LOOP COIL FOR VEHICLE SPEED DETECTING DEVICE

摘要

PURPOSE:To enable installation of a vehicle speed device of a loop type system by using an auxiliary loop coil and thereby enhancing the sensitivity of detection even when steel bar or steel frames are embedded in a roadbed. CONSTITUTION:The loop coil (hereinafter shown by LC) 1 in a vehicle speed measuring device is devised so that the speed of a vehicle is measured by detecting the passage of the vehicle 4 through the utilization of the apparent change in inductance caused when the LC1 buried under a road surface and supplied with a high-frequency current is connected electromagnetically with the vehicle 4 running on the road surface. By embedding the LC1 for detecting the vehicle and the auxiliary LC2 in layers on the conductor of the roadbed, coupling the auxiliary LC2 to the LC1 for detection and supplying thereto the current having the same frequency with the current supplied to the LC1 for detection and keeping a fixed relation of phase, the vehicle 4 can be detected with high sensitivity even when there is the connection of the steel bars 3 and the like embedded under the road surface.