Application of Measurement System R&R Analysis in Ultrasonic Testing

Transcription

1 17th Worl Conference on Nonestructive Testing, 5-8 Oct 8, Shanghai, China Alication of Measurement System & Analysis in Ultrasonic Testing iao-hai ZHANG, Bing-ya CHEN, Yi ZHU Deartment of Testing an Control Engineering, Nanchang Hangkong University, Nanchang, Jiangxi 3363, China Abstract Measurement system analysis (MSA) technique is an imortant metho which is use to analyze statistical iscreteness an measurement caability of a measurement system, an also one of quality imrovement techniques. The aer escribes analysis rincile an methos of reeatability an reroucibility (&) in MSA, introuces MSA techniques into the fiel of non-estructive testing (NDT). Base on an examle of ultrasonic testing, the value of & is calculate an iscusse. The results show that MSA technique can evaluate effectively measurement caability of ultrasonic testing system, an also can be alie in other NDT system. Keywors: Measurement system analysis, Ultrasonic testing, eeatability, eroucibility Quality ata is an imortant basis to carry out quality analysis an iagnosis. It is obtaine by the alication of measurement system in measurement roceure. The accuracy of a measurement system will have a irect influence on the right jugment for rouct an rocess quality. Measurement system, which is ifferent from the traitional measurement instrument, consists of the measure art, measurement metho, measurement rocess, measurement instrument, reference stanars, an measurement environment. It means the entire measurement rocess. Because of various reasons, each element of measurement system is ossible to bring variation an iscreteness into the measurement results, an affect the measurement accuracy. In orer to ensure the reliability of measurement system, it s necessary to analyze the measurement system so as to etermine an control the variation sources. So far research work on the statistical iscreteness in measurement system is rarely imlemente. If the iscreteness is great, it will increase the measurement error. In the view oint of mathematical statistics, the evaluation inexes of measurement system inclue bias, stability, linearity, reeatability an reroucibility, etc [1]. Among them the reeatability an reroucibility(&) is an imortant quality inex which can reflect measurement caability an recision, namely the iscreteness cause by statistical ranom effect. The iscreteness must be controlle within a certain range to ensure that measurement results are reliable. Ultrasonic testing is one of the most imortant testing techniques in NDT. Ultrasonic testing system consists of insector, ultrasonic flaw etector, ultrasonic robe, art, testing metho, testing environment, technical stanars an reference blocks, etc. The flaw etector [Founation roject]: S& roject suorte by the Eucation Deartment of Jiangxi Province (No6-168); Eucation esearch roject suorte by the Eucation Deartment of Jiangxi Province (JJG-6-7-)

2 an insector are two imortant factors to etermine the robability by which the flaw can be etecte. Thus, alying the & analysis metho to analyze their influence on testing results, consequently taking actions, the testing eviation can be effectively controlle. This aer is aime to focus the iscussion on alication of & analysis technique in the inustrial ultrasonic testing system. 1. eeatability an reroucibility of measurement system Most measurement systems (inclue ultrasonic testing system) are influence mainly by the insector an measurement instrument. So, it is necessary to analyze the reeatability an reeatability of measurement system eeatability eeatability is the variation between measurement values which are obtaine when one or several insectors reeately measure a same arameter of the same kin of arts by using a same instrument. It usually inicates the variation cause by measurement instrument. 1.. eroucibility eroucibility is the variation between mean values which are obtaine when ifferent insectors reeately measure a same arameter of the same kin of arts by using a same instrument. It usually inicates the variation cause by insectors.. & Analysis moel Suosing the quality ata is istribute as normal istribution N ( µ, ), then the total variance of is comose of the variance cause by measurement system an variance cause only by rocess variation without measurement errors [1]. + MSE + MSE where is the reeatability variance, is the reroucibility variance. For MSE,it is necessary to first analyze an of the measurement system. Select ranomly m insectors, n teste arts, an then measure each art r rouns by each insector..1. calculation The range obtaine by measuring each art r rouns by each insector is given by { } min{ } max k k, ( i 1,, L, m j 1,, L, n ) where k is the observation value. The mean value of range is given by then 1 m n m n i 1 j 1

3 Where is statistical constant of which the value eens on the samle number use to the range calculation an range number. With 99% confience robability, reeatability is reresente as calculation The mean values of the observation values measure by each insector are given by n r 1 i k, i 1,, L, m n r j 1 k 1 The range of the mean Then i obtaine for ifferent insector is { i} { i} max min, i 1,, L, m n r With 99% confience robability, reroucibility is reresente as Variation between arts There is ifference between arbitrary two teste arts, which can be reflecte by the measure results. The range of the mean value for the teste arts is { } min{ } max j j where j is the mean value obtaine by measuring the j th art r rouns by m insectors..4. & The ercentage of the & in the total variation is an imortant inex that can be use to evaluate whether a measurement system shoul be accete or not. The reeatability an reroucibility, &, of a measurement system is efine as: & 5.15 MSE + MSE MSE & % 1% + Accoring to general requirement, measurement caability of the system is consiere enough an accetable if & % is less than 1% an is not enough an shoul be imrove if & % is greater than 3%. However, its measurement caability is ambiguous

4 if & % falls within 1% to 3%. In this case, whether the system is accetable or not eens on the ractical alication. 3. & analysis for ultrasonic testing system Take the ultrasonic testing system as an alication examle. As state early, this system consists of ultrasonic flaw etector, robe, insector, art, etc. We carrie out thickness measurement of steel late, base on the result, an evaluate the & of the measurement system. The exeriment use PUT-7 ultrasonic flaw etector calibrate by 1:1 beam ath,.5mhz straight-beam robe, an emloye two ifferent insectors (m) to measure three rouns (r3) the thickness of each of five same steel lates (n5) by single surface an single robe testing metho. The thickness ata are shown in table 1. Part n Table 1 The thickness ata for steel late (mm) insector 1 insector roun r roun r 1 3 x 1 3 x x j !Division mean urch Null Before the & analysis is conucte, measurement rocess shoul be stable. Therefore, it is the first ste to use the reeatability range control chart to verify whether the measurement system is stable. The range control chart shoul be lotte by the range ata obtaine by reeate measurement, as shown in the figure 1. From the chart, it s seen that all of the ranges are uner control, an the measurement rocess is stable, then the & analysis can be conucte for the measurement system.

5 中心值 UCL LCL Figure1 ange control chart lotte by the range ata 3.1. eeatability calculation When m, n5, r3, we can fin (3, 5) 1.7 from the statistical constant table[-3], the reeate measurement variation an the reeatability are calculate as follow: ( ) 1 + ( ) eroucibility calculation From table 1, x , x 45.8.so the range.6 From the Statistical constant table, (,1) 1.41, then is n r The reroucibility is The value of & is given as + MSE & Variation between ifferent arts From table 1,.44.With (5,1).48, variation between arts is Therefore

6 MSE.8 & % 1% 1%.41 41% MSE Because the value of & is above 3%, measurement caability of the ultrasonic testing system is insufficient, an the system can not be use again. Through further analyzing the results above, we know the value of this testing system is great, which inicates that the reeatability of the system is ba. The ossible reasons resulte in it are that the erioic maintenance is not one when the etector is in service, its recision is oor, or there are ba hysical contact etc. 4. Conclusion In ractical measurement rocess, the insector only ays attention to the accuracy of measurement instrument itself. In other wors, the accuracy is imrove only by the erioic calibration, but statistical iscreteness of measurement system is rarely analyze. The calibration of measurement instrument can only tell the status of instrument itself, but not juge the measurement error an measurement caability of the system. Besies the &, measurement system analysis also inclues other statistical quantities, for examle, bias, stability, an linearity, etc. The & is an imortant inex that reflects the caability of measurement system, therefore this aer oes not o further analysis for other inexes. In foreign countries, the MSA technology is wiely use to imrove rouct quality in the large comany in the fiel of automobile inustry, aeronautical an aerosace inustry, electronic inustry, etc. NDT is an imortant metho for quality control, the reliability of ultrasonic testing, electromagnetic testing, raiograhic testing, an other new NDT methos are relate to the measurement caability of measurement system. This aer has introuce the MSA technology into NDT, an iscusse its alication in ultrasonic testing system. The analysis metho an results in this aer also can be use as the reference to analyze an evaluate other ultrasonic testing systems. eference [1] Zhang Genbao, Quality Management an eliability [M], Being: China Science an Technology Publisher, 5 [] Jia inzhang, Statistical Process Control an Evaluation -C k, SPC an PPM technology [M],Being: Electronics Inustry Publisher, 4 [3] Wu Zungao, Measurement System Analysis [M], Being: China Stanar Publisher, 4