Method and apparatus for producing electromagnetic surveillance fields
US4634975A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 17, 1984 |
| Grant date | Jan 6, 1987 |
| Priority date | — |
| Expiry date | Sep 17, 2004 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08B13/2488
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
Methods and apparatus for producing alternating electromagnetic fields for use in theft detection and surveillance systems include individual series-type electrical drive circuits for separately energizing each of the field-generating coil windings with maximum efficiency and control, and transformer-type coupling between the different field-generating coil drive circuits to effect balanced and equalized current flow in the different coil windings and thereby enhance both drive efficiency and field uniformity. Additionally, a current-sense winding provides for monitoring of field coil current flow, and for feedback control of the magnitude and/or frequency of the coil excitation drive. In a preferred embodiment, the fields are generated by at least two coils on each opposite side of the field, and the coils are separately energized through separate but commonly-coupled drive circuits.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.