Industrial Tunnel Metal Detectors Manufacturer | SAFELINE

    Tunnel Metal Detectors for Conveyors

    For loose or packed food and non-food industrial applications

    Products and Specs

    Inspection of conveyorized food and non-food applications

    Products and Specs


    Brochures for more information on Recangular Aperture Metal Detectors

    Product Inspection Guide

    Product Inspection Guides
    METTLER TOLEDO has republished its four definitive product inspection guides designed to help readers establish comprehensive checkweighing, metal det...


    ProdX Data Management Software
    ProdX allows you to connect and control your entire product inspection management process from a single point or from multiple remote locations, elimi...

    White Papers

    HACCP Versus HARPC- What is the Difference?
    This white paper explains the similarities and differences between HACCP and HARPC.
    HACCP in the Pet Food Industry
    This White Paper explains how HACCP can help pet food manufacturers avoid product recalls and gain a competitive advantage.
    Improving Bulk Food Inspection
    This White Paper explains how bulk-flow product inspection equipment can help to protect consumers and minimize the risk of product recalls.
    Conformity of Packaged Food
    White paper explaining how food manufacturers and brand owners can benefit from consistent conformity of packaged food.

    Case Studies

    La Provence Bakery Turns to Product Inspection Equipment
    In 2016 La Provence purchased a new cookie line and turned to METTLER TOLEDO for their new inspection equipment to maximize their final product qualit...
    Oakshire Cultivates Mushroom Quality With Metal Detection Technology
    Oakshire Mushroom Farm is an award-winning innovator and patent holder in the mushroom industry. When Oakshire needed a new metal detector in 2015 to...
    BAM Manufacturing
    To protect their product quality while meeting rising demand, BAM Manufacturing installed a Signature Touch metal detector from METTLER TOLEDO Safelin...
    The Black Pudding Company
    The Bury Black Pudding Company manufactures and sells the finest quality black puddings, serving the UK and International food markets.


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    What is a tunnel metal detector?

    A tunnel metal detector is used to inspect raw or processed foods or non-food products for metal contamination. Food processing companies use tunnel metal detectors to comply with food safety standards and retailer codes of practice. When integrated with a conveyor system, all types of metal contaminants can be detected and rejected, preventing metal contaminated products from reaching the end consumer.

    Where can I use a tunnel metal detector?

    A tunnel metal detector is a versatile industrial metal detection solution that can be used in a wide variety of product inspection applications. Tunnel metal detectors can be integrated with conveyor systems, to inspect raw, processed, or packaged food or non-food products for all types of metal contaminants. A HACCP analysis will establish the most relevant critical control points and thus where a tunnel metal detector should be installed.

    In-process inspection eliminates metal before it can be broken down into smaller pieces (which makes them more difficult to detect), protects downstream equipment from damage, and avoids product and packaging waste by subsequently rejecting a finished, higher value product.

    Finished product inspection may be required if supplying major retailers as it minimizes the risk of further subsequent contamination.

    A combination of bulk and finished product inspection will provide optimum protection.

    What is the correct testing procedure for a metal detector?

    It is important that manufacturers understand how to verify the performance of their metal detectors; if the system is not correctly tested at regular intervals, manufacturers run the risk of failing to comply with standards which could pose a serious threat to their business.

    When implementing a metal detection test procedure, manufacturers must firstly ensure their metal detector meets the required detection standards and are set up within the sensitivity guidelines.

    Guidance is given on non-ferrous and stainless steel ball sizes that can be detected, based upon actual ferrous ball size detected.

    For example, 1.5 x ferrous ball size = detectable stainless steel ball size (at 300kHz), and 1.2 x ferrous ball size = detectable stainless steel ball size (at 800kHz).

    Test cards or test sticks are the most common format for test samples used to test and verify tunnel metal detector performance. Test packs should be representative of the size, shape and weight of products travelling down the line. If inspecting bulk products, precautions should be taken to ensure test samples will not be lost if they are not detected and rejected, especially if the product is being fed directly into another processing machine after the metal detection system. The selection of correct metal contaminant types is also important.

    Testing procedure checks include detector performance levels and complete system integrity/functionality.

    There are no mandatory guidelines on the frequency of tests, unless these have been identified by a retailer code of practice or by requirements from a customer or external agency. However, it is recommended that testing is carried out at the start and end of each shift and of each new product run, and should be clearly documented within standard operating procedures.

    METTLER TOLEDO offers a wide range of products and services designed to support manufacturers in ensuring compliance with regulatory standards, and provides guidance on metal detector testing procedures.

    Related Content:

    What is the easiest way to integrate a tunnel metal detector within a food production line?

    The easiest way to integrate a tunnel metal detector within a food production line is to buy an integrated metal detection system consisting of a tunnel metal detector and a conveyor system, from a single supplier. Mettler Toledo Safeline manufactures a wide range of tunnel metal detectors and conveyor systems designed for food and non-food processing applications. Our metal detection systems for conveyorized applications can be tailored to suit specific inspection requirements, including a choice of aperture sizes, reject mechanisms, failsafe system components, conveyor belt materials, connectivity options and more.

    How does a tunnel metal detector work?

    The majority of tunnel metal detectors are balanced coil systems. Three coils are wound onto a non-metallic frame and each coil is exactly parallel with the other two. The centre coil (known as the transmitter) is energised with a high frequency electric current that generates a magnetic field. The two coils on either side of the centre coil act as receivers. Since these two coils are identical and are the same distance from the transmitter, an identical voltage is induced in each. When the coils are connected in opposition, these voltages cancel out, resulting in 'zero output'.

    As a particle of metal passes through the coil arrangement, the high frequency field is disturbed at the first receiver coil and then at the second receiver coil. This action changes the voltage induced in each receiver. This alteration in balance generates a signal that can be processed, amplified and subsequently used to detect the presence of unwanted metal.

    How sensitive is a tunnel metal detector?

    The sensitivity of a tunnel metal detector varies between detectors and between metal detector manufacturers. Sensitivity performance is usually expressed in terms of the diameter of a sphere made from a specific type of metal. The sphere must be reliably detectable when placed in the centre of the aperture of a tunnel metal detector. Japanese manufacturers state sensitivity performance using similar spheres and materials; however these spheres are often measured on the conveyor belt and not in the centre of the aperture. Using this form of measurement, the sphere will be closer to the aperture wall, which offers increased sensitivity levels compared to centre of aperture testing which delivers worst case sensitivity performance.

    A large aperture tunnel metal detector is less sensitive than a metal detector with a smaller aperture. Both aperture width and height have an influence on the metal detector's sensitivity, but changes in height (or the smaller aperture dimension) will have a greater effect. The geometric centre is the least sensitive part of the metal detector.

    Dry products such as confectionery and cereals, are relatively easy to inspect. Detectors operating at high and ultra-high tuned frequencies (typically in the region of 800kHz and above) are available which deliver high levels of overall sensitivity and are especially good at detecting stainless steel type contaminants.

    When inspecting wet or conductive products such as fresh meat, poultry, cheese, fish and metallized film packed products, the situation is different. The wet product itself creates a 'product effect signal' in the detector – and this signal needs to be cancelled out before inspection can begin. Innovative multi-simultaneous frequency technology can be used to overcome product effect, enabling significantly smaller metal contaminants to be detected.

    How do I choose the right tunnel metal detector?

    Mettler Toledo Safeline offers a wide variety of tunnel metal detectors for use in food and non-food processing applications. Industrial tunnel metal detectors can be used at various stages of the production process, including inspecting raw materials, in-process to protect downstream equipment, or after final packaging to provide peace of mind that there is minimal  risk of subsequent contamination.

    • Profile Advantage technology is ideal for challenging applications that are subject to product effect where food is hot, wet, chilled, cooling, or packed in metallized film. Sing multi-simultaneous frequency and product signal suppression technology, Profile Advantage metal detectors can detect smaller metal contaminants.
    • Profile metal detection technology is optimized for dry product inspection, delivering maximum sensitivity in a wide range of food and non-food processing applications.
    • Signature metal detector technology delivers reliable, proven metal detection performance in food and non-food processing applications
    • Profile RB tunnel metal detectors are optimized for bulk product inspection, delivering maximum sensitivity when inspecting large sacks, cases or cartons of food or non-food products.
    • Compact-format tunnel metal detectors are ideal where installation space is limited.
    • Tunnel metal detectors are also available as combi systems, where they are integrated with a dynamic checkweigher to provide multiple product inspection capabilities within a single unit, offering a compact footprint.

    Tunnel Metal Detector Systems

    Easy To Operate
    Operation of Safeline metal detectos is simple and depending on the operating system can be performed via a membrane style key panel or an intuitive full colour touch screen interface.

    Key Panel HMI - a robust, menu-driven membrane key panel provides access to the detectors operating system. A simple, multiple-language interface maximises operator efficiency and minimises training requirements. The operating system provides rapid auto set-up, product changeover and in-built performance verification routines, for reduced production downtime.

    Touch Screen HMI - a full-colour touch-screen interface, with an intuitive icon-driven menu provides easy operator access to additional features. This interface simplifies procedures and places a host of valuable process information at the fingertips of your whole manufacturing team. Standard and Select metal detectors are supplied with full software functionality, all pre-loaded and ready for installation. LS detectors can be upgraded (through a choice of software packs) so as to provide a future-proof solution which grows with your needs. Software packs are retro-installable and can improve operational functionality and further support compliance needs. LS models provide the flexibility to tailor functionality to suit the demands of your specific production process.

    A Wide Range To Cover All Product Applications
    R Series rectangular aperture metal detectors are designed for use in a wide range of conveyorised applications, including loose raw materials, processed products or packed, finished products.

    RB Series metal detectors are suited to the inspection of large products and packs such as bulk bags, sacks and boxes.

    Compact detectors are designed for the inspection of small packed products.

    Configurable To Suit The Working Environment
    Available in a choice of finishes and sealing standards, our detectors can be specified to suit virtually any working environment. Bead-blasted stainless-steel-finish metal detectors are suitable for wet wipe-down and light hose-down cleaning regimes, whilst painted-finish metal detectors are available for dry wipe-down environments. Sealing standards are available from IP65 for dry, non-aggressive plant conditions, through to IP66+ for harsh and heavy wash-down environments. In all cases, dirt traps have been eliminated, enabling manufacturers to meet exacting hygiene standards in all environments. All metal detectors support easy integration with standard METTLER TOLEDO Safeline conveyor solutions.

    Metal Detection Guide
    White Paper: Metal Detection, X-ray Inspection or Both?
    Metal Detector Applications
    Reduce Metal Detector Testing
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