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【正文】 sGag e l i n ea r i t y s t u d y(Se cti o n 3 )2 . Rep e at a b i l i t y Hav e t h e s am e s a m p l em ea s u re d re p ea t e d l y b yt h e s am e p er son . T h i sre v ea l s t h e variat i o n i nt h e m ea s u r em en t d e v i c e.Gag e Ramp。 R s t u d y(Se cti o n 2 )3 . Rep r o d u cib i l i t y Hav e m an y p eo p l e(i n str u m en t s o r l a b s ) *m ea s u re t h e s am e s am p l ere p ea t e d l yGag e Ramp。 R s t u d y(Se cti o n 2 )12 Ways to See if the Measurement System is Adequate (cont’d) Tes t Fo r How Tes t Na m e4 . St a b i l i t y Hav e t h e s am e p er s o nm ea s u re t he sa m e i t emo ver t i m e. Lo o k fo rs p e ci a l ca use s t hat w ou l di nd i ca t e l a ck o f s t a b i l i t yX , R Ch ar t(C ov er e d i n m o re d et a i l i nt h e con t rol m o d u l e)5 . A d e q u a t e Res olut i onMa k e s ure 5 o r m o red i s t i n ct v a l ues ar eo bse r v e d w i t h i n t hera ng e of p r od u c t v ar i a t i oni n a n y o f t he ab ov e t est s .(d on e w i t h t h e a b ov e t e s t s )13 Note on Calibrating Measurement Equipment Measurement instruments should only be recalibrated when they show special cause evidence of drift. Otherwise, variation could be increased by as much as 40%. This is because adjusting for true mon cause variation adds more variation. Measurements taken from stable instrument Measurements taken with stable instrument recalibrated before each reading Gage Ramp。R Study 15 0 50 1000 . 0 00 . 0 10 . 0 20 . 0 30 . 0 40 . 0 50 . 0 60 . 0 70 . 0 8I n d5n??pmThe Gauge R amp。R Problem ? We cannot measure p directly with the measurement system we have. ? The process variation is spread by the measurement error to t , where t = ( p 2 + m 2 ) (See Normal Module) ? m needs to be small pared with t or p . ?If we could measure exactly, each part would always look the same and the process variation would have a standard deviation p ?But if we measure any part with the system available, measurements on the same part are different. The standard error is m. 16 0 50 1000 . 0 00 . 0 10 . 0 20 . 0 30 . 0 40 . 0 50 . 0 60 . 0 70 . 0 8I n d5n??pm?The Gauge R amp。R study pares several repeated measurements by different operators on several parts. ?Then Minitab uses Analysis of Variance (see Hypothesis Testing module) to separate out measurement Repeatability amp。 Reproducibility ( m) from partto part variation ( p) How a Gauge Ramp。R Study Works ? m is pared with t in ?%Ramp。R = m / t If the process variation is small pared to the tolerance spread, then m may be pared a ―dummy‖ process spread : %P/T = m / (tolerance / ) ?Alternatively, Minitab shows the number of distinct categories the measurement system can distinguish : * p / m 17 Gage Ramp。R ?The Gage Ramp。R study is a set of trials conducted to assess the repeatability and reproducibility of the measurement system. ? Multiple operators measure multiple units a multiple number of times. ? Example: 3 operators each measure 7 units twice. ?―Blindness
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