Continuous Improvement in Metal Detection

Industrial metal detectors may be old technology, but greater sensitivity, fewer false rejects and ease of use are helping them maintain their relevance in food and beverage inspection.

By Kevin T. Higgins, Managing Editor

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Engineers at Mettler-Toledo Safeline were cognizant of the ease-of-use need while executing a recent upgrade. A full-color touchscreen with membrane key panel is standard in the firm's new Signature metal detector. "Automatic set-up on the fly" is not, however, according to Geri Foley, metal detector sales manager at the Tampa, Fla., firm: For that and Optimized Set-up, end-users will have to upgrade to the Pro Select series.

Pro Select allows users to dial in a frequency in the 200-850 kilohertz range to fit the product. A slight tweak can have a big impact, Foley says, particularly with highly conductive products like ice cream. User access codes help create an electronic record of who accessed the equipment and what changes were made, making the machines compliant with 21 CFR 11, if and when FDA begins applying the regulation to food as well as pharmaceutical manufacturers. Data export and performance monitoring is available through ProdX software, a management package that will be Ethernet I/P compatible by year end, she adds.

Condition monitoring capabilities are built into higher-end units. If inspection performance begins to drift, the system will generate an alert for recommended maintenance procedures. "In a heavy-duty washdown environment, this provides an early warning before the machine goes down," says Foley.

High-pressure spray has permanently sidelined many metal detectors, which is why Eriez upgraded protective covers for machine electronics to IP 69K, the European standard that exceeds NEMA 4X, according to Klinge.

Ries maintains Thermo Fisher has gone even further with Apex HD, a machine that not only resists moisture like a duck but also can withstand thermal shock in a refrigerated environment. After cycling the unit through a car wash 10,000 times, managers were sufficiently confident to offer a three-year warranty at no additional cost. "Poultry plants usually face huge (machine) repair bills after 1-3 years of use," he says. Five poultry processors are the first food companies to install the new heavy-duty units.

Many factors can disrupt a machine's detection ability: thermal shock, stainless steel and other nonmagnetic metals, ground loops from adjacent conveyors (Mettler-Toledo and Eriez are among the suppliers who offer turnkey solutions, including an "almost tool-less" hygienic conveyor from Eriez, according to Klinge). Without question, advances in sensitivity over the past 60 years are impressive, and they continue to be made. Aperture height and metal type have a bearing on sensitivity, but even at a height of 12 in., particle detection below 2mm can be delivered with today's machines, says Ries, about half the standard of a decade ago.

X-ray machines are gradually replacing metal detectors at the end of the line, but food processors are fitting metal detectors into upstream processes to intercept contaminants earlier. As performance improves and false rejects decline, these machines are securing their relevance for years to come.

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