Metal Detectors – Operation and Usage Restrictions

Metal Detectors – Operation and Usage Restrictions

Metal detection technology has been developed for many years, with the first detector being built in 1948 in the UK. This technology has grown and evolved from a transistor tube to the high-precision DSP (Digital Signal Processor) technology currently in use.

Metal detectors detect metal contaminants in all food products, regardless of product type, and operate a balanced coil system that transmits frequency, while receivers analyze the signals generated by the products.

A metal detector generally operates in two modes, “wet” and “dry”. A “wet” product is a conductive product, such as raw meat, liquid milk, cheese, fresh pasta, and fish. All these products are conductive and have what we call a product effect.

product passes through the metal detector

This means that when this product passes through the metal detector, the unit will have to “know” the impact of the product and eliminate it. If one of these products is contaminated, the metal detector will compare the “gained” product signal and the contaminated product signal will generate a detection.

“Wet” products tend to detect less contaminants, depending on how much product effect the reagent needs to learn. On average, a dry product, such as a loaf of bread, will detect 1.5 mm of ferrous material; 2.0-2.5 mm of non-ferrous material and 3.0-3.5 mm of stainless steel.

On the other hand, the 25kg fresh meat box is a product with a significant impact and is likely to reveal 5.0-6.0mm iron, 6.0-7.0mm non-ferrous, and 7.0mm stainless steel. This is because the reagent needs to overcome the effect of the product.

metal detector for several types

Another constantly repeated mistake in the industry is the purchase of a metal detector for several types of wet products, which are passed at the same time and on the same line, where only one type of product can be calibrated per production.

This is critical because the metal detector must “learn” about the product to maximize contaminant detection. Unfortunately, in production lines that pass several products at the same time, the metal detector cannot recognize all products and it is necessary to reduce the power of the detector to allow the passage of several products and thus sensitivity is lost.

In this example, the metal detector can detect only 10 mm of stainless steel. If the customer passes one type of product at a time, he can achieve better sensitivity, closer to 7mm for stainless steel.

My recommendation for wet products is to pass the production of only one type of product per reagent to maximize contaminant detection. On the other hand, dry goods are the best friend of the metal detector.

Little for the field of metal detector

Little for the field of metal detector. In this case, the metal detector will “learn” the vibration system, allowing detection to be maximized. Because the product and metal detector do not compete with signals, they can reduce the detection of samples for testing by using very small contaminants.

The best detection of “dry” product contaminants depends mainly on the size of the hole of the metal detector. The rule of thumb is that the larger the metal detector, the more difficult it is to detect the contaminant.

For example, a chocolate bar that passes through a 150mm ×150mm metal detector will detect 0.8mm of ferrous contaminants, 0.8mm of non-ferrous contaminants, and 1.2mm of stainless steel. Another example: 50 kg of sugar passes through a 700 mm × 300 mm detector that has a detection limit of 1.5 mm for ferrous materials, 2.0 mm for non-ferrous materials, and 2.0 mm for stainless steel. Metal detectors up to 700mm × 300mm that pass through “dry” products will have the capacity to operate 2.0mm of stainless steel, as long as the product does not consist of high salt contents or high-iron additives. If this is the case, you will discover the unit is 2.5mm stainless steel.

metal detector larger than mentioned above

If a product production line is operated on a metal detector larger than mentioned above, the facility will need to increase its detection standards to stainless steel with a diameter of 2.5 mm. Unfortunately, there is no other technology available in the market to detect 2.0mm in systems larger than 700mm ×300mm. These are the technologies available for metal detectors on the market today. With this information, you can create your own metal detection pattern in your factory.

Currently, ANVISA (National Health Surveillance Agency) published on March 28, 2014 RDC No. 14, which stipulates macroscopic and microscopic foreign substances in foods and beverages and their tolerance limits, according to the decision of mineral contaminants, the tolerance must be 2.0 mm in all food products.

Unfortunately for “wet” products, (unless your product is small and does not have a large product effect) the prescribed tolerance may not be reached by any metal detection systems (X-ray or metal detectors) on the market.

On the other hand, “dry” products generally will not face any problems as long as the metal detector remains smaller than 700mm × 300mm. It is important to note that even with this head size, only a few metal detector companies will be able to detect 2.0 mm of stainless steel and I recommend that you ask the detector manufacturer to test their product in the original size and condition, before purchasing equipment.

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