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How to Select the Right Metal Detector for Your Food Facility's Needs

Protecting your customers and brand is one of the most important functions a food manufacturer performs. To do so requires selecting the right inspection equipment and maintaining an effective, verifiable inspection program.

Protecting your customers and brand is one of the most important functions a food manufacturer performs. To do so requires selecting the right inspection equipment and maintaining an effective, verifiable inspection program.

Metal detection is an efficient and relatively inexpensive method of protecting your customers and brands. While price, delivery, and other commercial considerations are important, understanding the following points will enable you to choose the best metal detector for your needs:

  • Primary detection function: Food or equipment safety.
  • Characteristics of products to be inspected.
  • Sensitivity target for each metal type.
  • Wet or dry inspection area.
  • Temperature variations in the product or inspection area.      
  • Washdown:  High or low pressure, caustic agents.
  • Will the detector be integrated with other equipment or the plant’s data network?
  • Work with an experienced, supportive supplier.

Define the primary detection function

Metal detection sensitivity needs can vary according to the application. If your metal detector will be protecting a key piece of equipment, the goal would be to eliminate metal that is large enough to damage that equipment. At another part of the line, a different level of sensitivity would be required to inspect a bulk flow of product. Final package inspection requires the highest sensitivity to protect your product before it reaches the marketplace.

Characteristics of products to be inspected

The characteristics of your products will define the level detection technology needed.      Does product contain salt, moisture, or iron that may trigger product effect false rejects?  Are there variations in its temperature? How many different products do you inspect? Testing products on a detector before you buy will help you choose the most efficient detector and identify potential operating problems.

Product effect

Product effect is an important factor in the selection of a metal detector. If your products are conductive (usually due to water, salt, or iron content), they will affect the electromagnetic field of the metal detector, causing it to produce a false reject. Dry or neutral products generally do not cause this effect. 

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 use multi-spectrum technology. Instead of being limited to a small number of frequencies, these detectors use a spectrum of multiple frequencies simultaneously and continuously to filter out product effect signals. This greatly reduces false alarms without reducing metal detection sensitivity.   

Particle sizes & sensitivity targets 

Establish specific and realistic sensitivity targets for ferrous, non-ferrous, and stainless steel (type 316) contaminants.   These targets should be communicated to the metal detector manufacturer so the right equipment will be specified for each application. 

Consider the environment

Selecting a metal detector suited for your operating environment is critical to its efficiency and durability.  Start by evaluating your inspection area: Is it wet or dry?        Is washdown high or low pressure? What are the variations in temperature?  

Water intrusion damaging electrical components is one of the most common causes of metal detector failure. Check your detector for the appropriate International Production Marking, or IP rating. An IP65 rating means that the metal detector can withstand low pressure washdown with ambient temperature water. Detectors with the higher IP69K rating are suitable for sustained high temperature and pressure. But beware: these ratings are typically self-reported. The manufacturer’s reputation in the industry for the ability to withstand washdown can be a good indicator.

Pay attention to the specific stainless steel alloy used for the metal detector’s case and keyboard: Type 316L is more resistant to caustic agents.

For dry environments, beware of painted cases. Placed over the product stream, a painted metal detector could eventually shed chips of paint and contaminate your product.

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.

Auto-calibration and auto-learn advantages

Most metal detectors now perform self-checks to verify that the unit is in balance and performing properly.  Auto-learn allows the user to acquire the characteristics of the product in the unit so that the product can be inspected. An efficient auto-learn 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.

Communications considerations

Will the metal detector be a stand-alone item or does it need to be integrated into the plant’s network to provide periodic data reporting for statistical analysis? Does the unit have ready-made software that can provide these functions? Is it Ethernet ready? 

Some metal detectors allow for remote programming and diagnostics via laptop, including oscilloscope emulation via Bluetooth, eliminating the need to open the power supply cabinet.

Event tracking

As food manufacturing regulations become more demanding, capturing and accessing inspection event data is critical. Select the metal detector that offers the required access and event tracking in a way that works best for your operation. Start by determining the internal requirements for event tracking. Is it good enough to operate with the factory default passwords that everyone knows? Or should each user have their 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.

Choosing a supplier

As with any equipment purchase, you are not just buying a piece of equipment. Ideally, you are entering into a long-term relationship that includes ongoing technical support.  Strong vendor support will keep your inspection program running efficiently. Choose an experienced supplier that offers pre-sale application assistance and demonstrations, training, service, and rapid delivery of parts. 

Consider testing your products on the metal detector before you make a purchase.

In addition to evaluating the detector’s performance, you can get first-hand experience with set-up and changeover simplicity, calibration and maintenance requirements, integration with other equipment (such as a checkweigher), and general construction quality. 

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