This answer varies greatly. It is dependent upon the material of the contaminant itself, the speed of the line and the moisture content. The height of the detector head from the line is the most critical variable, as sensitivity decreases as height increases.
Machines must be calibrated to the food they are processing and then set to a threshold, determined by the company, in regards to the size of the contaminant they want the detector to reject. The type of product passing through the detector (wet or dry), its size, and speed affect the setting.
The metal detector manufacturer can assist with calibration setup.
If you don't test a metal detector's calibration, the metal detector can allow larger pieces of foreign contaminant to get through, compared to the threshold setting, threatening the finished product's safety.
How do you maintain metal detector calibration?
You want to periodically check calibration by passing a known calibration test tool under the unit to check for accuracy. These can be made of ferrous, non-ferrous, or stainless steel, and come in the form of rods, cylinders, balls, whips, cards and more.
Many metal-detectable products are colored blue for two reasons:
What makes tools and equipment metal detectable?
In plastic products such as scrapers, pens, and vinyl gloves, a unique manufacturing process involving the inclusion of a metallic pigment enables the plastic to be detected. In other products such as earplugs, a stainless steel ball bearing is enclosed in the plug to make them detectable.
What is the difference between embedded metal and impregnated material?
A product with embedded metal is only detectable if the product piece containing the metal goes through a detector. With a product that is impregnated, the entire piece has fine metal particles throughout, making the entire piece, or parts of it detectable.