Three Factors Associated With Analytical Balance Uncertainty

Three Factors Associated With Analytical Balance Uncertainty

One lesson we learn early in life is that nothing is perfect. Even a sophisticated piece of electronic equipment like the analytical balance is not infallible. Balances, in particular, need to be recalibrated regularly, so that the experimental measurement is as close as possible to the calculated result, although state-of-the-art analytical balances have become so sophisticated that they practically calibrate themselves.

Before we get into details, it would be better to familiarize ourselves with the three factors associated with balances.

Accuracy: This defines the extent to which the experimental reading of an analytical balance approaches the true value of the substance being weighed. Accuracy is dependent on the balance’s standard deviation and resolution. This is the main reason why calibration of an analytical balance is so important.
Repeatability: When the same load is placed more than once onto the weighing pan of a balance, it should give identical readings; but there is usually a very small difference. The difference between the largest and the smallest result for a specified number of measurements is known as the standard deviation.
Precision: This should not be confused with accuracy, which is the difference between the average measured value and the true value of the quantity weighed. Precision is a measure of the range of values found, when the same sample is weighed repeatedly.

Errors can be either systemic or random.

An error caused by a defect in either the balance itself, the way it is used, or the competence of the person doing the measurement are classified as systemic. For example, a balance that has been incorrectly calibrated may always give a reading that is very slightly less than the true value. The problem with systemic errors is that, although they result in high precision, they do not usually average out, even after repeated trials. Systemic errors are often not easy to spot.

Random errors are those that give differing results for the same sample when it is weighed several times. The variation is completely non-reproducible. Random errors, however, can be related to the precision of a calculated result by using statistical methods.

Therefore, selection of the appropriate analytical balance will determine the quality and accuracy of the weighing. Determining the accuracy / uncertainty factor is one requirement, but there are others that need to be considered. After all, the complete measurement system comprises the balance itself, the standards used, the environment in which the balance is located, the competence of the operator, the procedure adopted and the material being weighed. Each of these, or a combination of a few, contributes to the uncertainty of weight measurements. Moreover, potential sources of error exist within each component of the electronic balance and can cause uncertainties in the measured weight uncertain.

To recap, remember that analytical balance readings have a potential error that creates uncertainty about the absolute accuracy. However, if we can estimate the magnitude of the error, we can evaluate the quality of the measurement. Using statistical methods, we can arrive at an acceptably accurate value of the true reading.