Metal detectors good at finding 3D but struggles with almost 2D
In a perfect world, there would be no contaminants in your food, and in a slightly less-than-perfect world, any foreign piece of metal in your product would be spherical in shape, making it easy to spot in a conventional, single-planar field metal detector. However, unless a ball bearing fell into your product, you’re more likely to find metal flakes that—depending upon their position in your product—may completely evade your metal detector, which is better at detecting 3D objects than practically 2D flakes of metal positioned perpendicular to the sensor’s single electromagnetic field.
Why? A flat metal flake appears at best as a single line in a 2D plane (or a magnetic detector field), and when perpendicular to the plane (field), as a single point, which is extremely difficult to detect. For a better illustration, read “Flatland” by Edwin A. Abbott for a story in perception of points, lines and planes in single-, two- or three-dimensional spaces.
Steve Gidman, founder and president of Fortress Technology, talked with several food processors who were having iffy results in detecting thin, flat metal flakes in their products. Gidman, who began his company in his garage more than two decades ago, figured there had to be common issues in their upstream processes that would require a different kind of metal detector—one that was capable of “seeing” metal flakes in whatever position they became lodged in the food.
Gidman found certain upstream applications—which, for example, created very thin flakes of metal from using foils, mixing, rolling, scoring, molding or baking—presented limitations for conventional single-plane metal detectors. His design actually scans more than one field (dimension or plane), thus it’s more likely that a flat piece of metal will present itself in at least one of the detector’s sensing fields.
“Flat-shaped pieces of metal that are very, very thin are very hard to detect, and this is the weak point of the typical coil/field structure used in metal detectors in the food industry,” says Gidman. The standard coil can detect anything in a horizontal plane but misses a flat piece of metal perpendicular to the field. Adding a second electromagnetic field to work in the vertical plane can solve the problem, but such a system is not a piece of cake to design.
I asked Gidman about some of the challenges and successes in designing Fortress Technology’s Interceptor DF system.
FE: How long has the Interceptor DF been in development?
Steve Gidman: It’s taken about two years to get a production version released.
FE: Are there any more particulars in how it works?
Gidman: Basically, there is a “normal” metal detector field which is in a horizontal direction and to that we’ve added a second, vertical field. Together they cover each other’s weaknesses. Contaminants whose shape and position are very difficult for a normal detector field to “see” conversely generate a very large disturbance to the vertical field. The opposite is also true.
FE: Does the extra field improve the DF’s ability to screen out external “noise” sources that can decrease sensitivity for single-field detectors?
Gidman: The DF is significantly better at ignoring external noise. It is looking for a patterned, matched signal from two coils/systems operating in different frequency ranges. External noise sources are extremely unlikely to match that pattern and so get rejected by the detection algorithm.
FE: What were the complications of making this design reality?
Gidman: The real complication is getting two electromagnetic fields to cohabitate without compromising either’s performance. This was a difficult problem to overcome, but we eventually found a very good solution.
FE: Does the motion of the belt contribute to sensing?
Gidman: Only in that the product being inspected must be moving to generate detectable signals. Typically, anywhere between 3 to 1000 feet per minute is acceptable movement.
FE: What is the most typical elemental composition of metal flakes?
Gidman: It really can be any metal depending on the source. Stainless steels are certainly more often found in food processing equipment, but many molds and impression rollers are brass and even aluminum.
FE: Is stainless steel often an issue in flaking? How do you detect SS flakes?
Gidman: Yes, probably the biggest issues will be with stainless steels. These are usually the most difficult metal to detect because food quality stainless steels tend to be nonmagnetic and poor electrical conductors. Those are the two characteristics that disturb an electromagnetic field and are what all metal detectors measure. By using higher frequency fields, stainless steels become more detectable. By using two fields in opposing planes, they are much easier to detect, in some cases, hundreds of times easier.
FE: Some metal detectors use more than one frequency. Is this necessary in this unit?
Gidman: Yes, the fields tolerate each other better if there is a frequency separation. There are also some detection performance advantages that can be extracted with the additional spectrum of multiple frequencies.
FE: When was the Interceptor DF officially released?
Gidman: We displayed the first production version at PACK EXPO in Chicago last fall. That was the official release. We also showed it at PACKEX Toronto in June and will exhibit it at the International Baking Industry Exposition (IBIE) and PACK EXPO, both shows to be held in Las Vegas this September.
FE: Are food processors now using it and for what types of food? What has been their feedback?
Gidman: We have installed the initial units mainly in manufacturers of high-quality chocolate products and will add some cookie and gum inspection systems soon. The response has been great. Once processors see the DF in action, it really sells itself.
FE: Does any application software come with the unit?
Gidman: Yes, the system requires special algorithms designed to take full advantage of the extra information presented by the addition field.
FE: What does the software do?
Gidman: For fast setup and ease of use, the Interceptor DF learns and recalls the signature of any given product with just one pass. Halo automatic testing can be added to reduce the risk of human error when manually testing the performance of the detection system.
To increase supply chain transparency and product traceability, Contact Reporter software produces a full log of events. These electronic records can be viewed, filtered and exported, and can be used to supplement or replace manual documentation.
FE: Any thoughts for the future?
Gidman: Our customers always present us with new challenges. I expect we will expand on the Interceptor DF concept to improve performance across additional applications.
For more information, visit www.fortresstechnology.com.