Essential details of Measurement uncertainty

You may be interested in the uncertainty of measurement simply because you wish to make good quality measurements and to understand the results.

Error is the difference between the measured value and the ‘true value’ of the thing being measured.
For example: Assume a stick rod of True value of 25 mm and a measured value of 24 mm, here error is 1 mm.

Uncertainty is a quantification of the doubt about the measurement result.

It is important not to confuse the terms ‘error’ and ‘uncertainty’.

For example: Assume a stick rod of True value of 25 mm and a measured value of 24 mm, but the measured value depends upon environment factor that makes the doubt of plus or minus 1 mm.
So, here measured value could be 23 mm or 25 mm and uncertainty is 1 mm.

Whenever possible we try to correct for any known errors: for example, by applying corrections from calibration certificates.

But any error whose value we do not know is a source of uncertainty.

Source of uncetainty

Being aware of the uncertainty associated with the measurement is a very significant concept. You should not make any measurements unless you are aware of the related uncertainty. 

Some uncertainty sources are the following: 

1. Measuring Instrument: Measuring instruments may suffer from error. 
2. Environmental conditions: some measurements are affected by varying in ambient conditions. For example, Calibration of slip gauge depends upon the coefficient of thermal expansion. 
3. The Instrument or gauge’ being measured may change over time. 
4. The Measurement procedure may be difficult to perform. 
5. Operator’s skill: Some calibration procedure requires experience and/or judgment skill. 

Each of the factors contributes to the overall uncertainty in the measurement.  

The source of uncertainty is not a limited and very condition to condition. 

How to reduce Uncertainty?

It is important to reduce uncertainty for an accurate measurement. One simple method of reducing uncertainty is to repeat the measurement and find the average measured value. 

Here some points can help you with more confidence in the measurement process, 

• Reduce the random effect by repeating the measurement process 
• Use the best Measuring instruments 
• Always use the calibrated instrument for measurement 
• Apply correction if you know any systematic effect 
• Record the most common uncertainty components 
• Avoid mistakes by checking calculations 
• Check your measurement by different operator or method. 

In general National standards have the lowest uncertainty followed by calibration laboratories and Industrial instruments. 

Learn more about Uncertainty Measurement in our simple online course.

Please comment below for any query or suggestions about this blog.