Study On Electromagnetic Circumstance Of The Inductive Loop Detector In Highway Tunnel

Inductive loop detector is one of the most primary equipments used to detect vehicles in highway tunnels, with characteristics of the high ratio of performance and price, convenient application to project, without maintenance and simple technique, etc. It utilizes the theory of electric vortex detecting to work, and provides traffic data to information processor and issuance units via the communication network, as the significant foundation for surveillance and control central to analyze and judge and distribute information and implement control scheme. Accordingly, the detector plays a significant role in the traffic control and calamity preventing in highway tunnel, and much higher reliability has been bring forward to it. However, in order to ensure the traffic safety, large numbers of electronic and electric equipments have been installed in highway tunnels. These equipments radiate electromagnetic power to space while operating. Simultaneity, the electromagnetic interference sources, such as the electric system on motor vehicles passing in the tunnel, are also the potential menace to the loop detector.Going about the complex and severe electromagnetic circumstance, and combining with the theory of the detector, this paper has analyzed and researched all the potential electromagnetic interference source one by one, then the mathematics model of the uppermost electromagnetic source——the ignition system on vehicle has been built, lastly the finite integration technique has been used to computer numeric simulation. The result of simulation indicates that the radiated electric field coming from the fire system on vehicle has severe effect on the normal work of the inductive loop detector, without considering the shielding function of the metal shell of vehicle and the ignition system just on the loop. Therefore, some shielding measures should be taken to the detector. The concrete research content are summarized below:①Study the theory of the finite integration technique, including the Maxwell grid equations, the simulation excitation, the leap-frog scheme, numerical stability and the boundary condition.②Analyze the theory of the detector on the basis of consulting the current references.③Analyze the mechanism of all the interference and the radiating characteristics and the transmitted approaches. Research the computing theory and build the equivalent mathematics model of the ignition system on vehicle, which is the uppermost electromagnetic source affecting the normal work of the loop detector.④Verify the validity of the computing theory and equivalent mathematics model of the interference source, by utilizing the finite integration technique to simulating compution.⑤Discuss the valid methods and measures of interference suppression of loop sensor.