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Start up of the metal detector

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Posted 11 November 2015 - 03:35 PM

Good day!

I'm working as a QA assistant and my company has been certified ISO 22000.

My company has just bought a metal detector (manual setting of the sensitivity) to check pre-packed salad vegetable and therefore we need to build up some documentation and record to update our system.

However, there are few things I need help:


1) how often we should check monitor the metal detector?

I got lots of information that it should be "at the start of the production, after a period of time (e.g. every 2 hours), change of product, at the end of the production". May I ask why we should check at the end of the production? Is it to ensure the whole metal detecting process is under controlled?


2) We have 4 types of pre-packed salad vegetable (150g/bag), the combinations are different but at the same weight. We have test the 4 products with test pieces (FE, CU and SUS), and we chose the lowest sensitivity among these 4 products to be out critical limit (e.g. FE 1.5mm; Non FE 2.5mm for Spinach, FE 1.8mm; Non FE 2.5mm for Rocket --> we made the CL as FE 1.8mm; Non FE 2.5mm for all 150g pre-packed salad vegetable). We make these 4 products into a "category", can we not need to check the metal detector when change the type of pre-packed salad vegetable, instead, we make it check when there is change in product category. Is it reasonable?


3) For the start up inspection of the metal detector, according to the information from different website, it seems that the test pieces should be pass the aperture along with the test pieces. However, my manager has raised a question of how we can make sure the product using for the start-up is really free from metalic contaminant and he suggested as we've done validation test on the the detectable sensitivity of each products so when we start up the metal detector we only have to check if the test piece is able to be detected by the aperture using our setting. And I'm confused as I think the the product attribute may affect the sensitivity (probably lower the sensitivity).


Could anyone can help me? Thank you!!!

(Sorry that my english is not very good and maybe not easy to understand, I will try my best to explain)



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Posted 11 November 2015 - 06:41 PM

1. We checked at start up, product change or every 2 hours and end of shift. The reason for end of shift was if there was a failure the following morning we would have to place product from the last acceptable test on hold.


2.I do not see an issue with the product category scenario.


3. i am unfamiliar with salad. I know with cheese we used the size and type of cheese we were running along with the test wand for our verification. But I would use a piece that went through successfully without a test wand. 


Hope this helps a little!


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Posted 11 November 2015 - 09:08 PM

Some of the larger box stores will require you test every hour. We test at beginning and end of each shift as well as hourly All tests are recorded and we show we test for Fe, NFe and SS.

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Posted 12 November 2015 - 04:56 AM

Hi nata-c,


Thks yr query and Welcome to the Forum ! :welcome:


Yr English is excellent.


Yr queries have been discussed many times here with a variety of opinions. Some aspects such as sensitivity may relate to risk assessment, eg the relative importance of yr products and their contamination characteristics (both equal?). Many people tend to try and use the same standards across a wide range of products although different packaging sizes (heights) / product presentations, etc may prevent this in practice. There are a lot of variables involved.


Regarding system set-up, etc, the COP from Tesco attached here may help (there are many others on this forum) -



Kind Regards,



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Posted 12 November 2015 - 03:16 PM

It's better to do your validation test in the "worst case scenario". That's why they say to do the test with the metal pieces in the center of the aperture. Usually they say to test at the current line rate, and sometimes they and to test 3 bags in a row. Most customers will also require the validation to occur with product. While the product often adds to the signal (especially conductive product like your vegetables), it isn't just a pure addition of the product and metal signal that dictates if the metal will be detected...it can be more dynamic than that. Because the product can impact the magnetic field, the signal produced by the metal could be masked by the product, even if the product signal was accounted for in the sensitivity settings. This product effect will change depending on the product running, sometimes even within the same SKU if there is variability in product. The most true test to real conditions is with product that's being produced in that very instant, with metal placed at the center of the aperture and surrounded by product if possible.

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