• June 21, 2019

PTC XX. TEST UNCERTAINTY. Proposed Revision of PTC “ Test Uncertainty”. Par Adjustment in response to comment. TENTATIVE. The edition of ASME PTC will be revised when the Society .. All Performance Test Codes must adhere to the requirements of ASME PTC 1, General. Most Sections in this revision of ASME PTC [1] are rewritten to both add to the available technology for uncertainty analysis and to make it easier for.

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The results of these past tests were used to compute a standard deviation representing the dispersion of errors differences in average pipe velocities computed using 20 traverse points along each of the 4 radii versus those obtained using 10 traverse points.

ASME PTC 19.1-2005 试验不确定度 Test Uncertainty.pdf

Once the questions to be answered have been clearly stated, it should be easy to decide upon the correct intervals. If the sample standard deviation of the variable being measured is also expected to be representative of other possible random variations in the measurement, e.

The total uncertainty in a measurement is the combination of uncertainty due to random error and uncertainty due to systematic error.

For this type of evaluation, the uncertainties are independent and a simple comparison of the test results with the benchmark w value is adequate. This paragraph presents a method for determining nonsymmetric uncertainty intervals in these cases [11]. These may be such things as conduction, convection, and radiation on a sensor when installed in a gas turbine.

The results from each of the independent laboratories each de- termined as an offset to be applied to the instrument w when measuring a specific input level are used as input to eq.

Mean X p 1. American Society of Mechanical Engineers; The true value being measured is the integrated average of the velocity w over the cross-sectional flow area.

The effects of a time interval may also be important when considering the stability and control of a test process. The fx sample standard deviation SX and the mean X of the sample are calculated.


As part of this effort the effect of measurement uncertainty must be considered. Iyer, Colorado State University J.

Ptd could, in turn, lead to expression of an uncertainty interval for a test result that does not encompass the true value. The latter describes the limits to which a systematic error may be expected to go with some confidence.

That is, z R p f X1, X2. The values for t are given in Table B The difference between the results of these tests is an indication of the effect of the design change. It is assumed that these estimates are based on large degrees of freedom and that the population of possible error values associated with each elemental systematic error source is normally distributed. The large sample uncertainty expression given in eq. Each array was connected to a digital pressure indicator in a manner which yielded a spatially averaged pressure mea- Sometimes, z multiple calibrations are performed but the results are averaged into a single set of calibration constants for use in processing all data samples e.

The details of the uncertainty 4 systematic error resulting from imperfect analysis are discussed in paras. With high-speed computing capabilities, Monte Carlo methods have become popular for determining the test result uncertainty using the test input variable values and their associated uncertainties. Now suppose an experimental result, r, is wdefined as a function of certain measured variables, C A weighting principle which is statistically valid 4.

For situations in which the frequency distribution and degrees of freedom are unspecified, a normal distribution and large degrees of freedom are often assumed.

ASME PTC – Test Uncertainty

This section provides an overview of how the measurement process should be defined. The various statistical terms involved are defined in the Nomenclature subsection or Glossary subsection For a defined frequency distribution, the random standard uncertainty of the sample mean, sX, can be used to define the probable interval about the sample mean that is expected to contain the population mean with a defined level of confidence.

The last or Furthermore, it may be used to evaluate the need for calibration. The absolute systematic standard uncertainty, bP, associated with each gage is 3, Pa.


The results of this analysis are summarized in Table The necessary values for pa- first step is to define the individual systematic rameter sensitivity, systematic standard uncertain- and random standard uncertainties of the mean ties, random standard uncertainties, and combined in terms of their relative individual percentage standard uncertainty are summarized in the follow- contributions to the combined standard uncertainty ing table.

Since only a finite number of measurements are acquired during a test, the true population mean w and population standard deviation are unknown but can be estimated from sample statistics. Using the uncertainty model and associated assumptions presented in subsectionexpressions for the w percentage contributions from elemental sources of standard uncertainty were derived and are presented below.

Type B uncertainties are those that are estimated w or approximated rather than being calculated from data. The result is calculated as z R p f X1, X2, X3 Comparison ame the previously reported test result with the more exact value determined by eq. The facility simulates altitude by lowering system uncertainty can be obtained.

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The following comments are offered to serve as a guide to the engineer in this process. One particular type of bar chart is called a Pareto diagram after Vilfredo Pareto, an Italian economist who used this type of diagram in his studies of the unequal distribution of wealth.

In addition, the objective of the test may affect the categorization as discussed in para. If there is valid engineering justification, the suspected outliers may o be removed from the analysis of the test result and its associated uncertainty. They were developed by balanced committees representing all concerned interests and specify procedures, instrumentation, equipment-operating requirements, calculation methods, and uncertainty analysis.

Note that for this example the derivatives for eq.