Metal Detector vs X-Ray vs Checkweigher: Food Inspection for ASEAN Exporters

A metal detector, an X-ray inspection system and a checkweigher answer three different questions, so an ASEAN food exporter rarely picks one instead of another. A metal detector finds metal. An X-ray system finds anything denser than your product — metal, glass, stone, calcified bone — including through aluminium foil and inside cans. A checkweigher finds the wrong weight and no contaminant at all. Most export lines need a checkweigher plus one of the other two, and the choice between those is set by your packaging and your hazard analysis, not by the price gap. In Thailand, the X-ray route also needs a licence from the Office of Atoms for Peace before the machine runs.

Three Machines, Three Questions

| Machine | Finds | Misses or struggles with | |---|---|---| | Metal detector | Ferrous, non-ferrous and stainless steel | Glass, stone, bone, plastics; metal inside aluminium foil; weaker on wet or salty products | | X-ray | Metals, glass, stone, calcified bone, ceramic, PVC, rubber | Hair, insects, wood, cardboard, low-density plastics, cartilage, thin glass | | Checkweigher | Under- and overweight packs | Every foreign body |

The X-ray row follows the Manitoba government's food-safety guidance, which explains that detection "is directly related to the density of the product and the contaminant". No single machine closes every physical hazard; your HACCP plan decides which ones the machine must close.

The export stakes are concrete. US FDA Compliance Policy Guide 555.425 treats a ready-to-eat food containing a hard or sharp foreign object of 7 mm to 25 mm as adulterated, and FDA may also act on objects under 7 mm when infants or the elderly are among the intended consumers. Retailer-audited schemes reach into the line itself: BRCGS Food Safety Issue 9 clause 4.10.3.2 requires a detector to have automatic rejection into a secure unit accessible only to authorised personnel, a belt-stop alarm where product cannot be ejected, or in-line location of the contaminant.

Metal Detectors: Read the Stainless Steel Line First

A well-specified [conveyor metal detector](/en/products/ali-store-conveyor-belt-metal-tin-detector-food-metal-detector-machine) in this category is rated ≥0.5 mm ferrous, ≥0.8 mm non-ferrous and ≥1.0 mm SUS304 — stainless is twice the ferrous figure. That ratio is normal: austenitic grades such as 304 and 316 have low magnetic permeability and are the hardest metals to detect. They are also what your slicers, screens and mixer blades are made of, so the stainless number is the one to compare between quotations.

Three conditions sit behind every sensitivity figure:

• **Aperture.** Sensitivity is quoted for a test sphere through the geometric centre of the aperture, the least sensitive point, and it worsens as the aperture grows. Another [food-processing metal detector](/en/products/ali-store-professional-automatic-metal-detector-for-food-processing-applications) quotes Fe 0.8–3.0 mm, non-Fe 1.2–4.0 mm and stainless 1.5–5.0 mm across detecting heights from 80 to 350 mm: the range is the aperture choice. Ask for the figure at your aperture.
• **Product effect.** Wet, salty or conductive products — fresh meat, seafood, cheese, ready meals — generate their own signal, and temperature changes it. A frozen shrimp block and the same block half-thawed are different products to the coil. Send samples and require a test report run with your product at line temperature.
• **Packaging.** Standard balanced-coil detectors cannot inspect through aluminium foil, and ferrous-in-foil designs find ferrous metal only. If your pack is foil or metallised film, you are an X-ray buyer.

Then read the reject line. The same detector lists "reject system optional", which is normal on a base-price quotation. For a line supplying an audited retailer, the rejector, a secured reject bin and reject confirmation are the specification, not an option.

X-Ray: Density, the Room and a Licence

X-ray solves foil, cans, glass and stone. One [conveyor X-ray system](/en/products/ali-store-industrial-conveyor-food-x-ray-inspection-system-intelligent-defect-detection-ma) states a stainless steel ball of Φ0.3 mm and a glass or ceramic ball of Φ1.0 mm; a [dual-beam system for bottles, jars and cans](/en/products/ali-store-inline-dual-beam-xray-inspection-system-for-bottles-jars-and-cans) states Φ0.5 mm stainless and Φ2.0 mm glass from a dual source rated up to 120 kV. Another unit labels its figures "no product" — the honest way to write it, because every X-ray number is an empty-belt best case until your product's density and thickness sit on the belt.

Two items the brochure treats as footnotes decide the project:

• **The room.** X-ray cabinets are cooled by an industrial air conditioner, and the rated envelope matters. One system states −10 °C to 40 °C and 30–90% humidity without condensation; another is rated 0–35 °C, which leaves little margin in an un-air-conditioned packing hall in the hot season. Put the envelope in the contract.
• **The licence.** Under Thailand's Nuclear Energy for Peace Act B.E. 2559 (2016), possessing or using a radiation generator requires a licence (section 26). The Ministerial Regulation on Radiation Safety B.E. 2561 (2018) then requires the licence holder to keep a radiation safety measure reviewed at least once a year, delineate controlled and supervised areas, mount radiation symbols at the generator and keep monitoring records; the public dose limit is 1 millisievert per year. Import needs a separate Office of Atoms for Peace licence, which regulatory consultants report is processed within 45 days of submission. Malaysia licenses irradiating apparatus under the Atomic Energy Licensing Act 1984, and Vietnam, Indonesia and the Philippines have their own radiation regulators. The "<1 μSv/h" leakage line on a datasheet is where your licence file starts — ask for the leakage test report, not the brochure line.

Checkweighers: Judge Accuracy Against Your Pack Size

A checkweigher is a legal-metrology machine. ASEAN member states apply the ASEAN Common Requirements of Pre-packaged Products, endorsed in 2004 and aligned to OIML R 87 (2016 edition) in 2023. Three rules apply to a lot: the average must reach the nominal quantity; no more than 2.5% of packs may be short by more than the tolerable deficiency T; and no pack may be short by more than 2T.

| Nominal quantity | Tolerable deficiency T | |---|---| | 50–100 g | 4.5 g | | 100–200 g | 4.5% | | 200–300 g | 9 g | | 300–500 g | 3% | | 500–1,000 g | 15 g | | 1–10 kg | 1.5% |

Now read accuracy against that table. For a 250 g snack pack, T is 9 g, and a pack more than 18 g short is illegal. A [multi-level checkweigher](/en/products/ali-store-high-speed-multi-level-checkweigher-weighing-scales-dynamic-check-weigher) rated ±0.3–1 g resolves that comfortably. A unit quoted at ±20 g cannot even separate a legal 250 g pack from an illegal one; that accuracy belongs on multi-kilogram packs. Accuracy also drives giveaway: because the average must reach nominal, a coarser machine forces a higher target weight, and every gram above nominal is product you give away. Ask at which pack weight and line speed the accuracy was measured.

What to Put in the Purchase Order

• Ferrous, non-ferrous and stainless sensitivity at your aperture, tested with your product at line temperature
• Automatic rejector, a reject bin accessible only to authorised staff, and reject confirmation — not "optional"
• For X-ray: empty-belt and in-product sensitivity stated separately, the leakage test report, the rated ambient envelope, and which licensing documents the supplier provides
• Checkweigher accuracy at your pack weight and line speed, stated against T
• Washdown rating (datasheets in this category that state one mostly quote IP65 to IP67), site voltage and frequency, certified test pieces and operator training

Conclusion

Choose the checkweigher from your pack sizes, choose between metal detection and X-ray from your packaging and hazard list, and budget X-ray's licence and cooled room as part of the machine. Browse the [food inspection range](/en/products?category=pm-food-inspection), read our guides to [food processing equipment from China](/en/news/food-processing-equipment-china-asean) and [packaging line automation](/en/news/packaging-machine-automation-asean), review [China sourcing](/en/china-sourcing), or [talk to us](/en/contact) about testing your own product before you order.