MATERIALS HANDLING
commonplace single energy detection systems? In simple terms, there are two key aspects of a product that make it suitable for inspection by dual energy x-ray. The fi rst is where there is a large degree of overlap within the package, or where there are variations in thickness. Examples of the types of packs
where products overlap include packs of pasta, rice, nuts, and frozen goods such as French fries or potato wedges. Packs with variations in product thickness include chicken breasts and other fresh cuts of meat. Both scenarios produce an x-ray image with high levels of contrast. The second type of application
where dual energy x-ray is most suitable is where the likely contaminant in a food product is a low-density material, such as glass, plastic, rubber and calcifi ed bone.
HOW THE TECHNOLOGY WORKS If a product application has one or both of these aspects, then a case can be made for dual energy x-ray. However, it is important to understand how this technology works. Here, the key concept is material discrimination. Dual energy x-ray works by using
high and low x-ray energy levels to discriminate between materials of diff erent densities. Software algorithms enable the material that is the food product to be removed from a noisy x-ray image, leaving behind any material identifi ed by the second energy level, such as a contaminant. The most advanced dual energy
technology available today features an enhanced detector that collects detailed data about the product being inspected. When this is combined with sophisticated image analysis software, the result is even clearer leading to higher resolution images of contaminants.
BEST FIT Mettler-Toledo dual energy x-ray systems can detect more than eight times as many diff icult-to- fi nd contaminants as single energy x-ray systems. To ensure that a manufacturer’s application is best suited to dual energy x-ray buyers should look for a ‘Test Before You Invest’ service.
Dual energy x-ray works by using high
and low x-ray energy levels to discriminate between materials of diff erent densities
Dual energy x-ray systems can help manufacturers reduce false rejects The general rule of thumb is
that dual energy is best suited to applications where some or all of these factors exist: • the product being inspected is one with high contrast, caused by overlapping products or products with variable thicknesses
• the expected contaminants are low density materials such as glass, rubber, plastic and calcifi ed bone
• the packaging material used is low density, allowing low energy x-rays to pass through and inspect the product inside.
Improving the eff ectiveness of
contaminant detection with dual energy x-ray that is optimised to the product application is clearly benefi cial to food quality and consumer safety standards, but it also helps the food manufacturer’s business. Consider, for example, the degree
to which the sensitivity of a single energy x-ray system would have to be fi ne-tuned to detect very small contaminants such as 0.8mm pieces of stainless steel in packs of nuts. The sensitivity required for such an application would very likely cause many false rejects, which would result in a great deal of product throwaway. Turning down the sensitivity to reduce the false reject rate might mean that contaminated products pass undetected, leading to a product recall and damage to reputation.
Using dual energy x-ray will help the manufacturer to optimise detection around this application, without the resulting surge in false rejects and wasted products.
BALANCING WANTS AND NEEDS Food manufacturers have to balance a range of factors, including budget constraints, when deciding upon investments and improvements to their production-line capabilities, and product inspection is only one of their considerations. It is a critical one though since it is the guardian of food safety. With dual energy x-ray, everything
depends upon the application, including the nature of the product, the possible contaminant, and the packaging. If operating on a tight budget, a single energy x-ray system might seem superfi cially more attractive. However, the more advanced contaminant detection capabilities of dual energy make more accurate inspection of challenging applications possible, and can quickly provide a return on investment, when set against the mounting costs of waste through false rejects and potential product recalls.
For more information visit:
www.mt.com/xray-de-wp-pr
www.engineerlive.com 25
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