Analytical balances use enclosed weigh pans and come in two basic varieties: microbalances (accurate to 1 μg) and semi-microbalances (10 μg).
Modern balances come equipped with built-in applications for piece counting, density calculations, statistical analyses and other straightforward calculations. Additional features include color and/ or touch screens, faster microprocessors and stability times, better repeatability, hands-free operation, multiple interface options for open-architecture connectivity, and regulatory compliance (e.g., for pharmaceuticals).
Like many other instrument types, balances have come to rely heavily on electronics. Compensating physical weights were replaced long ago by strain gauges and frequencymodulated force measurement in low-end balances, and by electromagnetic force compensation in higher-end analytical instruments. According to Ryan Titmas, VP at Sartorius Mechatronics America (Bohemia, NY), the price of a balance is a function of its capacity (maximum weight handled) to readability (resolution) ratio, plus number of features. Users can expect to pay anywhere from $2,000 to $8,000 for an analytical balance.
“Customers with unique weighing needs often find that preloaded programs fall short,” says Steve Wildberger, product coordinator at Shimadzu Scientific Instruments (Columbia, MD). “Users always want an application to do one thing more than it can.”
The problem, Wildberger says, results from balances’ limited memory and data processing capabilities. This has, in turn, led to the emergence of “wedge” software packages that interface the instrument to the lab’s information backbone to provide automated data entry and other functions. These packages, Wildberger argues, add an additional level of complexity for users, and a higher validation burden for labs operating in regulated industries. The future, he says, belongs to [instruments] that act as sensors or input devices, directing data into familiar computing environments and applications, for example Microsoft Windows spreadsheets. “Microsoft Excel has tremendous capability for handling weighing operations, including statistical analysis and checkweighing [for determining that a piece falls within a specified mass range].”
Some experts believe the choice of analytical balance is relatively straightforward. For Steve Wildberger, the decision tree reduces to instrument capacity and resolution (“the first criteria”), followed by calibration capabilities (internal or external) and interface/data features. And in the experience of Ryan Titmas of Sartorius, “Most users take the middle road and choose a solid analytical balance with accuracy, speed, and a few other features.”
But Ian Ciesniewski, technical director at Mettler Toledo (Columbus, OH), recommends that users first generate a “design qualification” that accounts for the acceptable weighing uncertainty, and from this figure define the required precision (repeatability). “Repeatability is adversely affected by changes in the laboratory environment, which can cause both acute and long-term problems,” he says. “We recommend selecting a balance that is better than required by a safety factor of two or three. This will minimize out-of-tolerances and avoid the dreaded ‘do not use’ notice.”
Other factors to consider, Ciesniewski says, are “ergonomic and productivity” features such as the ability to enter data on sample identity, batch or users; touch-screen operation; color screens; built-in applications; communication and software capabilities; and maintenance/ calibration requirements.
• Measures to 0.1 mg
• Bi-directional RS-232 interface enables data transfer from the balance to computers or printers
• Features solid, durable metal construction and internal motorized calibration
• Built-in applications include density, percentage and comparison
• Includes a spacious weighing chamber with an automatic opening function
• Indicator can detach from weighing chamber, to reduce the risk of shocks and vibrations
• Features internal calibration, triggered by time flow or temperature conditions
• Includes a 5.7-inch touch panel color display
• Features mono-metal Tuning-fork Sensor Technology
• Includes internal calibration and RS-232C interface
• Includes an anti-electrostatic 360° transparent windshield
• Large back-lit 16.5 mm LCD screen displays 8 digits
Rice Lake Weighing Systems
One Click™ Weighing Solution
• Complete product bundles consist of an Excellence XP/XS balance, corresponding accessories and LabX 2010 software
• One Click performs all calculations and documentation automatically, shortening the time to prepare a standard solution from 15 minutes to less than four
• The complete solution can be customized to meet individual process requirements