Device for detecting metallic objects in a flow of non-metallic material
US4563644A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Mar 30, 1983 |
| Grant date | Jan 7, 1986 |
| Priority date | — |
| Expiry date | Mar 30, 2003 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V3/107
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A device for detecting metallic objects in a material flow, comprising as sensing member a scanning coil consisting of a primary coil and, for example, two oppositely connected secondary windings arranged symmetrically around the primary winding so that the voltage induced in the secondary winding becomes zero as long as no conducting objects appear in the scanning area. To eliminate irrelevant signals from conducting objects in the vicinity of the scanning coil but not in the material flow or from weakly conducting objects in the material flow, the primary winding is fed with at least two alternating currents having different frequencies. The corresponding secondary voltages are rectified in phase-controlled rectifiers, and in a calculating circuit the difference is derived between the output of one rectifier voltage and the output of another rectifier multiplied by a constant factor which includes the relation between the frequencies of the corresponding alternating voltages.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.