X-Ray Vs. Metal Detection: Which Do You Need?

By Melissa Lind, contributing writer

Detecting foreign contaminants is a must to ensure safety and customer loyalty in food products before they leave the processing facility.  There are some significant differences to consider when making a decision of x-ray vs. metal detection technology, many of which are more important than just cost.

Though quality and safety have always been of utmost importance in food supply chain, new regulations, specifically FSMA, are turning up the heat. FSMA has shifted the focus from response to prevention. The new regulations include significant penalties and costs for non-compliance, which increases the reliance on quality control equipment and methodologies.

How Is FSMA Impacting Food Manufacturing?

Retailers have also gotten into the mix, demanding that processors employ the latest technology as food contamination issues affect bottom lines too.  Food-quality professionals have to choose a system that will best protect food products from leaving the plant with contaminants, but this has left some confusion about which technology is best and there are some differences.

Metal Detection Systems

New metal-detection technology has improved from the three coil system to a multi-coil system.  The transmitter sends a high-frequency radio signal to the receiver coils.  Normally, each receiver coil produces the same output voltage and cancels out, resulting in an output of zero.  When a particle of metal passes through the coils, the field is disturbed and a non-zero output is received, triggering an alarm.  The newer generation multi-coil systems can detect metal contaminants that are 20% smaller in size and also reduce the number of false positives. 

Pros — Metal detection systems are usually less expensive and last up to five times longer even in harsh environmental conditions.  They detect all types of metal contaminants including difficult-to-detect aluminum and wires. They can be used most anywhere in a system and at a wide variety of speeds.  They also work with gravity or drop-through pipelines.

White Paper: Foreign Body Detection Of Metals

Cons — Metal detection doesn’t work well with wet or salty products or with metallic packaging which are conductive.  Contaminant detection is usually limited to particles that are larger than 1 mm in size.  Inspection capability may be limited due to aperture size; consequently they work best with small, dry products that can be sent through on a conveyor belt, drop-through system or pipeline.

X-ray Detection

X-ray systems are based on density of the product.  An area that does not have the same density will show as a variation on the image projection.  In most cases, a contaminant will have greater density than the rest of the product and will show as a dark spot on the image.  

White Paper: Food X-Ray Inspection Equipment — What You Should Know

Pros - X-ray systems will detect most types of solid particulates including most metal, glass, most plastic, most bone, and food accumulations.  They work well with different types of packaging and conductive materials such as wet or salty food products and metallic packaging.  X-ray systems can often find smaller contaminants and larger products and cases of material can be examined.  Many systems also have weight, shape, and counting measurement capability.

Cons – X-ray detection does not work well with gravity applications or with very dense products and must be run at a constant speed with limited flexibility.  Controlled environmental conditions are best for performance and X-ray systems are more expensive.  X-ray cannot yet detect aluminum or wire contaminants in most cases.  The systems are often significantly more expensive and tend to require maintenance and replacement much more quickly compared to metal-detection systems.

Neither system is effective for every application. Both technologies are significant investments and careful consideration should be taken of system limitations, costs, and processing line requirements when contemplating the implementation of food contaminant detection systems.