| 摘要 |
In a coin testing apparatus of the type in which the coins are brought to pass an electromagnetic detection field this field is generated from a single coil (6), which is concurrently supplied with a high frequent signal (500 kHz) and two mutually different low frequent signals (10 and 30 kHz), whereby a high selectivity is achieved in a simple manner. The selectivity is further increased by completing the receiver coil (8) with a series connected auxiliary coil (14) mounted next to the space between the two main coils (6, 8) and having its electromagnetic axis extending into this space, this causing a highly increased sensitivity particularly for one of the low frequent signals (30 kHz). |
