Why Specialized for Food?

• Product Effect: Wet, salty, or high-moisture foods (meat, cheese, bread) conduct electricity, interfering with detection. Food-grade detectors compensate for this "product signal."

• Hygiene: Constructed with food-safe materials (stainless steel, specific plastics) and designs for easy cleaning (IP69K rating common).

• Environment: Resists water, dust, steam, temperature fluctuations, and corrosive washdown chemicals.

• Integration: Designed to fit seamlessly into high-speed production lines (conveyors, pipelines, gravity systems).

Key Components

1. Aperture / Detection Head:

   • The "tunnel" through which product passes.

   • Contains transmit and receive coils generating the balanced electromagnetic field.

   • Made of robust, non-metallic, food-grade materials (e.g., FDA-approved polyurethane, fiberglass).

   • Often modular for different product sizes.

2. Reject System:

   • Critical Component: Automatically removes contaminated product upon detection. Types:

     • Pusher Arm: Knocks product off the conveyor.

     • Air Blast: Uses compressed air jets.

     • Diverter Flap/Conveyor: Diverts product to a reject bin.

     • Retracting Belt: Stops/drops the contaminated section.

   • Must be fast, reliable, and hygienic.

3. Control Unit:

   • Houses the sophisticated electronics and processor.

   • Features:

     • Touchscreen HMI (Human-Machine Interface).

     • Sensitivity adjustment & product learning/setup.

     • Automatic product compensation (handles product effect).

     • Reject verification sensors.

     • Data logging (event records, OEE tracking).

     • Password protection & audit trails.

     • Connectivity (Ethernet, PLC I/O).

4. Conveyor System (Integrated or Standalone):

   • Food-grade belt, often detectable (metal-free) or designed not to trigger the system.

   • Speed synchronized with detection and rejection.

5. Sensitivity Test Kits:

   • Includes test wands/spheres of known sizes (Fe, Non-Fe, SS) for regular verification.

Detection Principle (Advanced)

1. Balanced Coil System: Creates a "null" zone in the aperture.

2. Product Passage: As food passes through, its inherent conductivity/magnetism ("product effect") slightly unbalances the field. The detector learns and compensates for this baseline signal during setup.

3. Contaminant Detection: Metal contaminants cause a significantly larger and distinct disturbance than the product itself.

4. Signal Processing: Sophisticated algorithms analyze the signal's phase and amplitude to:

   • Distinguish metal from the product effect.

   • Identify the metal type (ferrous, non-ferrous, magnetic/non-magnetic stainless steel).

   • Pinpoint its location within the product stream.

5. Rejection: Triggers the reject mechanism precisely when the contaminant reaches the reject point.

Types for Food Applications

1. Conveyor Systems: Most common. For packaged goods (boxes, bags, trays) or bulk products on belts.

2. Pipeline Systems (Free-Falling):

   • For pumped liquids, slurries, powders, granules (sauces, soups, milk, flour, grains).

   • Product flows vertically through a non-metallic pipe surrounded by the detector head.

   • Rejection typically via diverter valve.

3. Pipeline Systems (Under Pressure):

   • For viscous products or those needing hygienic closed systems.

   • Detector head clamps around a section of existing metal pipe (requires special calibration).

4. Gravity Systems: For free-falling bulk products or individual items (e.g., apples, potatoes, frozen veggies).

5. Pharmaceutical & Chemical Variants: Similar principles, often with stricter material requirements.

Critical Performance Factors

1. Sensitivity: Measured by the smallest detectable metal sphere (Fe, Non-Fe, SS) at the center of the aperture. Affected by:

   • Aperture size (smaller = better sensitivity).

   • Product effect (worse in wet/salty products).

   • Metal type (SS 316 is hardest; ferrous easiest).

   • Packaging (foil packaging requires specialized systems).

2. Stability: Consistent performance despite environmental changes (temperature, vibration, line speed).

3. Reject Reliability: Must remove contaminated product every time without false rejects.

4. Ease of Cleaning & Validation: Sanitary design is paramount. Must be easy to verify performance (test pieces).