Development and Test of an Induction-Loop Speed Measuring System
Date Issued
2009
Date
2009
Author(s)
Lin, Ming-Tsz
Abstract
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.
Subjects
Eddy-current effect
Induction loop
Simulator
Speed measurement
Type
thesis
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