In materials testing systems it is critical to understand a measurement system and the accuracy of that system. One way of assuring a system is accurate is to calibrate the machine using a verified and traceable “master”, for example a known mass or load cell. While accredited calibrations are an important part of any quality system, further steps may be taken to understand the total measurement uncertainty of a measurement system. Measurement uncertainty is the result of any input into a measuring system that may skew or change a result.
A measurement system may be influenced by a number of factors including the properties of the specimen, the machine operator, specimen holding device, or environmental conditions. A gage repeatability & reproducibility study is a useful tool for measuring the amount of variation in a measurement system accredited to the measuring device and the operators performing the measurement. Gage R&R addresses both the repeatability and reproducibility of measured values. Repeatability of an instrument is the ability of a measurement system to give similar indications for a repeated application of the same measurement under the same conditions.
In contrast, reproducibility is the closeness of the agreement between measured results from the same specimen under differing conditions. Gage R&R studies are also part of six sigma and lean manufacturing because they may provide insights into the variations seen in a manufacturing process.A gage R&R study can statistically verify that a calibrated measurement’s repeatability is adequate for making process or production decisions. The critical values resulting from these studies are Cg and Cgk. Cg is a measurement of the deviation of values over a study, or repeatability. Cgk measures the deviation of measured values between the specimen and a master, or reproducibility. A measurement system is considered “capable” if the Cg and Cgk are both ≥1.33.
ZwickRoell is now offering gage R&R studies on a variety of calibrated instruments and measurement systems. The following calibrated instruments are available for these studies: Load cellsCrosshead displacementBoth contact and non-contact extensometersSwing duration or friction on impact testers If you are interested in having a gage R&R study performed by our service team, please contact ZwickRoell at firstname.lastname@example.org.