The latest equipment offers effective process control aid for today’s food plant.

There was a time when checkweighers and metal detectors were end-of-the-line afterthoughts, but no more. Reliability and performance improvements have elevated their status to essential process-control devices, and instrument improvements likely will enhance their applications in food and beverage plants.

"There's a shift among leading food companies in how they view the role of metal detectors in their plants," suggests Steve Gidman, president of Fortress Technology Inc. in Scarborough, Ont. Protecting expensive machinery from damage caused by metal fragments is one reason processors are placing detectors farther up line. "People slowly are beginning to put units upstream to pinpoint problem areas and make corrections, rather than wait until product reaches the end of the packaging line and hope they catch any contaminants, says Gidman. "Metal detectors are becoming process control instruments."

The same can be said of checkweighers. San Diego-based Hardy Instruments hopes to roll out a system in which data on weight variances is fed back to its fillers, where adjustments are made automatically, according to Ted Kopczynski, product manager. "Our processing units already talk to each other; next, we're going to extend that capability to our checkweighers," Kopczynski says.

Cintex USA's 4000 series checkweighers already have that capability, claims Dan Izzard, sales and marketing manager at the Kenosha, Wis., firm. Cintex's proprietary MIACS (Management Information and Control System) software package typically is used to control statistical parameters, change product set-ups and collect data for central record keeping and validation. It also can be extended to control other equipment. "We provide the specifications and the link to customers who want to link the system back to the filler for automatic adjustments," Izzard says.

Integrating checkweighers into process control is helping obliterate the distinction between these devices and weighbelt and filler control systems. The result is a marriage of the technological refinements that have occurred in both areas.

Thompson Scale Co. has produced custom filling systems for 20 years. It's now applying that expertise to checkweighers that can be combined with Eriez metal detectors. Four models have been designed to monitor weights ranging from 200 pounds down to 0.002 pounds, according to Jeff Kaveney, product manager at Eriez. "Marrying the two systems makes a lot of sense," he says.

Combination checkweighers-metal detectors can use a common reject device to kick off under and overweight packages and those with metal contaminants, Kaveney points out. Generally, suppliers discourage that approach, however, because it makes it difficult to determine why a package was rejected. That also is contrary to making these devices part of process control.

Combination units were a hot commodity a few years ago. Even with separate reject mechanisms, they promised reduced footprints, and space is always an issue in food manufacturing. But industry's ardor for combo units has waned. "Everybody's short of line space, and that lent itself to combination systems," points out Gary Wilson, president of Loma Systems in Carol Stream, Ill. "There's a niche for them, but it's not a growing niche."

Fortress's Gidman agrees. "People thought they were the cat's meow two or three years ago, but they're not as flexible as separate checkweighers and metal detectors. There's a little bit of a drift away from them now." Most combination units require partnership arrangements between equipment manufacturers, "so there were issues of support" when problems occur, he adds.

The digital age

The shift to digital from analog controls on both metal detectors and checkweighers is not about to reverse itself. Digital signal processing eliminates the manual adjustments necessary with analog systems and provides superior filtering and processing of signals. Digital systems are better able to adjust to variances in product conductivity, and they do a better job of filtering out nuisance signals from machine vibrations and adjacent machinery.

Digital load cells are becoming an option to standard analog load cells in checkweighers. The systems' electronics communicate calibration information to each individual load cell, improving accuracy. Lock Inspection Systems Inc. has incorporated digital processing of load cell signals on some of its WeighChek checkweighers, according to sales manager Mark D'Onofrio, and Loma Systems hopes to roll out a unit with a digital load cell later this year. Lock's units are backed by high-speed 32-bit microprocessors and real-time weigh signal processing to improve speed and accuracy.

Lock's WeighChek series feature waterproof, stainless steel construction to withstand food plant washdown conditions. Long-life brushless AC motors drive the transport conveyors. Units boast an IP 65 rating (IP54 for painted housings).

"Food plants are not electronics-friendly atmospheres," observes Fortress's Gidman. Servo-driven machines are replacing mechanical units in packaging departments, and the signals they emit can wreak havoc on RF-based devices such as metal detectors. "If you put those packaging machines in your house, you wouldn't be able to watch TV" because of signal interference," Gidman says. Filters and electronic algorithms are doing a better job of screening out the noise that disrupts efforts to make these devices simpler to use and more reliable.

Atmospheric factors such as temperature and pressure and salt and moisture content in food can distort signal sensitivity in metal detectors, D'Onofrio points out, so features like ADC software that "gives you a window to the detection envelope" and allows plant operators to perform a "visual diagnostic" on a touch screen or laptop computer help improve confidence in the unit's performance.

Recalibration on the fly is not an objective for everyone, of course. American Foods, a Methuen, Mass., packager of gummy bears and other candies, installed Lock's MET 30+ metal detectors and WeighChek units in December. Plant manager Jim Gilet deferred to Lock technicians to set the detectors' parameters.

American Foods repackages bulk candy into 2.5 to 24 oz. bags. Metal detectors and checkweighers are incorporated in a dual lane setup downstream from a vertical form/fill/seal machine. "The checkweigher software recalibrates itself several times a second and calculates weights to within a gram," Gilet says. The combination system weighs and inspects up to 80 bags a minute, enabling American Foods to maintain line speeds.

Rugged design and digital processing combine in the Thermo Goring Kerr DSP IP metal detectors. It is the latest version of the firm's digital signal processing (DSP) line, which features automatic sensitivity monitoring and abnormality reporting. DSP units also have an optional frequency optimization feature that automatically alters the unit's operating frequency.

DSP IP is certified to the European IP69K standard for washdowns at up to 1,450 psi and temperatures up to 176 degrees F. The company expects washdown durability to be a big draw among meat and dairy processors.

Thermo Electron Corp. recently realigned its 78 operating companies, grouping five of them in a new weighing and inspection business unit. Besides metal detection specialist Goring Kerr, the group includes Thermo Ramsey, which has produced microprocessor-based weighbelts since 1974.

Reduced conveying risk

Metal detectors are of little use where plastic contaminants are concerned, and the steady conversion to plastic conveyor belts in processing facilities increases the likelihood that belting material will leave with product. Plastic belts with embedded metal fibers have been offered as a solution.

Agribusiness giant J.R. Simplot Co. began experimenting with metal-detectable plastic belts in 1998 as a quality assurance safeguard for its customers. Metal increases the brittleness of the belting material, explains Nosh Makujina, maintenance engineering manager at Simplot's food group offices in Caldwell, Idaho. Striking a balance between sufficient fiber for detection and a belt with durability for production and washdown is the challenge. In March 2001, Simplot began testing detectable plastic conveyor chains from Rexnord Corp. "We feel that Rexnord found the right balance between metal content and durability in a superior metal-detectable belt," Makujina says. "We can easily pick up a one-gram sample of this material."

Nonferrous metal fibers are integrated in the polypropylene band, which is actually a chain. Chains provide several advantages over belts, he points out, not the least of which is longer service life. Friction and tension are needed to drive a belt, and too much tension can cause premature failure. Insufficient tension allows the belt to slip off its sprockets. "With a chain, you don't have to tighten to keep it on the sprockets, and that's a better design for food plants," Makujina says.

The Rex chain was improved early this year when Rexnord began incorporating Microban Products Co.'s antimicrobial element into Rex chain. Like the nonferrous fibers, Microban is part of the molecular plastic itself. It provides resistance to bacteria, molds and fungi.

"When we heard about the antimicrobial feature, we were all over it," recalls Makujina. "It's not a panacea; you still have to be diligent with your sanitation cycles." Still, plate counts on bacterial swabs on lines that have switched over to the new chain are lower, indicating it is a useful food-safety feature.

Two of Simplot's eight potato plants have converted to Rex chain, equaling about two linear miles of conveying, estimates Hans Anderson, marketing manager at Milwaukee, Wis.-based Rexnord. "We've been getting orders by word of mouth," he says, with fruit and vegetable processors exhibiting keen interest--a trend that has surprised the firm, which expected to find the most receptive audience among protein-food processors. Because of the electrical conductivity of water, slurries and other wet products pose a problem for the belting.

The same show-me attitude prevails when it comes to X-ray units. Metal-detector firms have been driving down the cost of X-ray, which holds out the promise of detecting glass, bone and other foreign particles, both metal and nonmetallic. "X-ray is more costly, but it's probably half of what it was a few years ago, and the industry is more and more accepting of the technology," Loma's Wilson says.

Loma installed its Axis Pipeline X-ray system early this year at Philadelphia Cheesesteak, which processes Philly-style beef and chicken steaks and other food products. "With more than 500,000 lbs. of meat coming through here per week, it's likely that a few small pieces of bone may have slipped through our suppliers' quality inspection programs," says Jim Trivelis, Philadelphia Cheesesteak's operations director. The X-ray unit was installed in line to inspect raw materials immediately before they are molded in a vacuum stuffer. If bone particles or other foreign matter are detected, product is automatically rejected and an alarm sounds, prompting workers to sift through the discharged material to find the contaminant.

Philadelphia Cheesesteak continues to deploy metal detectors at the end of the packaging line. Working in tandem, the systems have reduced customer complaints by about 80 percent, Trivelis says. Despite price reductions, X-ray units still cost about three times as much as metal detectors. But food safety concerns are prompting some processors to take the plunge, particularly when the units become part of process control, as is the case at Philadelphia Cheesesteak.