When deciding on a calibrator to purchase for your lab, the number one question that we hear is how accurate does my calibrator need to be? This is especially true as the more accurate the calibrator, the more expensive it can be. Which makes the choice even more difficult when working within a budget.

Here is a guide that will specifically give details on the accuracy, and common terms used.  In order to help you make the best choice for your lab.

Test Accuracy Ratio Definition

The Test Accuracy Ratio (TAR) is the accuracy of the calibrator compared to the accuracy of the device being calibrated.

Test Uncertainty Ratio Definition

What the Test Uncertainty Ratio (TUR) compares is the uncertainty of the device under test (DUT) to the uncertainty of the measurement process. A strict test that takes into account the uncertainty of the entire measurement process.  In which the accuracy of the calibrator is only one component.

Industry Norms Over the Years

For many years, a TAR of 10:1 was the industry norm. As they have made advancements in technology, the test equipment and DUTs became increasingly more accurate.  They are even lower in pricing. Because of that TARs of 4:1 became the new acceptable norm.

The concern is that the closer inaccuracy the DUT is to the calibrator, the highest possibility of false acceptance and false rejects. False accepts are the much larger concern as they can cause a traceability chain of false accepts. This can lead to inferior products being manufactured in critical industries, which can lead to fatal results. At the base of this problem is uncertainty. If a measurement is close to being out of tolerance, then the uncertainty in the calibration process might be enough to cause a false accept or reject conditions.

One Possible Solution

Guard-banding is a technique to protect against incorrect conformity decisions caused by measurement uncertainty or entity dispersion. Where the region of permissible values of the entity’s quality characteristic is reduced in proportion to the actual measurement uncertainty or dispersion.

It is a technique that looks at how large the calibration process uncertainty is.  And determines the likeliness that it could potentially cause a false accept. Guard-banding is the process of calculating a tolerance window to apply to the measurement to avoid these false concept situations.

The guard-banding calculation can assist you in following the 4:1 TUR rule recommended. It also helps determine the desired accuracy of the calibrator needed to perform calibrations on your device under test.

Work With An Accredited Laboratory Provider

At SRP control systems ltd, we work closely with leading manufacturers to provide our customers with the best products and services. If you are unsure about the best calibrator to fit your needs and budget, we can help. With over 40 years in the industry, we have a variety of calibrators that fit multiple industry’s specific needs. As an ISO 9001:2015 registered company with a state-of-the-art ISO 17025:2017 accredited laboratory, we understand the equipment. Contact us to discuss your needs for purchasing a calibrator.