Detecting ferrous objects

Citation

Hollingum, J. (2001), "Detecting ferrous objects", Sensor Review, Vol. 21 No. 1. https://doi.org/10.1108/sr.2001.08721aad.014

Detecting ferrous objects

Detecting ferrous objectsKeywords: Magnetic, Sensing

Applicant: Cherry Corp. (US)Patent number: US6127821Publication date: 3 October 2000Title: System for adjusting a magnetic sensor to detect the presence of ferrous objects

It is an object of the invention to provide a relatively simple, inexpensive and easily manufactured proximity sensor. It is a further object of the invention to provide such a sensor that utilizes interacting fields of two or more magnets to define a null flux point at the sensing plane of a flux sensor. It is another object of the invention to provide a flux sensor that uses at least two different kinds of magnets, one magnet having a high density flux field and the other magnet having a lower density field that can be easily tuned in the manufacturing process. Another object of the invention is to provide simple and relatively inexpensive proximity detectors that are very sensitive to flux changes caused by a ferrous object. The sensor utilizes at least two magnets that are positioned with like poles facing one another and a magnetic flux sensor disposed between them. The interacting flux fields of the magnets define a null field point with respect to the magnetic flux sensor. When a ferrous object is brought into proximity with the free end of either magnet, the null field is shifted and the magnetic flux sensor generates an electrical signal in response to the shifted flux field to indicate the presence of the ferrous object.