Choosing an inspection system for your production line can seem, at best, confusing and, at worst, daunting. There are many factors to consider. On the one hand, you may need to assess the feasibility of different approaches, based on a detailed knowledge of the physical space available at the locations in the process. On the other, you may simply need to prepare a careful economic justification, based on up-front lifetime costs.

There may well be corporate guidelines regarding the contaminant size that must be detected or growing pressure from customers who demand ever-increasing quality control standards. You may need to review the different types of contaminant and/or defects that occur in your production process and how best to combat them.

== Non-metallic contamination ==

Metal detectors are well-established across the food industry, with several hundred - if not thousands - installed in both plant and craft bakeries around the world. Their reliability can be depended on and the cost of installation, set-up and running is well understood. But what do you do if you need to find non-metallic contamination?

X-ray systems are capable of much more than simply detecting metal, but just how do you assess the risks in applying new methods to your plant? X-rays can detect non-metallic contamination - for example, stones, glass and PVC - but if these types of contaminants don’t figure in your contamination log, what else can x-rays offer in terms of a viable quality control tool?

X-ray systems are capable of defect detection, finding missing or misshapen product, and checking the mass of food in individual compartments of a multi-compartment package. So take time to consider if the greater cost implications associated with choosing x-ray systems are justified by these capabilities.

Understanding the technologies

Fully appreciating the significant differences between metal detection and x-ray solutions is a key step in making the right choice, so compare the technologies first.

For example, if you need to detect metal, including small pieces of aluminium, then metal detection is probably your only option. However, if it is vital you detect non-metallic dense contaminants or that you check part counts, detect misshapen product or estimate mass of product, an x-ray system is your most likely choice.

In certain instances, the whole production operation needs to be considered, as there may be a case for metal detection at one stage of the process and x-ray at other locations. And you should consider the need to equal - or preferably exceed - the quality requirements of your customer, while minimising the total cost of equipment ownership.

If you require detection of metallic-only contamination in product packaged in non-metallic materials, then in most cases, metal detection technology will do. But if your product is highly conductive - due to high moisture levels - then x-ray should be investigated. It may well outperform metal detection on a basic contaminant sensitivity specification, but the cost will be higher.

== Aluminium effects ==

Aluminium is a good electrical conductor, but has lower x-ray density than other commonly occurring metal contaminants. So if aluminium is a contaminant threat, metal detection will be the best option.

A good example of where the use of x-rays in the food industry would be challenged is in the detection of the ubiquitous ’blue plasters’. Specifically designed to be picked up by metal detectors, they are therefore undetectable by x-ray systems.

However, if aluminium is included in the packaging, either in the form of metallised film or as a foil tray, then its low x-ray density can be exploited, as the x-ray system will largely ignore it and will do a superior job of inspecting the product inside.

== product characteristics ==

Certain product characteristics limit metal detection performance. But equally, x-ray systems can struggle with ’challenging’ product characteristics. One good example is with products that contain a reasonably high level of salt - especially those with free salt crystals because these can appear as dense particles - potentially limiting the x-ray’s performance.

While it is important to be aware of and consider these issues before making your choice, the one thing to remember in both cases is that ’ignorance isn’t bliss’; it can be extremely costly and, if something sounds too good to be true, it probably is.

My advice to anyone considering either technology is to seek the help of a reputable supplier - a company without a vested interest in one particular solution.

Mettler Toledo’s product inspection division has produced a comprehensive guide covering all the issues above in far greater detail to assist you in making an informed choice. To receive a copy of the guide, email or call 0116 2357070. n