Food grade metal detectors are crucial to a food manufacturer’s quality assurance and safety program. How can you test your equipment to ensure detectors are performing accurately? Here are the top 10 food metal detector and equipment testing FAQs (Frequently Asked Questions) we receive regarding our food metal detectors (including Multiscan food metal detectors), and their best-practice answers.

A:  The size of the head is based on the dimensions of the package. Always simulate production conditions as closely as possible, including speed, temperature, and orientation of the product.

A:  For most applications, size the aperture 2 inches wider and 2 inches taller than the largest package intended to pass through the food grade metal detector.

A:  For wet and conductive products, center the package vertically in the head, ensuring the same amount of distance is above and below the package. Often this means the head height will be larger than the standard sizing recommendation. This helps reduce the product signal by moving the product away from the electromagnetic coils.

A:  ‘Frozen’ is a general term. For metal detection, it’s critical the actual product temperature and state are fully understood as results will change drastically. Products that are completely frozen to the core will often ‘learn’ as a dry product does with little to no product effect. In contrast, a partially frozen product will respond much differently passing through a metal detector and can cause excessive false rejects as production conditions vary throughout the day. Ideally, it’s best to set up the metal detector for frozen food industry in the production environment at the correct temperature and state.

A:  The default sensitivity setting is 6db (or 50%) below the peak signals encountered during the learn process. If the product has an inconsistent signal this generally is a safe setting.  If the signal is very consistent it may be able to increase sensitivity to 3db (or 30%) below the peak signalsSet the detect thresholds to about 1.2 to 1.5X the maximum product signal for standard metal detectors. For Multiscan food metal detectors, the equipment testing best practice is to set both in and out of phase 3dB less (1.4X) than reject signal (36dB).

A:  For all food grade metal detectors, eliminate as much background noise as possible. Then start with the manufacturer’s default settings. Ensure production samples are used for setup.

A:  Place metal spheres in multiple locations on the package, always trying to keep the metal at the midline of the head height and middle of the package. Test the leading and trailing ends, both sides, the absolute center of package (whenever possible), and the top. Specify the smallest metal detected in ALL locations.

Equipment testing best practices to ensure food grade metal detectors precision and accuracy

A:  When metal is missed on the leading or trailing edges of a standard food grade metal detector, adjust sensitivity per the manufacturer’s recommendation and when required increase metal size until it’s detected. 

A:  It is widely understood that ferrous is the easiest metal to detect due to its magnetic properties. Magnets attract iron. An electromagnetic field reacts most to ferrous metal, and the lower the frequency, the greater the reaction. Conversely, stainless steel, which contains only a small amount of ferrous metal, has little or no magnetic property. Metal detectors must run at a high frequency to find stainless steel because the high frequency field induces a current in the stainless steel which creates a new field that interacts with the original field in the metal detector to create a signal.

A:  Small metal foreign objects have very small signals. The metal detector is operating in a factory that has many possible noise sources that can confuse the metal detector electronics and software. Make sure you address some of these sources that can interfere with your testing:

  • Large motors turning on and off
  • Electronics boxes broadcasting wide spectrums of radiated noise
  • Production equipment vibrating and causing the antenna in the metal detector to move ever so slightly
  • Electrical power surging and dropping
  • Temperatures going from freezing to boiling and back again

Note that all metal detectors may not operate or perform the same way. Check with your equipment manufacturer for specific testing instructions.

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