Electromagnetic loop vehicle detectors

Three different electromagnetic loop vehicle detector designs are described: self-tuning, bridge balance, and phase-shift. Principles of operation, design limitations, and design trade-offs for each method are presented in detail. The characteristics of the lead-in wire used are shown to be the primary limitation in loop detector performance and stability. Characteristics of commercially available wire used in present-day loop detector installations are discussed. Design equations and graphs illustrate the tradeoff considerations in the determination of optimum loop configuration and inductance.