Uncertainty In Measurement

Uncertainty In MeasurementPresented by:Dijo PaulContentsIntroductionReporting of UncertaintiesCalibration LabTesting LabBasic TerminologiesStep by Step Procedures in Uncertainity MeasurementType AType BCombinedExpandedSolved ExampleUncertainity Budget

IntroductionMeasurement Uncertainity As required by ISO 17025Let us take the example of measuring the dimension of a dot . Considering the environment is controlled, the maximum probability in expected results in taking the dimensions is 11.But the true value is only one no.

IntroductionTrue ValueSpreadThe maximum spread possibility is called UncertainityAim: To reduce the spread is the quality of the data. Always the measurement has to be nearer to the true value

As per cl.5.4.6.1 of ISO 17025-A calibration laboratory or a testing laboratory performing its own calibration shall have and shall apply a procedure to estimate the uncertainty of measurement for all calibration and type of calibrations

Thus calculation/Evaluation/quantification for calibration is mandatory in calibration

Reporting of UncertaintiesReporting of Uncertainty-As per ISO 17025,Cl.5.10.4.1,the calibration certificate shall include the following, which are necessary for interpretation of calibration results:The environmental conditions under which the calibration are madeMeasurement Traceability StatementMeasurement Uncertainty Statement Or else the report is invalid

Reporting of UncertaintiesReporting in case of Testing Laboratory-As per ISO 17025-Cl.5.4.6.2 the uncertainity calculation is not mandatory and is conditional.i.e.Only applicable to some tests.As per International accreditation body APLAC TC-005,three types of test are involved in testingReporting of UncertaintiesThey are as follows:Quantitative Tests-Where the results are given in terms of units or numbers. In these type of tests it is mandatory to evaluate measurement uncertaintyQualitative tests: Where results are not given in terms of of units or numbers.e.g.Visibility test, Pass/fail test,color test environmental test.In this type of test uncertainity measurement is not required on test but on people conducting calibration, to ensure uniformity in decision

Reporting of UncertaintiesThey are as follows:Semi qualitative or Semi quantitative: Certain test results shall be given as pass/fail based on certain particular limit(nos)Reporting in Testing: As per ISO 17025 cl.5.10.3.1.c:where applicable, a statement on the estimated uncertainty of measurement; information on uncertainty is needed in test report when it is relevant to the validity or application of the test results, when a customers instruction so requires, or when the uncertainty affects compliance to a specified limit(i.e. M.U is optional and is required only if customer asks for or if required in decision making)

Parameters/ProcedureMethodRangeM.UReporting of UncertaintiesIf we go to the genesis of M.U,it is associated with the method

Defining the scope of testing by ISO 17025:

Uncertainty Range of the methodReporting of UncertaintiesExample: Suppose the range of the method is isIf