Laboratory Internal Mixer

Sensitivity is the most critical parameter – it defines the smallest metal fragment that the system can reliably detect. Sensitivity is usually expressed in millimetres (sphere diameter) and is adjustable for each product.

Several factors can significantly reduce or enhance effective sensitivity:

• Product type – Wet, salty, or conductive products generate a strong “product signal” that can mask metal contaminants.

• Packaging materials – Foil or metallised films interfere with the electromagnetic field.

• Environmental interference – Vibrating machinery, electrical noise, power fluctuations, and temperature changes all lower sensitivity in real‑world conditions.

While a higher sensitivity setting catches smaller particles, it also increases the risk of false rejects caused by normal product variability. Finding the optimal balance requires thorough testing with your actual production samples.

These two technologies are complementary, not interchangeable. The choice depends on your contamination risks, budget, and application.

Choose a metal detector if:

• Metal is your primary contamination risk,

• You have budget constraints, or

• You are inspecting free‑falling products (where X‑ray is not applicable).

Choose X‑ray if you also need to detect glass, stone, or dense plastics.

False rejects are a common frustration. They usually occur when the detector’s sensitivity is set too high, causing normal product variation to be misinterpreted as contamination.

Main causes and practical solutions:

• Product effect – Wet or conductive products generate strong signals. Fix: Center the package vertically in the detector head to minimise the product signal.

• Environmental noise – Vibrating equipment, nearby motors, and electrical interference trigger false alarms. Fix: Isolate the detector from these sources (use vibration‑damping mounts and shielded cables).

• Improper setup – The auto‑learning process must be performed with actual production samples under real conditions (speed, temperature, orientation). Fix: Re‑run the setup with representative samples.

• Sensitivity drift – Over time, the detector may gradually lose sensitivity to small particles. Fix: Reduce sensitivity slightly and re‑test using a certified test piece.

Yes, but these “difficult” products require special consideration. Wet, frozen, and salty products are electrically conductive, which produces a strong interfering signal that can mask real metal contaminants.

Best practices for difficult products:

• Position the product vertically and centrally in the aperture, with equal clearance above and below.

• Choose a detector with multi‑frequency or simultaneous frequency technology – these can “ignore” the product effect while maintaining high sensitivity.

• Use a larger aperture height to move the product farther from the electromagnetic coils, reducing the product signal.

• Always test and calibrate using actual production samples under real operating conditions, not just dry test pieces.

Regular testing and calibration are mandatory for food safety compliance, especially under HACCP and retailer standards.

Recommended frequency:

• Daily – Perform a routine check using test pieces (ferrous, non‑ferrous, and stainless steel) at the start of each shift.

• Per product change – Re‑test whenever you switch to a different product type, as sensitivity requirements may change.

• After maintenance – Re‑calibrate after any repair, adjustment, or significant environmental change.

• Per audit schedule – Follow your HACCP plan and customer requirements for formal validation testing.

Your metal detector supplier will provide specific guidance on test piece sizes and adjustment procedures tailored to your application. Always document every test for traceability.