Analytical Balance – Factors Causing Its Uncertainty
Most scientific researches and laboratory tests require weighing, which is a critical task. However there is a degree of uncertainty in the measurements. In fact, any weighing activity has an uncertainty level. This is irrelevant when dealing with large quantities but takes on a great deal of importance when considering minute amounts of substances that necessitate weighing as precise as 0.1 mg.
Does your work often involve weighing and measuring test samples? Is the accuracy of that data critical for your research or industry? Do you realize the factors that can influence the results obtained from your analytical balance?
An Analytical Balance is a precision instrument that can measure small amounts of substances or samples with the highest accuracy. There is still a huge difference between ‘exact’ and ‘most exact’. To put it simply, any measurement is finally tentative. The metrological sciences are based on ideal conditions of set parameters. Because of this, any weighing activity also has its uncertainties. To understand the working of an analytical balance, we also need to be aware of the factors that cause its uncertainty.
Comparison of data from different instruments is also hard to evaluate because field operation methods differ from specifications by the manufacturer that are conducted under ‘ideal’ circumstances.
There are also several other factors that can influence the accuracy of weighing results obtained. However they can be broadly classified into three categories. The first group of deviation in weighing results can originate from the instrument itself. Different models of analytical balances have a varying degree of susceptibility in non-linearity, repeatability, temperature coefficient and sensitivity accuracy.
The second cluster causing a deviation comes from actual environmental factors like humidity, temperature, air pressure, exposure to direct sunlight or heat radiation. Analytical Balances, especially the high-end ones are sensitive equipments. Even the whiff of a cold draft can get you pneumonic results!
The third and final group that can cause uncertainty in the weighing results comes from accounting for human influence. How the sample is loaded; technical errors while weighing etc. can all alter the weighed results. Even the accuracy of the calibration of the balance should be adjusted based on user-specific actual weighing capacity of the analytical balance so as to get the most precise results. Improved models generally provide the option of calibrating the scale of an analytical balance at several predetermined capacities.
How is uncertainty accounted for in weighing results?
Does the obtained result from weighing actually represent the value measured? While ‘uncertainty’ could mean a broad, general concept – the error in variation of results is generally minimized to what is called ‘standard uncertainty’. ‘Standard Uncertainty’ is an estimation of standard deviation in results obtained from an analytical balance from a combination of various factors. However, even the internal and external factors accounted for in ‘standard uncertainty’ holds good only when certain basic ‘ideal’ conditions are maintained. For example, the balance is put on a level surface and there are no unnatural variations in STP (Standard Temperature and Pressure).
This article was written by Anindita Biswas, a marketing professional with a streak of geek that just refuses to go away! At Tovatech she indulges in her passion for high precision engineering and scientific equipment. Tovatech is a leading North American supplier of analytical balances. For more information on this article visit the Tovatech site from any of the above links.