BS ISO 15971 : 2008

Foreword
Introduction
1 Scope
2 Normative references
3 Terms and definitions
   3.1 Calorific value and Wobbe index
   3.2 Water content of gas
   3.3 Performance classification
   3.4 Terms from metrology
4 Principles of measurement
   4.1 Introduction
   4.2 Direct combustion calorimetry
   4.3 Indirect methods
   4.4 Inferential methods
5 Performance assessment and acceptance tests
   5.1 Performance assessment for instrument selection
   5.2 Factory and site acceptance tests
6 Sampling and installation guidelines
   6.1 Sampling
   6.2 Installation guidelines
7 Calibration
   7.1 Calibration procedures
   7.2 Calibration gases
8 Verification
   8.1 Verification procedures
   8.2 Verification gases
9 Maintenance
   9.1 Preventive maintenance
   9.2 Corrective maintenance
10 Quality control
   10.1 General
   10.2 Environmental parameters and ancillary equipment
   10.3 Instrumental factors
Annex A (normative) - Symbols and units
Annex B (informative) - Examples of type-approval and technical
        specifications
Annex C (informative) - Class 0 mass-basis calorimetry
Annex D (informative) - Direct combustion calorimetry
Annex E (informative) - Stoichiometric combustion devices
Annex F (informative) - Effect of non-alkane gases on stoichiometric
        combustion devices
Annex G (informative) - Measurement of Wobbe index
Bibliography

Specifies the measurement of calorific value of natural gas and natural gas substitutes by non-separative methods, i.e. methods that do not involve the determination of the gas composition, nor calculations from it.