Inductive loop vehicle detector

US4668951A · kind A · utility

Assignee

• Sarasota Automation Limited · GB

Inventors

• Richard K. Duley · Winchester, GB
• David F. Evans · Winchester, GB

Key dates

• Filing date: Aug 10, 1983
• Grant date: May 26, 1987
• Expiry date: Aug 10, 2003

Classification

• Technology area (CPC G): Physics
• CPC primary: G08G1/042
• WIPO field: Control
• WIPO sector: Instruments

Abstract

In a vehicle detection apparatus having a plurality of channels, each arranged for detecting vehicles according to their influence upon the frequency of a respective loop oscillator the oscillation frequency of which is dependent on the inductance of a respective vehicle-sensing inductive loop, a common computer performs a calculation for each channel in turn whereby changes in the frequency of the respective loop oscillator are monitored and analysed. In one embodiment, the computer calculates an appropriate operational number, the time taken for that particular number of loop cycles to occur is measured and stored as a period count and the period count is compared with an environmental reference number to determine whether or not a vehicle detected flag should be raised or lowered. Neither the operational number calculated by the computer nor the reference number is fixed but provision is made for updating both. In another embodiment, the computer calculates an appropriate period of time and the number of loop cycles occurring in that time is counted and that count stored for use in determining whether the vehicle detected flag should be raised or lowered. Again, provision is mad…