SBS - The best value in QMS software

Intro to MSA of Continuous Data – Part 8: Comparison of Two Gages

Miner

Forum Moderator
Staff member
Admin
#1
This is the eighth in a series of articles about MSA. The focus of this article will be on assessing the measurement reproducibility between two measurement systems that must measure the same characteristic.

Does the following scenario seem familiar? An operator performs an online test on a product. The test shows a failure to meet specifications. This is an expensive product, so the line supervisor takes the part to an online tester located on an adjacent line and retests it. This time it passes. The supervisor instructs the operator to go ahead and use the part. Both of them lose confidence in the first measurement device. But which one provided the correct result?

There are several approaches that may be used to assess the reproducibility of two measurement devices.

One approach that is commonly used when the measurement devices are fully automated is to perform a standard R&R study and replacing the Operators with the Measurement Devices. Reproducibility is now tester to tester reproducibility. The operator*part interaction becomes the tester*part interaction. While this approach does quantify the reproducibility of the two devices, it has the drawback of providing little additional information if a significant difference between the two is noted. It is also limited to fully automated gages. You do have the option of adding gage as a third factor (Parts, Operators, Gages) and analyzing the resulting designed experiment using Analysis of Variance (ANOVA).

A second approach is known as the Iso-plot. This is a very simple graphical approach. An x-y plot is constructed with equal scales, and a 45º line is drawn through the origin. Parts are selected throughout the expected measurement range. Each part is measured using both gages. Each part is then plotted on the graph using the value measured by one gage on the x-axis and the value measured by the other gage on the y-axis. Ideally, the coordinates of all parts will lie on the 45º line. If the points fall consistently above or below the line, one gage is biased in respect to the other. The Iso-plot provides an excellent visual assessment of the reproducibility of the two gages, but does not provide quantifiable results. A linear regression analysis of the data used to create the Iso-plot will provide quantifiable results. Ideally, the regression constant should equal zero and the slope should equal one. The regression output will provide the relationship between the two gages as well as confidence and prediction limits.

A third approach is the Bland Altman plot. Parts are selected throughout the expected measurement range. Each part is measured using both gages. Calculate the differences between the gages (Gage1 – Gage2), the mean of each pair of measurements and the mean of the differences. Plot the differences on an x-y plot with the differences on the y-axis and the mean of the paired measurements on the x-axis. Draw a horizontal line for the mean of the differences. Draw two more horizontal lines at + / - 1.96 standard deviations of the differences. Approximately 95% of the differences should fall within the limits. The mean line indicates the bias between the two gages. A trend indicates that the bias changes with the size (a linearity difference between the gages). An increase (or decrease) in the width of the pattern with size indicates that the variation of at least one of the gages is dependent on size. If the variation within the limits is of no practical importance, the two gages may be used interchangeably.

Do not overlook the differences between gages when evaluating your measurement systems. Your operators will be quick to discover gages that inconsistently accept and reject product between the gages. They will then lose confidence in them and the test itself.
 
Elsmar Forum Sponsor
B

basselope

#2
As has been said before, Excellent articles! Thank you so much for sharing your experience with us.
 
M

Mr.Happy

#4
Hi Miner,
Again a good article, however I still have a question/remark.
In your case the part is measured again with a different gage but also by an different operator (the line supervisor) so this is to be considered also. Before I would do a gage to gage study I would rather do a standard MSA with the operators and the line supervisor involved and than have a good look at the "REPRODUCIBILITY - APPRAISER VARIATION (AV)" and also the Appraiser measurement instructions.

Cheers,
Mr.Happy
 
Thread starter Similar threads Forum Replies Date
Miner Intro to MSA of Continuous Data - Part 10: Creating gauge families Imported Legacy Blogs 10
Miner Intro to MSA of Continuous Data - Part 9: %Tolerance for One-sided Specs Imported Legacy Blogs 3
Miner Intro to MSA of Continuous Data – Part 7: R&R using Wheeler’s Honest Gage Study Imported Legacy Blogs 17
Miner Intro to MSA of Continuous Data – Part 6: R&R for Non-Replicable Measurements Imported Legacy Blogs 18
Miner Intro to Measurement System Analysis (MSA) of Continuous Data – Part 5b: R&R Imported Legacy Blogs 14
Miner Intro to Measurement System Analysis (MSA) of Continuous Data – Part 5a: R&R Imported Legacy Blogs 5
Miner Intro to Measurement System Analysis (MSA) of Continuous Data – Part 4: Stability Imported Legacy Blogs 2
Miner Intro to Measurement System Analysis (MSA) of Continuous Data – Part 3: Linearity Imported Legacy Blogs 15
Miner Intro to Measurement System Analysis (MSA) of Continuous Data – Part 2: Bias Imported Legacy Blogs 4
Miner Intro to Measurement System Analysis (MSA) of Continuous Data – Part 1: What and Why? Imported Legacy Blogs 22
T Intro & ISO 9001:2006 Question - Is ISO 9001:2006 Released? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 1
E French Intro to Quality - Introducing ISO 9001 to New Employees Book, Video, Blog and Web Site Reviews and Recommendations 1
Nihls MSA Study Type 2 (special conditions ) IEC 60601 - Medical Electrical Equipment Safety Standards Series 0
Nihls When the MSA results show no operator influence Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
S MSA for attribute relation gage Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
Nihls MSA Study Type 1 (CMM) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
M MSA Study Type 1 not capable. We are at the limit. And manufacturing wants to continue producing. Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 7
I Overwhelmed with attribute MSA requirement for visual inspection IATF 16949 - Automotive Quality Systems Standard 8
H Need MSA 4th ed. compliant attribute MSA template General Measurement Device and Calibration Topics 4
P MSA for titration Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
P MSA - what exactly mean "system" and master sample Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
P MSA study for visual system with artifical inteligence Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
D MSA strategy Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
K Updated MSA with the Annual PPAP validations APQP and PPAP 8
E MSA for Push and Pull test Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 9
6 MSA for Calculated Clearance Dimension Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
Ron Rompen MSA on automated measurement system - Multiple Step Vision System Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
G MSA check list to audit IATF 16949 - Automotive Quality Systems Standard 10
R MSA for ATE (Automatic Test Equipment Embedded Software) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 9
Bev D MSA Tools Misc. Quality Assurance and Business Systems Related Topics 3
R MSA studies for Heat Treatment Equipment Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
C Industrial scales and MSA (IATF 16949 requirement 7.1.5.1.1) IATF 16949 - Automotive Quality Systems Standard 30
M Difference between MSA and MSE? General Measurement Device and Calibration Topics 1
M Test method validation - Is MSA (MSA1, MSA2, MSA3 and linearity) a good solution? Medical Device and FDA Regulations and Standards News 2
A MSA results differences - Supplier results vs. My results Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
R Preliminary MSA and Sockets' correlation Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 0
I MSA requirement for 5 Micrometers + CP changes need customer approval? IATF 16949 - Automotive Quality Systems Standard 2
T Correct MSA study for an automated camera system which makes attribute inspection Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
Bev D MSA Misc. Quality Assurance and Business Systems Related Topics 46
Emran.mi Measurement system analysis - Can you help me about implementation MSA for CMM device Manufacturing and Related Processes 2
N MSA Study for a Leak Testing Device Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
N Justifications for not performing MSA (Measurement System Analysis) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
D Do I need part variation while doing Destructive Variable Gage R&R MSA study Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 19
Prashant G MSA Study - AS 9100 and and our customer want us to do MSA study for their parts dimension Reliability Analysis - Predictions, Testing and Standards 4
D Compression Spring Force MSA Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
E MSA Study on MTS dynamic rate measurements Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
A The FILE recommended by AIAG MSA 4ed for LINEARITY Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 0
S IATF 16949 Audit MSA IATF 16949 - Automotive Quality Systems Standard 10
C Do Calibration Reference Standards require an MSA study? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
A MSA When an Instrument Measures More than One Parameter Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 7

Similar threads

Top Bottom