Precision Balances

Precision laboratory balances, also called top loading balances, are a form of scale designed to offer highly accurate results, within the sub-milligram range. Used for the measurement of small samples, precision balances provide an accurate, quick, and simple way of determining the weight of items such as particulate matter. Electronic precision balances offer a wide range of weighing capacities, with maximum capacities up to 64 kg. They allow readability in the range of 1 mg (0.001 g) to 1 g, or 0-3 decimal places. High precision laboratory balances can extend this accuracy to 4 decimal places, on the display of the precision balance, 0.0001g (0.1mg) increments are used.

Precision balances produce steady readings in a wider range of environmental conditions than analytical balances which must always be used under strict conditions to ensure accurate readings. Being less sensitive to temperature fluctuations and air currents, precision balances can serve as the more convenient method of measurement. While a draft shield is not always necessary for the accurate use of a precision balance, when working in a fume hood or under normal conditions with a high-resolution precision balance of 1 mg readability, one should be employed to maintain performance.

The innovative SmartPan™ weighing pan used by METTLER TOLEDO’ XPR and XSR precision balances provides extraordinary stability and significantly reduces the impact of air currents on results. Repeatability is improved by up to 50% and even on 1 mg precision balances, accurate results can be acquired without a draft shield. Used in a fume cupboard, 5 and 10 mg models deliver results in as little as half the time of standard models.
White Paper: Outstanding Weighing Performance – Even Under Harsh Conditions

A wide range of industry areas rely on the precision of balances, chemistry being the most common, to deliver exact results. Use for a precision balance range from research and quality control laboratories of pharmaceutical, chemical, food and textile industries, to educational institutions.

Applications for a precision balance in a laboratory setting include: simple weighing, dynamic weighing, sample preparation, statistical quality control, formulation, and interval weighing. Highly accurate and reliable, a precision balance is the ideal choice for any daily weighing task in the lab.

High precision, top-loading laboratory balances of 10 kg or more, equipped with a larger platform, are typically used in aggregate, pharmaceutical, chemical and adhesive formulation applications.

A precision balance calibration assesses the behaviour of the chosen instrument. Calibration should only be performed by an authorized service technician. An adjustment changes the behaviour of a weighing instrument and requires an intervention which, in most cases, permanently alters the measuring instrument. Adjustment should not be mistaken for calibration, the terms are not interchangeable, and calibrations should always be performed after any adjustment procedure made to the balance. Many times people refer to "calibration" when "calibration and adjustment" is more accurate.

In many cases it is, in fact, the results of a calibration procedure that indicates a need for an adjustment or other repair to be made. After the adjustment or repair is complete, the calibration procedure should always be repeated to verify the proper measurement relationship has been re-established. In between regular calibrations by a technician, routine testing by the user should also be made using two external weights. These user tests allow for early detection of potential issues and deviations from weighing process requirements.

METTLER TOLEDO has developed a globally applicable scientific standard for the correct selection, calibration and operation of weighing equipment known as GWP®, or Good Weighing Practice™.

Further clarification of terms regarding Calibration and Adjustment of weighing equipmentread the document.

As cited above, electronic precision balances do not directly measure a mass, rather the force of its weight. The uncertainty of this force depends not only on the technical specification of the measuring instrument, but also on many environmental effects such as temperature variations and air drafts. In the case of measurements of 0.001 g or less, the force exerted by moving air is easily detectable. A draft shield or enclosure, usually made of plastic or glass, fits around the weighing pan in order to shield the pan from these effects.

Recent innovations of METTLER TOLEDO in the design of weighing pans for precision balances and scales help to minimize any errors due to air drafts. The innovative SmartPan™ weighing pan makes it possible to deliver results up to twice as fast, even under harsh conditions. The results show an outstanding 86% improvement in repeatability (precision) for a 1 mg readability balance under harsh conditions (inside a safety cabinet), delivering exceptional performance for any application.
White Paper: Influence of air drafts on balances

Temperature fluctuations can cause non-reproducible weighing results. For best stability and performance of measuring instruments, balances should be used in an area where room temperature can be regulated and where the instrument should remain with power ON continuously. Balances should be ideally set up on a dedicated workbench, with a suitable, maintained room temperature.

When a precision balance is first connected to the power supply or switched on, a warm-up time of approximately 1-2 hours is recommended. This period allows the balance to adjust to ambient temperature and stabilise to its environment. This warm-up should be repeated every time the balance is turned on after a period of inactivity.

METTLER TOLEDO precision balances are equipped with “FACT” (fully automatic motorized internal self-adjustment) which compensates for temperature drift. When a defined temperature difference is exceeded, the adjustment procedure is triggered automatically. This makes it possible to ensure the accuracy of the balance without operator intervention, delivering better usability across all applications.