Loop detector for traffic signal control
US4430636A · kind A · utility
27Cited by
2References
7Claims
0Family size
Inventor
Key dates
| Filing date | Jun 29, 1981 |
| Grant date | Feb 7, 1984 |
| Priority date | — |
| Expiry date | Jun 29, 2001 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08G1/042
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
A circuit used in a traffic control apparatus for detecting changes in the frequency of an oscillator which has an inductive loop-sensor as a resonating element. The circuit comprises a phase-locked loop oscillator with restricted tuning range and a high impedance amplifier followed by threshold detectors adjusted to sense the entry and exit of a vehicle over the area covered by the loop-sensor. The high-resolution of the circuit overcomes long-term drift problems inherent to loop-sensor detectors with analog circuitry.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.