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Recommended Testing Procedures
A complete and thorough test of the metal detector system must be done upon initial installation and whenever a major
component of the system has been changed or altered (i.e. reject device repair, etc.). A complete check of the metal detector
must include the reject device. Any test procedure designed for your application should take into account the following:
1. The metal detector’s least sensitive point in the aperture is along the center line of the opening. Any
testing should be done so that the test sample passes approximately through the center line of the opening. If the test sample is
run at the side of the aperture, this will produce a larger signal than through the center line. The test procedure should take
this into account for consistent results.
2. Sensitivity capabilities of different detectors used in different applications will vary. A smaller aperture
is capable of detecting smaller pieces of metal. Product effect may also interfere with the detection capability. It is dangerous to
rely on a corporate standard to determine and test the detector’s operation. Ideally, each detector should have it’s own
standards of operation and a corporate outline should be used only as a maximum allowable guide. Sample sizes should be
selected so that they are clearly detectable (peak signal size of 150 - 250) when compared to the signal produced by the
product or other interfering signals. If samples are established which are very close to the product signal, frustration on the
part of operators can lead to a lack of confidence in the detector’s operation.
3. The detector should be tested at its normal operating speed. Test samples should be placed on the belt so that they will
pass through the detector at normal speed.
4. The detector is not equally sensitive to all types of metal. Depending on the type of product and application there can be
three typical metal groups which will produce three different levels of detection:
Ferrous - any magnetic metal and is typically the easiest metal to detect
Non Ferrous - any good electrical conducting metals such as aluminum, copper, brass, etc.
Stainless Steel - the 300 series stainless steels which are non-magnetic, these tend to be the
most difficult metals to detect
If a single test sample is to be used for regular testing, it should be a stainless steel sample. This will ensure that other metal
types will be detected to this same level or better (smaller).
5. Test samples used should contain spherical metal contaminants. Any other shape will produce a different size signal
depending on it’s orientation as it passes through the detector. This can lead to inconsistent results.
6. Any test procedure established must allow for the test product to be completely rejected by the reject device. The reject
device will tend to be the most likely point of failure in any detector system.
7. Care must be taken so that if the detector or reject device fail to operate correctly the test sample can be recovered safely.
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