This can result in significant pavement movement that can stretch or break the wires and connections, causing the loop to malfunction. For example, if the loop were not sealed properly during the installation process, moisture could reach the wire and change its electrical characteristics. Older loop sensors have additional problems. Improved technology has significantly reduced these problems. Unless the traffic-control box is struck by lightning or is poorly grounded or a utility company backhoe digs through the loop, the modern systems perform much better.
Every loop sensor has an oscillator on the front end.
The oscillator has a frequency determined by the loop s inductance. By measuring that inductance and how it changes, the arrival and passage of a vehicle can be detected. Unfortunately, some kinds of vehicles cause much smaller shifts in inductance, and thus they are more difficult to detect. These include high-bed trucks, which carry their conductive surfaces much higher farther from the loop. Similarly, bicycles have a minimal effect on the field of the loop because they have much smaller conductive surfaces, and the surfaces they do have are structured perpendicular to the loop.