Good Practice - Loma IQ2 User Manual

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Using the metal
detector

Good practice

The following procedures are recommended for ensuring and maintaining an effective metal
inspection regime. There are three essential components in using the IQ 2 Metal Detector
effectively:
• Establishing detector sensitivities
• Regular in-line detector sensitivity testing
• Effective handling of rejected products.
Establishing detector sensitivities
Once the metal detector has been calibrated with the product it is important to establish
what size of metal contaminant the detector is capable of finding.
In dry or resistive mode ferrous and non-ferrous sensitivities are approximately equal. In
reactive mode non-ferrous sensitivity will be poorer than ferrous sensitivity.
The metal detectors are normally supplied with a selection of metal test wands. There are
three types of wands: ferrous (chrome steel), non-ferrous (brass), and stainless steel.
Stainless steel is included because sensitivity is generally poorer than to other non-ferrous
contamination due to the relative conductivity of the material. The wands are supplied in a
range of sizes depending on the particular instrument you are using.
In dry or resistive mode the sensitivity can be measured by placing the test wand at the
trailing and leading edges of a representative sample of the product, and then passing the
product through the detector. The test wands should be placed at a height so they pass as
near as possible to the centre of the aperture. Test wands are placed at the leading and
trailing edges of the product to ensure correct product rejection. This is particularly
important in metal detectors with no photo-eye system, as the reject time is determined by
the position of the contaminant relative to the product.
In reactive operation the signal generated by the metal contaminant can be masked by the
product itself. It is therefore important to test the product with test wands not only at the
leading and trailing edges, but also at the product's centre.
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