by marketing on 9 de August de 2023

What is X-ray inspection?

X-ray inspection systems are increasingly being used in the quality control of food, chemical and pharmaceutical products in order to ensure that the final product reaching the consumer is completely safe and free of foreign bodies. Many manufacturers are incorporating this type of equipment into their production lines, but what should be taken into account when choosing the right machinery?

First of all, we should clarify what x-rays are. X-rays are electromagnetic radiation of the same nature as radio waves, microwave waves or infrared rays. Thanks to their particularities, these types of rays are very useful for inspecting opaque bodies such as foodstuffs, detergent bottles or any kind of product for foreign bodies.

But how does an x-ray inspection system work?

Broadly speaking, an X-ray generator emits the required energy and the product moves linearly on a conveyor belt until it is passed through by an X-ray beam. The energy values resulting from this process are fed to the detector, which composes a digital image. This is processed by Varpe's software, which accurately detects any foreign bodies that may be inside the product. If a foreign body is detected, the equipment automatically rejects it.
Before making the choice of equipment, several general questions must be asked: can the equipment be easily adapted to the line? how many products will we be working with? are they very different formats? can the production be fully controlled?

In addition to all these questions, several points intrinsic to the equipment and production must be analysed:

1. SUPPLIER: Look for experienced suppliers.
2. PRODUCT TYPE: Consider the type of product we wish to analyse.
3. FOREIGN BODIES: Consider the type and size of the foreign body to be searched for.
4. BEAM GEOMETRY: Consider the geometry of the X-ray beam and the characteristics of the image.
5. SPEED: Consider the speed of passage and inspection of the product.
6. PERFORMANCE: Consider the performance of the equipment.
7. ELECTRICAL POWER: Take into account the power of the equipment that we are going to need.

Tips for choosing X-ray equipment

1.Seek out experienced suppliers

When you want to incorporate a system such as X-ray inspection in a production plant, it is important to have the support of a well-established manufacturer who can offer high-performance, stable and reliable equipment.

Points to be taken into account include experience in similar projects, value for money and technical support service.

In addition, we must consider that these systems, regardless of the manufacturer, require certain maintenance, generally preventive, for optimal long-term operation. Approved annual revisions are also necessary. For all these reasons, it is advisable to consult the maintenance plans together with the purchase of the equipment.

2. Consider the type of product to be analysed

There is a product effect that depends on its physical characteristics. The level of sensitivity achieved in a homogeneous product is not the same as in a heterogeneous product with a variety of textures. In the first case, because it is very uniform, it is relatively easy to detect practically any foreign body of a given size. However, in the second case, due to the high contrast of the product itself, the detection of these same foreign bodies becomes more complex and imprecise and may require more complete technologies, such as Dual Energy or double shot equipment to detect foreign bodies of the same size.

On the other hand, the dimensions of the product must also be taken into account. The taller the product, the more projection it will suffer and consequently the shadow zones will increase, decreasing the area of greatest inspection possibility.

3. Consider the type of foreign body

In addition to everything explained so far, there is the added difficulty of the foreign body. The density of the product will be decisive in this case. Denser products absorb a greater amount of energy and, therefore, the X-rays will penetrate less, making the detection of foreign bodies more difficult. In these cases, more powerful equipment will be required.

On the other hand, there are special cases. A very special case is that of glass. This type of foreign body is of very low density and therefore has low energy absorption, making it difficult to detect. In the case of a product contaminated by glass, it may be more difficult to detect depending on the position it has adopted within the product.

The most unfavourable case is that of a flat glass of a certain size that is housed in a jar and the X-ray beam passes through the thinner area. In this scenario, a lateral double shot is the ideal equipment for this type of inspection as it is much more effective in this situation, as one of the two shots will reliably detect the foreign body.

The position of the foreign body will also influence its detection. If the inspected product has a certain uniformity, where it is located does not have too much influence, but if the product is not homogeneous, the resulting image may have a high contrast content. This makes detection very difficult depending on where the foreign body is located and may also require the additional technologies discussed above.

5. Product throughput rate

The relationship between product throughput speed and X-ray inspection speed is another element to be considered when selecting equipment for the production line. It is important that the inspection speed is in line with the throughput speed. If we have a high-speed line, it will be important that the x-ray equipment we incorporate can keep up with the inspection pace of production to avoid bottlenecks, delays, unnecessary stops or even failure to detect foreign bodies. Similarly, if we have a slower production speed, there is no point in having equipment that can inspect much faster. Therefore, you should choose a machine that gives the expected response depending on the type of production.

6. Consider the performance of the equipment in terms of image quality.

As a main premise, it must be taken into account that X-ray inspection equipment is built with a series of components that particularly condition the sensitivity value of the equipment. These components are mainly the X-ray generator and the X-ray detector or linear array.

The generator is the element where the X-rays are produced. Generally speaking, two types of tubes are used in the construction of an X-ray generator: tubes with a Glass emission window and tubes with a Beryllium window. The beam in Glass window tubes has a higher scattering index, producing images with less focus, although acceptable for the detection of many foreign bodies. The beam in the Beryllium tubes has a lower dispersion, producing images of very good resolution. Another decisive component in achieving a good image is the detector or Linear Array.

Different models and types are available to suit the needs of the market. The choice of the right detector is determined by several factors, such as product density, linear production speed, complexity of the product packaging and the X-ray generator used. X-ray detectors are high-precision instruments and their operation is based on sensitivity over a line of sensors (pixels). The physical characteristics of the pixel determine mainly the light it receives and its operating speed (linear velocity).

Using a detector with smaller pixels has a more detailed resolution, but more energy has to be used to achieve a good image because less light enters. As a consequence, the signal-to-noise ratio also increases, and the speed is affected.

In the end, what is important is the combination of all the features to be able to meet the needs of the particular product.

4. Consider X-ray beam geometry and image characteristics

Depending on the product to be inspected, equipment with a different type of X-ray beam geometry should be chosen.

Depending on the spatial position of the generator, different angles of attack are defined with respect to the product:


This type of vertical beam is the most common and almost any product can be inspected with this trigger mode.

In the representation you can see in yellow the inspected area and in red the areas that are not inspected by the beam. These areas are commonly known as twilight zones and refer to places where it would be very difficult to detect a foreign body. This is why it is so important to choose the type of beam according to where foreign bodies are likely to be located in the product.


Side firing of the X-ray detection system is typically used when the product is taller than it is wide. This type of beam can be bottom-up or top-down.

The bottom-up side shot is widely used for inspection of jars, jars or bottles where the interior is dense. In these cases, the foreign body is usually lodged in the top or in the lid, and therefore this beam is suitable, as it places special emphasis on the area. The top-down side shot is used for inspection of products where the interior is not very dense and the foreign body can be easily lodged in the base.


Double shots use two generators with different angles of attack to better inspect the product.

The double side shot can be bottom up or top down, with the same application logic as the single side shot: bottom up when you want to pay special attention to the lid and top down in case you want to focus on the base. However, being a double shot, it provides a greater inspection volume and greater detectability of foreign bodies.


Vertical double side shot is a type of geometry that uses two generators, combining vertical and side shot. This type of inspection is particularly suitable for cases where the variability of formats and types of products is unavoidable, for example, a factory with very different containers.
There are two types of vertical double side shot.

From top to bottom: This type of geometry has masking zones determined by the projections that are generated, as an example, the behaviour on a glass jar is shown. The combined action of the two shots results in the non-inspection zones that are reflected.

Bottom-up: This type of geometry is recommended when there is a possibility of foreign bodies being lodged in the upper area of the container, just below the lid.

The sum of the two projections would show a sensitivity result approximately as shown in the figure below. As with the side shot, one option or the other would be chosen depending on where the foreign body tends to be lodged.

7. Take into account the electrical power of the equipment

Finally, the amount of electrical power needed in an X-ray machine is directly related to the density of the product to be inspected. The denser the product, the more energy it will retain. This high level of absorption makes it more difficult for the X-ray beam to pass through the product; to achieve this, the voltage (kV) must be increased to give the beam the necessary strength to pass through the material.

Another important factor influencing the power required is the thickness of the product. Its behaviour is similar to that of the density: the thicker it is, the more energy absorption it will have and, consequently, the more difficult it will be for the X-rays to penetrate it. In this case, it is also advisable to increase the voltage according to the thickness.

We should not confuse density with hardness. Density refers to the amount of mass in a given volume and hardness is the degree of resistance a material has. For example, ice is clearly harder than water; however, its density is lower: an iceberg floats on water instead of sinking.

Therefore, the voltage essentially controls the penetration and contrast capability of the equipment. If we need to penetrate dense or thick materials, we will have to increase the number of kV we apply to the tube.

Another electrical parameter that must be taken into account to define the power of the equipment is the intensity. If we need very sharp images, we will have to emit a higher number of photons and, therefore, increase the mA. On the other hand, if we do not need so much resolution, we can work with lower intensities.

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