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How to choose between single-energy or dual-energy X-ray systems

  • 2020-07-02 10:50:31

There are currently two types of X-ray technology used for cargo inspection-Single Energy X Ray Inspection System and dual energy X Ray Scanner. Some processors believe that dual energy X Ray machine is always the best regardless of the application. However, this is not always the case. Regardless of the application, it is a myth that dual energy automatically provides better sensitivity.


The correct choice of technology depends on five factors:

1. Contaminants that the manufacturer may encounter;

2. Products;

3. Type of packaging;

4. Production speed;

5. Customer specifications.


How they work


Simply put, an X-ray system uses an X-ray generator to project a beam of low-energy X-rays onto a sensor or detector. X-ray inspection involves passing the product or package through an X-ray beam before reaching the detector. The X-ray energy absorbed during the beam passing through the product is affected by the thickness, density and atomic number of the product.


When the product passes through the X-ray beam, only the residual energy reaches the detector. Measuring the absorption difference between the product and the foreign body is the basis of the foreign body detection in X-ray inspection.


The X-ray Machine is essentially a scanning device. When the product passes through the system at a constant speed, the X-ray detector captures a "grayscale" image of the product (see image below). This is generated by measuring the amount of X-ray energy reaching the detector. Each image is composed of pixels, and the X-ray energy absorbed by each pixel creates a value in grayscale (from black 0 to white 65,535). When the product or package passes through the detector, each row of grayscale data is added to the previous row, just as slices of bread can be added to form a loaf of bread, thereby generating a complete product image. The software in the X-ray system analyzes the image and compares it with predetermined acceptance criteria.


Based on this comparison, the system accepts or rejects the image (and the product/package it represents). In the case of rejection, the software sends a signal to the automatic rejection system, which then removes the product from the production line.


Like the above-mentioned traditional Single Energy X Ray Inspection System technology, dual-energy technology involves using a generator to project an X-ray beam onto the detector and pass the product through the beam. However, dual-energy X-ray detection is different from single-energy X-ray detection because it uses two energy spectra to distinguish high-channel and low-channel X-rays, as well as double-layer detectors. The top detector is sensitive to lower energy (longer wavelength X-rays), and the bottom detector is sensitive to higher energy (shorter wavelength X-rays). The two detectors are separated by a small copper plate. The copper plate filters out low-energy X-rays, allowing only high-energy X-rays to pass through and reach the high-energy detectors.


When the X-ray beam is projected through the product, some energy will be absorbed while other energy will pass through. What is absorbed and passed depends on the composition of the product.


Two separate images are generated from two energy spectra, and the relative ratio of absorbed energy can be calculated to determine the composition of the material. Therefore, in fact, dual-energy X-ray systems measure the ratio of two sets of different X-ray energies passing through the product. This measurement can distinguish organic and inorganic materials. Therefore, the detection of foreign objects using dual-energy X-ray technology is based on chemical composition (atomic number), not just density changes like single-energy X-ray technology.


Which technology is best for your application?


The single-energy X-ray detection technology used to detect food contamination can effectively detect foreign objects, which show X-ray absorption peaks relative to the absorption of surrounding products. Such systems provide food manufacturers with excellent detection levels for stainless steel, ferrous and non-ferrous metals. They are also very good at detecting glass, calcified bone, mineral stone, and high-density plastics and rubber, regardless of their shape, size, or location in the product.


However, single-energy X-ray detection technology cannot detect thin glass, stones, rocks, low-density plastics and rubber in most food products.


Dual energy technology is better at detecting objects with small changes in X-ray absorption. This means that it is easier to detect dense foreign objects in dense products using dual-energy technology than with single energy. For example, dual energy makes it possible to detect flat glass and stones in mixed nuts, while using a single energy detector to detect both cases is challenging.


The dual-energy technology basically eliminates most of the effects of product thickness changes, and leaves an image showing density differences based on chemical composition (atomic number). Food is usually organic in composition, and if it is solid or liquid, it contains water. Chemically, food is mainly composed of hydrogen, carbon and oxygen. Using dual energy technology, any foreign objects containing elements with higher atomic numbers than carbon or oxygen become easier to detect.


Single-energy technology usually finds foreign objects that are visible in X-ray images, but dual-energy technology can detect many foreign objects that are not easy to see in X-ray images. For example, dual energy has obvious advantages when detecting inorganic foreign objects such as flat glass (as opposed to cylindrical glass), bones, stones, rocks, low-density rubber and some plastics. Plastics and rubbers containing inorganic fillers or containing chlorine, bromine or fluorine also fall into this category.


Dual-energy X-ray technology has some similarities with single-energy X-ray technology, but there are also differences. Dual Energy's ability to distinguish materials based on their chemical composition can detect inorganic foreign objects that have not been detected historically, and also enables food manufacturers to inspect products with complex density levels and innovative packaging styles.


However, as we mentioned, dual-energy X-ray systems are not suitable for all food applications. In some cases, dual energy sources will be the best, while in many other cases, single energy sources will provide a better solution. The correct choice of X-ray energy depends on the five factors outlined earlier in this article: possible contaminants, product, packaging, production speed, and customer specifications.


One thing is certain: there is usually no overlap in the choice of single-energy or dual-energy X-ray technology. Each application should be independently evaluated, and food manufacturers should seek advice from a reputable X-ray system supplier before making a decision.


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