Measurement assurance programs

Abstract

This document is a guide to the logical development of a measurement assurance program in which the tie between a measurement and its reference base is satisfied by measurements on a transfer standard. The uncertainty of values reported by the measurement process is defined; and the validation of this uncertainty for single measurements is developed. Measurement sequences for executing the transfer with NBS and procedures for maintaining statistical control are outlined for eight specific measurement situations with emphasis on characterizing parameters of the measurement process through use of a check standard.

Uncertainty and traceability for the CEESI Iowa natural gas facility

“…Instead of using the manufacturer’s quoted value for drift, statistical methods are employed to determine the random effects of the transducer. Based on the control charting methods of Croarkin [ 18 ], the random effects are categorized into short term random effects (i.e., random effects occurring during the calibration process) and long term random effects (i.e., random effects occurring between calibration cycles). When the historical calibration data is analyzed using this method, the short term random uncertainty equals 56 × 10 −6 while the long term random uncertainty is 52 × 10 −6 both at the k = 1 level.…”

“…Measurements of the gas composition are necessary to determine the TMS K -factor. Although gas composition does not explicitly appear in the determination of the K -factor [see ( 18 )], the gas composition is necessary to determine the compressibility factor, Z TMS ; the molecular mass, ℳ gas ; and the critical flow function, . As such, these variables are reflected as sensitivity coefficients in the expression of the total uncertainty in gas composition as given by Among the three terms in the sensitivity coefficients, the molecular weight is the most important.…”

“… 4 The short term and long term uncertainties discussed in later sections are also computed using this statistical procedure [ 18 ]. …”

The NIST length scale interferometer

“…This approach to measurements was pioneered by Churchill Eisenhart [ 17 ] in the 1960s. Its applications were developed and expanded by Paul Pontius [ 18 ], Joseph Cameron [ 19 ] and Carol Croarkin [ 20 ] among others.…”

“…In the 1986 evaluation [ 20 ] of M1 through M4 data, a possibility of real secular lengthening of M5727, as suggested by the slope of a fitted line, was considered. It was rejected for several reasons.…”