Single vs Dual Energy X-ray Technology for Food Inspection – 4 Factors to Help You Decide

Food & Beverage

Food processors have relied on x-ray technology since the early 1990s to safeguard their brands and protect customers. Both single and dual energy x-ray technology are used for foreign body contaminant detection today, with some manufacturers believing that, regardless of the application, dual energy is always best. However, this is a myth; dual energy doesn’t automatically give better inspection results.

This article explains that both technologies have their place and that the correct choice of energy depends on four factors: the likely contaminants and product, packaging, production speed and customer specifications.

X-ray Technology Choices

An x-ray system is essentially a scanning device. When a product passes through the system at a constant speed, the single energy x-ray detector captures a ‘greyscale’ image of the product. This is generated by measuring the amount of x-ray energy reaching the detector.

Each image is comprised of ‘pixels’, and the x-ray energy absorbed by each pixel creates a value on a greyscale (from black 0 to white 65535). As the product passes over the detector, each line of grey level data is added to previous lines, much like slices of bread can be added to form a loaf, resulting in a complete product image. Software within the x-ray system analyzes the image and compares it to a pre-determined acceptance standard.

On the basis of this comparison, the system either accepts or rejects the image (and the product it represents). In the case of rejection, software sends a signal to an automatic reject system, which then removes the product from the production line.

Like conventional single energy x-ray inspection technology described above, dual energy technology involves using a generator to project an x-ray beam onto a detector and passing a product through the beam. However, dual energy diverges from single energy x-ray inspection as it uses two energy spectrums to discriminate between high and low channel x-rays, as well as a dual-layer detector. While the top detector is sensitive to lower energy (longer wavelength x-rays), the bottom detector is sensitive to higher energy (shorter wavelength x-rays). The two detectors are separated by a small copper plate which filters out the low-energy x-ray and only allows the high-energy x-ray to pass through to the high-energy detector.

Eagle introduced dual energy Material Discrimination X-ray (MDX) technology almost two decades ago, raising expectations for food inspection. In 2020, we debuted our exclusive dual energy Performance X-ray Technology (PXT™) as the new standard in x-ray detection. It captures more detailed product data than ever before, advancing bone detection down to 1 mm!

Deciding Factors of X-ray Technology

1. Likely Contaminants and Product

Before selecting a technology, it’s important to consider the type of product and the likely contaminants. For example, in whole potatoes, the most likely contaminants are stone or a piece of golf ball, whereas in cookies or ready-to-eat foods, the most common contaminants are small metal and glass.

Single energy x-ray technology gives exceptional levels of detection for stainless steel, ferrous metals and non-ferrous metals. It’s also extremely effective at detecting glass, calcified bone, mineral stone and high-density plastics and rubber in products that are homogeneous in texture such as butter or yogurt. However, single energy is unable to detect thin glass, stones, rocks and low-density plastics and rubber in heterogeneous products such as a bag of hard candies.

In contrast, dual energy x-ray technology offers a clear advantage when detecting inorganic foreign bodies such as flat glass (as opposed to cylindrical glass), bone, stones, rocks and some low-density rubber and plastics. An inorganic foreign body in a heterogeneous product is also more detectable using dual energy x-ray technology. For example, dual energy makes it possible to detect flat glass and stone in mixed nuts, which can be challenging to detect using single energy detectors. Read this application note for unpackaged walnuts.

Single energy x-ray technology provides safety and quality assurance at every stage of the production process for raw, bulk, pumped and packaged applications. However, identifying foreign bodies in products with many density levels can prove more difficult for single energy detectors as the varying densities create ‘busy’ x-ray images. For example, the density variance caused by overlapping stems and leaves in bags of mixed salad leaves makes it difficult for single energy technology to identify contaminants. Download an example on how x-ray technology helps packaged salad bags manufacturers to ensure total quality and safety of their foods.

In contrast, dual energy x-ray technology lends itself to inspecting ‘difficult’ or ‘busy’ x-ray images caused by products with high variations in density due to its ability to discriminate materials by their chemical composition. It’s therefore capable of detecting flat glass and stone in multi-textured foods, such as trail mix, cereal and confectionery, something which single energy technology would find more challenging. Furthermore, dual energy is also capable of detecting rocks, golf balls and rubber grommets in potatoes.

2. Packaging

After considering the product and likely contaminants, it’s important to focus on the type of packaging material and whether or not the product will be inspected on its own or as part of a multipack.

Glass jars and bottles are one of the most difficult types of packaging to inspect. This is mainly because the primary contaminant is glass, the same material as the packaging. What’s more, metal cans and glass jars can also be challenging to inspect as parts of the containers will always be present in the inspected image. Single energy technology is ideal for inspecting a glass jar of jelly where the likely contaminant is glass, and modern special adaptive masking and inspection routines offer unsurpassed detection by dynamically adjusting to each individual pack.

Single energy x-ray technology is also capable of inspecting unpackaged foods, as well as products in a variety of other packaging types such as metal and ceramic containers, plastic containers, cartons/boxes, pouches, bags/sacks, trays and tubes.

Dual energy x-ray technology is able to detect inorganic contaminants in a variety of packaged products, and lends itself to finding foreign bodies in innovative packaging designs, such as fold-out cardboard sandwich packaging and corrugated card encasements, that can prove troublesome for traditional inspection tools. In addition, dual energy detectors are ideal for inspecting multipacks such as a multipack case of chips. This is because the dual energy essentially removes the edges of the individual packages within the case, making it easier to see contaminants that could potentially be hiding inside the box.

3. Production Speed

As a rule of thumb, high-speed applications such as metal cans and flow-wrapped products like energy bars tend to be more suited to single energy x-ray inspection. Single energy x-ray technology is ideal for most packaging lines with products travelling at speeds between 150 and 400 feet per minute (FPM). In contrast, dual energy technology is better at inspecting incoming raw materials/ingredients such as nuts, which typically tend to be slower applications, travelling at speeds of between 80 and 200 FPM.

4. Customer Specifications

Customers’ requirements also determine the x-ray energy choice. For example, retail stores may specify that their suppliers have inspection technology that’s capable of detecting contaminants as small as .4 mm, which can easily be achieved with many applications using single energy x-ray technology.  This is because products will have been processed which increases the risk of small contaminants, in particular metal.

Alternatively, a processor may stipulate that a grower or farmer has the capacity to detect 3 mm tramp metal or rock/stone, which can be easily achieved using dual energy technology. Field contaminants are the only likely contaminants this far up the processing stream as the fresh crops won’t yet have been processed. Read how Higos El Pajarero, a Spanish leading manufacturer of dried figs, implemented an Eagle™ Bulk 415 PRO with MDX technology to enhance the quality of their fruit and comply with their customer specifications.

Bone contaminants are also a huge concern for poultry and seafood processors. The best choice for unparalleled detection of bone fragments is Eagle’s propriety dual energy technology, PXT™. It can detect bones in seafood down to 0.5 mm and poultry bone down to 1 mm.

If you are interested and testing your product to find out which technology is right for you, contact us at eaglesales@eaglepi.com.

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