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Meeting retailers’ metal detection testing requirements

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Meeting retailers’ metal detection testing requirements

Meeting retailers’ metal detection testing requirements
April 14
10:52 2023
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By Rob Stevens, Market Manager, Mettler-Toledo Safeline Metal Detection

Retailers are increasingly including the requirement that food suppliers be able to prove regular
testing of metal detection equipment as part of their codes of practice. Here we consider the tests
that food manufacturers must undertake to comply.

For food companies operating metal detection systems for product inspection, it is imperative to
understand both the capabilities of their equipment, and how these fit in with their retail customers
requirements. Testing is a critical part of both aspects. Retailers are increasingly specifying the need
for suppliers to undertake stringent testing of metal detectors and specify that they have the data
to prove it.

Frequent and appropriate testing of a metal detection system verifies that the system and its
associated components, such as reject systems, beacons, and fail-safes, continue to perform to the
necessary standard. It is proof that best practice is being used.

On tunnel-type metal detectors, there are three main tests, plus a fourth type of test that some
retailers may also mandate. Each test should be carried out using ferrous, non-ferrous, and stainless-
steel test packs, inserted in that same order.

In the first of these, the Standard Test, metal detector operators insert the three test packs in
sequence into the middle of the normal operation of the system, with random numbers of clean packs
between them, but with correct spacing maintained between packs (both clean and test). In a
successful test, only the test packs should be rejected.

Sometimes, retailers will require that the reject mechanism of the detection system can cope with
multiple contaminated products in succession. In this scenario, the Consecutive Test becomes
appropriate. The operator introduces the test packs in the correct sequence one after the other,
with normal pack spacing and at normal production speed, but without clean packs in between. If
the test is successful, the metal detector will reject all three test packs.

The third test is an enhanced version of the Consecutive Test and is preferred by some retailers. The
Memory Test introduces a clean pack between the test packs, which are again inserted in the
ferrous/non-ferrous/stainless steel sequence. All packs should be correctly spaced. If successful, the
the test will see the three test packs rejected, and the two clean packs in between passed as good

Where companies are using metal detection equipment with a photogate side reject device, such as
a pusher or air blast, a fourth type of test might be requested. This test checks that the reject timers
on the systems are correctly set up. If they are not set up correctly, then contaminated packs might
be missed by the reject system. Known as the “Large Metal Test”, this test requires the operator to
place a large metal sample (often a 20-millimeter diameter ferrous ball) into the test pack. If the
photogate timer is correctly set up, the reject mechanism will successfully divert the test pack into
the reject bin. If it is not correctly set up, the mechanism may act too early or too late, and reject a
good pack instead.

To ensure consistency, with each of the tests the ferrous test piece should be positioned at the front
of the ferrous test pack, the non-ferrous test piece in the middle of its pack, and the stainless-steel
test piece at the rear of its pack. The test pieces should also pass through the geometric center of
the detector’s aperture.

Codes of practice

Food manufacturers should get used to an increased focus on their commitment to these metal
detector tests being enshrined in retailers’ codes of practice. Alongside the food safety imperatives,
retailers are also embracing the move toward digital supply chain data that brings transparency and
clarity to a food product’s origin and the processes it has been through on its journey to the

Testing data is an important part of this desire for transparency, proving that best practice has been
observed. It is part of the bigger picture that shows retailers are meeting the regulations and
expectations imposed on them by the government, industry, and consumers.

Food manufacturers face a burden of proof, but they can benefit by retaining valued businesses and
safeguarding their own brand reputation. They must keep records of their testing regime for product
inspection equipment – not only for retailers but for auditors too. This is where the increasing
sophistication of metal detection and other product inspection systems comes to the fore. The use
of digital metal detector systems alongside ProdX™ data management software by Mettler-Toledo
means that users can benefit from automatic prompting of compliant testing within prescribed
intervals, electronic storage of test results, and smart optimisation of production and line operation.

Automation of many testing procedures for metal detection systems is therefore making the burden
of proof much easier to bear for food manufacturers, in turn making compliance with retailer codes
of practice simpler to maintain.

For more information click here or visit

About the Author:

Rob Stevens is the Market Manager for Mettler-Toledo Safeline Metal Detection, supporting a
number of territories with the sales and service of metal detectors. Rob has a degree in
Manufacturing Engineering and many years & of experience in working with various engineering
companies including Siemens, Rolls-Royce, and others around the world. Rob has worked in the food
industry internationally, providing solutions to some of the world & biggest food producers.

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