Test Uncertainty Ratio or TUR is a common term used in calibration. It is the ratio of the tolerance or specification of the test measurement in relation to the uncertainty in measurement results. It is used to evaluate measurement risk and validate the suitability of calibration methods. The most common requirement for many calibrations is a 4:1 TUR. However, not all calibrations meet a 4:1 TUR. Let’s learn how to calculate TUR, so you can evaluate calibration results like a pro.

To calculate the Test Uncertainty Ratio, we must know the value of:

• The tolerance or specification; and

• The uncertainty in measurement.

Once this information is known, we can use the following equation to calculate TUR.

Now that we have seen the TUR equation, let’s put it use with the following example.

Example:

Imagine you are calibrating a digital multimeter at 10-volts. To conform to specifications, the digital multimeter must measure the sourced voltage between 9.995 and 10.005 volts. The estimated uncertainty of the measurement result is 0.0012 volts. Calculate the Test Uncertainty Ratio.

The Test Uncertainty Ratio for the measurement result in our example is 4.2:1. According to most Metrologists, this would yield comparative measurement results with a high degree of confidence for determining conformance or non-conformance to specification.

Now that you know the equation and how to use it, plug it into your excel spreadsheets during your next calibration to calculate TUR.

## =ROUND((F2-E2)/(2*D2),1)&”:1″

If your TUR is 4:1 or greater, Awesome! If not, then you may want to evaluate your results further to determine your measurement risk.

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