How to Maximize the Performance of Your Metal Detector

Tests and steps you can take to optimize metal detector sensitivity.

Food manufacturers and processors rely on product inspection technology to protect consumers, meet industry standards and maximize operational efficiency, and metal detection plays a critical role. Jordan Davis, Metal Detection Product Line Manager with Mettler-Toledo explains key factors affecting metal detection, and steps you can take to achieve optimum operating sensitivity:

1. What is operating sensitivity and how is metal detector sensitivity measured?

A: Sensitivity is the measure of a metal detector’s ability to detect a specific type and size of metal contaminant. The better the sensitivity of the metal detector, the smaller the pieces of irregularly-shaped metal it can detect.

Metal detector performance is usually expressed by the diameter of a test sphere made from a specific type of metal, such as ferrous, non-ferrous (aluminum, brass), or stainless steel.

To measure the sensitivity of a metal detector, a test piece must be reliably detected and rejected when passed through the center of the aperture of the metal detector. Several factors can affect the sensitivity of a metal detector. An experienced provider can help you select the right solution to overcome these challenges.

2. Why is it critical to start with a Hazard Analysis of Critical Control Points (HACCP)?

A: The aim of the HACCP audit is to identify the risk of various metal types at vulnerable points along the production line. A metal detector’s sensitivity can vary depending on the type of metal contaminant present. Typically, ferrous is the easiest to detect, and stainless steel is the hardest to detect. Therefore, starting with a HACCP can help determine which metal detector to install. A manufacturer should choose a metal detector that is optimized for their requirements.

3. How does the process speed of the packaging line impact metal detectors?

A: This is not necessarily a limiting factor for most metal detection systems. However, it is important to ensure the metal detector can operate at optimal performance levels, considering any potential variations in speed or product throughput on the line. The reject type required can also be influenced by line speed.

4. Does product orientation affect metal detection?

A: A metal detector’s ability to identify a non-spherical contaminant, such as wire or swarf, is partially determined by the type of metal contaminant (ferrous, nonferrous, or stainless steel), as well as the metal object’s orientation. Orientation effect becomes a limiting factor when the contaminant’s cross-sectional area (i.e. diameter of a wire) is less than the metal detector’s spherical sensitivity. Increasing the sensitivity of a metal detector is the best way to reduce orientation effect.

5. Which environmental conditions and product characteristics can impact metal detection?

A: Factory conditions can affect the metal detector’s performance, so it is important to use a metal detector which has built-in noise and vibration immunity to minimize the risk of airborne electrical interference and local plant vibration affecting the metal detector’s performance.

In terms of product characteristics, some products are electrically conductive or magnetic and as such behave in the same way as metal when passing through the detector. For example, products with high moisture or salt content, such as meat and poultry, exhibit this phenomenon, often referred to as ‘product effect’. Without the right technology, this can result in a high level of false rejects and therefore unnecessary costly waste.

6. Is technology available to minimize false metal detection readings and rejects?

A: The latest innovative metal detection solutions combine two or more frequencies simultaneously along with product signal suppression technology to overcome product effect and false rejects by minimizing the active product signal.

7. What is the difference between validation, verification and routine performance monitoring?

A: Validation is the initial qualification of a product or process against the stated design specification and aims to answer the question, “will this piece of equipment meet the specified objectives?”. Re-validation may also be required if substantial modifications to the equipment, or the products being inspected (size, packaging material, etc.), are made at any point after installation.

Verification is the periodic qualification that the equipment continues to be effective. It uses standard, formal processes to answer the question, “is the specified equipment under control and operating as expected?”. Best practice is to use a third party – ideally the equipment manufacturer or the manufacturer’s representative – to conduct the annual performance verification.

Routine performance monitoring (or “monitoring” for short) differs from the processes of validation and verification in that it is a series of performance checks completed at frequent, regular intervals by a trained operator. These checks are designed to determine if processes are under control.

8. How can operators ensure optimal metal detection sensitivity?

A: Choosing a stable, reliable metal detector that delivers enhanced sensitivity levels is an integral part of a food safety program to minimize metal contamination going undetected. However, having a metal detector is not enough – it must also be correctly installed, operated, and maintained for optimal performance.

About the Author

Jordan Davis has been with METTLER TOLEDO for 10 years and has a breadth of knowledge about metal detection as well as other product inspection solutions. He began his career at METTLER TOLEDO as a Regional Service Manager for the Product Inspection Division overseeing field technicians for all product inspection technologies (checkweighing, metal detection, x-ray inspection, and vision inspection). In his current role as Product Line Manager for Metal Detection, he is responsible for bringing innovative technology and new features to the market which meet the needs and expectations of customers. Jordan holds a bachelor of science in Electrical Engineering Technology with a Minor in Design from University of Central Florida.