Metal Detection or X-Ray Inspection?

Culture of Food Safety
A Culture of Food Safety with the Right People
June 24, 2021
X-ray Basics
August 24, 2021
metal detection or x-ray inspection

The difference between metal detection and x-ray inspection

Metal Detection or X-ray Inspection

metal detection or x-ray inspection

Metal detection or X-ray inspection are typically your first defense to identify the foreign contaminants in food before they leave the manufacturing facility.  Your selection of a system for detection involves quality assurance professionals, process engineers and corporate safety executives.  Together, you make the decision as to which kind of technology will protect their product from foreign contaminants.  Most often, this is based on three criteria: the best detection point (hopefully near the center of the aperture), the application capability and the cost to benefit ratio. Still, while technologies have been used in food manufacturing for decades, hardware and software enhancements continue to develop new standards for quality.  At times, this can create confusion about which methodology will work best for your application.


The type and size irregularity you are seeking out as well as the degree of speed of the production line can present a daunting challenge for any system.  The  challenge in front of you isn’t always finding the contaminant but in ignoring the product effect, the actual packaging and/or the environment (vibration, radio transmission, etc.).  You may have to deal with false positives, and that can add up to lost revenue, so the process has to be exceptionally dependable and consistent. In addition, detecting systems in the food industry must be very sensitive, operator friends, as fully automated as possible and cost effective. And the system must be capable of tolerating whatever conditions surround it, including a hot, moist, dusty or even freezing environment.


Performance is governed three ways: contaminant type detectability, smallest contaminant size and likelihood or probability of detection.  At the bottom of this article is a summary of detectability contaminant types by technology as well as a table of densities for a variety of materials. These are intended only as a general guideline. Contaminants can be missed, or unexpected foreign objects found you thought didn’t exist. This is especially true considering that metal detectors will not find anything but metals and x-ray systems will rarely be able to detect smaller size plastics or other contaminant types.  As a general rule, if the contaminant floats in water (as wood will), it will not be detectable.

With X-Ray, you may find it works best to test many samples with different contaminants. At we make a thermoform multi-card that is designed specifically for this purpose.  You can choose from 10 different contaminant types including:  Ferrous, Non-Ferrous (Brass), Stainless Steel 316, Aluninum, Soda-Lime Glass, Ceramic ZR02 and AL203, PTFE (Teflon), Acetal (Delrin) and Rubber in a wide variety of sizes.  We can place as many different types and sizes on a single card as you need.  That way, you can look at a single image and determine what types and sizes you can achieve.  Once you know the capabilities of your system, you can purchase single contaminant cards for regular testing during production.

As an additional note, we have even developed a bone simulate card using precision cut aluminum.  If you were to purchase a multi-card for bone simulate, you can easily compare the bone you’re looking for against the various sizes of aluminum.  Then, again, you can purchase single contaminant cards for regular testing during production.  Call 866-977-8663 or email for more information about the multi-cards.


The probability of detection is defined as the chance of missing a contaminant during production with real products running at normal speed. Of course, the bigger the contaminant, the higher the better chance of detection. A HACCP plan should be designed and documented to manage the food safety process. Hazard Analysis determines which contaminant issues are most expected to occur. The Critical Control Point can appear in multiple places, so the entire line should be examined for potential danger.  Limiting or eliminating problems early in the process is the goal in order to diminish the cost of a product rework.  You should never need to scrap an end product to make certain the marketplace is safe.

Ultimately, the best technology for your product will be determined by all the aforementioned items.  But it will also include (though not limited to): the type and size contaminant, the speed of production, the type of product, the container/packaging and the demands of the various CCPs. Make sure your employees are educated, trained and taught to think critically about all these variables, and then build a culture of food safety.  Finally, make sure you have the best testing equipment at hand.  Call us at 866-691-8560 or email and let us answer any questions you might have.  As a general guideline for metal detection or x-ray inspection, use the following breakdown.

Contaminant Type                             Met Det                    X-Ray
  • Metal – Ferrous                    X                         X
  • Metal Non-Ferrous               X                         X
  • Stainless Steel                      X                         X
  • Aluminum                              X                         X
  • Wire                                        X*                       X*
  • Ceramic                                                             X
  • Glass                                                                  X
  • Rock                                                                   X**
  • Bone                                                                   X***
  • Plastic                                                                X
  • Wood, pits, shells,  insects, etc.                     ****

* Dependent on orientation

** Dependent on type and size

*** Only calcified bone and still very difficult based on animal type, age, etc.

**** Not conductive for MD or typically not dense enough for X-Ray

  • Polyethylene                      0.857 g/cm3
  • Polyvinyl                             0.892 g/cm3
  • UHMW                                0.931 g/cm3
  • Rubber                                1.2 g/cm3
  • PETG                                   1.38 g/cm³
  • Acetal (Delrin)                   1.4 g/cm3
  • PTFE                                   2.2 g/cm3
  • Borosilicate                       2.23 g/cm3
  • Soda-Lime Glass              2.5 g/cm3
  • Aluminum                          2.7 g/cm3
  • Ceramic (AL203)              3.7 g/cm3
  • Ceramic (ZRO2)               5.6 g/cm3
  • Stainless Steel 316         7.82 g/cm3
  • Ferrous                             7.85 g/cm3
  • Non-Ferrous                    8.48 g/cm3

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