The resolution is the specified gage resolution.Quality Glossary Definition: Gage repeatability and reproducibility (GR&R) For more information on C gk, go to Minitab measures bias with the Cgk metric. Capability indices are calculated only when the tolerance range is specified. When C gk is less than the commonly used benchmark value of 1.33, the measurement system cannot measure parts consistently and accurately. What is the difference between CGK and capability index? C gK is a capability index that compares the tolerance range with the total of the bias and the measurement variation from the gage and the operator. For more information on C g, go to Minitab measures repeatability with the Cg metric. What is the difference between cg and CGK?Ĭapability indices are calculated only when the tolerance range is specified. Minitab measures repeatability with the Cg metric Repeatability is the gage’s ability to make consistent measurements of the same part. How does Minitab measure repeatability of Gages?Īfter you certify the gage itself with a type 1 gage study, use Minitab’s other gage study tools to broaden your MSA and consider other sources of measurement variation. In addition to repeatability, Minitab also assesses the gage’s bias, which is the difference between the gage’s average measurement and the official reference value – the “true” value that your gage targets. This Cg value indicates the gage’s effectiveness within this tolerance range. This means that all measurement systems should be assessed statistically. The rule is very simple: Whenever a measurement is being used to assess the quality or quantity of a product, a measurement system study is required. Understanding Gage R & R allows us to predict the percentage or probability of measurement error and understand the source of the variation (equipment or appraiser). What does a gage R&R tell you?Ī Gage R & R study examines repeatability of the equipment and reproducibility of the appraiser. If the % Gage R&R is over 30%, the measurement system is considered to be unacceptable. If the % Gage R&R is between 10 % to 30%, the measurement system may be acceptable for some applications. If the % Gage R&R is under 10%, the measurement system is generally considered to be an adequate measurement system. Gage repeatability and reproducibility (GR&R) is defined as the process used to evaluate a gauging instrument’s accuracy by ensuring its measurements are repeatable and reproducible. each operator) was randomly sampled from a larger population. The analysis treats Operator, Part and Gage as random factors because each of these factor levels (e.g. To carry out the analysis in Minitab, choose Stat > Quality Tools > Gage Study > Gage R&R Study (Expanded). Negative values indicate that the gage is biased to measure low. Skewness and repeatability index Cgk of the measuring device is calculated using formula: The Cg in- dex value takes into account the measurement conformity, cgk value the conformity as well as systemac error of the measuring process from the reference value set by the standard. If Cg = 1.33, about 75% of the study variation fits into the tolerance band (P). Cg is the ratio of the tolerance band chosen(P) to the study variation. Since p ≤ 0.05, the bias is statistically significant. Cg refers to the ratio between precision and tolerance (the potential capability) while Cgk denotes the ratio between the accuracy and the tolerance (the actual capability). Gage capability is also commonly expressed as Cg and Cgk. Formula is basically the same as for Cp & Cpk, but it uses 20 Sigma & 10 Sigma respectively instead! What is a good CG value?Ī Cgk value of 1.33 is a common benchmark value to denote a capable gage – one that is both precise (good repeatability) and accurate (low bias). Cg & Cgk – A Measurement System Capability Index from a customer.
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