Overall Measurement Accuracy

Author: Paul J. La NasaDownload File

This paper presents methods for determining the uncertainty of both differential and positive metering stations. It takes into account the type of meter, number of meters in parallel, type of secondary instruments, and the determination of physical properties. The paper then relates this information to potential influence on system balance


Gas measurement uncertainty is a function of the following items:

  •   Selection of the appropriate metering device.
  •   Correct Installation of the metering device.
  •   Proper meter operation and processing of the metering information.
  •   Proper maintenance of the metering device.

    Understanding how measurement uncertainty applies to metering requires a basic knowledge of the terminology and assumptions used in the calculation of measurement uncertainty.

    Measurement uncertainties can be categorized as the following:

    Pseudo Pseudo uncertainties are potential human errors or those associated with the malfunction of an instrument. Once identified, these errors can usually be corrected and are not included in the calculation of measurement uncertainty.

    Random Random uncertainties are potential measurement errors that have an equal chance of being higher or lower than the true value of the measured variable. If a large number of measurements are made, the random error in the individual measurements cancel and the mean of the measurements will be approximate to the correct value.

    Systematic Systematic uncertainties are measurement errors that are directional or contain a bias. Because these errors are directional, they do not cancel as additional measurements are made.