Plan Automation Technology Blog

X-Rays vs. Metal Detectors for Food Inspection

Posted by PLAN Automation Blog on Wed, Jun 17, 2015 @ 11:06 AM

Making sure that food products are safe and free of contamination is a huge concern for all food producers large or small.

When contaminants such as metal, stone, plastic, glass, or bone make their way into food product packages, they become a public health safety hazard and a potential PR nightmare. To prevent contaminants from making it through, manufacturers in the food industry often use automated product inspection equipment such as metal detectors and x-ray machines.

Which system is better for your production process? What are the unique advantages/disadvantages of each?

Here, we’ll take a look at both metal detectors and x-ray inspection machines to help you determine which type of system would best help maximize your quality control.

Metal Detectors

Gravity Metal Detector 399 resized 600Metal detectors are devices designed to detect magnetic or electrical interference which indicates the presence of metal.

Most modern metal detectors for product inspection use a system known as the balanced coil, full loop system. In this system, three coils are wrapped around the aperture or channel through which the product being checked passes. The transmitter coil is placed in the center of the enclosure, while two receiver coils are spaced equally distant from the transmitter.

The transmitter coils continuously emits an electromagnetic field. As objects that are magnetic or electrically conductive enter or exit the aperture of the metal detector, they cause a disturbance in the electromagnetic field. If the disturbance exceeds a pre-set minimum threshold, the metal detector will register the presence of a metal contaminant.

Key advantages of metal detectors include:

  • The ability to detect all metal contaminants. All metal alloys are either magnetic, conductive, or both. Metal detectors work on these criteria, allowing them to detect metal with great accuracy, even lighter metals such as aluminum (lower in density) which are more difficult to detect using x-ray.
  • They work well with bulk conveyed and gravity flow products. Metal detectors trigger based on interference with their electromagnetic field. The density and consistency of the shape of the product does not impact the ability of a metal detector to work as much as it would impact an x-ray machine.

Disadvantages of metal detectors include:

  • Only able to detect electrically conductive or magnetic objects. If a contaminant is neither ferrous nor conductive, it will be essentially invisible to a metal detector. Because of this, metal detectors are rarely used on their own for quality control.
  • Some dry and wet foods can create false positives. Iron-enriched dry foods such as cereal possess a strong magnetic signature which has to be accounted for. The moisture and salt in wet foods such as cheese can make them slightly electrically conductive, which may also create a false positive.

X-Ray Inspection Equipment

X-ray inspectionX-ray inspection devices work very differently from metal detectors. Rather than relying on electromagnetic interference to pick up the presence of contaminants, x-ray inspection machines take a snapshot of the product using x-rays. This x-ray picture is then analyzed for anomalies.

With x-rays, the determining factor in whether or not a contaminant will be detected is its density (as measured by how effectively the material prevents x-rays from penetrating it) instead of its electromagnetic properties.

Because of this, x-ray machines can detect many non-ferrous and non-ductile contaminants that would slip by metal detectors, including glass, bone, rock, high density plastic/rubber.

Benefits of x-ray inspection over metal detection include:

  • Ability to detect a wider variety of materials. The x-ray detection method relies on object density, not electromagnetism. As such, x-ray inspection machines can detect many objects that metal detectors would miss.
  • Ability to check for missing materials. Beyond finding contaminants, an x-ray machine can also check for missing objects in a sealed package. This prevents incomplete packages from reaching the market.
  • Check-Weighing of your product: The X-ray system can also check-weigh your product to assure that the correct amount of product is in each products. This is achieved using mass measurement and is achieved without that addition of mechanical components.
  • Documentation of contaminants and Traceability. Every inspection's characteristics and an X-ray image showing the contaminated product can be saved for future reference and documentation. This provides an unsurpassed level of traceability, which cannot be provided by metal detection.

A couple of disadvantages to x-ray equipment would be:

  • Inability to detect less dense objects. Contaminants such as paper, fabric, hair will not show up in an x-ray because they are not dense enough. However, there are no inspection technologies on the market that will be able to detect such contaminants in a finished package.
  • May be confounded by products with high densities and random textures. When scanning food products that are dense, x-ray machines might have a difficult time differentiating contaminants from the food product itself. Also, products that have very random textures can make it difficult to establish a quality acceptance standard.

Which Should I Use?

Overall, your choice of whether to use an x-ray machine or a metal detector in your quality control process will depend on several factors, such as your budget and what kind of contaminants are most common to your product.

If you have to worry about a lot of different non-metal contaminants, x-ray inspection machines will typically be your best option. However, if your production process more frequently sees the introduction of metals, including aluminum, into your production process, then the use of metal detectors might make more sense.

If you have to contend with both metallic and non-metallic contaminants, and have the budget for more than one device, consider using both machines in your production process. This improves the flexibility of your inspection process and helps ensure that you can spot a wider variety of contaminants.

Please remember that in most applications, the best inspection solution is a combination of two or more inspection technologies.

Learn more about the benefits of both x-ray inspection and metal detection for the packaged food industry today by contacting us here.

Topics: Metal Detection, Product Safety, X-Ray Inspection, Product Quality, X Ray Inspection for Food, Product Inspection