Gauge repeatability and reliability are two important concepts in quality control that are used to assess the accuracy and precision of measurement systems. Measurement systems are used in a wide range of industries, from manufacturing and construction to healthcare and education, to ensure that products and services meet quality standards. Gauge repeatability and reliability are essential to ensuring that measurement systems are accurate, reliable, and consistent over time.

What is Gauge Repeatability?

Gauge repeatability is the variation in measurements obtained by the same operator using the same measuring instrument, under the same conditions. In other words, it measures the ability of the measurement system to give consistent results when measurements are taken repeatedly by the same person using the same equipment. This is also known as the operator or appraiser variation.

Gauge repeatability is usually measured using a repeatability study. A repeatability study involves taking multiple measurements of the same item using the same equipment by the same operator. The study is typically designed to measure the variation in the measurements due to the measurement system rather than the variation in the item being measured.

For example, consider a manufacturing process that uses a measuring instrument to measure the length of a part. A repeatability study would involve taking multiple measurements of the same part using the same measuring instrument by the same operator. The results of the study would be used to determine the variation in the measurements due to the measurement system rather than the variation in the length of the part.

What is Gauge Reliability?

Gauge reliability is the variation in measurements obtained using the same measuring instrument by different operators or appraisers. In other words, it measures the ability of the measurement system to give consistent results when measurements are taken by different people using the same equipment. This is also known as the reproducibility or appraiser variation.

Gauge reliability is usually measured using a reproducibility study. A reproducibility study involves taking multiple measurements of the same item using the same equipment by different operators. The study is typically designed to measure the variation in the measurements due to the operators rather than the variation in the item being measured.

For example, consider a laboratory that uses a measuring instrument to measure the concentration of a chemical in a sample. A reproducibility study would involve taking multiple measurements of the same sample using the same measuring instrument by different operators. The results of the study would be used to determine the variation in the measurements due to the operators rather than the variation in the concentration of the chemical in the sample.

Gauge Repeatability and Reliability Analysis

Gauge repeatability and reliability analysis is a statistical method used to assess the accuracy and precision of measurement systems. The analysis involves calculating several statistical measures, including:

  • The repeatability standard deviation (sR) – This measures the variation in measurements obtained by the same operator using the same measuring instrument, under the same conditions.
  • The reproducibility standard deviation (sA) – This measures the variation in measurements obtained using the same measuring instrument by different operators.
  • The equipment variation (sE) – This measures the variation in measurements due to the measuring instrument.
  • The total variation (sT) – This measures the total variation in measurements, including repeatability, reproducibility, and equipment variation.

The analysis also involves calculating several other statistical measures, including:

  • The %R&R – This is the percentage of the total variation due to repeatability and reproducibility.
  • The %Tolerance – This is the percentage of the tolerance or specification limit that is accounted for by the measurement system.

The %R&R and %Tolerance are important measures of the capability of the measurement system. A measurement system is considered acceptable if the %R&R is less than 30% and the %Tolerance is less than 10%. If the %R&R and %Tolerance are higher than these thresholds, the measurement system is considered to be inadequate and further investigation and improvement are required.

Gauge Repeatability and Reliability Case Study

To illustrate the importance of gauge repeatability and reliability, consider a case study of a manufacturing process that produces electronic components. The process involves measuring the length and width of the components using a digital measuring instrument. The measurements are used to ensure that the components meet the required specifications.

A gauge repeatability and reliability study was conducted to assess the accuracy and precision of the measuring instrument. The study involved taking multiple measurements of the same component using the same measuring instrument by the same operator (repeatability) and by different operators (reliability).

The results of the study showed that the repeatability standard deviation (sR) was 0.002 mm, the reproducibility standard deviation (sA) was 0.005 mm, the equipment variation (sE) was 0.003 mm, and the total variation (sT) was 0.006 mm.

The %R&R was calculated to be 83.33%, which indicates that the measurement system was not capable of meeting the requirements. The %Tolerance was calculated to be 16.67%, which means that the measurement system accounted for only a small portion of the tolerance or specification limit.

Further investigation revealed that the measuring instrument was not calibrated correctly, which was causing the variation in the measurements. The instrument was recalibrated, and a new gauge repeatability and reliability study was conducted. The results of the study showed that the repeatability standard deviation (sR) was 0.001 mm, the reproducibility standard deviation (sA) was 0.002 mm, the equipment variation (sE) was 0.001 mm, and the total variation (sT) was 0.003 mm.

The %R&R was calculated to be 20%, which indicates that the measurement system was now capable of meeting the requirements. The %Tolerance was calculated to be 6.67%, which means that the measurement system accounted for a significant portion of the tolerance or specification limit.

This case study highlights the importance of gauge repeatability and reliability in ensuring the accuracy and precision of measurement systems. By conducting a repeatability and reproducibility study, it was possible to identify the sources of variation in the measurements and take corrective action to improve the measurement system.

Conclusion

Gauge repeatability and reliability are important concepts in quality control that are used to assess the accuracy and precision of measurement systems. Repeatability measures the ability of the measurement system to give consistent results when measurements are taken repeatedly by the same person using the same equipment, while reliability measures the ability of the measurement system to give consistent results when measurements are taken by different people using the same equipment.

Gauge repeatability and reliability analysis is a statistical method used to assess the accuracy and precision of measurement systems. The analysis involves calculating several statistical measures, including the repeatability standard deviation, the reproducibility standard deviation, the equipment variation, and the total variation.

By conducting a gauge repeatability and reliability study, it is possible to identify the sources of variation in the measurements and take corrective action to improve the measurement system. A measurement system is considered acceptable if the %R&R is less than 30% and the %Tolerance is less than 10%.