Metal Detector Validation, Verification, Calibration & Challenge

An auditor recently asked how we challenge our metal detectors. 

Our response: we calibrate via 3rd party once per year, we validate/verify by the production team running test cards during the run / QA observing this check daily. 

They responded that wasn't sufficient. We needed to have a challenge to make sure the equipment was working at its optimal settings. 

How would you challenge your metal detector? 

*Note: We have some finished product bag metal detectors and some in-line gravity fed metal detectors.  

Hi AtomicDancer,

In an ideal world the metal detectors should be challenged using a test pack of the food with a test piece inserted into the pack. It doesn’t seem that you do although that doesn’t seem to be unusual. Maybe the auditor was looking for challenge tests with test packs?

Gravity fed is a different ball game as using test packs isn't feasible.

Do you have the metal detector commissioning data which should have included setting up the metal detector with test pieces in the product (test packs)?

If you aren't doing so, I would normally be running an annual validation using test packs and also when there are changes to the product, product size, packaging material or equipment including conveyor speeds. It would make sense to do that during your annual calibration.

Kind regards,

Tony

This is one of the best sources I've ever found for explaining metal detector technology including how to test them etc.

Guide to Metal Detection Technology

It's good as a reference for HACCP plans etc and free to download. 

In general you normally want to make up test packs with the test piece in the lowest sensitivity portion of your metal detector (normally the middle) which might or might not be inside the test pack depending on the size of the aperture and the depth of your pack. You'd normally use these test packs to test the machine at the start of run, end of run and an appropriate frequency throughout production where the product would still be in your control in the event of a test failure. Also sites often choose this test frequency by how much product will need to be rechecked if a test fails. It depends a lot on throughput and how much on site storage you have.

The manual you can download from the link explains it all though and is very useful.