When it comes to metal detection sensitivity performance, not all systems are created equal. A small difference in spherical sensitivity performance can make a big difference to the level of brand protection you receive. This guide explains the concept of metal detector sensitivity, factors that impact performance, and why size matters when comparing spherical sensitivity specifications.

What is metal detection sensitivity?

Sensitivity is the metal detector’s ability to detect a specific type and size of metal contaminant. The higher the sensitivity of your metal detector, the smaller the pieces of metal that can be detected.

Metal detector sensitivity performance is usually expressed in terms of the diameter of a test sphere made from a specific type of metal, such as ferrous, non-ferrous, aluminum or stainless steel. This test piece must be reliably detectable when passed through the center of the aperture of the metal detector. However, there is a significant difference between the test piece’s spherical sensitivity and the actual length of wire that can be detected due to the metal contamination’s ‘orientation effect.’

Orientation effect means certain types of metal are easier to detect when passing through the metal detector’s aperture in a particular orientation, compared to other orientations. Using the diagram below, ferrous contaminants are easier to detect when they are presented parallel to the direction of travel (A), and are more difficult to detect when they are at 90 degree to the direction of flow (B). Non-ferrous and stainless steel metals are the opposite. However, orientation effect is only evident when the diameter of the wire contaminant is less than the spherical sensitivity of the metal detector. The type of metal as well as the diameter of the wire contaminant has a significant impact on the length of wire that can be detected.

How test ball size relates to actual physical metal contaminants

The type of metal as well as the diameter of the wire has a significant impact on the length of wire that can be detected. How test ball size relates to actual physical metal contaminants The type of metal as well as the diameter of the wire has a significant impact on the length of wire that can be detected. The data in the table below shows reducing the size of the test sphere that can be detected significantly decreases the minimum length of wire contaminant that can be detected. Conversely, decreasing the sensitivity means larger pieces of metal will go undetected, increasing the risk of metal contamination reaching the consumer.

It clearly shows why users should seek to achieve the highest on-line sensitivity possible from their equipment suppliers.

Download the free guide “Understanding Sensitivity in Metal Detection” to learn more about maximizing metal detection performance and how to reduce your risk of product recalls.