Inductive Loop Relay Problem

Hi all

Well I tried googling this but could not find a satisfactory answer , so here I am seeking help from all you experts

So my question is regarding inductive loop sensors used on the road to give presence, vehicle classification etc information. These inductive loops are connected to a vehicle detector ( Relay - pulse or presence output). This relay ( all kind/ not specific to a brand) produce a digital output - it gives 1 when the vehicle is over the inductive loop and 0 for the rest of the time. This data is collected for lets say 30 sec and then transferred on to higher level to be used with SCATS or SCOOTS.

OK so what ive found is the digital output sometimes get stuck on/off ( regardless of vehicle going over loop or not), or the output is broken, also problems such as chattering and hanging on/off occurs. I cant seem to get to the core of these problems. Why do they occur? The inductive loop does its job by providing the magnetic profile of the vehicle as it goes over loop , then why is relay incapable of detecting it?

Any suggestions/ ideas are welcome :-D

Thanks

It is not the relay that produce a digital level. The inductive loop is a part of a tuned self-oscillating LC circuit. When a car narrows this circuit decreases frequency as inductive value increases and opposite when a car leaves the loop.
Resulting varying frequency can be demodulated as FM or FSK resulting in a analog level. This signal can then be feed to a level detector with some hysteresis to avoid detecting minor variations due to what particular part of a vehicle that is passing by. Output from this circuit is now digital and can be feed to a relay or similar.

This was a bit simplified explained. In a real circuit must self regulating dynamic oscillators and dynamic detecting levels be used to be able to correct detect small thing such as a bicycle and avoid multiple signals due to a long truck. Another problem is shifting road conditions such as temperature and moisture. Feedback in analog circuit part keep the system stable. Even if another car is parked close to the inductive loop, must it be able to detect other cars and a part of the circuit must set a limit how low inductive changes that should be accepted as a vehicle passing by. A vehicle with very low magnetic signature or at a very low speed will therefore normally not be detected.
It requires relative simple logic to discriminate unlikely long output pulses avoiding that the switching get stuck detecting a vehicle or opposite.
All electronics gets faulty sooner or later or a circuit can be poor designed but else should it not be a problem with that circuit output hangs in a specific level.
Say for example that the inductive loop becomes partly broken. As it is a rather common situation due to freezing or movement in pavement must a good design be able to detect also that situation (signaling an error condition).

You can think the leakage as Q (Charge) in heteresis loop may other than your framework , so you must make path to control the Q leak . Thing can be using for Energy Saver or blinking light or Direction light . And there are superregeneretive technic that use only Cap for making inductorless circuit .

Fuzzy logic is the technics to smooth adjust such a Angle velocity , ω in transfer function of multi-point and more specific sensor . And try single Chip Design is best good facturing for minimun area and weight board.