Inductive loop for vehicle axle detection from first concepts to the system based on changes in the sensor impedance components

This paper presents the state of currently used technological solutions employed in research regarding the use of inductive loop sensor (IL) for vehicle axle detection. Inductive loop sensors are less expensive and more durable than other sensors available on the market. What is more, they are the only type of sensor that enables lifted axle detection. System with such sensors may be used for measurement of speed, number, distance and arrangement of vehicle axles. Available know-how of sensor constructions and signal conditioners are also presented, in particular: LC-generators, microloops, “blade” sensors, AC-bridge base system, and a new system based on changes in the IL impedance components. The new solution of the system cooperating with narrow IL is the original part of the paper. This system allows independent measurement of the changes in the IL impedance components. Latest research has shown that the efficiency of the vehicle axle detection of this system, ranges from 98-100 %, and 71.8 % for vehicles traveling with a lifted axle. It should be stressed that other sensors do not allow the detection lifted axles at all. This means that the inductive loop sensors can successfully replace the less durable and more expensive traditional vehicle load axle detectors.