I want to make a vehicle detection prototype. I find there are multiple choices of sensors that can be used to detect a vehicle, such as acoustic, ultrasonic, infrared, magnetic inductive sensor.
I am only familiar with infrared sensors, which are low cost, can be a good choice of detection of approaching objects, whereas the acoustic and ultrasonic are much more expensive.
However an infrared sensor is not a complete solution. In order to find whether the approaching object is either a vehicle or any other objects, I suppose I need either a magnetic or an inductive sensor. I learned that scalar magnetometers are suitable for the vehicle detection, because it measure the total strength of the magnetic field to which they are subjected. However then I learned that magnetic sensors can be also divided into DC and AC sensors.
in wiki, it says "AC" if they measure fields that vary relatively
rapidly in time, and "DC" if they measure fields that vary only slowly
(quasi-static) or are static. AC magnetometers find use in
electromagnetic systems (such as magnetotellurics), and DC
magnetometers are used for detecting mineralisation and corresponding
geological structures.
Can anybody explain the difference between DC and AC based magnetometers? Currently my idea is to use a magnetometer with an infrared sensor. What do you think of this approach? My evaluation criteria is performance first, then power consumption, and cost last.
Best Answer
"Vehicle detection loops, called inductive-loop traffic detectors" are one pretty common method. A groove is cut in the pavement, wire is layed in the groove, the groove is filled in with a sealant, and the wires go to a processor which makes the wire act like a metal detector - the vehicle interacts with the e-mag field, and the processor detects that.
Are you allowed to sawcut the area in question? If not, then a different method should be selected. Maybe just tubes across the road as one finds leading into or out of a town so the local municipality can count how many cars are using a road. I imagine they just detect change in air pressure as cars drive over the tubes.