B004 – Composition
Description
This block calculates the uncertainty of each component in a measured gas composition. The resulting uncertainties in gas components will be used in other uncertainty calculations for composition dependent parameters e.g. for calorific value.
Options
Composition Uncertainty
Using the drop down box, select which method of calculation to apply to the composition uncertainty.
- ASTM D1945
- NORSOK I-106
- Custom
ASTM D1945
When this option is selected the uncertainty of each gas component is calculated according to ASTM D1945.
Linearity
- Include
If box is checked, includes a user-entered linearity of each gas component value. This should be determined according to an accepted test method.
Note: This option is available if ASTM D1945 is selected from the composition option. When the check box is ticked this enables the user to enter linearity data if available as per clause 6 of the standard.
Input
Component value
Enter the value for each gas component. The composition should be entered using molar percentages.
Calibration gas uncertainty
Enter the value of the uncertainty in each component of the calibration gas. This information can usually be found on the accompanying certificate provided by the supplier.
Note: this is to be entered if user is using either ASTM D1945 or NORSOK I-106
NORSOK I-106
When this option is selected the uncertainty of each gas component is calculated using to NORSOK 1-106 in accordance with subsequent options.
- Detailed Method
When this option is selected the uncertainty in each gas component is determined according to clause 12 and Annex F of the NORSOK I-106 standard.
- Simple Method
When this option is selected the uncertainty in each gas component is determined according to Table 4 clause 12 of the NORSOK I-106 standard.
Input
Calibration gas uncertainty
- User entered
- Uncertainty limit
This option is used to determine whether calibration gas uncertainty is user entered or calculated using Table 2 of clause 12 of NORSOK I-106.
Repeatability
- User entered
- Uncertainty limit
This option is used to determine whether repeatability is user entered or calculated using Table 3 of clause 12 of NORSOK I-106.
Linearity
Enter the linearity of each gas component value. This should be determined according to an accepted test method.
Custom
When this option is selected the uncertainty of each gas component is to be manually entered by the user.
Uncertainty
User is to enter the expanded uncertainty in the mole fraction of the gas component. A normal distribution will be assumed with a coverage factor of k = 2 which will be applied in later blocks.
Note: This input is only available if a custom composition uncertainty is selected.
Calculations
Uncertainty
This is the expanded uncertainty in the mole fraction of the gas component. It is calculated according to the options selected and the inputs entered by the user. A normal distribution is assumed with a coverage factor of k = 2. These are the values that will be brought forward and used in blocks where uncertainty is dependent on the gas composition.
References
Standards
ISO 5168:2005 – Measurement of fluid flow – Procedures for the evaluation of uncertainties
ISO Guide 98-3 – Uncertainty of measurement – Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) (2008)
ASTM D1945-14 – Standard Test Method for Analysis of Natural Gas by Gas Chromatograph
NORSOK I-106 – Fiscal metering systems for hydrocarbon liquid and gas