稻米金屬檢測器之開發

本論文利用電磁感應理論進行微小金屬的探測，我們將螺線管當作電感並搭配電容和電晶體製做出LC振盪電路，振盪出來的交流訊號使螺線管內磁場不斷變化，這個現象能讓通過螺線管的金屬待測物，其內部產生渦電流，進而產生磁場，螺線管及金屬待測物的兩者磁場的互相影響下，原本的螺線管的交流訊號將產生頻率或者是峰對峰值的變化，本篇朝向振幅的變化來進行研究，另外在金屬探測相關文獻上表示，振盪頻率接近80Hz對鐵感度較好，接近800kHz則是對高碳鋼，所以我們將振盪頻率設定在大約275kHz，來實現全金屬的感測。我們將參考最小可測得直徑0.6mm金屬球的商用機台，透過剖析其電路的特性，並找出其振盪電路進行應用，經由重新設計及更改感測用電容後，我們使用Arduino 取代舊式沉重的控制面板，來收取我們所設計的系統輸出結果，並同時控制伺服馬達或電磁閥將產線中含有金屬微粒的稻米篩選出來。

關鍵字

電磁感應；金屬探測器；線圈； LC振盪電路； Arduino

並列摘要

In this research,we applied the theory of electromagnetic induction to detect small metal. We use a solenoid as inductor, then combined with capacitors and transistors to make an LC oscillator circuit. The AC signal makes a variable magnetic field in the solenoid. The metal passing the solenoid is affected by this phenomenon. Eddy current is generated inside the metal and produces its own magnetic field. Because of the interaction between the two magnetic fields, the original AC signal on the solenoid will change in frequency or amplitude . the amplitude change is the keypoint of this research. For metal detection, the frequency is usually between 80 Hz to 800 kHz. If the frequency is close to 80 Hz , the amplitude will easily be influenced by iron. If it is close to 800 kHz , the amplitude will easily be influenced by High-carbon steel. Hence, the oscillation frequency was set to approximately 275kHz, in order to achieve all-metal sensing. A commercial machine which can detect the 0.6mm diameter metal balls was referred to in this work. Its original circuit has been redesigned by changing the capacitor's type and value on the new oscillator. The old and heavy control panel were replaced by using Arduino as the system's interface, and also as a servo motor or solenoid valve control to pick out the metal from production lines of rice packaging.