What change is monitored by the amplifier when a vehicle enters the detection area?

When a vehicle enters the detection area of an inductive loop system, the primary change that the amplifier monitors is a frequency change. This occurs because the presence of a larger metallic mass, such as a vehicle, modifies the inductance of the loop, which in turn affects the oscillation frequency of the system. As the vehicle approaches and enters the detection field, this change in frequency is detected by the amplifier, allowing it to recognize the presence of the vehicle and trigger the appropriate response from the traffic signal control system.

This method is highly reliable for detecting vehicles due to its sensitivity to changes in the electromagnetic field around the inductive loop, making it a standard practice in traffic management systems. Understanding this principle is crucial for traffic signal technicians, as it forms the basis for how vehicle detection is implemented and managed within the technology used at intersections.