Direct answer
Choose the inspection principle from the contaminant and product, not from a generic sensitivity claim. Metal detection responds to conductive and magnetic material; X-ray identifies density differences and may detect additional dense foreign bodies or product defects, subject to the product and pack.
Why this matters
Detection performance changes with product moisture, salt, temperature, orientation, pack material, aperture and speed. A quoted test-piece size is meaningful only under named conditions.
Decision table
| Factor | Metal detection | X-ray inspection |
|---|---|---|
| Primary signal | Electrical and magnetic response | Density contrast |
| Packaging | Foil or metalised structures may limit options | Metal packaging can be possible with suitable setup |
| Product effect | Can reduce sensitivity | Product density and thickness affect image |
| Other checks | Normally contaminant-focused | May inspect count, mass or shape in some applications |
| Validation | Test pieces and challenge procedure | Test cards, images and reject challenge |
Information to collect
- Define likely contaminants from the process risk assessment.
- Provide final product and packaging.
- State the smallest relevant contaminant and orientation.
- Check line rate, aperture and available space.
- Define reject confirmation and secure reject storage.
- Agree test frequency and record requirements.
Practical method
- 1
Run representative product-effect trials.
- 2
Compare worst-case pack orientation.
- 3
Validate detection and reject as one system.
- 4
Control setup by product recipe.
- 5
Review performance after product or packaging changes.
Common mistakes to avoid
- Selecting by headline sensitivity alone.
- Testing air instead of product.
- Ignoring foil or metalised packaging.
- Challenging only one contaminant position.
- Failing to confirm the rejected pack left the line.
Questions people also ask
Can X-ray detect every contaminant?
No. Detection depends on density contrast, size, orientation, product and pack.
Can metal detectors inspect products in foil packs?
Conventional systems may be limited; assess alternative configurations or X-ray against the real pack.
Which system is more sensitive?
There is no universal answer. Sensitivity must be demonstrated with the actual product, contaminant and pack.
Should inspection be before or after packing?
Place it where the relevant hazard can still be detected and the affected product can be contained, based on the process risk assessment.
Continue from the requirement to the equipment
Use the specialist route that matches the product, pack and process. Final suitability requires representative samples, output targets and site information.