals arriving from all the sensors.</p> |
