Foreign Object Detection Compliance with Retailer Codes of Practice.

To assure the highest level of food safety possible for their customers, leading retailers have established requirements or codes of practice regarding foreign object prevention and detection. One of the most stringent food safety standards was developed by Marks and Spencer (M&S), a leading retailer in the UK. Its standard specifies what type of foreign object detection system should be used, how it must function to assure rejected products are removed from production, how the systems should “fail” safely under all conditions, how it should be audited, what records must be kept and what the desired sensitivity is for various size metal detector apertures, among others. It also specifies when an X-ray system should be used instead of a metal detector.

M&S requires the following system features to meet its basic requirements. Please note all these items are standard on Thermo Scientific™ M&S-compliant systems.

  • All system sensors must be failsafe, so when they fail they are in the closed position and trigger an alarm
  • Automatic rejection system (including belt stop)
  • Pack registration photo eye on the infeed
  • Lockable reject bin
  • Full enclosure between the inspection point and the reject bin to prohibit removal of contaminated product
  • Reject confirmation sensing (reject activation for retracting belt systems)
  • Bin full notification
  • Bin open/unlocked time alarm
  • Low air pressure switch with air dump valve
  • Key switch to start the line
  • Lamp stack with:
    - Red lamp where on/steady indicates alarms and blinking indicates bin open
    - White lamp indicating the need for QA Check (audit software feature)
    - Alarm horn

For applications where a higher level of compliance is requested, systems should include an exit check sensor and a speed encoder. These items are supported but optional on Thermo Scientific M&S-compliant systems.

To ensure all production is inspected correctly, the following failsafe features create faults or alarms to notify operators. They are standard in all M&S-compliant systems with the exception of Exit Check.

  • Fault and alarm notifications (on screen and via the light stack).
  • Metal detector fault
  • Reject confirmation alarm
  • Reject bin full alarm
  • Reject bin open/unlocked alarm
  • Air pressure failure alarm (for standard pusher and air blast rejection)
  • Reject device failure alarm (for retracting conveyor belt systems only)
  • Exit Check pack detection (higher level compliance, optional)

Please note all faults and alarms must persist after a power cycle and only a QA manager or similar high-level user with a key switch can clear them and restart the line. If desired, this clear function can also be implemented on the Sentinel metal detector or NextGuard X-ray system front panel.

All standard Thermo Scientific M&S-compliant systems include the capabilities to execute the following rejection-related tests, assuring system integrity at all times.

Reject Confirmation Test

  • A key switch is used to enable this test
  • When the key switch is turned to the “Test” position, the electrical supply to the reject solenoid valve is disconnected
  • A test pack with a contaminant can then be passed down the line
  • The inspection system should detect the contaminant and provide a reject signal
  • Because the supply to the reject valve has been disconnected, the reject device should not operate. 
  • The system should recognize the reject did not enter the bin, alarm and stop the conveyor belt.

Bin Full Test

  • A mechanical device is installed in the reject bin that breaks the beam of the Bin Full photo eye simulating that the bin is full of product
  • The system should recognize that the bin is full, alarm and stop the conveyor belt.

Belt Stop systems will include an audible and/or visible reject indicator and a key-switch to restart the system. Retracting belt systems should be used when more than one pack is being inspected across the width of the belt or products are randomly positioned on the conveyor in bulk mode.

All Thermo Scientific metal detectors and X-ray systems include software to automate the auditing process while in production. The system will notify the operator when it is time to audit and prompt them to pass the challenge products with foreign objects. With APEX metal detectors, this feature is called QAT (Quality Audit Test) and with the Sentinel metal detector and NextGuard X-ray system it is called QA Check. Reports are saved on the system showing the time of an audit and if it passed or failed. To meet the M&S auditing requirement it is necessary to create test products for a metal detector with metal in three positions – leading edge, center and trailing edge. To facilitate this test, QA Check can be configured to run three times instead of just once.

Level 1 Sensitivity: This is the target range of test piece sizes which should be detectable based on the height of the product on the conveyor and the use of an appropriately sized metal detector. It is expected that the best sensitivity (i.e. smallest test sample) is achieved for each food product.

Level 2 Sensitivity: This range should only be used where documented evidence is available to show that test piece sizes within the Level 1 Sensitivity range are not achievable due to high product effect or the use of metallized film packaging. Again it is expected that the best sensitivity (i.e. smallest test sample) is achieved for each food product. When using metal detection in the Level 2 range it is recommended to use the Sentinel metal detector with multiscan technology. Its adjustability, higher sensitivity and increased probability of detection will yield the best results.

Metal Detection and X-ray Inspection of Food

Keep consumers safe, protect your brand

Do you have the right food product inspection equipment in place to keep consumers safe and protect your brand? X-ray inspection systems and metal detectors can find virtually any foreign object in your packaged food products. To find out how they work, and which one will work best for you, read
A Practical Guide to Metal Detection and X-ray Inspection of Food.

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