| 摘要 |
<p>PROBLEM TO BE SOLVED: To obtain a detector with no necessity of changing parts even with the change of conveyor speed by processing with digital filter the digital value converted from the signal after synchronous detection and making the filter characteristic of the digital filter freely variable. SOLUTION: Signals synchronously detected 7a and 7b are converted into digital values with A/D convertor circuits 11a and 11b. The converted digital values are stored in a memory means 101. To judge from the data converted to digital values after synchronous detection whether metal is mixed or not, it is necessary to extract only metal detection signals. Therefore, only frequency component about a few Hz to tens Hz which is the frequency component of metal detection signal is let pass in digital filter processing with an operation means 102. If the data of metal detection signals obtained due to the change of conveying velocity of a conveyor and the like is small, the coefficient of the digital filter can be made larger through a filter characteristics setting means 104 and a coefficient calculation means 105.</p> |
