Getting accurate weighing results is critical for your manufacturing process. Pharmaceutical weighing standards provide a solid metrological foundation for implementing risk-based quality management systems for the weighing function.
A number of factors can impact weighing accuracy, including air currents, vibrations and temperature fluctuations. Following METTLER TOLEDO’s Weighing the Right Way guidelines can help minimize these factors.
Weight
In physics, weight is the magnitude of the force exerted on an object due to gravity. It is calculated as the product of an object’s mass and its acceleration, which is related to its position in a specified frame of reference (on Earth). This definition differs from the operational weight that is measured on a spring scale or when an object is subjected to a centrifugal force (for example when riding a roller coaster). However, the term weight continues to be used commonly where it should be replaced with the word mass.
In everyday use, pounds and ounces are a convenient system for describing the weight of objects. Other systems are more precise and used in scientific experiments or commercial applications. In these cases, kilograms and milligrams are preferred.
Mass
The weighing of materials is crucial to the accuracy of laboratory experiments and industrial processes. Precise weight measurements rely on a variety of factors including the characteristics and calibration procedures of analytical balances, as well as the conditions under which they are operated.
While the terms weight and mass are often used interchangeably, they are distinct concepts. Weight is influenced by gravity, while mass is a measure of the amount of matter in an object.
Performing precise weighing requires following a standard operating procedure, keeping the analytical balance in draft-free and stable conditions and avoiding vibrations. Before placing a sample on the balance, zero it and center it. If the sample is hot, let it cool before weighing it. During the weighing process, do not touch or bump the balance and avoid touching your hands to the weighing pan or hygroscopic samples as this can cause inaccurate results. After a sample has been weighed, close the door and wait for the balance to stabilize before recording the result.
Volume
A pound is a measure of weight, but it can also be used to measure the volume of an object. Since trucks, ships, and airplanes are limited in their capacity by both weight and volume, it is often necessary to convert between the two measurements. This can be especially useful when shipping freight where the weight and volume are both known.
In chemistry, where a precise volume of an ingredient or substance is required for a particular chemical reaction, it can be helpful to know how to convert from pounds to liters. For this, the density of the ingredient or material must first be determined. Once this is known, the weight in pounds can be converted to liters by multiplying the density by 2.2046.
When weighing in a laboratory, it is important to remember that any chemical substance should only be added directly to the tared container which will hold it. Never directly to the pan of an analytical balance as this can produce errors.