The development of simultaneous multi-frequency metal detector technology was driven by the food industry ’ s need to address product effect and to target specific target contaminants .
To identify a metal contaminant within conductive products , a metal detector must remove or reduce this product effect . Single pass calibration is meant to do this . However , the underlying operating frequency of the metal detector impacts how effective a calibration can be at eliminating the product effect . With single frequency metal detectors running ‘ wet ’ products there is often a trade-off between ferrous and stainless-steel performance depending on the selected frequency . Typically , higher frequencies exhibit increased performance in detecting stainless-steel versus ferrous metals . The best approach is to find a frequency that provides a balance between the lowest product effect and the detection of target contaminants .
Using simultaneous multi-frequency technology is the most reliable way to remove product effect without compromising the sensitivity of a metal detector . This processing technology powers the Fortress Interceptor , enabling it to run realtime analysis of the low-frequency and a high-frequency signals in parallel .
The increased sensitivity was one of the primary reasons why dairy processor Vepo Cheese selected seven Interceptor metal detectors
to integrate with their vertical packing machines . The cheese giant specifically requested “ state of the art inspection equipment that could deal with variations in density and product effect .”
Technical Operations Manager at Vepo , Hugo van Put recounts : “ These metal detectors are really sensitive . This helps us to feel confident that the risks of contaminants are minimal , with less chance of a food safety issue . Having the double readings within the Interceptor system also lowers the risk of falsepositive rejects , which saves on food waste .”
TEST SPHERES : SHAPE AND SCIENCE
The standard technique for measuring the sensitivity of metal detectors in food inspection is to use metal test spheres . Yet , metal contaminants typically enter the production line as flat metal flakes , shards , swarf or thin wires , rather than globular shapes . So why test using spheres ?
The main rationale is it provides machinery suppliers and food processors with a comparative sensitivity control . A sphere does not exhibit orientation effect and will always produce the same signal when passed through the same position of a metal detector ’ s aperture .
The food metal detection industry has general sphere size guidelines . For example , a wet block of cheese measuring approximately 75mm high , currently has sphere size parameters of 2.0mm for ferrous metals , 2.5mm for non-ferrous and 3.5mm for stainless steel . However , these levels are not always one size fits all , as the product effect from different types of cheese as an example , can vary greatly .
FREQUENCY FOCUSED
There are multiple variables that can affect a metal detector ’ s performance , from the potential size and composition of possible contaminants to the liquid content and consistency of the product matrix .
It ’ s equally important to note that there is no ‘ best ’ metal detection frequency . There are only ranges of frequencies , each better for different purposes . As with any aspect of food safety , there ’ s always a cause and a consequence . Having sufficient scientific understanding about how dairy products behave and conditions that can trigger a false positive reaction is important . If in doubt , seek expert guidance .
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