In this post we’re going to go through the last two types of test and why we do them; the memory test and the large metal piece test…
The memory test
This test is where you have your 3 test packs and in-between them, you have good product, as shown below.
The purpose of this test, is to prove that the metal detector can see metal in the ‘test pack 1’, reject it and then reset itself, so that it can see that there’s no metal in ‘good pack 1’. Then it has to be able to see and reject ‘test pack 2’, then reset itself so it doesn’t reject ‘good pack 2’ and so on.
If the machine cannot reset itself fast enough, it may also reject the good packs. Plus, we are testing the machine, to make sure it does actually reject the test packs and not, the good packs by mistake, allowing the test packs to go through. So, this means that if the machine does not reject all 3 test packs AND, does not allow all 3 good packs to go through, the test has failed.
It is a common mistake to think that the purpose of the test is only to reject the test packs and that it’s ok for the good packs to be rejected too. Rejecting the good packs shows that the machine is not set up correctly and so, you’ll get false rejects.
Also note, how there are 3 good packs – the last pack is there to prove that the machine resets itself after test pack 3, if it’s not there, then you’ve not proven that the reset mechanism worked for all 3 packs. Also, it’s good practice to always have a good pack at the end of the test, as you may find you need this pack to ensure that all the products go through in normal product flow. You may find that, that last pack is needed to ‘nudge’ the test pack through the detector.
Large piece of metal test
One of the most recent tests to be introduced is the large piece of metal test. This test was introduced to replicate a large piece of metal going through the detector, like a spanner for example.
It seems odd that we’d check that the machine can see a large piece of metal, when we’re already checking the machine with smaller pieces of metal – surely, it’s obvious it’s going to reject? Well yes, you’re right! But this is where this test is very often misunderstood…
When a large piece of metal goes through the detector, it causes such as large signal, that this can sometimes send the machine haywire! This means, that it will reject the large piece of metal, but once that’s gone through the machine may not work as it should anymore. Which then means, that if a product was to contain metal and go through the machine, it may not be detected and rejected.
So, the key part of this test is that the machine not only sees and rejects the large piece of metal, but actually the most important check – is that it will still see and reject your normal 3 test pieces afterwards.
Passing the 3 test pieces through the machine after this test, is the part that’s very commonly forgotten. Make sure your procedure is to do this, because otherwise putting a large piece of metal through the machine on its own could cause the machine to break and you wouldn’t even know it!