Is Your Measurement System Stable?
QI Macros Control Charts can be used to Evaluate Gage Stability
Why it Matters:
Gage stability is used to determine if your measurement system changes over time due to wear and tear or other types of deterioration. A measurement system must be stable and consistent over time to be effective.
Step by Step Instructions for Performing Gage Stability Analysis
- Obtain a sample and establish its reference value(s) relative to a traceable standard. If one is not available, select a production part that falls in the mid-range of the production measurements and designate it as the master sample for stability analysis. The known reference value is not required for tracking measurement system stability.
- On a periodic basis (daily, weekly), measure the master sample three to five times. The sample size and frequency should be based on knowledge of the measurement system. Factors could include how often recalibration or repair has been required, how frequently the measurement system is used, and how stressful the operating conditions are. The readings need to be taken at differing times to represent when the measurement system is actually being used. This will account for warm-up, ambient or other factors that may change during the day.
- Plot the data on an XbarR or XbarS control chart in time order.
- Once you have established your control limits, evaluate for out of control or unstable conditions using standard control chart analysis.
It may be desirable to have master samples for the low end, the high end, and the mid-range of the expected measurements. Separate measurements and control charts are recommended for each.
Reference: MSA 4th Edition, pgs. 85 and 86.
QI Macros add-in provides two ways to create control charts in Excel
In addition to control chart macros, QI Macros also has ready made control chart templates for Excel. You can find them in the "Control Chart Templates" drop-down menu:
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