A metal detector is a device designed to generate a signal whenever metal or ferrous, non-ferrous (copper, lead and aluminum) and stainless steel particles are detected during the process of making food, plastic or pharmaceutical products. It does this using one of three possible metal detecting technologies: induction balance or very low frequency (VLF), pulse induction (PI) or beat-frequency oscillation (BFO).
How A Metal Detector Works
Balanced, Three-Coil, System - coils are wound on a non-metallic frame, each parallel with the other. The center coil is connected to a high frequency radio transmitter. Coils on either side of the transmitter coil are receivers. As these two coils are identical and placed the same distance from the transmitter, they receive the same signal and produce an identical output voltage. When the coils are connected in opposition, the output is cancelled, resulting in a zero value.
When a particle of metal passes through the coils of a metal detector, the high frequency field is disturbed under one coil, changing the voltage by a few microvolts. The state of balance is lost and the output from the coils is no longer zero. It is this phenomenon that is used to detect metal.
Metal Free Zones
An important aspect of metal detector operation is the metal free zone, which is needed for proper operation. The zone includes a space on each side of the aperture that must be free from any metal structure such as rollers and supports. As a general rule, this needs to be approximately 1.5 times the aperture height for fixed structures and 2 times the aperture height for moving metal such as reject devices or rollers.
What Can Be Detected
All metals are either ferrous, nonferrous or stainless steel.
Ease of Detection depends on two things: magnetic permeability and electrical conductivity. Size, Shape and Orientation (with respect to the detector coils) of the metal particles are also important. Since size, shape and orientation of metal contaminants is not possible to control, it is best to operate a metal detector at the highest possible sensitivity setting.
Especially high quality requirements are demanded from foodstuffs, since our body absorbs them. Thus, the ultimate consumer expects that food producers undertake all the necessary measures to ensure that no products contaminated by metal get into the distribution chain.
In order to be able to sell foods and luxury foods or pharmaceutical products internationally today, certain requirements must be observed during the manufacturing process; these have been outlined by the U.S. Food and Drug Administration in Guideline 21 CFR Part 11. These requirements, frequently also referred to as the FDA guidelines, are used to guarantee the quality standards for foodstuffs.
In the foodstuff industry, one must ensure that no contaminants get into the final goods, which would result in cost-intensive production losses and in the worst case, harm the consumer\u2019s health, not to mention the potential loss of image at the hands of the press or TV media.
The new generation of devices using M-Pulse technology was developed in order to meet the increasingly more stringent requirements of the FDA guidelines. With M-Pulse technology, is possible to setup a quality management system in accordance with HACCP requirements. This equipment must possess a modern metal detector, in order to pass an audit in accordance with the FDA requirements. Although, the major points that have to be fulfilled are the incoming inspection, managing any changes and storing data for the metal detection systems.
How do metals come into food?
The main causes of metallic impurities are:
- Cuttings (e.g. maintenance work)
- Broken off machine parts
- Dirty Containers
- Production Flows
- Quality lacking of the vendors