“The North American market is changing now,” says Wilson. “Accuracy is becoming more important. Production needs to be more efficient. Giveaway is an issue because profit margins are an issue.”
“It is common for checkweighers to run at 200-300 packs per minute in the United States and even Europe,” agrees San Sin, who heads sales and marketing for Singapore-based Virtual Measurements. “In Asia, lines tend to run at slower speeds.”
His company has established a North American base in Santa Rosa, Calif. It views the American food industry’s growing demand for greater accuracy as an opportunity to serve. He points to high quality strain gauge load cells and the high processing speeds of the CPU for his equipment’s ability to achieve accurate weight readings at high speeds.
“The tolerances are tighter today,” says Kyle Thomas, marketing manager for Hi-Speed Checkweigher Co., Ithaca, N.Y. (www.hispeedcheckweigher.com). “Not only are companies concerned with compliance with net contents laws and giving the customers what they are paying for. They are also making sure they are not giving away too much.
“The more sensitive we can make our devices, the more we can diminish shrinkage, material loss,” he continues. “It’s a matter of increasing productivity. Checkweighers enable you not only to be a good steward of the consumer, but also to be a good steward of your own business by being profitable.”
The latest introduction to Hi-Speed’s line is Starweigh, a device that delivers the precision performance of a static scale â€“ down to 5 mg -- in a high-speed, in-motion instrument, according to Thomas. Initially used in the pharmaceutical industry, food processor demands for increased accuracy have opened Starweigh to food application.
“It’s like getting laboratory balance into an in-motion packaging line,” says Thomas.
“Everybody wants a faster, better, more accurate checkweigher â€“ and at lower cost,” says Ha Dinh, vice president of engineering for the Alpha checkweigher division of All-Fill Inc., Exton, Pa. (www.all-fill.com). “Your customers also want versatility, easy changeoverâ€¦machines that are easy to clean and maintain. We try to come up with equipment that meets all these needs.”
An asset management tool
The motivation behind many current sales of checkweighers is their value as asset management and production tools. They help to manage throughput, the amount of saleable product that comes off the production line.
“We are challenged to make sure our checkweighers can keep up with cartoners and other devices in the packaging line or to run them at faster speeds,” says Thomas. “In some cases, it’s trying to get from two lines the production you normally get out of three.”
Managing assets encompasses maintenance and documentation. Cleanability and high washdown resistance are mandatory in the food manufacturing environment since material buildup of any kind can thwart accuracy.
Maintaining a history of an entire product run is vital as well. “Traceability is important in food and pharmaceuticals,” continues Thomas. “In this sense, a checkweigher is an important tool. It gives you an electronic signature on each product.” Hi-Speed’s “S” line, coupled with the available statistical program, supplies security and “checkability,” he says.
“More customers are using checkweighers not only as weighing devices but to make their statistical processes better,” says Thomas.
All-Fill’s Trend Tracker software also has important feedback and control features. “If trending is overweight, the filler will adjust. The same if a package is overweight,” says Dinh. “You can automatically adjust your filler or your conveyor speed, depending on the trend of the production line. And you have a statistical package to see the standard deviation, average fills, the number of good and bad packages that have gone through, along with bar graphs. Your checkweigher can be a quality control instrument that reveals not only how well your filler is working but how well the line is running as well.”
Sophisticated software may enable instant adjustments when a line changes over to run another product. Once all critical control measures for a product have been set and registered, they can be called up instantly, even if the product has not run for two months.
“With the programming capability of our equipment, changeover is usually done seamlessly,” says Loma’s Wilson. “With Ethernet compatibility, you can also tie directly into the data management system of the company. You can change from product A to product B from the manager’s office automatically.”
Getting accurate weight measure for a package traveling on a high-speed packaging line is, indeed, challenging. Packages moving on and off a scale at rates of hundreds per minute can’t be measured with the consistent accuracy of a single package on a static scale. The speed of a moving package offers little time for a weigh cell to settle before the next package arrives.
The food environment poses natural difficulties to accurate measures with dramatic temperature fluctuations, product mess and dust. High-pressure water in washdown applications poses another serious threat to sensitive equipment.
The strain gauge on the load cell must be protected against moisture and contaminants. The checkweigh area must be clean. Foreign matter and loose product can offset the tare settings. Buildup on platforms and conveyors will compel the scale to re-zero repeatedly. With the sensitivity of the current generation of checkweighers, even drafty air can affect accuracy.
Vibration from a conveyor, hopper or other equipment brings background noise that can interfere with weighing accuracy. The latest generation of equipment attempts to filter out or isolate the scale from such interference.
Loaded for accuracy
The heart of the checkweigher is its load cell, which converts weight or force into electrical signals that actuate measuring. Pharmaceutical applications have demanded greater accuracy than the food industry historically, but profit pressures have turned food processors to reduce waste and giveaway, putting a higher premium on accurate measure.
“We went to a digital load cell over two years ago,” says Dinh of All-Fill. “It has fewer electronic components. Compared to the analog cell, it reduces electrical noise. You are using the same strain gauge load cell, but now everything is done inside the load cell to isolate interference.”
“Most checkweighers are equipped with analog load cells,” says Loma’s Wilson. “Our new AS checkweigher line’s state-of-the-art load cell has nine digital filters that remove background static.”
Promising greater accuracy at faster pack rates, Loma’s FIT (Fast Intelligent Transducer) load cell, produced by sister company HBM for the AS line, features “high torsion and bending stiffness” with outputs of up to 600 measurements per second.
The AS line is also designed to minimize interference from vibrations from nearby machines or the conveyor belt or from air pressure surges. The FIT load cell, unlike analog cells, does not need to compensate for temperature.
Manufacturers of highly accurate checkweighers argue the long-term advantages of accuracy outweigh the cost (or diminished flexibility) of higher-end equipment. Savings from reduced giveaway, waste and rerun accelerate return on investment.
“It’s just like plasma TV,” says Wilson. “People looking to buy checkweighers in the future will want digital load cell technology simply because of the range of features it offers.”
Sidebar: Uses of Checkweighers
Check packages for underweight or overweight filling
Guarantee net contents compliance
Validate the presence of components or package
Check mixes against weight limits
Reduce waste or giveaway by making accurate filler adjustments
Classify product by weight or contents
Helping to fulfill reporting requirements
Measuring and recording the efficiency of a production line
Assuring compliance with customer, agency, regulatory, or other specifications