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Monitoring and Controlling Package and Batch Accuracy

October 30, 2009

By Travis Junkermeier

Static checkweighers may be used as standalone weighing solutions, confirming each mixing bin or package contains the proper amount of ingredients, or they may be used alongside in-line checkweighers.

For those weighing the benefits of integrating scale systems into packaging and batching operations, the justification for the capital investment can be clearly summed up in two words: consistency and accuracy.

When consumers purchase a commodity, whether it is soda pop, pancake mix, or even cough syrup, they expect the product to deliver consistent taste, texture, nutrients, and—in the case of pharmaceuticals—provide the same symptom relief with each purchase. This requires manufacturers to know the precise weight of each ingredient that is needed to develop the product and ensure the correct amount of ingredient is consistently used in each batch. Likewise, whether an end-user is purchasing a bag of grain or a batch of dough, they expect to receive the exact mix and amount of product they pay for each time.

Consistency is only half the battle, as an unreliable weighing process yields an inconsistent—or consistently poor—product. Accuracy is key, both in weighing the ingredients used and the overall package produced. An underweight package may lead to returned product and unsatisfied customers. Conversely, if the package is overweight, manufacturers could face shipping rejects and a significant loss in revenue, especially in larger operations. A package that weighs 1 mg over its intended amount does not result in great financial loss; when thousands of these packages are produced each day, it does.

Along with maintaining product quality and keeping customers happy, as well as optimizing revenue, incorporating weighing into packaging and batching lines helps improve inventory management. The same equipment that ensures batches are comprised of the proper ingredients before leaving the plant can also track how much of each raw ingredient is used, delivering more efficient, accurate inventory records and helping manufacturers determine more readily when reorders are needed.

Several weighing technologies are commonly used in these applications: weight sensors, which may be incorporated into existing batching lines to monitor filling operations and ingredient mixing; checkweighers, which readily determine if a product is under or overweight to ensure consistent packaging; and indicators, which acquire, store, and communicate the results of all weighing transactions while allowing both onsite and remote operators to monitor and control processes. The savings in product giveaway and minimized returns, as well as careful tracking of ingredient use, ensure many scale systems quickly pay for themselves.

Weight Sensors

To effectively monitor raw material inventory, as well as ensure the consistency and accuracy of product batches and packages, scale systems measure, communicate, and apply product weight data in manufacturing and packaging processes.

To turn a traditional bin, tank, or hopper into a high-accuracy, in-line scale, electronic weight sensors are placed under each leg of the material container. The sensors’ electronic design helps ensure reliable results, with no shock-sensitive check rods or delicate moving parts to keep adjusted, and keeps maintenance to a minimum. As weight is placed on the container, the electrical current running through each weight sensor is changed, and this altered current is brought to and combined at a junction box. From here, the collected data is sent via interface cable to a scale indicator, which converts the current to a digital weight display.

The scale indicator is a key component of this process, as it can be programmed to control filling and batching applications through monitoring bins or hoppers, observing each operation until its designated container meets a user-programmed set point. If a bin can only be filled up to the point that it weighs 50 lb, ±.25 lb, the indicator can be programmed to shutdown the hopper precisely at this point. This additionally proves useful for ingredient mixing, as the indicator can be programmed to shutdown each hopper after it releases its designated ingredient amount, ensuring the appropriate ingredient mix is achieved every time.

As weight sensors are simply added to existing packaging and batching equipment, installation is very unobtrusive, resulting in only minimal disruption to operations. The sensors may also be equipped with a stainless-steel housing to withstand washdown in food processing and chemical applications, or a self-leveling chain link design that allows the sensors to resist the vibration and off-center loadings.

Checkweighers

Another way to monitor package weights is through adding efficient checkweighing to an automated packaging line. Consisting of a scale base, weight sensors, and a scale indicator, checkweighers are used to deliver high-accuracy, legal-for-trade weighments, allowing manufacturers to confirm the quantity of product included per package is correct. Whether used for straight weighing or in-line checkweighing and designed to keep in step with fast-paced automated processes, checkweighers deliver instantaneous, precise readings in numeric or easy-to-interpret graphical formats.

In-line checkweighers verify that each product is of the proper weight within a designated tolerance, so that any item that does not pass muster can be diverted from the line before shipping, avoiding costly product giveaway or returns. A static checkweigher can be used for either periodically checking product weights, or it can be used in conjunction with in-line checkweighers. After an in-line checkweigher notes that a product is overweight or underweight, a static checkweigher can determine by how much the product deviates from its desired weight. This knowledge can help manufacturers troubleshoot production lines and adjust product development accordingly.

Checkweighers simplify process monitoring by incorporating indicator display features such as over, under, and accept fan graphs, allowing operators to identify at a glance if products are of the correct weight. Many checkweighers are made of stainless steel and designed to withstand washdown conditions, making them particularly useful for food and beverage as well as pharmaceutical applications. Checkweighers can also be set up to print results or communicate and store data using serial or Ethernet communications, which is particularly useful for product traceability.

Indicators

Allowing operators to track ingredient use by using stored recipes to confirm the correct ingredients are used in the proper quantities is one of the greatest benefits of incorporating a scale system into a batching application.

At the heart of each of these scale systems is the indicator, collecting and communicating data such as package and product weights and storing recipes for batching applications. Indicators deliver process control that not only improves accuracy, but also assists in inventory tracking and revenue optimization.

The brain of the weighing operation, a sophisticated scale indicator offers a standard memory that can store custom start-up and shutdown sequences, tare values, multiple recipes, print formats, and data logging. The data can then be put to use through the indicator’s connectivity with serial devices, such as printers, bar code scanners, and remote displays, as well as communicated to a host PC for further formatting and evaluation. This communication capability, through intranet or Internet, is particularly advantageous for remote applications, as it allows operators to monitor and control operations from a PC anywhere in the world.

Display flexibility assists users in monitoring and evaluating processes. Indicators are multitaskers; some are capable of simultaneously monitoring several independent scales, as well as directly control automated weight-based operations in conjunction with weight sensor through the set point programming mentioned earlier. Employing a combination of text and graphics, indicators clearly convey process states and product weights, reducing read errors, and allowing operators to quickly take action if a process becomes obstructed or products do not meet weight regulations. Horizontal bar graphs can display over/under readings in checkweighing operations, for instance, while vertical bar graphs display ingredient amounts or pie graphs track rapid fill operations.

The same display that keeps operators apprised of package weight and filling status can also display faults and errors. Through the communication ability of the more advanced indicators, operators can be notified offsite of these error states, facilitating an immediate response to fault conditions. This notification system is isolated from other weighing operations, so that the line experiencing the error is the only one affected.

Conclusion

From intelligent indicators to the high-accuracy weight sensors and multifaceted checkweighers that use them, scale systems optimize profit margins and maintain customer satisfaction, delivering the consistency and accuracy needed to keep packaging and batching lines operating at their finest.

Travis Junkermeier is global product manager, Dillon/Printers at Avery Weigh-Tronix (Fairmont, MN), a manufacturer of industrial scales and weighing equipment. For more information, visit www.wtxweb.com.