Detectors operate in either the pulse or presence mode. Many detectors today employ digital technologies which sense a change in the resonant frequency of a loop due to a decrease in inductance. Digital techniques allow more reliable and precise measurements than their analog counterparts. These features can significantly reduce detector maintenance costs and calls. A consistent and fast response time is crucial for accurate speed measurements.
Response time is affected by vehicle size, speed, detector type, sensitivity, and wire type.
Response time decreases with smaller vehicles, which have lower ground clearance and a shorter distance to the engine block and axle. Faster speeds tend to reduce response time, as does increased sensitivity. Recovery time - the time required for a loop to return to normal operation after a period of sustained occupancy. Recovery time is particularly important for vehicle counting. Loops should also be stationed around access and egress points, and at any locations where operational problems occur.