Metal detection principles

Product passes through an electromagnetic field; metal disturbs the field, triggering an alarm and automatic rejection. Detectors detect ferrous (iron and steel), non-ferrous (aluminium, copper, brass) and stainless steel metals; stainless steel is the most difficult. The detector does not improve the product; it stops contaminated product reaching the consumer, so validation, routine challenge testing, maintenance and complete records are essential.

• Placement: immediately before packaging or on finished bottles, for a final inspection.
• Common problems: wrong sensitivity, failed challenge tests, poor calibration, reject failure, false rejects, damaged conveyor parts.
• IPQA checks: challenge tests, test-piece sizes, sensitivity, reject operation and records.
• Auditors review: SOPs, validation, calibration, challenge logs, maintenance, deviations, CAPA and batch records.