EBSILON®Professional Online Documentation
This method aims at fulfilling the quality standard specified by VDI 2048 sheet 1 and especially to enable the quality checks described in VDI 2048 sheet 1 section 5 as well as to fulfill the requirements stated in the criteria catalog for a certification as per VDI 2048. For this reason, the calculations shown in Chapter 5 are realized equivalently in EBSILON®Professional on the basis of the definitions mentioned in the guideline. The following advantages result for the evaluation of the measurement data sets:
The prerequisite for using this method is the specification of confidence intervals for the measurement values, and if applicable, the correlations between them (correlation coefficients).
It is possible to consider the correlations, because the empirical covariance matrix can be filled fully. When converting the temperature in specific enthalpy, either the respective line pressure is used (in each iteration step the calculated value of the previous step is used) or else the pressure measurement value specified via a correlation including its confidence interval is used. The transformation of the covariance matrix regarding pressure and temperature to pressure and specific enthalpy is done automatically with the necessary partial derivations. Thereby, an uncertainty of the table values (e.g. according to IAPWS specifications for displaying the specific enthalpy) can be considered, which leads to a propagation of the confidence intervals in the sense of a suitable error observation.
Special specification values can also be validated along with by creating a pseudo measurement value on a auxiliary line, which is connected with the affected specification value via a reference that must be entered. This means that coefficients in balancing equations (e.g. isentropic efficiency of turbines, heat transmission coefficient multiplied by area in heat exchangers) are handled like measurement values.
If both sides of the inequation 140 from section 5.4 VDI 2048 sheet 1 are divided by the value of the Fisher-distribution present on the right-hand side, then the left side is called the Chi^2-test ratio, which represents the relative mean error square with the expected value 1 divided by the value of the Fisher-distribution.
As far as this has a value of above 1, the specifications made can be used for broadening the confidence intervals of the concerned measurement values as per the error analysis described in VDI 2048 sheet 2 section 7.7.2, to reduce the Chi^2-test ratio to a value of 1 or smaller, whereby the inequation 141 from sheet 1 of the guideline VDI 2048 must be adhered to.
The analysis according to inequation 140 should be preceded by an examination of all measured values according to inequation 141 VDI 2048 sheet 1. Only both procedures together can yield to reliable results.
Owing to the covariance to be set for a measurement point for the values before and after retrofitting, the evaluation of the retrofitting measures represents a special feature. To be able to enter these in the covariance matrix, the models for the state before and after the retrofitting must be incorporated in a cycle.
You will find further information in the following subchapters:
Comparison of the validations in EBSILON and VDI2048