| 摘要 |
A metal detector (20) has a metallic enclosure (21) with entrance and exit apertures (30, 31). A coil system inside the enclosure has an energized transmitter coil. First and second receiver coils (24, 25) bound a detection zone (28) between the apertures, through which inspected objects (2) travel. The receiver coils are on opposite sides of the transmitter coil, with regard to the direction of travel (13). The receiver coils are connected in series, but their windings are wires oppositely in a rotational sense. Metal contamination in the object generates a detection signal in the receiver coils. A first and second flange (26), arranged at the entrance and exit, cancel the undesirable influence of metal contamination beyond a first distance upstream of and a second distance downstream of the coil system. The respective flanges differ from each other and, consequently, the first and second distances are different. |
| 主权项 |
1. A detector for inspecting an object for the presence of metal, comprising:
a metallic enclosure having an entrance aperture through which an object being inspected enters the enclosure and an exit aperture through which the object exits the enclosure, the respective apertures defining a travel direction;
a coil system, arranged inside the enclosure, the coil system comprising:
at least one transmitter coil, arranged to generate a primary electromagnetic field when energized by an alternating electric current;at least one first receiver coil, arranged so that the primary electromagnetic field induces a first voltage therein; andat least one second receiver coil, arranged so that the primary electromagnetic field induces a second voltage therein, the respective receiver coils bounding a detection zone, extending between the entrance and exit apertures, through which the object being inspected moves;wherein the first and second receiver coils are arranged asymmetrically relative to the transmitter coil, with the first receiver coil positioned, relative to the travel direction, at a first predetermined distance ahead of the transmitter coil and the second receiver coil positioned at a second predetermined distance after the transmitter coil, the first and second predetermined distances being different;wherein the respective receiver coils are connected in series, the wires of the respective receiver coils wound with the opposite sense of rotation relative to each other; and at least one of: a first cancelling means and a second cancelling means for cancelling an electromagnetic field, the first cancelling means arranged at the entrance aperture to cancel the primary electromagnetic field beyond a predetermined first distance from the coil system, and the second cancelling means arranged at the exit aperture to cancel the primary electromagnetic field beyond a predetermined second distance from the coil system, such that, when both the first cancelling means and the second cancelling means are present, the respective cancelling means are different from each other and the respective first and second distances are likewise different from each other, and that the first and second induced voltages are in a balanced state with each other when no metal is present in the objects under inspection. |
