Themoform Multi-Cards
What are Thermoform Multi-Cards and Why Do I Need One?
February 4, 2021
Stainless Steel 316 vs. 304
Stainless Steel 316 vs 304
April 20, 2021
Themoform Multi-Cards
What are Thermoform Multi-Cards and Why Do I Need One?
February 4, 2021
Stainless Steel 316 vs. 304
Stainless Steel 316 vs 304
April 20, 2021

OPERATING SENSITIVITY

There are a wide range of variables determining the operating sensitivity of a metal detector.  This, of course, affects its ability to detect various types and sizes of metal.  Understanding these influences is important to get the best your metal detector can achieve.

Metal Detection SensitivityBasically, operating sensitivity is the metal detector’s ability to discover a contaminant based on its specific kind and size metal. The greater the sensitivity, the smaller the fragments of unacceptable metal it can locate. But setting the sensitivity too high can create false positives. That means lost product on the production line.  Peak function is expressed by the diameter of a test sphere and the specific type of metal.  In the food industry, 4 categories of metal are hunted in processing food: ferrous, non-ferrous, aluminum and stainless steel 316.  When the metal detector is operating at its best, the smaller pieces of metal it can identify. That archetypal operation, however, can be complex because of an assortment of dynamics.

Diameter of the Test Sphere

The diameter of a ball is most often used to identify a metal detector’s operating sensitivity. For instance, a  detector that can locate a 0.6mm ferrous ball is more sensitive than one that can only detect 1.0mm.  The lower the number the better, that is, assuming no false positives.  What is not true is to say that a detector that can “see” a 0.6mm contaminant is twice as sensitive as one that can only see 1.2mm.  That’s because detection is based, in part, on surface area.  A 0.6mm ball has a surface area of just 1.132mm2.  The surface area of the 1.2mm ball is 4.524mm2.  This means the better detector is nearly 300% more sensitive.

To know the true sensitivity, you’ll need a certified, reliable test piece (see testrods.com).  This testing device must be detectable when traveling through the middle (horizontally and vertically) of the aperture of the detector. This is the most difficult location for the metal to be discovered.  This is the point at which the magnetic field between the receiving coils is the least sensitive.  If the test piece is closer to the wall of the aperture, it will be easier to detect.

But it’s important to keep in mind that there can be a considerable variance between the metal sphere in the test piece and the length of an irregular piece of metal or wire in your product.

HAACP Plans

Any HACCP plan and audit may find a metal hazard of the previously mentioned metals. The sensitivity, however, of the system can vary depending on those metal types. Most often, quality assurance speak in terms of the varying differences of metal.  For example, you may hear that the sensitivity is 1.0 Ferrous, 1.5 Non-Ferrous and 2.0 Stainless Steel 316.  You might even just hear 1.0, 1.5 and 2.0.  The ferrous material is typically the easiest to detect because of its magnetic properties.  The Non-Ferrous (Brass) is harder to find and the Stainless Steel 316 (the industry standard) even more difficult. It’s important to test with SS 316 not only because it’s the chosen industry standard,  but it’s also the most difficult to detect.  If you can find 316, you’ll detect other types, but not the other way around.  Still, as with many standards, there are exceptions to this.

We’ve already seen how the metal classification (Fe, NFe, SS 316, Alum) can determine its detectability,.  But sensitivity is also determined, in part, by the orientation of the metal as it passes through the aperture.  If the object’s cross-sectional area is less than the detector’s sensitivity, then that object will pass through without detection.  This is one reason why it’s so critical to get the most out of your metal detector and write your HACCP accordingly.

The Greatest Sensitivity  

In order to achieve the greatest sensitivity, you should use the smallest possible aperture possible.  This will be determined, of course, by the type of product and its packaging.  You’ll need to take into consideration the speed of the belt in a conveyor system.  There are also other factors in the case of gravity fed and/or overhead configuration.  And you’ll need to make room for the test piece used.  Ideally, the test piece will be inserted into the middle of the product, but this is not always possible.

The material used for packaging a product will sometimes offset sensitivity if the material is conductive.  This can happen, for instance, when recycled cardboard is used, because it often contains bits of metal.  To adjust for that, you might want to decrease sensitivity.  That comes at the expense of the product, in which you may be missing metal.  The location assigned for testing should be determined carefully. This may be just prior to packing or, in other cases, e.g. when metallized film is required, a solution may be available to conquer the potential issues the material creates.

Environment

Factory plant surroundings can also negatively impact the metal detector’s success in relation to its operating sensitivity.  Built-in noise and vibration reduction will minimize the potential interference affecting the metal detector.

The conductivity of the product can cause it to behave the same way as metal when passing through the detector’s aperture.  Products with high moisture or salt content, like meat and poultry, can detract from the detector’s sensitivity.  This is often referred to as Product Effect. Large products, like large blocks of cheese (which also have conductivity) can be a difficult assignment in reaching the highest levels of sensitivity desired.  When a metal detector is setup, the operator should “calibrate” the metal detector to the product.  In other words, the detector is set so that when good product is run through, there will no signal created in the detector.  “Calibration” is often confused with “Verification.”  Technically, a metal detector has no calibratable parts.  It is design to validate that it can achieve the levels of metal(s) you pass through it.

Leave a Reply

Your email address will not be published. Required fields are marked *


Some applications involve large tubs, vats, or some other type of product travel where it would be nice to have a test piece that floats. Once again, our thermoform cards provide the simplest solution. We simply insert some type of structure that forces the thermoform card to retain air, which, of course, is what makes it float. We have also manufactured floating rods, which are more difficult because there is less space to close in enough air to make the rod float but is doable.

We took an ordinary plastic “chip clip” as defined by the customer and embedded the contaminant into the clip. The clip can be attached to the product on the line without damaging or opening the product for testing purposes.

Bone is a difficult contaminant to find because it can vary widely based on the size, age, and calcium content (as well as feed used) of the animal. After working with several customers, Regal Packaging Services offers Pork, Beef and Chicken Bone Simulate. We have a small range of sizes at a variety of depths to simulate whatever you might expect to find in the product. Our recommendation (assuming your x-ray has visual display) is always to start with a multi-card. Using a multi-card gives you an easy way to test several sizes and depths to determine what matches the bone you’re using. Once you’ve made a comparison, testing the card against the bone you’re looking for, you can purchase a card with a single contaminant for regular testing.

This small pill shaped test piece is used in a system with a vacuum tube that shoots the test piece through the aperture and returns it to the “home” base. Your system may never be like it, but the point is that we can make a customized solution no matter how unusual or impossible it might seem.

As you may have seen in some of the other thermoform card descriptions, we can put nearly as many seeds as you can imagine on a single card. Pictured here you will find a wide variety of configurations and contaminants. Just let us know your specs: size of the card (up to 8” x 8”) along with size and type contaminant(s) and we’ll get you a quote as quickly as possible. Working with a multi-card is especially helpful when you are looking for multiple types of contaminants or when you want to determine what size of the same contaminant you are able to detect. In that event, once the size is chosen, you can order individual card(s) for regular, standard inspection and detection.

There are a wide range of applications that require a test piece much longer than our standard 5” or 6” Testrods. We can make up to 3/8” x 34” or 1/2” x 34” rigid test pieces which can then be extended well beyond that length with a “handle” made of acetal cylinder larger than the 3/8” or 1/2” extension. In the photos, we used a 1” x 24” cylinder handle with a 3/8” x 24” inch extension.

Test pieces can be made in a variety of sizes and given a pointed end in applications that require the contaminant (metal) to be inserted into a food package such as sugar or some other soft packaged food product. This allows the metal to reach the center of the aperture.

Double-End Test Whips are also available, with metal in both ends. One consideration is to make certain that the whip is long enough to keep the metal on the non-testing side of the whip outside the metal free zone of your detector. If you insert, for instance one end of a whip with 2.0mm and 3.0mm Ferrous, you need to make certain that the 2.0mm metal doesn’t affect the detection of the 3.0mm metal (and vice versa). If the 3.0mm metal is inside the metal free zone, then the detector will be reacting to the 2.0 as well as the 3.0 as if they were combined.

Multi-seed laminate test cards are designed for seeds 4.0mm or less. Multi-cards are useful in x-ray inspection to determine what sizes and types of contaminants your system can achieve. They can be especially useful in temperate environments and applications. If your application is rugged or wet, or your standards are larger, we recommend our thermoform multi-cards.

We can simulate a variety of packaging in an application where you need the test piece to mimic what is traveling down the production line. In this case, we manufactured a clear “package” with the seed inside. With this method, the customer is able to reject the container appropriately, and, in the event the package is not rejected, it is easily seen by the line worker for manual removal.

There are two types of “candy bars” pictured here – one similar to a flat candy bar and the other in a custom, near perfect copy of a candy bar. Since we’re now able to produce many variations using colored material, the copy was made in red (Fe), green (NFe) and blue (SS 316). We have the equipment to accomplish nearly anything you can imagine, and these kinds of designs are proof positive.

Need a test piece that looks and handles like chicken nugget? We can do it. Interestingly enough, in this situation, our first version for the customer left too much “void” in the hole where the metal was placed. Given the sensitivity the customer system was using, the void had the effect of causing false positives. We were able to minimize that hole and supply the test piece with almost no void. It’s an example of how we can work with you before, during and after manufacturing to ensure all the specifications were met.

Our standard acetal card is 2 1/4"x3 3/8,” but if needed, we can cut that size down to as small as 1 1/4” x 1 1/4” (with limited engraving). If a larger card or a card with multiple seeds is needed, see our Custom Shape-Size Blocks and Tablets.

This distinctive test piece was created to mimic an actual hamburger patty. The customer supplied photos of the raw product, which we were able to reproduce and then we placed blue glove contaminant. Using this configuration, the customer was able to determine what size piece the vision scanning system could detect with the raw burger as the background. Had they simply used a blank card with the glove, the system could easily have achieved contaminant rejection, but they needed to be sure the system could “see” the blue against the product itself.

A card with 100 seeds in a 10x10 configuration is used to place beneath whole chickens on a production line. This gives the x-ray system operator the ability not just to see IF the equipment can detect the metal in the card, but also WHERE the equipment can detect it. If there is a problem, the operator (or company) can make any changes necessary to achieve the end goal – safe chicken in this case. This card really highlights another valuable facet of our thermoform cards.

In this scenario, a company processing sugar needed to have a “bag” simulated with the same weight in order to accurately fall through the reject mechanism. A lighter test piece had the risk of passing over the reject mechanism.

Our standard cubes are 1” and 1.5,” but we can also manufacture other sizes if needed. The cubes shown here are 1/2" in dimensions. Cubes can be helpful in applications where a ball or cylinder may bounce or roll away during testing, making their retrieval difficult, or, in some cases, present a hazard to the product or production equipment.

This is a test piece that is dropped into a bottle. It’s designed so that the metal appears in the center of the aperture when testing the metal detector. In addition, the round stop makes the test piece easily removable after testing.

Hexagonal Shaped test pieces can be very useful in places where a cylinder or ball might roll or bounce around a production floor whether dropped by a line worker or ejection from a reject mechanism. Hexagons are similar in weight to the 1inch cylinders without having the smooth, rounded cylinder edge.

Our customer in this plant needed a test piece with a thickness less than 5.0mm. Because we have the capacity to customize sizes and shapes, we were able to mill down a product that met their specifications. That’s always our goal, meeting the specs you need for your product, testing environment and contaminants.