Measure and Allow Margin
The detection opening of a needle detector, often called the tunnel or aperture, directly determines whether products can pass through smoothly and whether the required sensitivity can be achieved. Before selection, measure the maximum dimensions of the product, including height, width and length after packaging, and allow a suitable margin. As a rule, the opening height should exceed the product's maximum height by several centimeters, so that vibration or misalignment on the conveyor does not cause the product to scrape the inner walls and affect detection stability.
Opening Size vs. Sensitivity
A larger opening makes it harder to keep the magnetic field uniform, which can affect the ability to detect small metal contaminants. For this reason, buyers should not pursue a large aperture at the expense of precision. A more reasonable approach is to first define the types and minimum sizes of metal contaminants likely to appear in the product, then evaluate opening size together with sensitivity specifications. Where necessary, ask the supplier to test with actual product samples on site or by sending samples.
Adjustable Multi-Spec Options
For companies with many product specifications, a model with a slightly larger opening and adjustable sensitivity can cover different batches. If product heights vary significantly, ask the supplier whether replaceable tunnels or custom openings are available. Before selection, organize product dimensions, packaging, conveying method and detection standards, and communicate them fully with the manufacturer to reduce fitting problems during later use.