Top tips for contamination detection

Mettler Toledo - Metal DetectorMetal contamination in the supply chain is usually a result of tainted ingredients, or an imperfect production process. It is difficult to eliminate risk entirely. Metal detectors are an accepted element of many FDA recommended Hazard Analysis and Critical Control Point (HACCP) programmes in the food and beverage industry.

In spite of the best intentions from plant engineers and quality professionals during the evaluation, purchase and installation phase, many things can still go wrong. This can result in failed audits, loss of customers, quarantined products, lawsuits and negative press for the company or brand.

Thermo Fisher Scientific developed some practical tips to offset these problems. The company draws on years of experience in the installation, support and service of metal detectors in plant settings globally.

Common metal detection problems

  • MATCH THE SET-UP TO THE PRODUCT RUNNING: The way a metal detector is configured is not always best suited to the product. Ensure operators and technicians are properly trained to operate equipment. Laminated short-form instructions and test procedures kept by the detector can be created and used as a handy reference.
  • REGULAR REJECTOR CHECKS: Most rejectors are set-up to go off at a fixed distance or time from the metal detector head. They are also programmed to fire for a certain duration. If the rejector is moved or the line speed is changed, the metal detector may not be rejecting a contaminant correctly. Carry out a simple rejector test: pass a metal piece through the system and watch when and how it is rejected. If the system misfires, all that is needed is a simple settings change.
  • THE WORST CASE DETECTION SCENARIO: The least sensitive position in a metal detector is at the centre of the system. In this position, metal is the furthest from the coils. Metal test cards are placed on top of the product flow to audit the detector. This could mean the card is closer to the coils than a metal contaminant inside the product. When installing and commissioning a metal detector, carry out testing under the worst case scenario. Set up procedures to do this regularly.
  • CONVEYING SYSTEMS AT WORK: Metal parts can get into everything in a factory. This includes conveyor belts. To determine if a belt is contaminated, watch the display to see if there is a peak in the signal at regular intervals. In the event there is a peak in signal, clean or replace the belt. Change the belt regularly and keep an eye out for metal contamination. This could desensitise the detector.
  • LIMIT VIBRATION: The smallest movement of a metal detector’s coil can result in reduced sensitivity. The detector-mounting should be as vibration-free as possible. Ensure the metal detector is detached from production equipment, such as mixers, feeders or baggers.
  • KEEP THE BALANCE: If there are doubts about the balance of a metal detector system that is based on regular, consistent false rejects of the same type, call a technician.
  • AVOID WATER LEAKS: As with any sealing system, a metal detector might eventually leak. This could pose a problem when cleaning the machine. Check whether the control electronics are tightly connected to the metal detector. Ensure the incoming and outgoing electrical cables are sealed. Inspect the aperture to ascertain the line has not been damaged.
  • AVOID FALSE REJECTS: Variable frequency AC drives can emit electromagnetic noise through air, which can cause false rejects. To debug this, turn on each piece of equipment adjacent to the metal detector. This should assist in determining which machine is the culprit.
  • THE NOISE FACTOR: Metal detectors are designed to reject products when small changes are detected. Noise spikes or ripples on a power line can fool the detector into thinking metal is present. Make sure there is a dedicated power circuit feeding the detector. This will result in the best possible performance.
  • CALL THE EXPERTS: All metal detector vendors offer convenient services to check, adjust, clean and certify systems. This is also what is needed to keep auditors happy. Do not hesitate to call an expert for regular metal detector maintenance and calibration.


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