In some applications, it is obvious which type of inspection technology to opt for, since only one of them can reliably detect the contaminants that pose the risk you are trying to mitigate. However, it’s not always as straightforward. The two technologies will often succeed or fail depending on two different sets of criteria. Success with metal detectors tends to depend on the materials involved (the product, the packaging and the contamination), while x-ray detectors are more likely to be affected by other parameters such as the shape of product and the mode of transport through the unit, in addition to density differentials.
Putting this into context, x-ray systems cannot generally be used on free-falling products because of the inconsistent density within the falling product stream. This rules them out of many bagging operations, such as vertical form fill and seal (VFFS) lines. Meanwhile, if stone, glass, high-density plastics or bone poses the biggest risk, a metal detector will obviously be unable to spot them. It is, however, worth noting that even an x-ray system will only be able to deliver reliable protection against these non-metallic contaminants under certain conditions.