When a current is applied to a conductor, a magnetic field is formed around the wire. If the current source is removed, the magnetic field collapses into the wire trying to maintain the current flow. This resistance to the change of current flow is defined as inductance. 

What is an inductive loop?

When wound in the form of a coil, the magnetic field becomes concentrated because of the mutual inductance. Applications of coils are transformers, solenoids, relays and inductive loops for loop detection. The field component of an inductive loop system consists of one or more turns of insulated loop wire wound in a shallow slot, typically sawed into the pavement, and a lead-in cable from the curbside to the enclosure, which houses the inductive loop detector module. 

How do inductive loops detect vehicles?

An inductive loop is basically a pickup coil, similar to a transformer.  When a coil is loaded, change occurs. To cause a load on a transformer coil, a short could be applied to the secondary coil and a change is seen on the primary coil. An inductive loop works the same way. When the loop is loaded there is a change seen at the loop detector. Typically, this loading is done with a vehicle passing over or stopping atop the loop.

 

L = inductance (Henries)

C = capacitance (Farads)

Since 2π is a constant and never changes, the resonate frequency will only change if L or C varies. If L or C decreases, f will increase. When the frequency change becomes greater than the threshold set by the sensitivity level the loop detector will output to indicate a vehicle is present. The formula indicates a good loop design maximizes the change in L and minimizes the change in C (XLPE insulation and preformed loops).

Please join us on August 11th for an informative 45-minute webinar on the iCITE™ Data Aggregator™ (DA-100B™) Series field monitoring device - the first system capable of accessing real-time intersection and cabinet data from any traffic cabinet via a high-speed communications connection, regardless of the traffic controller or central ITS system. The iCITE™ DA-100B™ delivers real-time traffic data through an encrypted wireless or Ethernet Cloud-based IP connection. The data set can be customized for anyone wishing to provide performance measurement data to traffic engineers, traffic planners, consulting firms, traffic management agencies and commercial traffic data providers.

Presented by Matt Zinn, RAE (Reno A&E) Applications Sales and Technical Services Manager, the webinar will demonstrate live, how traffic signal technicians and engineers can access real-time arterial traffic and intersection information such as vehicle counts by phase, phase status changes, cabinet alarms, and overall health of the traffic cabinet status from remote, non-interconnected intersections.

To register for this webinar, click here.