Method of detecting foreign matter and apparatus therefor

(54) METHOD OF DETECTING FOREIGN

MATTER AND APPARATUS THEREFOR

(75) Inventor: Harunori Tokutsu, Kurita-gun (JP)

(73) Assignee: Ishida Co., Ltd., Kyoto (JP)

( * ) Notice: Subject to any disclaimer, the term ol this patent is extended or adjusted under 35 U.S.C. 154(b) by 150 days.

(21) Appl. No.: 09/604,257

(22) Filed: Jun. 27, 2000

(30) Foreign Application Priority Data

Jun. 30, 1999 (JP) 11-185412

(51) Int. CI.7 G01N 27/72

(52) U.S. CI 324/233; 324/202; 324/239

(58) Field of Search 324/233, 202,

324/239, 241, 243, 225, 226, 204; 209/567, 570, 571; 702/38, 106

(56) References Cited

U.S. PATENT DOCUMENTS

An apparatus for detecting the presence or absence ol foreign matter in a product is provided which includes a reaction signal generating circuit 2 for outputting a reaction signal associated with the product by detecting a change in pattern ol distribution ol magnetic fluxes when the product P is passed through an alternating magnetic field; a determining circuit 10 lor comparing a value ol the reaction signal at a predetermined phase point pi with a threshold value SH to thereby determine the presence or absence ol the foreign matter in the product; and a sensitivity adjusting circuit 12A for adjusting a sensitivity ol the reaction signal generating circuit 2 so that the value ol a first test reaction signal A at the predetermined phase point pi, which is obtained when a product P added with foreign matter ol a minimum size to be detected is passed through the alternating magnetic field, attains a desired level relative to the threshold value SH. Thereby, the foreign matter ol a predetermined size can be detected assuredly.

5 Claims, 6 Drawing Sheets