Tham khảo tài liệu 'engineering statistics handbook episode 3 part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Readings . Instrument calibration over a regime NIST SEMATECH HOME TOOLS AI OS SEARCH ACK NEXT http div898 handbook mpc section3 3 of 3 5 1 2006 10 12 23 AM . Models for instrument calibration Special case of linear model - no calibration required An instrument requires no calibration if a 0 and b 1 . if measurements on the reference standards agree with their known values given an allowance for measurement error the instrument is already calibrated. Guidance on collecting data estimating and testing the coefficients is given on other pages. Advantages of the linear model The linear model ISO 11095 is widely applied to instrument calibration because it has several advantages over more complicated models. Computation of coefficients and standard deviations is easy. Correction for bias is easy. There is often a theoretical basis for the model. The analysis of uncertainty is tractable. Warning on excluding the intercept term from the model It is often tempting to exclude the intercept a from the model because a zero stimulus on the x-axis should lead to a zero response on the y-axis. However the correct procedure is to fit the full model and test for the significance of the intercept term. Quadratic model and higher order polynomials Responses of instruments or measurement systems which cannot be linearized and for which no theoretical model exists can sometimes be described by a quadratic model or higher-order polynomial . An example is a load cell where force exerted on the cell is a non-linear function of load. Disadvantages of quadratic models Disadvantages of quadratic and higher-order polynomials are They may require more reference standards to capture the region of curvature. There is rarely a theoretical justification however the adequacy of the model can be tested statistically. A The correction for bias is more complicated than for the linear model. The uncertainty analysis is difficult. http div898
