A Close Look At Today's Analytical Balances

Date: September 1, 1997 Comparison Chart Laboratories pressed with weighing needs can choose from several classes of balances comprised of virtually hundreds of models with unique designs, functions, and capacities. Balances have been redesigned and upgraded from year to year, and the list of available features and options keeps growing. What exactly makes an analytical balance an analytical balance? For the purposes of this profile, we will define an analytical balance as an instrument capable of weighing to 0.1 mg and possessing a draft shield. As opposed to strain gauge or capacitance-based weighing cells, analyticals generally utilize magnetic force-restoration cells. These cells incorporate a suspended coil surrounded by magnets, and weights are derived from the sensitive changes in coil voltage when mass is exerted on the system. Since these cells are so sensitive, a few manufacturers are currently constructing them out of single aluminum blocks, eliminating the need for precise torquing and bracing of miniature parts. Although there are other "classes" of balances capable of achieving 0.1 mg sensitivity or greater (semi-micro, micro, ultra-micro, and even several toploaders), LabConsumer gathered information with the needs of analytical users in mind - "I need four decimal sensitivity with a lab budget four numbers long". Factors that should influence your purchasing decision are balance readability (or the smallest unit of measure a balance will display), capacity (the maximum weighing capability of the balance), and price. Once these basic criteria are met, knowing exactly what you want in an analytical balance will save time and money. Balances do much more than simple weighing. Application programs include determining densities, averaging weights, counting parts based upon an initial reference sample weight, printing data, filtering vibrations, and much more. If you are tired of converting units, the number of weighing modes balances have might be of particular interest; some balances offer as many as twenty different weighing modes, from pennyweight to pound. Many balances allow researchers to perform animal weighing, which will average a selectable number of animal weights as they shift on the weighing surface. Dual range balances permit weighing through two ranges, which is like having two balances in one. Calibration methods have also evolved. As opposed to calibration with an external mass, internal calibration is now commonplace among balances. This feature allows automatic calibration using a built-in calibration mass, an excellent option for those requiring high accuracy at all times. Many balances now enable compliance with numerous quality assurance systems such as ISO and GLP. Frequently, these balances allow the user to print out weighing data, scale identification, calibration information, date, and time. Interfacing with peripherals such as computers, printers, or other balances by way of RS232 or current loop is now possible with most analytical balances. Some manufacturers have automated their draft shields, facilitating "one-touch" or remote opening and closing of the draft shield. For weighing extremely large or massive objects, below-balance weighing is an option to consider. By the weigh The list of accessories for analytical balances is quite long. Spill covers, weighing pans, foot switches for remote weighing, printers, and data input keyboards start the long list. Regardless of options, though, an analytical balance should provide the accuracy and precision required for specific applications. Before you go putting your fingerprints all over the draft shield of a new analytical balance, LabConsumer recommends you read on. HA, HM, HR, and HX Series The HA-200A is designed for robotic/automated applications or for any other hands-free operation. Its automatic door can be controlled via the front keypad, computer, or foot switch. The unique round weighing chamber has three circular doors to provide a 200¡ panoramic open access. In addition, the HA-A offers Hi/Lo limits, a detachable keyboard, and environmental digital filters for use in any condition. The HR Series offers multiple units of measure and output of identification number, serial number, and calibration data, complying with GLP, GMP, Laboratory Information Management Systems (LIMS), and most ISO 9000 requirements. Digital tare entry via a keyboard or from a computer, especially important with LIMS, allows the HR to adapt to job changes. Also standard are underhook capability (for density measurements) and Counting and Percentage modes. The HR-60, HR-120, and HR-200 offer an optional battery pack for portability. The HM Series has all the features of the HR Series, and in addition offers internal calibration masses, allowing for manual or automatic one-touch calibration. Range control, digital tare, and adjustable calibration weight values are also standard. Additionally, the weighing chamber of the HM allows excellent viewing capability and unrestricted use. The HX-100 is designed for rugged environments and comes with thirteen weighing modes. Automatic Self-Calibration calibrates at three points to ensure proper readings. A graphic capacity indicator visually shows current weight relative to total capacity. The display also features a comparator Hi/Go/Lo readout and audible signal. All A & D balances are covered by a five-year warranty. LA-Series The LA-Series from Acculab offers three analytical balances designed to be durable, cost effective, and user friendly, with capacities of 60, 110, and 200 grams. All balances in this series contain seven application programs, including mass unit conversion, tare memory, weighing in percent, counting, animal averaging, and net total formulation. Acculab LA-Series analytical balances feature motorized auto-calibration with built-in weight; RS232 interface for computer, printer, or GLP/GMP compatibility; and nineteen weighing modes. Also standard on all LA-Series balances are stability and ambient condition presets, an AC adapter, a hanger for below balance weighing, a level indicator, lock down capability, and an all-glass weighing chamber with three-way access. A-Series and M-Series The A-Series incorporates advanced electromechanical weighing technology with state-of-the-art microprocessor-based electronics. This series includes motorized auto-calibration and options that allow the operator to customize lab procedures by scrolling through the options on the display. Selectable filters allow users to compensate for environmental conditions. Die-cast construction and a sealed silicone keypad offer protection and longevity. According to Denver Instrument, the M-Series is designed to handle numerous weighing applications. These balances are housed in die-cast aluminum with stainless steel weighing pans for increased durability. Plus, the keypad is sealed to provide spill protection, and each unit includes overload and shock protectors to increase the durability of the weighing pan in case of accidental blows. All Denver Instrument analytical balances feature vacuum-fluorescent displays, full-range taring, noncorrosive stainless steel weighing pans, and below-balance weighing capabilities and are covered by a five-year warranty. Denver Instrument also offers no-risk "test drives" prior to purchasing. AB-Series, AG-Series, and AT-Series Mettler Toledo offers several analytical balances capable of performing a variety of tasks. The AB-Series is part of Mettler Toledo's Basic Level line, designed to be simple, reliable, and economical. A frameless draft shield provides an unobstructed view of the weighing chamber and full access to the weighing pan. Several functions are available with this balance, including piece counting, dynamic weighing, and variable weighing units. AG-Series analytical balances represent Mettler Toledo's Standard Level, manufactured to be compact and easy to clean. A hexagonal draft shield provides users with a glare-free view of the weighing chamber. Calibration is facilitated by FACT (Fully Automatic Calibration Technology), which automatically calibrates via an internal weight when sensors detect changes in the environment. Also incorporated into these balances is LocalCAN, a universal interface that provides bidirectional, programmable interfacing with computer, printer, bar-code reader, and balance. Also, a set of short-form, pull-up operating instructions is built in to AG analytical balances. The AT-Series represents Mettler Toledo's Professional Level analyticals. All AT-Series balances utilize proFACT, which is similar to FACT, but proFACT allows for pre-set, timed calibrations (e.g., everyday at 8:00 AM). A cube-shaped weighing chamber offers maximum space, while a broad, fixed front panel shields samples from drafts and body heat from lab technicians. The door mechanism allows sample access from above and both sides. The motorized draft shield opens and closes with the push of a button or with the AutoDoor function. Another standard feature on AT analytical balances is ASD (automatic stability detector), which automatically detects the stable weighing result. Mettler Toledo also manufactures AT Comparator Balances, which conduct comparison measurements with a reference mass. ExplorerTM and VoyagerTM Analytical balance users now can select Explorerª and Voyagerª balances with the capacity, readability, calibration, features, and functions required-from basic capabilities to more sophisticated applications. The basic Explorer offers custom LCD display with seven alphanumeric characters and user-friendly functions: parts counting, animal weighing, percent and GLP, time, and date. When their requirements change, users can easily upgrade to a larger and higher resolution Voyager display module, which can be "snapped" in place when the Explorer module has been removed. Ohaus's Voyager balance, which like Explorer is available with or without internal calibration, features a large, high resolution, backlit graphic display with pop-up windows and offers more advanced capabilities. Users can access up to eleven functions including differential weighing, statistics, formulation, and ProgramLinkTM, which allows them to run multiple applications simultaneously. Explorer and Voyager balances are available with capacities ranging from 62 g x 0.1 mg to 8,100 g x 0.1 g. Higher capacity Explorer and Voyager balances are available in a choice of three capacities up to 32,000 g x 0.1 g. All Ohaus balances are backed in the United States and Canada by a five-year warranty. Basic Plus Series, MC1 Series, and Master Series The Basic Plus line of analytical balances from Sartorius Corporation incorporates vibration-dampening software, allowing the balances to adapt to various locations. These balances are equipped with a built-in, motorized calibration weight, facilitating one-touch calibrations, a feature that is especially useful when weighing a series of samples. Below-balance weighing, RS232 interface, overload protection, and numerous application programs (including counting, percent weighing, net totaling, animal weighing, and unit conversion) are standard on all Basic Plus analytical balances. Sartorius's MC1 Series also features internal calibration via servo motor, as well as common laboratory application programs such as counting, formulation, animal weighing, percent weight, checkweighing, and measuring unit conversion. Standard features on this series include backlit LCD display, linear fill guide, overload protection, and RS232 interface. The MC1 Series of analytical balances is also available with an extra large, all-glass chamber that is ideal for weighing oversized samples or 8" x 10" filters. The Master Series of analytical balances was developed to provide accuracy in measuring and to satisfy quality control and assurance programs, such as GLP/GMP and ISO 9000. The ISOcal system incorporated into the Master Series registers thermal changes in the operating environment and compensates by recalibration at a specific point. Each self-calibration is documented automatically by RS232 interface (standard) and printer (optional); also documented are date, time, model, identification code, and serial number. Built-in application programs include formulation, statistics, time control, mathematical calculations, density determination, animal weighing, check weighing, counting, and percent weighing. SBA-Series and SBC-Series Scaltec Instruments is a worldwide distributor for a laboratory balance product line manufactured in an ISO-registered facility in Germany. The line comprises fourteen models whose features extend beyond analytical specifications. Scaltec balances offer four dedicated application programs in every model. By entering a menu code, users can select animal weighing, percent weighing, parts counting, or net totaling (formulation). The standard built-in RS232 data interface can provide a GLP/GMP-compliant record or a copy of weighing data when utilized in conjunction with the optional SPR01 printer. This feature allows quality assurance management. Data such as date, time, serial number, model, identification number, calibration data, and weighing information can all be traced. All analytical balances are equipped with a large, square draft chamber allowing three-way access to the sample. In addition, all balances are equipped with a built-in hanger for below balance weighing applications such as density determination, or a suspension wire can be attached to weigh extra-large samples. Scaltec balances feature one-touch calibration protocols and offer internal motorized calibration, where an internal motorized weight automatically calibrates the balance, as well as external calibration models. Scaltec balances also feature large, stainless steel weigh pans, LCD displays, and an all-English keypad, which eliminates the need to interpret "universal" symbols. SA Series Finite analysis was the design foundation for the new SA Series of analytical balances from Scientech. Utilizing this advanced technology in tandem with computer-aided electronic modeling, engineers were able to reduce the number of parts, decrease weight, and increase ruggedness while enhancing overall performance and reducing cost. The resulting quality of this new design is demonstrated by the CE mark of conformity and Scientech's ISO 9000 certification. Scientech's SA Series includes numerous standard features such as GLP/GMP/ISP compatibility, live animal weighing, percent weighing, multiple units of measure, RS232 data interface, analytical windscreen with three sliding glass doors, zero tracking, a stability indicator, checkweighing, parts counting, a graphical capacity tracker, selectable vibration filtering, below-balance weighing, remote AC adaptors, metal cases, large LCD displays, a security bracket, and automatic calibration programs. Scientech's analyticals are microprocessor-controlled with a real-time temperature compensation algorithm. According to Scientech, this internal software yields accurate, reproducible results without the need to recalibrate as the ambient temperature varies. An outstanding feature that can be added to any SA model is the optional motor driven, built-in calibration weight. This feature is optional since users wanting traceability rely on an external calibration mass. The SA Series offers eight analytical balance models spanning capacities from 80 g to 510 g. Scientech reports the SA510 is the only 510 g analytical model available anywhere. Another unique model is the SA525D, which is a dual-range balance with a 500 g capacity. Coupled with Scientech's Floating TareTM feature, this model allows low range readability of 0.1 mg throughout the 500 g capacity of the balance. AEG-Series and AEX-Series Shimadzu AEG and AEX balances offer standard features such as temperature-activated calibration, NIST standards, and high-speed measurement. Temperature induced errors are eliminated on Shimadzu AEG and AEX Balances. Automatic Calibration/Temperature Activated (AC/TA) systems, a Shimadzu innovation, ensure that weighing accuracy will never be compromised by temperature fluctuations in the laboratory. Instability due to convection from elevated sample temperatures is minimized, and a Constant Power Pulse-width Modulation (CPPM) minimizes the effect of heat generated by the balance mechanism. Typical stabilization time to display an accurate reading of Shimadzu AEG and AEX balances is less than six seconds. A soft-touch membrane keypad with large display and single-function keys simplify operation. From start to finish, calibration and set-up typically take less than 30 seconds to perform. To further maximize productivity, an operator can optimize weighing conditions to meet specific laboratory requirements. During high-speed weigh/fill operations, the display of AEG and AEX Balances will change smoothly and predictably as the sample is poured without confusing, erratic values. Shimadzu reports that validation and automation with its analytical balances are simple and inexpensive. An optional printer and RS232 interface simply plug into the rear of the unit; no interface boards or balance disassemblies are required. A simple command structure puts automation development within the reach of most laboratories. Comparison Chart Shane Beck can be reached at sbeck@the-scientist.com

A Close Look At Today's Analytical Balances

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