A Type 1 Gage study is used to evaluate the bias and repeatability of a measurement device by repeatedly measuring a known reference sample a number of times. By comparing the measurements recorded to the reference, we can evaluate the bias and repeatability of the measurement system. This can be compared to the tolerance to check if the variation in the measurement device is small enough to be acceptable.
In this study, we will look at measurements on fill volumes. A known volume of 15 ml is measured 20 times. The specifications for the process are 14.25 and 15.75. The worksheet Type 1 Gage.mtw
contains 20 measurements on this syringe in the Measure
column.
Type 1 Gage.mtw
by using Open Worksheet… from the File menu.Measure
in the Measurement data field.15
in the Reference field.1.5
in Upper spec - lower Spec.Type 1 Gage studies will output a Bias measure and a Capability measure, namely Cg and Cgk. A one-sample T-test is run on the mean of the measurements against the reference value to check for bias. The results of this data should show a significant bias with a mean of 14.916
.
The run chart will display the measurements in the order they appear in the worksheet. The data should be presented in the collection order to allow a check for trends or patterns in the results.
The red lines plotted on the chart represent as 10 percent of the tolerance interval. Ideally, a good measurement device should have measurements well within the interval. Results exceeding the interval show a measurement device with too much variation. The measures displayed are as follows:
Ideally, Cgk is above 1.33.
The Type 1 study only checks the variation around one sample. As such, it only gives an indication of bias around the reference value. More in-depth checks of bias can be run with a Gage linearity and bias study, which checks the variation of the bias across a range of reference samples.
Usually, Type 1 studies are used as initial checks on a measurement device; uses, for example, might include assessing a new measurement device for suitability or assessing a current device for its suitability for use in a new application. One would then look at Gage R&R studies to examine operator variation, or bias and linearity studies to observe bias across a range.
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