| 摘要 |
A method of detecting impurities in a mass, such as detecting metallic and/or plastic particles in a stream of tobacco particles or filter material for tobacco smoke, includes the steps of moving the mass relative to a microwave field and/or vice versa, and analyzing the influence of the mass upon the microwave field. The analyzing step involves simultaneously measur- the actual values of a first and a second parameter of the microwave field, ascertaining the presence or absence of those changes of the parameters which are attributable to the presence of impurities in the mass, determining whether or not the changes are within an acceptable range, and generating signals for segregation of impurities-containing portions of the mass from the other portions when the changes are outside of the acceptable range.
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