Calibration characteristics

For interpretation of measuring results, calibration characteristics obtained on the samples in advance is used in the above instruments. However, if number of impediment factors increases, the interpretation of the signals detected becomes more complicated in many times. This fact causes the position that the object thickness T and crack length I are not taken into consideration in the above-mentioned instruments. It is considered that measuring error in this case is not significant. 

Fig. 2 Calibration characteristics of electropotential transformer for cracks of various length (I).

Fig. 3 Calibration characteristics of electropotential transformer in case of object thickness (T) varying.

The calibration characteristics of the pressure transducer are described by the following relationship ... 

Calibration Characteristics and Uncertainty - Indicating Starting Points to Optimize Methods... 

The method s standard deviation (DIN 32645, DIN 38402 T51) represents the key parameter of performance. It is calculated by dividing the residual standard deviation by the sensitivity of the method and it essentially determines the maximum precision for evaluation of analytical results. The standard deviation of a method provides the scale to estimate the accuracy of a method early on the basis of its calibration characteristics. 

Due to the software that is widely available for evaluating calibration characteristics, calibration formulas are not explicitly written out here. Instead, we refer to plots of the calibration function and especially of the residuals, which provide a suitable basis for discussion by transparently showing the expected range of possible but still reliable results. More so than the confidence range of the calibration fimction, the prediction interval enables an evaluation of the precision and trueness. For this reason, we included the prediction limits in the residuals plot in a manner first published in Ref. [1]. 

Calibration Characteristics and Uncertainty - Indicating Starting Points to Optimize Methods 1119 Table 1. Measurements provided in two calibration series by methods of different sensitivity. 

Additional extensive test series to complete one s own calibration characteristics will provide no further essential information to assist in correctly choosing the better method. This effort is only suitable for validation purposes, in order to provide the most realistic information about the performance of the method of one s choice to be established in a routine application. 

As can be seen, it is simply impossible to introduce an optimization strategy that should be applicable for the entire desired operating range. We do not have to refer to statistics or calibration characteristics. Looking at Fig. 4, the question obviously arises as to why anyone should calibrate by further diluting standards to below 1% anyway. 

The sum of squared differences of each standard to the middle of the operating range (Qxx) and the squared standards (Sxx), both given on the concentration scale, are the only parameters that were additionally required to proceed with comparing linear calibration functions directly [5]. All other input refers to common calibration characteristics. On the important left-hand-side of the spreadsheet, one can see the calculation proceeding step-by-step in the way which is commonly known in chemical laboratories for validation purposes [7], i.e. explicitly comparing precision data and mean values applied to two measured series rmder repeatable conditions (F-test, t-test). 

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