感應式線圈測速系統之研製及測試

Abstract

感應式線圈在台灣用於十字路口機動車輛闖紅燈與超速的偵測已有超過二十年的時間，且該種設備的數量亦相當多。為了盡可能地確保偵測的準確性，執法設備必須實施定期的檢定檢查，在感應式線圈系統的年度校正法規中，要求以模擬器輸出速度訊號至主機，以驗證主機對於車輛速度偵測的能力。 本研究設計一套縮小比例的感應式線圈模擬系統、速度訊號輸出模擬器以及兩點式速度偵測系統，並以完整的實驗方式測試渦電流訊號變化以及車輛底盤高度、通過速度、通過面積與路面鋪面厚度等對於感應線圈觸發的影響。同時，也以單晶片AT89C51成功設計研製了速度訊號輸出模擬器與兩點式速度偵測器。 本研究主要測試項目與其重要結論如下：1.模擬實驗觸發點與線圈的距離：結果顯示，即使鐵片未通過線圈上方，在一定距離內，線圈依然有偵測到鐵片的能力；2.模擬實驗鐵片高度對觸發的影響：結果顯示，在不同的靈敏度下，觸發高度會有明顯區別；3.模擬實驗鐵片面積對觸發的影響：結果顯示，鐵片通過線圈的面積對觸發有顯著的意義；4.模擬實驗鋪面厚度與材料對觸發的影響：結果顯示，除了鐵磁性物體之外，存在的介質並不會影響觸發的成功率；5.模擬大線圈對於小鐵片的偵測能力：結果顯示，大線圈對於小鐵片具有良好的偵測能力；6. 測試線圈磁場延伸的偵測範圍：結果顯示，線圈磁場比預期更能夠有效地偵測鐵磁性物體的存在；7.測試線圈被鐵片涵蓋面積對於渦電流振幅的改變量：結果顯示，愈大的被涵蓋面積有愈大的振幅改變量；8.設計雙線圈速度偵測器並驗證時間偵測準確度：比較PLC步進馬達控制位移檯速度與模擬器計算值是否一致，結果顯示，得到的時間值誤差不超過10%；9.設計速度訊號輸出器並驗證輸出時間準確度：結果顯示，速度訊號輸出模擬器可準確輸出30, 60, 90, 120, 150, 180, 210與240 km/h等八個訊號。

Taiwan’s police have used induction loops for red-light monitoring and speed measurement at intersections for over 20 years. A lot of these devices are in use. In order to keep their accuracy in a definite range, they must be calibrated and inspected regularly. In the annual inspection of these systems, a simulator is used to provide various speed signals to the machine’s detectors to check their ability to detect a vehicle’s speeds. In this paper, a series of experiments on the interaction between the induction loop and a vehicle were done. These experiments addressed the following issues: the signal variation caused by an eddy-current effect, and the effects of chassis height, vehicle travelling speed, dimension of detection area and pavement thickness on the trigger of the induction loop. A scale-down simulation system for speed measurement and a device for speed signal output were also developed with the help of a chip, named AT89C51. The main testing items and the important results are as follows: 1. Distance between the practical detection point and induction-loop: the results show that the induction loop has still the ability to detect a steel sheet at a definite distance even if this sheet does not pass over the loop; 2. Effect of the height of a steel sheet: the results show that different sensitivity settings in a simulator will cause changes in detection height; 3. Effect of the area of a steel sheet while passing over the loop: the results show that there is a great significance if the passing area of the sheet to that of the induction-loop is considered; 4. Effect of pavement thickness and pavement material: the results show that there is no evident effect caused by pavement depth or materials except iron materials; 5. Detectability of larger induction-loop to small steel sheet: the results show that a large induction-loop has a better detective performance for a small iron surface; 6. Extended range of magnetic field caused by induction loop: the results show that this extended range exceeded our expectation in detecting the existing iron surface; 7. Influence of the covering area percentage of a steel sheet on the amplitude variation caused by an eddy-current effect : the results show that the larger percentage of covered area will induce a larger amplitude variation; 8. Design and verify a dual induction-loop device for speed measurement: compared the speeds produced by this device and a table moved by a PLC-driven stepping motor, the results show that the time error is under 10%; 9. Design and verify a speed signal output device: the results show that this device can detect the following eight speed signals output accurately: 30, 60, 90, 120, 150, 180, 210 and 240 km/h.