This document provides the means for energy determination of natural gas by measurement or by calculation, and describes the related techniques and measures that are necessary to take. The calculation of thermal energy is based on the separate measurement of the quantity, either by mass or by volume, of gas transferred and its measured or calculated calorific value. The general means of calculating uncertainties are also given. Only systems currently in use are described. NOTE Use of such systems in commercial or official trade can require the approval of national authorization agencies, and compliance with legal regulations is required. This document applies to any gas-measuring station from domestic to very large high-pressure transmission. New techniques are not excluded, provided their proven performance is equivalent to, or better than, that of those techniques referred to in this document. Gas-measuring systems are not the subject of this document.
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Sisällysluettelo
Foreword
Introduction
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols and units
5 General Principles
6 Gas measurement
6.1 General
6.2 Volume measurement
6.3 Calorific value measurement
6.4 Volume conversion
6.5 Calibration
6.6 Data storage and transmission
7 Energy determination
7.1 Interfaces
7.2 Methods of energy determination
8 Strategy and procedures
8.1 General
8.2 Strategies for energy determination
8.3 Plausibility checks
9 Assignment methods
9.1 Fixed assignment
9.2 Variable assignment
9.3 Determination of the representative calorific value
10 Calculation of energy quantities
10.1 General formulae for energy
10.2 Calculation of averaged values — Calculation from average calorific values and cumulative volumes
10.3 Volume and volume-to-mass conversions
10.4 Energy determination on the basis of declared calorific values
11 Accuracy on calculated energy
11.1 Accuracy
11.2 Calculation of uncertainty
11.3 Bias
12 Quality control and quality assurance
12.1 General
12.2 Check of the course of the measuring data
12.3 Traceability
12.4 Substitute values
Annex A Main instruments and energy-determination techniques (informative)
Annex B Different possible patterns in the change of the calorific value (informative)
Annex C Volume conversion and volume-to-mass conversion (informative)
Annex D Incremental energy determination (informative)
Annex E Practical examples for volume conversion and energy quantity calculation (informative)
Annex F Practical examples for averaging the calorific value due to different delivery situations (informative)
Annex G Ways of determining substitute values (informative)
Annex H Plausibility check graphical example (informative)
Annex I Uncorrected data, bias correction and final result graphical example (informative)
Annex J Single-reservoir calorific value determination (informative)