Food Safety Magazine, August/September 2009

cased in stainless steel for protection), they should never be dropped or struck. Magnets are also susceptible to damage from excessive heat. Follow the manufacturer’s instructions and include them in initial and refresher training for personnel who are handling magnets.

Magnets can also lose strength over time, either naturally—which is typically a slow loss—or through damage, which can be very fast. So, regular pull tests should be conducted to check magnets’ attractive force against their original strength. (Pull tests use a device with a piece of metal of a specific size and a meter that measures the amount of force needed to pull the piece of metal loose from the magnet.) These tests are probably only needed every couple of years to monitor how fast your magnets are decaying. If a magnet has been subjected to excessive heat (possibly from a fire) or has been dropped or struck, it should be pull-tested immediately.

By monitoring your magnets over time, you can predict when they will need to be replaced, and capital dollars can be budgeted in advance.

“There is no doubt that product safety

devices…have helped make the food and beverage

industry safer.”

FMDs need the most care and maintenance of all of the devices discussed. Calibration/validation/verification, training and interference issues are all essential considerations.

Foreign Matter Detectors
(FMDs)

FMDs are devices that operate by creating an electromagnetic field and monitoring changes as product passes through it. A disruption of the field will be detected. The FMD must be calibrated for the specific product type, and can be designed to scan product either before or after packaging. The FMD should be connected to a reject device to prevent any material that trips the FMD from continuing downstream. Some FMDs operate similar to sifters/strainers and magnets early in a product stream to allow for removal of foreign matter that might damage equipment. Others are placed directly before or after the product is packaged as a final quality check.

FMDs will not pick up all foreign objects, just those that disrupt the electromagnetic field. They have an advantage over magnets in that they will identify stainless steel. However, the size of the stainless steel particles that FMD will detect is typically larger than that of ferrous metals since stainless steel disrupts electromagnetic fields less.

Calibration/Validation/
Verification

Initial setup of the FMD is critical to ensure that it will accurately detect foreign matter. The device must be carefully calibrated to the product by the manufacturer’s technical representative. Make sure to follow the manufacturer’s requirements in terms of metal-free zones and vibration elimination. An alarm counter should be included in the setup.

Once the calibration has been completed, a regular program of validation must be implemented to ensure the device continues to function properly. Typically, a coupon containing a specific size sphere of stainless, non-ferrous or ferrous metal is run through the FMD with the product. The device should detect the coupon and sound an alarm, and the reject should capture the coupon and associated product. If all of

these do not happen, then maintenance will need to troubleshoot the issue. All of the metal types must be run to validate the device’s ability to detect each type. Stronger programs will periodically validate each coupon three or more times in a row as a more stringent challenge of the device.

The program often will also use more frequent verification without product running. This is especially common when the device is positioned immediately before packaging, and using a coupon in the product stream puts the coupon in the package, resulting in having to open the package to retrieve the coupon. A plastic wand containing either ferrous or non-ferrous metal on one end and stainless steel on the other is inserted into the FMD aperture. The alarm should sound, but without product running, the reject mechanism cannot be checked.

A log for each FMD is needed to record each alarm, including checks. The findings of the alarm must also be recorded, including any false alarms. Any findings of foreign material should

(continued on page 47)

Examples of Interference

A plant was troubleshooting excessive false alarms. The cause was determined to be an extra-long FMD cable that was the standard length ordered by the company. The extra cable length was coiled near the FMD, causing interference. The correction was to shorten the cable.

In another example, carts used to transport weigher hoppers to a nearby equipment washer were causing excessive vibration, leading to false alarms. The plant adjusted procedures to stop using these carts during production. This change reduced the ability to use the washer during flavor changeovers, however. The plant is still searching for a solution that will allow the washer to be used during flavor changeovers without causing excessive vibration.