Principals of Metal Detection

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Estimated detectability of our products

Detectapro a leading supplier of metal detectable products is frequently asked how small of a piece of our products can be detected by metal detection equipment. The answer to this question is based on a number of variables but we hope this information gives you some idea in regards to an answer.

Every food processing facility that uses metal detectors to eliminate foreign objects contamination, must calibrate their detectors to the food they are processing and then set to a threshold. The threshold is determined by the company in regards to the size of contaminant they want the detector to reject. The type of product passing under the detector (dry or wet), it’s size, speed of the line and orientation also have an effect. These companies must maintain the calibration of these units by passing a known size of Ferrous,Stainless Steel or Non Ferrous test sticks or spheres under the unit to make sure they are calibrated correctly. All manufacturers of metal detector heads have these testing products available for companies to use to maintain the correct calibration of these metal detectors. It is critical for the processor to continually check calibration as the same product can possibly give off a different signal due primarily to moisture content of the product. (As a block of Ice Cream melts it needs to be re-calibrated due to the increase in moisture content). Without continuous calibration the metal detectors can allow larger pieces of foreign contamination to get through compared to their threshold settings.

Most metal detector manufacturers use different frequencies so there is not a specific standard in regards to the frequency setting across the board. One thing they all agree on is that the opening of the aperture is critical to the size of the piece of material you are trying to pick up. This is the height and width of the opening you are using to pass the product underneath to search for foreign objects. The height of the head from the line is the most critical variable as sensitivity decreases as height increases. The smaller the piece you desire to pick up the closer to the line the head needs to be. Most agree that 300KHz is common for dry foods and 25 KHz for wet foods.

Using this information we can provide the following estimate of the size piece of our typical product you can pick up at 25 KHz and 300KHz. As you can see the critical variable is the height from the line in regards to the size of the piece. These heights are also what manufactures of metal detection would recommend given a customer calls and requests that they want to pick up this size of piece of foreign objects as again the height of the head above the line is the critical variable in regards to picking up certain sizes of foreign objects contamination. As previously mentioned there are other variables being the speed of the line and the orientation of the foreign object when it passes underneath the head. It is also beneficial for the user to be able to provide some input in regards to what type of contaminants might cause an occurrence. This is needed by the manufacturers of these products to typically determine the setting Fe, Stainless or Non Ferrous they should set the equipment at.

We hope this information gives you some idea of what size piece of our product can be picked up but again there are a lot of variables in this question. Let us know if you need any other information about our products as we can be contacted at 866-441-5572.

DRY 300KHz

WET 25KHz

Setting	Size of Piece	Height	Setting	Size of Piece	Height
1.5mmFe	3mm	5 in	3.5mmFe	4mm	8 in
1.2mmFe	2mm	4 in	2.5mmFe	3mm	6 in
0.8mmFe	1mm	3 in	1.8mmFe	2mm	5 in

Principals of Metal Detection

Click Here for Technical details