If product effect is a factor, the correct frequency must be selected to move the product effect signal away from the signal of the contaminants. A metal detector that uses a single frequency cannot accommodate much signal variation thus making it unsuitable for inspecting a variety of product types or those that may vary in temperature. A three frequency, or better still, a multi-spectrum metal detector would be more suitable for these applications.
The most sophisticated metal detectors on the market today use multi-spectrum technology. Instead of relying on just one frequency, a spectrum of multiple frequencies work simultaneously to filter out product signals in a way that is much more effective than a single frequency. In addition, the number of false alarms is greatly reduced.
Autocalibration and autolearn advantages
The autolearn routine allows the user to acquire the characteristics of the product in the unit so that the product can be inspected. An efficient autolearn gives the best sensitivity and the least number of false rejects with a minimum of manual adjustment. This gets the unit into production with a new product in a minimum amount of time.
Sensitivity & communication
In another part of the line, a different level of sensitivity would be required to inspect a bulk flow of product. And because final package inspection should be the most demanding, even higher sensitivity would be needed to protect your product before it reaches the marketplace.
Your plant's quality control group should have specific sensitivity targets for ferrous, non-ferrous, and stainless steel (type 316) contaminants for each inspection operation. These targets should be communicated to the metal detector manufacturer so that they can select the right equipment for each application. Be sure to set realistic and achievable goals.
Consider the environment
Does the wash down include caustic agents? If so, careful attention should be given to the specific alloy of the stainless steel used for the metal detector's case. Type 316L is more resistant to these caustic agents.
For dry environments, is the finish of the metal detector painted? Placing a painted surface in the product stream could eventually contaminate your products with chips of paint.
Also consider impact resistance. Plastic covers and membranes are subject to wear or impact penetration. A robust display screen and keyboard avoid downtime and parts replacement costs.
As food manufacturing regulations become more demanding, equipment must keep up. What are the internal requirements for event tracking for a metal detector? Is it good enough to operate with the factory default passwords that everyone knows? Or should each user have his or her own password allowing access to only those levels that management considers appropriate for their position? In this case, each machine entry (product change, sensitivity change, reset etc) can be traced to a specific operator. A metal detector must be selected that can offer the required access and event tracking in a way that responds to these internal requirements.
Choosing a supplier
Before you buy
Heat and Control provides demonstrations of CEIA metal detectors, along with Ishida checkweighers and X-ray inspection systems.
Todd Grube, Inspection Systems Manager at Heat and Control, Inc. is responsible for sales, service, training and applications development for CEIA metal detectors and Ishida X-ray systems.