Iron ball figure meaning
When purchasing a needle detector, buyers and quality staff often see a sensitivity figure expressed as an iron ball diameter, for example the ability to detect a 0.8 mm or 1.0 mm iron ball. This value generally refers to detection of a standard test ball at the center of the aperture under interference-free conditions. Actual performance depends on the product size, packaging, passing speed and position, so the figure should not be read as a guaranteed result in every situation.
Aperture size and selection
Aperture size also affects the achievable sensitivity. A larger opening usually means lower sensitivity under otherwise equal conditions, so selection should start from the maximum dimensions and passing method of the inspected products, then match the appropriate aperture. For textile and garment products, features such as multi-point scanning help reduce the risk of missing broken needles.
Product effect and testing
Product effect is another key factor. Products containing moisture, salt or metallic coatings may generate signal interference, in which case metal detection or X-ray inspection should be evaluated together. Testing with actual products at normal production speed is recommended to confirm repeatability and stability, and routine checks with standard test pieces help turn the sensitivity figure into practical quality control.