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Metal Detection Steps Up

Not that long ago, there was no product learning or automatic teaching in a metal detector.  The operator manually tuned the system by repeatedly inserting the product into the aperture with one hand and adjusting a variable capacitor or potentiometer with the other.


Significant innovations in metal detection came in the early 1980s with crystal-controlled oscillators and automatic balance circuits.  By the late 1980s, the first microprocessor-based metal detectors enabled automatic product learning and delivered digital information on the metal signals.


Metal Detection Since then, there have been incremental improvements in detection performance.  With the introduction of food safety programs that started with Hazard Analysis and Critical Control Points and are now ramping up to meet the requirements of Food Safety Modernization Act and other regulations, metal detector companies have introduced software features to support compliance.  Features such as alerting the operator when to challenge the metal detector’s performance, log book recording, automatic control of the reject bin lock and reject confirmation provide real benefits in terms of compliance to the latest food safety programs.  But little has changed in the balanced coil technology.  Metal detectors detect metal from a phase shift within a balanced electromagnetic field.


With the introduction of x-ray inspection in the late 1990s came predictions that this technology will supersede metal detection.  Today, most x-ray systems are highly reliable and less expensive than even 10 years ago, x-ray systems provide additional benefits by detecting non-metal foreign materials such as glass, stone, bone and plastics.  Another plus, x-ray inspection systems capture data from a line scan and create a product image to deliver improved foreign material detection.  Using the assembled image information, x-ray systems also can confirm product quality characteristics such as weight, completeness and broken pieces.


But there are limitations to x-ray and metal detection technologies.  So choice of technology must be based on which one best addresses the food safety risk. In many plants where glass is banned, Good Manufacturing Practices (GMPs) are maintained at a high level and the products are not too conductive, metal detection can be the viable solution.  X-ray has become the system of choice in applications such as metalized films and foils, where it is necessary in order to best comply with food safety standards and address the foreign material risks.


The imaging capability with x-rays leads to better operator understanding of what is happening when product is rejecting because the resulting image is visual.  Up until now, metal detectors have depended on a bar graph signal or a numerical representation of the resulting signals.  However, metal detectors from Sesotec can offer similar image construction capability by converting the electromagnetic signals to a visual electromagnetic signature, which delivers graphical data in a 360-degree dimension.


So, the operator sees a “ virtual picture” of the product being inspected.  Detection sensitivity is heightened too, because this new breed of metal detector pulls out data that previously has been hidden within the signals of conventional balanced coil phase shift systems.  “This breakthrough is metal detection will prove itself to be the biggest change in the technology since late 1980s,” predicts Doug Pedersen, Business Unit Manager, Product Inspection Food North America at Sesotec.


The technology includes concurrent signal analysis using multiple variable frequencies simultaneously and them digitizes the signals.  Once this information is in a digital format, sophisticated mathematics embedded within the software complete the analysis to assemble the image so it can be viewed and then mined for metal.  “So going forward, performance enhancement will be driven mainly by software”, he explains.


In fact, this new technology is such a departure that the equipment eliminates the phase angle and sensitivity settings that exist in soon-to-be-obsolete systems.  Pedersen adds, “Current metal detectors have limitations due to fixed thresholds and phase angles, so small fragments can be hidden if their signal doesn’t exceed thresholds.  Plus, metals that are the same phase angle as the product are not detectable”.


A metal detector with electromagnetic signature capability traces the shape of the image and follows it as it changes thereby finding metals that would have otherwise been hidden.   The operator sees imagery that displays the signal and the spike in the signal over the intuitive dynamically positioning threshold.  The technology is at a level where reject images constructed with the visual electromagnetic signature software have far more meaning to the human eye than simply a bar graph moving on a screen.


Another feature is the ability to tell the operator what test sample sizes it is capable of detecting, giving the operator much higher security about equipment performance.  In addition, using information within the electromagnetic image, the metal detector recognizes the product has changed and can signal the line operator that deviations are happening to the product or on the best that could affect compliance to food safety standards.


For the operator, usage is extremely intuitive because the human brain is good at capturing, analyzing and verifying complex visual images and determining deviations or variations in real-time.  Metal detectors that display a visual electromagnetic signature can show the user the source of the deviation.  A conventional metal detector tells the user that there is a deviation, and he has to further evaluate this information by himself. 


Compare this with a complex situation in traffic. Conventional metal detection technology would tell the driver that there is danger ahead.  A metal detector that provides an image of the product signals would tell the driver where the danger is coming from and, to an extent, what kind of danger he is facing.


Of all foreign materials found in food today, metals are still the most prevalent.  The benefits of metal detectors that use electromagnetic signatures include:


  • Highly intuitive systems achieve a new level of simplicity.
  • Capability of uncovering small pieces of material pushes the boundaries of detection standards.
  • Image information provides superior data for the user.
  • Systems cost less than even “low cost” x-ray units.


“It’s a very large step to ensuring that metal detection still has its relevance in today’s highest standards of food safety”, concludes Pedersen



Metal Detection

Screen shot shows detection of metal fragment

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