MSF Food Metal Detector: Stop False Rejects in Wet Food Lines

Walk into almost any high-speed poultry, fresh meat, or seafood processing facility, and you will likely observe a frustrating scene at the end of the packaging line: a reject bin overflowing with perfectly good, uncontaminated product.

1. Direct Material Waste: Good product is discarded or routed for manual reprocessing, consuming valuable labor and reducing overall throughput.

To understand why conventional metal detectors struggle on wet or salty production lines, we must look at the underlying electromagnetic physics.

A standard conveyor metal detector generates an electromagnetic field across an aperture using a central transmitter coil and two balanced receiver coils. When a metallic object passes through this field, it disrupts the balance, creating a measurable electrical signal.

● Magnetic Permeability: Ferrous metals (such as iron) distort magnetic flux lines, generating a strong, easily identifiable signal.

The primary inspection challenge arises with Austenitic Stainless Steel (SUS316). Widely used in food processing machinery for its corrosion resistance, SUS316 is non-magnetic and possesses relatively low electrical conductivity.

High-moisture products—such as raw meat, fresh fish, cheese, or pickled items—contain water and dissolved salts (electrolytes). As these products pass through the detector's aperture, the conductive moisture creates a secondary electromagnetic field of its own.

In a conventional single-frequency metal detector, the phase angle generated by wet, conductive food overlaps directly with the phase angle of a small SUS316 spherical contaminant.

When operating on a single frequency, the detector cannot distinguish the signals. If you increase sensitivity to catch a 1.2 mm SUS316 sphere, the product's natural moisture triggers a false alarm. If you back off sensitivity to ignore the product signal, real stainless steel fragments pass straight through.

Legacy inspection systems attempted to solve this issue with "tunable" or "selectable" single frequencies. While these machines allow operators to pick a different operating frequency for different product profiles, they still operate on only one frequency at a time during active inspection. If the product's core temperature or moisture content fluctuates mid-shift, a single-frequency unit inevitably misinterprets the phase shift.

Multi-Simultaneous Frequency (MSF) technology fundamentally changes this dynamic.

● Low-Frequency Waves: Penetrate deep into the product matrix, measuring bulk moisture, salt content, and overall conductivity.

Inside an advanced system—such as our SameGram Conveyor Metal Detector Series—a high-speed Digital Signal Processor (DSP) receives these concurrent frequency signals.

When evaluating line equipment, engineering teams often weigh MSF metal detectors against traditional single-frequency units and X-ray inspection systems. The matrix below outlines how these technologies compare across critical operational parameters:

While X-ray equipment excels at detecting non-metallic dense contaminants (like glass, stone, or bone fragments) and inspecting thick metal foil trays, MSF metal detection remains the most cost-effective, durable, and low-maintenance solution for un-packaged, poly-bagged, or top-sealed fresh product lines.

For factories seeking broader quality automation, exploring comprehensive SameGram Industrial Inspection Solutions helps identify whether standalone metal detection or multi-sensor combination systems best match specific line layouts.

To ensure a new metal detector performs reliably under harsh plant conditions, engineering and purchasing teams should evaluate these five core criteria:

Never base a purchasing decision solely on "empty aperture" specification sheets. An empty aperture test measures clean electromagnetic space, not actual factory conditions. Always demand dynamic testing with your actual product—at line speed, at operational temperatures, and with standard test cards (Fe, Non-Fe, and SUS316).

Food processing plants experience notable temperature fluctuations. A conveyor moving from a 2^°C cold processing room through a washdown cycle can suffer phase drift if the detector head lacks thermal compensation circuits. Ensure the detector includes hardware-level temperature stabilization to keep phase angles locked during long shifts.

Sanitation in meat and dairy plants involves aggressive chemical application and high-pressure hot water washdowns. Equipment must feature robust stainless steel construction with full IP66/IP69K ingress protection ratings to prevent water from entering the coil housing or control electronics.

Modern food safety standards—such as HACCP, BRCGS, and IFS—require verifiable audit logging. Ensure the equipment records every calibration event, test wand check, and rejection occurrence with timestamped data export capabilities via Ethernet or USB.

Plant floor space is always at a premium. Installing separate checkweighing and metal detection units requires extended conveyor lengths, complex wiring, and multiple control interfaces.

Where space is tight, integrating inspection steps into a single machine is an effective approach. Deploying a unified SameGram Combination Checkweigher and Metal Detector System allows facilities to verify net weight compliance while performing high-sensitivity MSF metal inspection—saving up to 50% in footprint while unifying operator control under a single HMI touchscreen interface.

Investing in Multi-Simultaneous Frequency technology is not just an equipment upgrade; it is an investment in direct cost reduction. Let us examine the financial return through a practical factory scenario.

Consider a facility producing 50,000 package units per day of marinated fresh chicken breasts, with an average product value of $4.00 per unit.

Due to variations in brine distribution and surface moisture, the legacy single-frequency detector experiences a False Reject Rate (FRR) of 0.40%.

● Daily False Rejects: 50,000 × 0.0040 = 200 packages/day

By upgrading to a SameGram MSF system featuring dynamic Product Signal Suppression (PSS), the concurrent frequency algorithms dynamically subtract brine interference, dropping the FRR down to 0.01%.

● Daily False Rejects: 50,000 × 0.0001 = 5 packages/day

● Increased Overall Equipment Efficiency (OEE): Line operators no longer stop the conveyor to inspect false alarms or clear backlogged product bins.

For operations processing varied package sizes, tailoring equipment across different Food Industry Inspection Applications ensures both weighing precision and contaminant security line by line.

Product effect no longer needs to compromise detection sensitivity or limit your packaging line throughput. By deploying Multi-Simultaneous Frequency (MSF) technology, processing facilities can confidently detect tiny stainless steel contaminants while maintaining high line speeds and zero-drift operational stability.

At SameGram, we engineer robust, user-friendly inspection equipment tailored to demanding factory environments. Whether you need an IP69K standalone metal detector, a high-speed dynamic checkweigher, or an integrated dual inspection system, our application engineering team is ready to evaluate your product characteristics and supply line layout.

Curious to see how your product performs under Multi-Simultaneous Frequency inspection?

Contact SameGram engineers today to arrange a complimentary sample testing session. We will run your actual product through our MSF systems and provide a comprehensive sensitivity report featuring Fe, Non-Fe, and SUS316 test wand evaluations.

● Explore SameGram Industrial Inspection Solutions

“At SameGram, every innovation starts with listening — to machines, to data, and most importantly, to our customers.”