Below is an excerpt from the Smiths Detection FAQ’s: Frequently Asked Questions about X-Ray Inspection Machines?
X-ray systems cost more than metal detectors, so are there compelling reasons why I should consider this technology?
Yes. When you purchase inspection technology, you should do so with an eye on your customer complaints. Reducing the maximum number of complaints should be your goal. X-ray inspection will greatly reduce complaints. In addition, to foreign object detection, the Eagle systems detect and reject product defects you may have never considered. In short, the X-ray system can likely detect and eliminate many more complaint causing defects than all your other inspection technologies combined. Thus, the value in benefit versus cost easily justified.
Here is another snippet from an article I found then lost again.
Metal detection
Electromagnetic metal detection is perhaps the most prevalent form of on-line packaging inspection. Metal detectors can be found at various points throughout all kinds of consumer-goods packaging facilities.
Metal detectors can be useful for monitoring incoming as well as outgoing goods, says George Louli, director of marketing for Safeline Metal Detection,
"A little bit of contaminant [in ingredients] can spread throughout a lot of product," Louli says. "Some people would argue, well, if you got the metal detection at the end, then who cares. But if you get a little piece, by the time it's mixed up and blended, it can get into a sizable amount of product, which you would be rejecting and having to dispose of, versus just catching maybe a half-pound of flour."
The biggest advantages of metal detection over competing systems are price and robustness. Metal detectors are less expensive than systems that interpret images, such as vision or X-ray, because they don't depend on computer processing technology. They also tend to be sturdy, solid units that stand up well to wash-downs and other in-plant stresses.
X-ray detection (visual)
X-ray units are among the most versatile on-line inspection systems. They can find a range of problems, including missing elements in primary or secondary packages, deformations in product, bad fill levels and more.
One of the biggest advantages of X-ray inspection is its ability to find non-metal contaminants, such as cherry pits or plastic film shards, that electromagnetic metal detection can't. X-ray systems also can handle metal packaging.
Visual X-ray inspection (as distinguished from analog, below) depends, like vision systems, on computerized interpretation of images. Advanced systems, like the eXaminer from Heuft inc., use advanced algorithms to analyze X-ray images, allowing, them to find hard-to-find contaminants in odd-shaped packages.
X-ray systems tend to have higher initial capital costs. However, their advocates say that when installation and operational expenses are taken into account, they are cost-competitive with less complex technologies. This is especially true in applications where the X-ray system supplants more than one type of inspection technology, such as a case-inspection system that can take the place of both metal detection (finding contaminants) and checkweighing (detecting missing packages).
If you want to go the whole (unbiased) hog CCFRA have a guide for sale on their website, not sure how up to date it is with latest developments as it was published in 2004.
Foreign bodies in foods: guidelines for their prevention, control and detection
Identify and exploit the latest technology for the prevention, control and detection of foreign bodies in foods, as part of a systematic food safety assurance programme.
The seriousness of foreign bodies as hazards in foods is well recognised by both food companies and enforcement bodies. A foreign body incident can jeopardise consumer health, result in prosecution and significantly undermine a company's image. A wide range of measures, exploiting various technologies, is now available to food companies to help with the prevention, detection and control of foreign bodies. Understanding these - including their strengths, applications and limitations - is an essential part of devising an effective strategy for food safety assurance with regard to foreign bodies. This guide is designed to help food companies achieve that understanding and use it to implement foreign body prevention, control and detection systems appropriate to their processes, products and business.
The guide builds on the widely used first edition, with extensive revisions reflecting the significant technological advances and the practical experience gained in the intervening nine years. Developed by a working group of foreign body experts drawn from food companies and equipment manufacturers, the emphasis of the guide is on practical systems and procedures, from which companies of all sizes can identify those most appropriate to their needs. Part A deals with control and prevention of foreign bodies whilst Part B covers detection and removal, and Part C provides useful reference information - such as contact details for suppliers.
Contents
Introduction
Part A - Effective control and prevention of foreign bodies in foods
· Definitions
· Scale of the problem
· Reasonable precautions and due diligence
· Suggested procedures for investigating a foreign body incident
· Control factors
Part B - Foreign body detection and removal methods
· Selection of detection and rejection systems
· Metal detection systems
· X-ray detection systems
· Vision and optical detection systems
· Physical separation systems
· Manual sorting
· New and emerging foreign body detection technologies
· References
Part C - Appendices
· Theory and operation of metal detection systems
· Theory and operation of X-ray detection systems
· List of suppliers for metal detection and X-ray detection of foreign bodies
· Bibliography
· Glossary of terms
Softcover - 86 pages
