Inductive Loop Detectors at Hight Vehicle Speed

Hello Everyone

I am currently studying the inductive loop detectors used in the traffic control department. I believe the data from the detectors is highly unreliable and noisy. A lot of research has been going on on the 'Fault detecting algorithm' and other means to improve the accuracy of an ILD(Inductive Loop Detector).

My question is, How do these ILD detect a fast moving vehicle. Lets say a vehicle going at 100 km/hr on a motorway. It would go over a normal (4m x 4m or even smaller) inductive loop within FRACTION of seconds.

IDL works in the following way : ILD have a magnetic field around them---> incoming vehicle disturbers the magnetic field --> the ILD induces eddy currents into the conductor part of the vehicle --> thereby reducing its own inductance -->if this decrease in inductance crosses a threshold value, a call is made to the electronic unit and the vehicle presence is identified.

This is quite a LONG process. I fail to understand how all this can be done within FRACTION of seconds. Surely the conductor(vehicle) needs to be in the magnetic field (over loop) for 'some' time to be able to disturb the magnetic field PROPERLY. :roll:

PLEASE PLEASE PLEASEEEEEEEE Can someone give me some tips on how ILD works in high speed environment ! Thanks !

Neyolight

Why are you considering that’s a long process?
At 150km/h = 41.66m/s, if the inductive loop =1m, this means 20 ms to process a single car.
And it’s a simple process, not involving image detection, number plate recognition and so on… :-D

I already doubted your statement about unreliable operation of inductive loops in a previous thread. I can say, that they are used in Germany and other European countries at least on city and regular roads (up to 100 km/h speed limit), while highway traffic monitoring often uses radar sensors. The latter is more for ease of installation rather than due to technical restrictions, I think.

Response speed is a matter of resonant circuit quality factor and signal filtering. No reason, why a multi 10 kHz circuit won't be able to react in 10 ms.

Thanks a lot for your comments!

FvM - Yes you are correct on ILD being the most common sensors in traffic managment. Even in Auckland, IDL are used at almost all traffic lights and also on the motorway. Despite being such an old technology, IDL still does not provide accurate data due to many factors. IDL is sensitive to the speed of the approaching vehicle, height of the conductor (vehicle) , weather, installation procedure used, detector technology used etc . I've been reading up on ILD for the past 1 month now and so far I haven't come across a hardcore formula saying that at this speed, this height, this many turns in the loop -THIS would be the change in inductance. It is very difficult to parametrize the ILD output. The problem increases even more when the output is used by a traffic control program (ie SCATS).