Metal Detectors vs. X-Ray For Food Inspection
Choosing between X-ray inspection systems and metal detectors depends on several factors, including the types of contaminants you need to detect, the range of materials you’re inspecting, and specific industry or product requirements. Both technologies have their strengths and weaknesses, which we will cover below.
TLDR:
If you must choose between them, the fastest solution is to call a tech and they will know. But in general, metal detectors are much cheaper, and if you just want to prevent breaking teeth and to set-and-forget it, they will work fine. X-ray machines are more expensive but are good for non-metal contaminants as well as other data-points like fat analysis, item-count, and package integrity, and when buyers require x-ray (this is becoming more and more common). But because of their differences, it’s best to have both.
Overview
It should go without saying that metal detectors only find metal, and X-ray machines will find bone, glass, plastic, etc., as well as fat content, package integrity, and item count and fill level. So for the purpose of this discussion, we will focus on when to use x-ray as opposed to metal detection when looking for metal. In general, X-rays are using difference in densities to find objects that you’ve trained it to look for, and metal detectors are just looking for metal. The impacts of this principle are applied below.
Metal Detectors
When to Use:
- Wire, Foil, and Aluminum: Metal detectors are strong with these because x-rays rely on density, which will make aluminum difficult for x-ray because it’s a similar density to so many products. Wires can also trick X-ray machines if they’re pointed right at the detector so they only look like a small dot. This is unlikely but can happen.
- Cost-Effectiveness: Metal detectors are always less expensive than comparable X-ray systems, both in terms of initial investment and maintenance.
When Not to Use:
- Non-Metallic Objects: Glass, stone, bone, plastic, rubber, etc. are obviously not detectable.
- Frozen Product That May Thaw During Inspection: Frozen product can be treated like dry product, but water undergoes a diamagnetic shift when changing states to liquid, which will cause false rejects. This effect is worse in the presence of salt.
- High-Salt Products: Metal detectors are finicky with salty products because sodium is a metal.
- You Need High Precision in Both Ferrous and Non-Ferrous Metal: Metal detectors can be tuned to be very sensitive to one and not the other, but not to both.
X-ray Inspection Systems
When to Use:
- Broad Range of Contaminants: X-ray systems can detect a wide range of foreign objects, including metal, glass, stone, bone, high-density plastics, and product clumps and voids. This makes them versatile for comprehensive inspection needs.
- Product in Cans and Foil Packaging: X-ray systems can inspect products regardless of their packaging. They are effective for products packaged in metal cans, foil, or other materials that metal detectors cannot penetrate.
- Quality Control Checks: Beyond detecting contaminants, X-ray systems can perform quality control checks such as measuring mass, identifying missing or broken components, and inspecting seal integrity.
- Dense Products and Packaging: X-ray inspection is effective for products that are dense or have variable densities, where metal detectors might struggle.
- Product is Frozen or Salty: Thawing products will trigger metal detectors, and because of salt’s conductivity, it can trigger metal detectors. Consistent salt will only require you to reduce MD sensitivity, but if it varies too much it makes detection unreliable.
- You Plan to Sell to Large Retailers: X-ray looks good for all retailers, and large ones—most famously Costco—are beginning to require it. Learn about how we make this easy with our software here.
When Not To Use:
- Wires, Foil, and Aluminum Are Big Concerns: Wires and foil can get by X-ray if they are oriented in just the right way, and aluminum can pass it if it’s small enough and the product density is similar to aluminum’s.
- You Don’t Have The Resources: X-ray requires a larger monetary investment and takes longer for personnel to master.
Factors That Don’t Matter:
The internet has a few misconceptions about this topic.
- Line-Speed: X-ray machines and metal detectors have very similar relationships between speed and accuracy and have similar maximum rates.
- Packaging and Product Mass: If there is more product or packaging to be inspected through, an X-ray machine will simply need a larger generator and a metal detector a bigger coil. Generators and coils are the most expensive parts of each machine, so they will proportionately increase the price of each.
Conclusion
The choice between X-ray inspection systems and metal detectors should be based on your specific needs:
- When metal contaminants are the only concern and the packaging has no metal in it, metal detectors are often sufficient and more cost-effective.
- For a broader range of contaminant detection and quality control capabilities, especially in products with varied densities or packaged in metallic materials, X-ray systems provide a more comprehensive solution.