Weighing uncertainty can be defined as the range of values that can be reasonably assumed to be within proximity of the exact value of a given measurement. Uncertainty is a factor in many different sciences and aspects of science. In regards to laboratory balances, uncertainty is not talked about as much as accuracy or readability, but is still an important factor, particularly when it comes to calibration laboratories.
Lab professionals will set tolerances to account for uncertainty, and it’s based on these guidelines that balances are deemed acceptable or unacceptable. Being that uncertainty is such a vital variable in the lab, we need to explore it in depth, and further explain its role in the lab.
Why is Understanding Weighing Uncertainty Important?
Let’s first explore in more detail why good uncertainty controls are important for the purpose of laboratory accreditation. Instrument calibration, sensitivity, readability, repeatability, and standard deviation are all things that are affected by weighing uncertainty. With the help of uncertainty controls, you can ensure high-standard consistent results and that a test, or a product, is acceptable.
Since uncertainty allows for repeatability at a high standard, being able to measure uncertainty comes in handy when working in a lab where you have to deal with small samples of substances that can be dangerous in larger quantities. In calibration laboratories, uncertainty measurements are essential because they act as the guidelines by which every result is judged by. Uncertainty is also useful in judging the quality of an experiment and allowing people to make comparisons of their results in the lab. The accuracy of results produced is a lot more trustworthy when we have a metric that measures how certain we can be about the reliability of lab experiment results.
What is The Difference Between Readability, Accuracy, Error and Uncertainty
Getting a clear idea of the differences between these terms will help us to better understand what uncertainty is. This is also especially important since terminology concerning data collection and analysis can often be mistaken for each other.
Readability and accuracy are often confused with uncertainty. Readability, however, is affected by the number of decimal places that the balance reading goes to. If a balance reads 0.0030g it has a higher readability than a balance that reads to 0.030g.
Accuracy is another term that uncertainty can get confused with. These terms have similar meanings as they both refer to how correct the reading on the balance is in comparison to the real sample weight. However, accuracy refers to how close a reading is in comparison to the real weight and uncertainty refers to how reliable a result is, dealing with the factors that could alter the result’s reliability.
The term accuracy can specifically be defined as how close a measurement can be produced for an known weight. So it indicates how similar a measured value and an exact value are, and uncertainty quantifies how reliable a value is.
Let’s say you’re measuring a hypothetical sample, and your measurements read 0.0300g, 0.0301g, 0.0302g and 0.0301g. Since your measurement results read between 0.0300g – 0.0302g, based on your lab balance’s class and your lab’s requirements, to know the accuracy of your measurements you can make sure they fall in a certain percentage (0.10% is the most commonly used, but this might vary depending on your local metrology and your own laboratory). However, calculating uncertainty will give you a figure (usually a percentage) that will indicate just how certain you should be about the measurements you have recorded actually falling within that percentage range.
Uncertainty is also often confused with the term error. Errors are mistakes that cause a balance to produce an incorrect result. Errors can affect uncertainty but the two variables have different denotations.
Weighing uncertainty is inevitable. No matter the nature of something, there’s always the possibility that the value of mass measured will slightly deviate from the actual mass of a sample. So no matter how accurate and correct a balance might be, and no matter how much you expect it to weigh, because we don’t know the exact weight of the sample there might be a slight variance, and even if we do know the exact weight of a sample, external factors outside of our control may change it. This is different from an error which causes the balance to give an incorrect reading because a mistake occurred.
How Do You Calculate Uncertainty?
Uncertainty isn’t associated with a single measurement as much as it measures how trustworthy results are. Calculating uncertainty is useful in regard to a lot of factors that influence a value, including readability, repeatability, calibration, density, reference mass, error, weighing result, environmental influences and other factors.
The uncertainty results of each factor are combined in relation to their importance and how much they affect each other. This can be quite complicated, and so uncertainty is usually tested and calculated by calibration laboratories with the specialist knowledge to execute this accurately. Since uncertainty is measured differently for different values, there really is no standardised way to calculate and measure uncertainty.
How Does Standard Deviation Affect Uncertainty?
Understanding the difference between uncertainty and standard deviation can be just as difficult as understanding the difference between uncertainty and accuracy! Standard deviation can be defined as the difference between measured values and true values. There’s a direct correlation between standard deviation and uncertainty, meaning that the higher the standard deviation is the higher the weighing uncertainty is, the same can be said vice versa. Even though uncertainty is affected by other variables, the standard deviation deserves to be noted as it tends to be a good gauge by which to assess uncertainty.
Uncertainty can be difficult to understand because there will always be external factors that influence measurements, in most cases it is likely that there will be a deviation between a sample’s real weight and its recorded weight, making it imperative that lab professionals understand and account for uncertainty in their operations. Selecting the correct high-quality laboratory balance is a great start to reduce uncertainty, if you need help picking out the perfect lab balance or other lab supplies for your weighing requirements, contact us. We have a broad range of lab supplies to choose from.
