HOW ACCURATE ARE PRECISION BALANACE SCALE
A balance is a crucial and fundamental piece of equipment for any laboratory. The first and foremost consideration in shopping for a laboratory balance is clarity of thought on use and application. The purpose of the balance, the type of materials, and the amount of materials all factor into the choice of instrument. For solid, inert materials of a kilogram or more, an industrial balance would be the right choice. For measuring microgram quantities of pharmaceutical compounds, a precision analytical balance would be necessary. Similarly, consider the laboratory and the overall environment. For a dusty environment, such as a factory floor, look for Precision Balances that are sealed against outside materials. If there are drafts, vibrations, or temperature fluctuations, a sensitive analytic balance may not function well. Some balances come with their own enclosures, to keep contaminants out. If the work being done requires certification, or involves toxic or radioactive materials, regulatory and personnel training requirements may need to be satisfied. In addition, the frequency of use will influence the choice. A balance that is used all day, every day, needs to be very durable and reliable. According to METTLER TOLEDO (Columbus, OH), a manufacturer of analytical balances, customers frequently underestimate the level of accuracy required by their processes. Once the application has been clarified, it can be determined what is expected in terms of accuracy according to the relevant international norms and guidelines. High readability does not necessarily equate to high accuracy, according to a company spokesperson. For example, a customer may choose a balance with 0.1 mg readability (4 decimal places). The accuracy of the balance relates to the measurement uncertainty of each reading, i.e., the ± tolerance in the result. A fast, stable weighing result is not necessarily an indication of accuracy. A balance that is inaccurate cannot reliably produce repeatable results. Different types of balances are selected according to the function they must perform. Laboratory balance types include toploading balances, portable balances, analytical balances, semi microbalances, and microbalances. There are some overlaps in terms of readability and accuracy. In these cases, the user’s application and weighing environment will generally determine the type of balance required. Balances may also be defined according to their weighing sensor. Some balances use a strain gauge, which is essentially a metallic object that deforms as strain is applied, resulting in a change in electrical resistance that can be correlated to the magnitude of the strain induced by the weight. Strain gauges are frequently found in shop scales and other larger instruments. In scales of higher accuracy, a sensor based on electromagnetic force compensation may be used. In that type of sensor, the weight applied to the scale is compensated for by an electromagnetic force. Vertical position changes in the coil trigger a current that returns the position to zero. Since the current is proportional to the weight, a weight value can be calculated from the current. The crucial requirement to fulfill when purchasing a balance is to meet the accuracy requirements of the laboratory. After that, it is up to the user to decide what other factors are important, such as built-in applications, protection against external influences, corrosion protection, user safety, cross-contamination risk, balance longevity, spare parts warranty, and service. Scientists on a budget may choose to compromise in certain areas, but the price/performance ratio and the return-on-investment should also be considered. Read the full article
