Detection system

A detection system comprising:

• an electromagnetic induction sensor comprising a transmission coil, a first reception coil combined magnetically with the transmission coil and positioned apart from the transmission coil, and a second reception coil that is differentially connected to the first reception coil;
• and
• a vehicle detection unit configured to detect that a vehicle has passed through an area where the electromagnetic induction sensor is installed;
• characterized by:
• a trajectory image output unit configured to plot detection waveforms in a coordinate system represented by a reception level defined as a differential output of the first reception coil and the second reception coil, and a phase difference of the received differential output and a signal transmitted by the transmission coil, and to output a 2-dimensional trajectory image in a time series;
• and in that,
• the first reception coil is positioned apart from the transmission coil along a traveling direction about which a vehicle can travel;
• the first reception coil, the transmission coil, and the second reception coil are positioned along a traveling direction of the vehicle in sequence, so that a distance between the transmission coil and the second reception coil is equal to that between the first reception coil and the transmission coil;
• and
• the vehicle detection unit is configured to detect that a vehicle has passed through an area where the electromagnetic induction sensor is installed based on the trajectory image.