approximations and assumptions incorporated in the measurement method and procedure. inexact values of measurement standards and reference materials.Personal bias in reading analog instruments, an example is the resolution or smallest value that you can read.Inadequate knowledge of the Effects of the environmental conditions on the measurement.Some of the main reasons why we have doubt or uncertainty in measurements are: Why do we have uncertainty or doubt in our measurement? There is always a doubt that exists, an error included in the final result that we do not know, therefore, there are no perfectly exact measurement results, Uncertainty or Measurement Uncertainty is defined as the quantification of doubt. My point here is to show you the difference and relationships of uncertainty results with the other measurement terms. This will be in a different post because there are many processes involved before we can come up with a single expanded uncertainty result. I will only explain here what measurement uncertainty is, not how to calculate measurement uncertainty. “The wider the tolerance Interval, the more product or measurement results will pass or accepted.” Is the final product specification pass or fail? How do you know that your measurement result is within the acceptable range?Ģ. If you know the calibration tolerance limits, it will help you answer the questions like:ġ. If we perform a measurement, the value of tolerance limit will tell us if the measurement we have is acceptable or not. Tolerance Limits are provided either by manufacturer or process requirements. UTL or LTL is the value based on tolerance limits. The formula is Upper limit – lower limit (UTL-LTL) Manufacturer specifications (based on Accuracy).Prescribed by regulatory bodies (based on Accuracy Class).Calculated from the process design by the user.Tolerance is a range of values that is acceptable or permitted by the user from the result of the process or product measurement. Tolerance Formula, Tolerance Interval and Tolerance Limits This is where the value of error will be used.Īccuracy can be calculated using the formula: The more close the percentage value to ZERO (0%), the more accurate.Īccuracy is more on a qualitative description which means that it does not present an exact value.Īccuracy is equivalent to or a percent error (%error). This ‘closeness’ is usually represented in percentage value (%) and can be shown in the same unit by converting it into an error value ( %error). Uncertainty or measurement uncertainty = non-negative parameter characterizing the dispersion of the quantity values being attributed to a measurandįirst Let me present each term in a simple way that I understand (I hope for you too)Īccuracy is the closeness of UUC results to the STD (true) value.Tolerance =difference between upper and lower tolerance limits. Error or measurement error = measured quantity value minus a reference quantity value.Accuracy = closeness of agreement between a measured quantity value and a true quantity value of a measurand.The relationships between Accuracy, Error, Tolerance, and Uncertainty in Calibration ResultsĪs per JCGM 200 and 106: 2012, below are the actual definitions:.The Difference between Tolerance and Uncertainty (Tolerance vs Uncertainty).The difference between Error and Uncertainty (Error vs Uncertainty).The Difference Between Accuracy and Error (Accuracy vs Error).Moreover, I will share with you below topics to answer the questions above: Now in this article, I will present the difference, relationships and Interpretations of the following terms: Accuracy, Tolerance, Error, and Uncertainty. See this link if you did not read it yet > Calibration-Verification-Validation In my last article, I have presented the difference between Calibration, Verification, and Validation in the measurement process. One way to easily learn, implement the results in a calibration certificate, and to properly understand most of the calibration procedure is to understand the measurement terms in it. What is the difference between Tolerance and Uncertainty? I am unable to understand the relation between Accuracy, Error, and uncertainty. I have recently received the below question to most of the comments in my posts, And therefore, it is worth a topic to discuss. Knowledge in these terms is the key to proper understanding and execution of your measurement results which is also an important part of a calibration awareness training that you should consider. There are so many terms that we always use or read during our measurement process. Are you familiar with the differences and relationships between Accuracy, Error, Tolerance, and Uncertainty in calibration Results?
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