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  Measurement, Test and Calibration
  Bias and Linearity

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Author Topic:   Bias and Linearity
Thothathiri
Lurker (<10 Posts)

Posts: 7
From:Chennai,Tamilnadu, India
Registered: Dec 2000

posted 01 December 2000 04:01 AM     Click Here to See the Profile for Thothathiri   Click Here to Email Thothathiri     Edit/Delete Message   Reply w/Quote
We purchased a New Digimatic Micrometer of a reputed make. We conducted the Bias and Linearity study with Slip Gauge, and we anlysed the result using the Regression. The R square value we got from the study if 0.69 as against 0.98. can any one comment on the study result. What might went wrong with the Micrometer as its new. At the same time we conducted GR&R study with this instrument and we got GR&R value less than 10%.

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Drew H
Forum Contributor

Posts: 11
From:Kelowna, B.C., Canada
Registered: Oct 2000

posted 03 December 2000 12:34 AM     Click Here to See the Profile for Drew H   Click Here to Email Drew H     Edit/Delete Message   Reply w/Quote
Either there was an error in conducting the linearity study or the gage is very non-linear. Did you graph the results of the linearity study - could give you some idea of the source of the problem. The GR&R study is telling you things are consistent - i.e. repeatable. It gives the same measurement each time and the operators don't have any trouble making the measurement. I would look closely at the bias over the range of use and the linearity - if these don't meet manufacturer's specs, send it back!

[This message has been edited by Drew H (edited 07 December 2000).]

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David Drue Stauffer
Forum Contributor

Posts: 25
From:St. Louis, MO63132United States
Registered: Feb 2000

posted 08 December 2000 11:19 AM     Click Here to See the Profile for David Drue Stauffer   Click Here to Email David Drue Stauffer     Edit/Delete Message   Reply w/Quote
Hi. Just like to remind y'all that bias is defined as the observed average deviation from the target value (measurement standard) before any calibration adjustments are made to the instrument and thereby used to discern if there is a need to do an impact study on product acceptance. Sorry bout the long sentence. Linearity, is a study to determine the accuracy of a gage throughout its measurement range for the same purpose. All those calculated values really don't mean that much. The goal is to discover if THIS gage is capable of controlling your process to acceptable SPC Indices. IF there is a problem, then it becomes necessary to investigate to find out IF this has impacted product acceptance. Remember the tire company?

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