| 摘要 |
The method serves for monitoring the operation of a metal detection system that comprises a balanced coil system (2) with a transmitter coil (21) that is connected to a transmitter unit (1), which provides transmitter signals (s1) having a fixed or variable transmitter frequency (f TX ) and with a first and a second receiver coil (22, 23) that provide output signals (s22, s23) to a receiver unit (3), which compensate one another in the event that the metal detection system is in balance. According to the invention a carrier signal (s01, s1) having the transmitter frequency (f TX ) and a monitoring signal (s3) having a monitoring frequency (f MON ) are provided to a modulation unit (15) that suppresses the carrier signal (s1, s1') and provides a modulated monitoring signal (s300), which is supplied to a monitoring coil (24) that is inductively coupled with at least one of the receiver coils (22; 23), whose output signals (s22, s23) are demodulated in a demodulation unit (34) that provides a demodulated monitoring signal (s30), which is compared in phase and/or in amplitude with a reference (s3). In the event that the measured deviations exceed a given threshold value an alarm is provided.
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