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From: Food Quality & Safety magazine, August/September 2012

Anatomy of a Metal Detector

by Jeff Kaveney

Understanding the fundamentals Of metal detector layout and operation will enable you to select the correct equipment for a given task, while also permitting more effective metal detector operation.

An industrial metal detector consists of four main components: the sensor, the control, the signal processor, and the output device.

The sensor will react to the proximity of metal. The reaction of the sensor is transmitted to the filter, an electronic device that interprets the sensor signal. If the filter determines that the sensor has detected metal, it activates the output device, which may range from a simple display or alarm to an array of timed automatic reject devices. The operation of all these components is governed by the control.

In addition to these four components, which are embedded in all metal detectors, there are five auxiliary components frequently found in a metal detection system: the feed device, the reject device, the alarm device, the record keeper, and the power supply.

The feed device presents the product that may be contaminated to the sensor. The feed device is generally a conveyor, but other possibilities include chutes, pipelines, vibrating trays, and even manual presentation.

Metal detector power must typically be very “clean,” because detectors will frequently register any surges in the power supply. Consequently, special power supplies have been developed for detectors and their auxiliary equipment.

Reject devices are designed to remove the metal from the product stream. They include trap doors, pusher arms, air jets, and retracting head pulleys.

Record-keeping software is frequently embedded in the metal detector control and/or in networked computers that can communicate with one or more detectors. In cases where the production and storage process is highly automated, the record-keeping device may enable contaminated product to be located and isolated after the fact by accurately tracking the time and magnitude of a metal detection, thus eliminating the requirement for immediate action on the alarm.

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