Abstract
Three different electromagnetic loop vehicle detector designs are described; self-tuning, bridge balance, and phase-shift. The 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. Furthermore, the characteristics of commercially available wire used in present-day loop detector installations are discussed, after which design equations and graphs illustrate the trade-off considerations in the determination of optimum loop configuration and inductance.